Europe's Quest for the Universe - Laboratoires de Recherche

Europe's Quest 

for the Universe 

Lodewijk Woltjer

Europe’s Quest 

for the Universe 

ESO and the VLT, ESA and other projects 

Lodewijk Woltjer 

EDP Sciences 

17, avenue du Hoggar 

Parc d’activités de Courtabœuf, BP 112 

91144 Les Ulis Cedex A, France

Cover: THE VLT Array on the Paranal Mountain. © ESO. 

ISBN : 2-86883-813-8 

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© EDP Sciences 2006

CONTENTS 

Preface.................................................................................. 3 

Préface.................................................................................. 4 

Acknowledgements.............................................................. 5 

Introduction ........................................................................ 7 

I. The Development of European Astronomy during 

the 20 th Century .................................................................. 11 

II. ESO, La Silla, the 3.6-m Telescope, Other Telescope Projects 

in Europe ............................................................................ 25 

III. Origin of the ESO VLT Project; The NTT ........................ 43 

IV. Technological, Financial and Scientific Planning 

of the VLT............................................................................ 59 

V. Construction of the VLT .................................................... 69 

VI. Sites for Telescopes ............................................................ 87 

VII. The VLT Observatory: Adaptive Optics, Instruments, 

Interferometry and Survey Telescopes .............................. 109 

VIII. Ground and Space Based Optical Telescopes.................... 123 

IX. Radio Astronomy; ALMA and SKA.................................... 139 

X. Europe in Space: ESA’s Horizons 2000 .......................... 161 

XI. European Space Missions: IR, X- and Gamma Rays ...... 175 

XII. European Space Missions: The Solar System .................. 203 

XIII. European Space Missions: The Sun and the Heliosphere .. 219 

XIV. Astroparticles and Gravitational Waves ............................ 231 

XV. Looking for Planets and Life in the Universe .................. 243 

XVI. Publications ........................................................................ 253 

XVII. European Astronomy: Researchers and Funding ............ 265 

XVIII. The Future .......................................................................... 277 

XIX. Epilogue .............................................................................. 289 

Notes .................................................................................... 291 

Acronyms ............................................................................ 301 

Index .................................................................................... 317 

Photo credits........................................................................ 325

Preface 

What a magnificent title, “Europe’s quest for the Universe”, for the 

opening of this new book by Professor Woltjer, which presents and expands 

on two grand themes. 

Since the days of Copernicus, Galileo, Tycho Brahe and Kepler, as a 

research community Europe has been at the cutting edge of science, in its 

incessant quest to understand the universe we live in. 

In this book we trace the history and development of more recent 

institutions such as the ESA and ESO. This is thanks to the great skill and 

experience of the author who, by writing this work, passes on the fruits of 

a unique and exceptional career. 

Great pride and optimism for European science comes across on 

reading these pages, all beautifully illustrated. Written to a high scientific 

level, this book provides the reader with a top quality reference on the subjects 

covered, and gives us ample reason to believe in a European research 

environment directed firmly to the future. 

The second theme is that knowledge and exploration of the universe 

are fundamental elements of the human psyche, a drive inherent in all of 

us to understand and discover our destiny. 

The Universe is a magnificent question which inspires scientific and 

technological development. At the same time it remains that star studded 

sky which acts as a source of wonderment and inspiration for our thoughts 

and dreams. 

Thank you Professor Woltjer for returning us, through this book, to 

the very roots of our humanity, and revealing to us such marvellous 

advances in understanding. 

Philippe BUSQUIN, July 2005 

European member of parliament, 

Former European commissioner for Research

Préface 

Quel magnifique titre pour l’ouvrage de Monsieur Woltjer “Europe’s 

Quest for the Universe” qui exprime deux idées fortes et l’évolution de celles-ci. 

L’Europe, comme espace commun de recherche, depuis Copernic, 

Galilée, Tycho Brahe, Kepler, a été à la pointe de la science et de cette quête 

incessante de compréhension de notre Univers. 

L’histoire et le développement des institutions plus récentes comme 

l’ESA et l’ESO sont retracés grâce à l’expérience et à la compétence de l’auteur 

qui, par le truchement de cet ouvrage, nous transmet les fruits d’une 

carrière unique et exceptionnelle. 

Quelle fierté et quel optimisme pour le savoir européen à la lecture 

de ces pages si bien illustrées et d’un haut niveau scientifique qui contribueront 

à nous donner une référence de très haute qualité sur les sujets 

abordés et nous fournissent toutes les raisons de croire en un espace 

européen de la recherche tourné vers l’avenir. 

La deuxième idée est que la connaissance et la conquête de l’Univers 

sont des éléments fondamentaux du besoin inhérent à l’homme de comprendre 

et de découvrir le sens de son destin. 

L’Univers demeure cette magnifique interrogation qui inspire le 

développement scientifique et technologique mais aussi le ciel étoilé propice 

aux rêves, aux réflexions et à l’émerveillement. 

Merci, Monsieur Woltjer, de nous replonger, grâce à votre ouvrage, 

aux racines de l’humanité et aux merveilleuses avancées de la connaissance. 

Philippe BUSQUIN, juillet 2005 

Membre du Parlement Européen, 

Ancien Commissaire Européen à la Recherche

Acknowledgements 

First of all I would like to thank Ulla Demierre Woltjer without whose 

active participation this book would not have come about. Jean Pierre Swings 

and James Lequeux read the whole book, Roger Bonnet, Daniel Hofstadt, 

Marc Sarazin and Giancarlo Setti some chapters and provided much information. 

Many persons supplied data or contributed in less formal discussions. 

I mention here Arne Ardeberg, Adriaan Blaauw, Roy Booth, Jacques 

Breysacher, Harvey Butcher, Giacomo Cavallo, Roger Cayrel, Thierry 

Courvoisier, Rodney Davies, Margo Dekker-Woltjer, Michel Dennefeld, 

Franca Drago, Hilmar Duerbeck, Daniel Enard, Peter Fischer, Robert 

Fosbury, Reinhard Genzel, Roberto Gilmozzi, Alvaro Gímenez, Michael 

Grewing, Einar Gudmundsson, Martin Harwit, Günther Hasinger, Martin 

Huber, Henning Jørgensen, Martin Kessler, Pierre Léna, Duccio Macchetto, 

Kalevi Mattila, Brian McBreen, Jorge Melnick, Evert Meurs, George Miley, 

Alan Moorwood, Antonella Natta, José Miguel Rodriguez Espinosa, Francisco 

Sánchez, Aage Sandquist, Richard Schilizzi, Hans-Emil Schuster, John 

Seiradakis, Peter Shaver, Boris Shustov, Jason Spyromilio, G. Srinivasan, Jean 

Surdej, Yasuo Tanaka, Virginia Trimble, Sergio Volonté, Malcolm Walmsley, 

Roland Walter, Robert Williams, Ray Wilson. Edmund Janssen, who drew 

the map in Figure VI, 3, Hans-Hermann Heyer and Claus Madsen searched 

the ESO archives for photographs. To all my thanks. 

I wish to thank Catherine Césarsky, Director General of ESO, and 

David Southwood, Director of the ESA Science Programme, for having contributed 

towards making the publication of this book possible, and EDP Sciences 

for taking the risk to publish it in color. 

Parts of this book were written while “chercheur associé” at the Observatoire 

de Haute Provence ; I thank the directors Philippe Véron, Antoine 

Labeyrie, Jean-Pierre Sivan and Michel Boër, as well as Mira Véron-Cetty, 

for their support. Other parts were written while “Rossi Fellow” at the Osservatorio 

Astrofisico di Arcetri, and I thank the directors Franco Pacini and 

Marco Salvati, as well as the chairman of the Astronomy Department Claudio 

Chiuderi for their support. Some sections were written during visits to 

the Raman Research Institute in Bangalore, and I thank the directors 

V. Radhakrishnan and N. Kumar for the friendly reception I received there.

Introduction 

The progress of science depends on the technological development of 

its instrumentation. This is particularly true for the astronomical sciences 

where the study of remote objects requires sophisticated and costly detection 

techniques. In this book I shall analyze some of the large European astronomical 

projects, both on the ground and in space, their development during 

the last two decades, and their prospects in the future. While scientific 

progress is intimately related to technology development, both are contingent 

on professionals and funding, and I shall consider the situation with 

regard to both of these. 

This book is addressed to a varied audience: scientists who wish to see 

what is happening outside their own domain, students who look for fruitful 

areas of thesis research, functionaries who need some background for decision 

making, amateur astronomers interested in knowing what is going on 

in the profession, and also to an educated public that wants to get the flavor 

of what is behind the newspaper articles reporting scientific results and to 

know how European activities compare to what is being done elsewhere. The 

more detailed description of the development of the VLT, ESO’s Very Large 

Telescope, illustrates how a large technological project gets underway and 

after some pitfalls reaches completion. 

In the first half of the twentieth century observational astronomy was 

ipso facto astronomy done from the ground in the visible part of the spectrum. 

While in the USA ever larger telescopes were being built, in Europe 

developments were much more modest, partly owing to unsuitable meteorological 

conditions, but even more because private donors on the scale of an 

Andrew Carnegie did not exist here. In the early fifties some proposals were 

made to construct a large European telescope at a suitable location. Political 

and financial conditions for science were much improving, and in 1964 ESO, 

the European Southern Observatory, was founded by half a dozen countries 

as an intergovernmental organization; in the meantime most countries in 

Western Europe have become members. In writing this book, I have placed 

ESO at the beginning because of its increasing role in several areas of 

European astronomy. 

The early evolution of ESO has been well described by Adriaan Blaauw 

in his book “ESO’s Early History” 1) , so I shall give only a brief recapitulation 

and then sketch the origin of the VLT, which has brought Europe to the forefront 

of contemporary optical astronomy. Following a brief overview of the

8 Europe’s quest for the Universe 

development of the astronomical sciences, subsequent chapters of the book 

deal with the origin, development, construction and siting of the VLT, its 

interrelation with the Hubble Space Telescope and with possible successors 

of these instruments. 

Also during the fifties radio astronomy became a major contributor to 

scientific progress. The European radio community has made many advances 

– in part by tying national facilities into a network, the EVN (European VLBI 

Network). The French-German-Spanish IRAM has been successful in radio 

astronomy at millimeter wavelengths. ESO entered this field with SEST, the 

Swedish-ESO Sub millimeter Telescope. ESO is the European partner in 

ALMA – the Atacama Large Millimeter Array, the major Europe-Japan-US 

venture in submm astronomy. 

With the advent of the space age other parts of the spectrum became 

observable. Thus, infrared, ultraviolet, X- and gamma-ray observations 

allowed entirely new objects to be discovered and studied. Moreover, possibilities 

opened up for in situ exploration of the solar system. At about the 

same time as ESO, the precursors of the European Space Agency ESA came 

into being. The ESA has constructed large facilities for space research. Again 

I shall be brief on early ESA history, since it is described by Roger Bonnet 

and Vittorio Manno in their excellent short book “International Cooperation 

in Space: the example of the European Space Agency” 2) , while early worldwide 

space science developments are comprehensively covered in 

“The Century of Space Science” edited by Johan A.M. Bleeker, Johannes Geiss 

and Martin C.E. Huber 3) . Subsequently, I deal with recent and future European 

scientific projects in space. Most of these have been developed in the 

ESA context, but also some national projects have had an important role. ESA 

and ESO are increasingly cooperating: The European Coordinating Facility 

for the Space Telescope is one example; joint studies in interferometry 

another. The latter may be essential in one of the most exciting astronomical 

subjects: the search for earth like planets and life. Also archiving the enormous 

data flows is a common interest of ESA and ESO. 

A more sociological discussion of European astronomy follows. How 

many astronomers are there in the different countries and how much is spent 

on astronomy? The end product of the astronomical activity consists of publications, 

and the productivity of the different communities is evaluated. The 

final chapter deals with the future and the difficult selection of expensive projects 

in a relatively less favorable economic and political environment, but 

ending on a positive note: the past achievements augur well for the future 

in which the countries now entering the EU should also play their part. 

The present book deals with European achievements and prospects 

which do not seem to have been described previously in a coherent way. 

Others have described their achievements elsewhere. Of course, comparisons 

are made with what other nations – in particular Japan, Russia and 

the US – are doing. Also cooperative projects with these countries play an

Introduction 9 

important role. But is is important to realize that Europe has the full capacity 

to an autonomous role in science. Sometimes the necessary self-confidence 

seemed to be lacking among Europeans who measured their own success by 

how they are regarded across the Atlantic. The press services are not very 

helpful in this respect; even European results appear to become more 

respectable after a round trip across the ocean. Cooperation is a very good 

thing with mutual benefits. But such cooperation can only be profitable if it 

is based on equality, self-confidence and mutual respect. Europe has the 

capacity to autonomously plan its scientific future and does not have to try 

to fit into plans made elsewhere. It only has to strengthen its will to do so. 

Two caveats should still be made. In this book I discuss mainly the 

larger astronomical projects. Many smaller ones are also important, but 

including these would require a much more voluminous tome. Secondly, when 

I discuss collaboration, it refers to institutional collaboration. Individuals participate 

in an infinite number of collaborations with fellow scientists in their 

researches without regard to nationality or to political factors. This contributes 

much to the liveliness of the field and may also be beneficial in the 

creation of a more harmonious world.


The Crab Nebula. First catalogued by Messier as M1, it was named by Lord Rosse 

who observed it in the middle of the 19th century with his six foot telescope in Ireland. 

It is the expanding remnant of the supernova which was extensively observed in 1054 

in China and Japan. The Nebula remained mysterious until 1968 when a pulsar – a 

rotating neutron star – was discovered at its center. The strong magnetic fields of 

this star accelerate cosmic rays, including energetic electrons which produce synchrotron 

radiation in the nebular magnetic fields. That radiation is observed from 

the longest radio waves at 30-m through infrared, visible and ultraviolet light to the 

hardest X- and gamma-rays. In visible light it is seen as a smooth bluish continuum. 

The reddish filamentary structures on the image are due to emission lines from gas 

ionized by the ultraviolet radiation. Since almost all important cosmic processes may 

be studied in the Crab Nebula, it has been called the Rosetta stone of astrophysics. 

The image was taken with the FORS instrument (PI Immo Appenzeller) attached to 

ESO’s VLT, the Very Large Telescope.

I. 

The Development of European Astronomy 

during the 20th Century 

Praised be your intellect, you interpreters of the heavens, 

you who understand the Universe, discoverers of a 

theory by which you have bound gods and men. 

Gaius Plinius Secundus 1) 

A visitor to one of the hundred odd observatories in the world early 

in the 20th century would have found some astronomers at work during the 

night at telescopes with diameter generally less than a meter. Some would 

peer through an eye piece and note down their findings, but photographic 

plates were coming into widespread use which gave a more quantitative and 

less subjective record of the observations. Mostly the astronomers would be 

measuring the positions of planets, asteroids and stars. By a comparison with 

previous observations they also determined their motions across the sky. The 

brightness (generally denoted magnitude) and the color of the stars were also 

ascertained, and some of the more venturesome professionals had begun to 

use spectrographs with which the stellar light could be split into different 

wavelength bands. This allowed the detection of absorption and emission lines 

in the spectra. By measuring their wavelengths precisely and comparing 

these with the wavelengths at which gases in the laboratory emitted or 

absorbed radiation, they could identify the main chemical elements present 

in the stellar atmospheres. Variable stars were also extensively studied, 

different types were recognized and their detailed characteristics identified. 

If he returned during the day, the visitor at the larger observatories 

would see numerous employees at work who would make the extensive calculations 

needed to establish catalogues of positions and motions of celestial 

bodies and to compare the results with theoretical models. Calculations were 

made with multiplication tables, tables of logarithms or very simple 

mechanical machines.


The photographic plates used behind the telescopes were terribly inefficient; 

less than 1% of the incoming light (or as one would frequently say 

nowadays: of the incoming “photons”) was actually detected. Nevertheless, 

progress was made. By 1920 the magnitudes, colors, spectra and motions of 

many thousands of stars had been determined, and some ideas had been 

formed about their distances. So one could begin to construct more fact based 

models of how the stars are distributed in space. In fact, most stars were found 

to belong to a flattened system, with the Milky Way globally corresponding 

to its plane of symmetry. In this “universe” systematic streaming motions were 

suspected. Somewhat later it was concluded that the whole system is rotating. 

Whether there was anything outside this “universe” was unclear. Subsequently, 

evidence was found from photographic plates taken with the new 100-inch 

telescope on Mt. Wilson, California, that the faint luminous patch called the 

Andromeda Nebula was an independent stellar system, far away from our 

Milky Way Galaxy. Other “nebulae” were also resolved into stars and the 

“universe” was gradually growing in extent (Figure I, 1a). 

Figure I, 1a. VLT image of the spiral galaxy NGC 1232; blue light comes from 

massive young stars which have formed recently in the spiral arms, while the yellow 

light around the center is contributed by older stars formed earlier in the history of 

the galaxy. To the left is a dwarf galaxy tied gravitationally to NGC 1232.

Development of European Astronomy 13 

Most of the early observatories had been constructed on small hills in 

the neighborhood of towns. As the towns grew and street lighting increased, 

they were sometimes moved a bit further out. In Europe most observatories 

were located in unfavorable climates, and in the north east of the US the 

situation was not much better. Turbulence in the atmosphere caused the 

stellar images to be smeared out over several arcseconds on the photographs. 

This made it hard to detect faint stars. It was G.E. Hale who decided that 

the solution was to go to the calmer skies in California. Raising enough private 

money, he founded the Mt. Wilson Observatory, which would be equipped 

with a 60-inch and later a 100-inch telescope. When the city lights of 

Los Angeles became too strong, a more distant site was developed at 

Mt. Palomar. As a result of these developments, the Californian astronomers 

were able to take the lead in investigating fainter stars and galaxies, and 

thereby to explore a much larger part of the Universe. This led to the 

discovery of the expansion of the Universe – the fact that more and more 

distant galaxies move away from us at larger and larger speeds. In our own 

Galaxy stellar populations with different chemical compositions were recognized. 

The important conclusion followed that most of the chemical elements 

were not created in the birth of the Universe, but have their origin in 

processes in the deep interior of stars. When stars die they may eject gas 

containing these elements out of which new stars may form (Figure I, 1b). 

Some of the European countries had founded observatories in their 

colonial empires, the UK in S. Africa, Australia, Canada and India, the French 

in Algeria, and the Dutch in Indonesia. Also Germany had considered the 

possibility. While these observatories collected useful data on a variety of 

objects, in particular on parts of our Galaxy invisible from Europe, they 

hardly contributed to a redirection of efforts in the mother countries. Of 

course, a few individual researchers could make visits to the Californian 

institutions, but most European observatories continued with the types of 

research they had been performing before. In addition, the second world war 

had a very damaging effect. So by 1949, when the 200-inch telescope at 

Mt. Palomar was inaugurated, the astronomical center of the world had 

largely moved to the US. 

In theoretical astrophysics much strength remained in Europe. This 

had led to a basic understanding of conditions in the stellar atmosphere and 

interior and of the nuclear reactions which produce the luminous energy 

radiated from the surface. A beginning had been made with studies of stellar 

evolution, while also the dynamics of our Galaxy and the orbits of stars 

therein were being explored. However, the rise of theoretical physics in the 

US (in part due to European refugees) and the early availability there of 

powerful computers also threatened the European pre-eminence in the 

theoretical domain. 

Four very different developments led to a rebirth of European observational 

astronomy: the discovery of radio waves from cosmic sources,


Figure I, 1b. VLT image of the “planetary nebula” M27, a gaseous shell ejected by 

the star at the center. The interstellar gas may become enriched in elements synthesized 

in the star, which now ionizes and excites the shell. Different densities and 

temperatures in the gas lead to different emission lines and thereby to different 

colors in this image. 

the availability of government money for research, the development of air 

travel and European cooperation. Soon space research would add further 

possibilities for observations of celestial X- and gamma-radiation and in the 

infrared part of the spectrum. In the appendix to this chapter the definition 

and units of measurement of the electromagnetic spectrum are indicated for 

future reference. 

Cosmic radio waves had been serendipitously discovered in 1933 by 

K. Jansky, an engineer at AT&T, but until the end of the war only some very 

limited follow up had been done. So the field was wide open. The poor 

climate in Europe did not matter, since radio waves pass through clouds and 

atmospheric turbulence unhindered, except at short mm wavelengths. Some 

of the leftover military radar equipment could be quickly converted to astronomical 

use, and so the cost of the first radio telescopes was modest. It soon 

turned out that the scientific returns were very large. Radio emission due to 

cosmic ray electrons throughout the Galaxy could be extensively studied.


The 21-cm emission line emitted by diffuse interstellar hydrogen gas provided 

a means for studying the whole galaxy without the problems associated with 

absorption by interstellar dust which had stymied the attempts to derive its 

structure by observing stars. Discrete sources of radio emission were discovered 

which turned out to be frequently associated with remote galaxies. So 

here was a whole new universe, and scientists in Europe, Australia and the 

US started its study at about the same time in conditions of equality 

(Figure I, 2). However, the radio sources that were discovered had to be identified 

with visible objects to determine their nature and distances. Since even 

strong radio sources are frequently very faint optically, this still required the 

large telescopes in the western US. 

An important contribution to the American prominence in astronomy 

had been made by the availability of ample private money. During the period 

of the wildest capitalism huge fortunes had been built, and some of the 

owners of these or their heirs were fascinated by the astronomical universe 

or liked having telescopes carry their names. Thus, Carnegie had financed 

Mt. Wilson and Hooker had contributed much to the cost of the 100-inch 

telescope. Even very recently the Keck Foundation provided an important part 

Figure I, 2. The 76-m radio telescope near Manchester. Completed in 1957, it illustrates 

the rapid growth of radio astronomy in Europe after the war. For 15 years it 

was the largest radio telescope in the world.


of the funding for the two 10-m telescopes at Mauna Kea, Hawaii. No similar 

tradition existed (or exists today 2) ) in Europe, and so most observatories lived 

a more precarious existence. After the war, and because of the important role 

science and technology had played for the winning side, this changed and 

governments began to consider it their function to sponsor research. With 

radio astronomy having some connections to radar and telecommunications, 

both funding and competent engineers were available. 

Typical optical observatories had resident staff. Especially in poor 

climates it was necessary to use every clear hour, and this could be done only 

when the astronomer lived on the site. However, with air travel becoming 

cheaper and faster, a different modus operandi became possible in which 

observatories could be located in optimal places anywhere in the world and 

astronomers would travel there just for an observing period – initially months 

or weeks, nowadays frequently no more than a few days. 

Constructing large observatories in remote places was expensive. To 

provide adequate funding remained difficult for individual governments. 

With Europe gradually becoming more unified, it seemed appropriate to 

consider the possibility of financing expensive scientific installations on a 

wider basis. Thus, CERN – the European center for nuclear and particle 

physics – was founded at an early date. Later ESO, the European Southern 

Observatory, and ESA, the European Space Agency, followed. These collaborations 

created the intellectual and financial basis for Europe to have the 

ambition to compete on the world level. By now, more than a third of all 

astronomy spending in Europe is done on a European rather than on a 

national basis. 

Few things happen very fast in Europe and it took a rather long time 

before ESO was organized. Its first “large” (3.6-m) telescope was completed 

only in 1976, some 23 years after it had been first proposed. In the meantime, 

other telescopes of similar size were being developed by several countries. 

Not surprisingly, many European astronomers wanted to continue to do the 

things they had done before: to study the distribution and motion of the stars 

in our Galaxy, variable stars of every kind, the motions of double stars, 

stellar atmospheric structure, comets and asteroids. Even though valuable 

research was done in these areas, European optical astronomy lacked some 

of the excitement that prevailed on the other side of the Atlantic, where the 

unknown deeper reaches of the Universe were being explored. The difference 

in astronomical orientation is conspicuous if one compares the ambitions for 

the Palomar 200-inch telescope and that for ESO. In his 1928 proposal for 

the construction of a 200–300-inch telescope, Hale 3) indicates the principal 

areas of research which three quarters of a century later have lost none of 

their interest, though today we might phrase them somewhat differently. The 

topics were: 

The structure of the Universe. 

The structure of our Milky Way Galaxy.


The evolution of stars. 

The successive stages in the development of spiral galaxies (“the 

greatest of these problems”). 

The Universe as a cosmic laboratory to investigate the nature of matter. 

In a much narrower way the preamble to the ESO Convention places 

the emphasis strongly on the second item of this list, with the following 

statement: 

“Considering that the study of the Southern celestial hemisphere is 

much less advanced than that of the Northern hemisphere, that the data on 

which the knowledge of the Galaxy is based are accordingly by no means 

of the same standing in the different parts of the sky and that it is essential 

to improve and supplement them in all instances where they are inadequate,…” 

This is effectively a statement that the principal reason for founding 

ESO was to fill in the missing southern parts of the structure of our Galaxy, 

including its satellites the Magellanic Clouds. The first instrument built for 

the 3.6-m was a stellar photometer mainly suited for Galactic research. 

Certainly such research was important, and it had provided the justification 

for placing ESO’s facilities in the southern hemisphere. But for European 

astronomy to partake in the newer developments, a change of attitude and 

more suitable instrumentation would be needed. Several astronomers were 

well aware of this, and in some places researches were initiated on extragalactic 

topics, on interstellar matter and on high energy astrophysics. When 

ESO finally could organize a scientific division, the emphasis was mainly on 

the new domains. Young postdocs staying for a few years before returning 

to national institutes would develop cooperations in these subjects and later 

contribute to the creation of a strong coherent European astronomical 

research community. The increased coherence of that community would 

allow ESO thereafter to become much more ambitious and to build the 

world’s top telescope, the 16-m equivalent VLT. 

As in radio astronomy, the development of high energy astrophysics in 

Europe was very rapid once the essential tools became available. Less than 

five years after Sputnik, the UK observed cosmic-rays and solar X-rays with 

the Ariel 1 satellite. Particularly successful were Ariel 5 (1974) which made 

an X-ray sky survey and Ariel 6 (1979) which determined cosmic-ray composition. 

In 1974 the Dutch launched the ANS satellite with X-ray instrumentation 

and the Germans the first of the Helios spacecraft to study the solar 

wind. In the meantime, ESRO, later transformed into ESA, the European 

Space Agency, had launched its first satellite ESRO-II (1968) which observed 

solar X-rays. Among the European astronomical satellites TD-I (1972) for uv 

operations and COS-B (1975) for γ-rays were quite successful. IUE (1978), the 

International Ultraviolet Explorer, a NASA-UK-ESA collaboration, was also 

important in integrating the astronomy and space communities in Europe. 

Thereafter ESA missions became larger, more competitive and well centered


on the newer astronomical research areas: EXOSAT (1983) and XMM-Newton 

(1999) in X-rays, INTEGRAL (2002) in γ-rays, ISO (1995) in the infrared, 

supplemented by a participation in the Hubble Space Telescope from 1991 

onward, gave European astronomers access to much of the wavelength range 

of space astronomy. In addition, the national X-ray satellites ROSAT (D, 

1990) and BeppoSAX (I, 1998) made major contributions. Hipparcos (1989) 

gave Europe the lead in astrometry, determining positions and motions of 

100,000 stars. 

In the exploration of the solid bodies of the solar system Europe was 

a latecomer. Of course, planets, asteroids and comets had been observed with 

telescopes on earth, but only limited results could be obtained from large 

distances. The first space mission to observe such an object from close by 

would be Giotto in 1985, which obtained the most detailed information ever 

on a cometary nucleus. It took 18 years before the next such European 

mission arrived at Mars. Both Russia and the US had left Western Europe 

far behind in planetary exploration. Ulysses (1990) and SOHO (1995), both 

joint missions with NASA, and Cluster (2000), continue to study the Sun and 

the heliosphere with advanced instrumentation. 

All of the IR, X- and γ-ray missions require much follow up with 

optical telescopes, and it is fortunate that ESO is now able to provide unique 

possibilities for this with the VLT. When today one looks at European 

astronomy, one sees a vibrant community active and competitive in all the 

exciting areas of research on the Universe, its contents and evolution. 

Not surprisingly, in parallel with the increased instrumentation also 

the number of professional astronomers has much increased (Figure I, 3). 

Less than a century ago they were rare and frequently considered as oddballs 

with rather doubtful economic prospects. Few parents would approve their 

daughter marrying an astronomer! Their nightly work also set them apart 

from the typical social schedule. Today being an astronomer no longer makes 

one very different from people in other scientific professions. In the developed 

world there are typically ten to twenty astronomers per million inhabitants. 

And while most are not particularly rich, their material prospects are 

no different from those in other academic professions. They used to work as 

individuals or in groups of two or three. Nowadays it is not unusual to see 

research projects of fifty scientists, postdocs and graduate students. This has 

had several consequences. Such groups tend to have a hierarchical structure, 

with the leaders not only controlling the research of the more junior staff 

but also their economic well being. This would seem to be unavoidable, but 

it makes the jobs of the junior staff less attractive. All of this is accompanied 

by a certain “industrialization” of the research, with projects defined and 

executed on financial and time schedules. Since many staff members are 

needed in such projects and insufficient long term academic positions are 

available, a system of temporary postdocs has arisen with appointments on 

time scales of typically two or three years. This was not too serious when

Total reflecting surface area in m2 of fully steerable telescopes/number 

of members of the International Astronomical Union (divided by 10) 


1000 

100 

10 

1 

1900 1950 2000 

Year 

Figure I, 3. Astronomers and telescopes. The total reflecting surface area in m 2 of 

fully steerable telescopes for the world (green) and for Europe (blue) compared to 

the number of members of the International Astronomical Union (divided by 10, in 

red) for different years. Exponential growth is noticeable in all, though now the 

numbers of IAU members are beginning to flatten off. It is seen that after the war 

Europe had fallen far behind in telescope construction, but that by now it has caught 

up again. The cross indicates what would be the result of the construction of OWL 

(Chapter VIII). 

overall employment increased and more continuing appointments were available 

but now long term positions are not easy to find, and a large number 

of postdocs are floating around from one temporary position to the next. 

Some ultimately quit and take jobs in industry or government. Young astronomers 

tend to be well qualified in subjects like programming, image 

processing and the handling of large data sets. In addition, they are used to


arrive at conclusions concerning systems about which insufficient information 

is available. So, at least in some European countries, they fit relatively 

easily into jobs in insurance, banking and government planning offices. 

For example, in Holland two out of three people with a degree in astronomy 

wind up in nonastronomical positions. There is nothing wrong with this, but 

it implies that astronomy education should not be too narrow. Of course, 

some astronomers also become science teachers in high school. Nevertheless, 

one may wonder if the postdoc system has not been overstretched. Especially 

at a time when alternative jobs become also more difficult to obtain, the prospects 

become so uncertain that many of the more perspicacious students may 

choose other directions. 

To summarize, there thus were three phases. Till the early years of the 

20th century astronomy was largely a European affair. During the subsequent 

decades, the American dominance was established partly by a better funding 

situation and also by the unfortunate developments in Europe which paralyzed 

research and caused many prominent researchers to leave, never to 

return. After the war ended European astronomy began a slow recovery 

process which accelerated in the seventies and eighties. By now Europe has 

reached again a position of equality in most astronomical fields and 

leadership in some. Two fundamental factors have contributed to this: a well 

educated pool of young talent and nearly adequate funding. If these would 

begin to be lacking, a decline would be rapid. In this respect, some fears for 

the future are justified. At the political level in Europe there is much talk 

about the “knowledge based economy”, while at the same time the financial 

underpinnings of such an economy are being weakened. Besides, the 

evolution of high schools and universities is not always encouraging. 

So what around 1975 were the main problems that the world astronomical 

community perceived as essential to tackle, and which have shaped 

astronomical technology in the subsequent decades? Perhaps clearest was that 

only a very small part of the Universe had been surveyed. A few quasars at 

larger redshifts were already known, but since they were not understood, they 

did not yet help much in cosmological studies. The key to further progress 

was the ability to observe fainter galaxies at greater distances and also fainter 

stars in our own Galaxy. Second, it was also evident that we had only a very 

washed out view of astronomical objects ranging from remote galaxies to the 

planets. Much of the essential physics would only be seen when angular resolution 

would be improved by better observational techniques or in the case 

of our solar system by in situ studies. Third, we had seen enough to realize 

that the view at visible wavelengths was very incomplete. More satisfactory 

radio observations were in sight, but in the IR, X- and γ-rays and in the study 

of particles like neutrinos or of gravitational waves we had just scratched the 

surface sufficiently to know that our ignorance was complete. Thus, the trio 

that since then has dominated progress was increased sensitivity, increased 

angular resolution and increased wavelength coverage.


Increased sensitivity could be achieved by larger telescopes and by 

more efficient detectors. Some of the first CCD detectors were developed for 

space imaging; infrared detectors were developed by the military for night 

vision devices and other purposes. X- and γ-ray and particle detectors were 

developed by physicists for a variety of aims. By now CCDs of large formats 

and low noise are abundantly available; even a 100 € camera has a CCD. To 

obtain better sensitivity and angular resolution, larger telescopes now are 

needed. We have a general idea how to build these, but more and more the 

cost is a limiting factor. So to the above mentioned trio we have to add a 

fourth: cost reduction. 

The story of ESO, ESA and European astronomy in general over the 

last 30 years has been one of finding better and cheaper solutions to instrumental 

problems so as to be able to afford what we can conceive. Of course, 

the scientific utilization of our instruments is the ultimate aim. But it may 

well be that the good scientific use of these instruments is easier to achieve 

than their development at acceptable cost. 

Observational results will remain isolated facts if there is not a theoretical 

framework in which they find their place and for which at the same 

time they provide the foundation. Such a framework is also needed to see 

which future observations are most likely to increase our understanding. 

Thus, theoretical research is an essential part of astronomy, though its 

detailed aspects are outside the scope of this book. 

Annex: Electromagnetic Radiation 

Different aspects of electromagnetic radiation are described in terms 

of waves or particles. When we discuss diffraction of light through a small 

opening or interference of light beams, the wave description is more convenient; 

when we study the effect of light on a solid state detector like a CCD, 

it is simpler to think in terms of photons ejecting electrons from the material. 

However, both descriptions refer to the same underlying physical phenomenon. 

In image forming systems (lenses, mirrors) the image is formed by the 

interference of refracted or reflected light beams. An important result 

concerns the angular resolution – the minimum separation in angular 

measure (degrees, arcminutes, arcseconds) which allows us to see two stars 

as separate objects. At a wavelength λ the angular resolution θ of a telescope 

with a diameter d is given approximately by θ = 200 000 λ/d arcsec, where 

λ and d are in the same units. Thus, at visible light with λ 0.5 µm a 

telescope with a circular aperture of 1 meter diameter has an angular resolution 

of 0.1 arcsec. If we inspect two stars or other objects at a distance D, 

the linear separation l corresponding to the angle θ is about θD/200 000 and, 

therefore, the linear resolution l = λD/d. Thus, with our 1-m telescope we


would be able to see details on the moon (D = 400 000 km) 200 m in size. 

This would, in fact, be the case in space. However, from the ground the 

angular resolution is degraded due to atmospheric turbulence to values typically 

ten times larger, unless adaptive optics (Ch. VII) is implemented. 

Astronomical measurements extend over a range of a factor of about 

10 21 in wavelength. Three types of units are commonly employed in different 

parts of the spectrum: wavelength, frequency and photon energy (Figure I, 4). 

In the radio part of the spectrum frequency ν is most commonly used, or 

alternatively wavelength λ. The relation between the two is νλ = c, with c the 

velocity of light 3 × 10 8 m/sec. Frequency is measured in Hz (cycles/sec). In 

the IR, visible and uv it is more common to use wavelength. In the X-ray 

region of the spectrum the eV (electronvolt) is the unit of choice, with a 

photon energy of E expressed in eV corresponding to a wavelength λ 

expressed in µm by the relation E (eV) = 1.24/λ (µm). 

Wavelength atmospheric transparency frequency/energy name 

km m mm µm 

nm 

MHz GHz THz eV 

keV MeV GeV TeV 

Radio IR V UV X-rays γ-rays 

Figure I, 4. The electromagnetic spectrum. The tickmarks correspond to factors of 

ten, but those of the Hz and eV scales are not continuous. The prefixes n, µ, m, k, 

M, G and T correspond to 10 -9 , 10 -6 , 10 -3 , 10 3 , 10 6 , 10 9 , 10 12 . The blue parts of the 

spectrum in the figure cannot be directly observed from below the earth’s atmosphere. 

Above 10 GeV indirect measurements are possible by observing the interaction of the 

very energetic photons with the atmosphere. The atmospheric transmission in the IR 

is more complicated than indicated here with some narrow “windows” in the 2–30 µm 

and the 200–1000 µm spectral domains. Common terminology for the latter is 

“submm” or “far IR”, while “near IR” refers to 1–2.5 µm. Terminology at shorter wavelength 

is less well defined, with “near uv”, followed by “far uv” and “EUV”, the 

extreme ultraviolet. The EUV gradually becomes “soft X-rays” ( 1–2 keV), “hard Xrays” 

( 5–10 keV), and “soft γ-rays” with a considerable overlap.


The southern Milky Way and the Magellanic Clouds (photo: C. Madsen). Just under 

the Small Magellanic Cloud is the second brightest globular cluster 47 Tucanae, just 

above the bar of the Large Cloud the Tarantula Nebula, a region of dense gas and 

intense star formation. The dark area in the Milky Way is the “Coal Sack” due to a 

nearby cloud of dust which blots out the stars behind it; at its top is the star α Crucis, 

which with the three bright stars to the left constitutes the “Southern Cross”. The two 

bright stars below the Coal Sack are α and β Centauri. Just outside this image to the 

left are ω Centauri, the brightest globular cluster in the sky, and Centaurus A, the 

nearest radio galaxy (Fig. IX, 1).

II. 

ESO, La Silla, the 3.6-m Telescope, 

Other Telescope Projects in Europe 

Among the other most remarkable spectacles which we 

have beheld, may be ranked the Southern Cross, the 

cloud of Magellan and the other constellations of the 

Southern hemisphere. 

Charles Darwin 1) 

During a visit to Jan Oort in Leiden, Walter Baade, a German astronomer 

working in Pasadena, gave the impetus to the idea of a joint European observatory. 

At Lick Observatory in California a 3-m telescope was under 

construction, and the proposal was to quickly build a copy and place it in 

the southern hemisphere which was the optimal location for the study of our 

Milky Way Galaxy and the Magellanic Clouds. Since some connections already 

existed to South Africa, the first thought was to go there. The emphasis on 

Galactic research was not unnatural since because of their relatively small 

telescopes European astronomers had not participated much in the study of 

remote galaxies which had remained the prerogative of the large Californian 

telescopes. As a consequence, many of them saw such an observatory as a 

means of extending their researches in stellar and galactic astronomy. By a 

fortunate coincidence, preparations for CERN, the Center for European 

Research in Nuclear Physics, were just coming to a satisfactory conclusion 

and so a ready made model for a European scientific research organization 

was in place. Nevertheless, it took another decade before the convention establishing 

the European Southern Observatory was agreed on (1962) and 

ratified by five European parliaments (1964): Belgium, France, Germany, the 

Netherlands and Sweden, followed in 1967 by Denmark. The United Kingdom 

had participated in some of the discussions. However, the Commonwealth 

Astronomer, later Astronomer Royal in England, R.v.d.R. Woolley strongly 

opposed a project with the Europeans, while the eminent scientist F. Hoyle,


seeing the governmental lawyers at work armed with French-German dictionaries, 

concluded “I thought that an observatory organized this way is not 

going to work” 2) . So in 1961 the UK decided on a joint project with Australia 

instead. History repeated itself in 1987 when I had discussions with the UK 

representatives on participation in the VLT, which were followed by the UK 

joining the Gemini project of the US. Finally, when the superiority of the 

completed VLT had become clear and even larger telescopes were beginning 

to be discussed, the UK joined ESO in 2002. It had to pay a substantial 

entrance fee without its industry having had a chance to profit from the 

project. In the meantime Italy and Switzerland (1982) and Portugal (2001) 

had also become full members. Finland followed in 2004. Well before the 

convention was signed, a beginning had been made with studies of possible 

sites in South Africa, where several European astronomers had scientific 

contacts and where a functioning observatory already existed. In retrospect, 

the long delay in getting ESO started may well have been advantageous; by 

1964 the superiority of sites in the Andes had become clear 3) and it was still 

possible to opt for a place in Chile. 

The ESO convention specified that the principal instrument would be 

a telescope of “about 3 meters aperture”. At the time it was considered 

necessary that such a telescope have three focus positions (Figure II, 1): a 

prime focus for very deep photography and low resolution spectroscopy, a 

Cassegrain focus for photoelectric photometry and medium resolution spectroscopy 

and a fixed coudé focus for very high resolution stellar spectroscopy. 

Since remote control was still beyond the horizon, it was necessary 

to have the observer in a “prime focus cage” to guide the telescope and to 

change the photographic plates. Because such a cage had to accommodate 

a human being it could not be so very small, and with a 3-m telescope an 

unacceptable amount of light would be intercepted by the cage. So finally 

the wording of the convention was stretched and the aperture enlarged to 

3.57 m. 

The long delay before the ESO convention was concluded had also 

some negative consequences. While in the sixties a 3.6-m telescope in the 

southern hemisphere would have been unique, by 1976 the 4-m US telescope 

at Cerro Tololo and the Anglo-Australian 3.9-m had already been operating 

for more than a year. Even more serious for ESO, some of its member countries 

were building their own 3.5-m class telescopes. France was involved with 

Canada in the 3.6-m CFHT (Canada-France-Hawaii-Telescope) on the 

excellent site on Mauna Kea at 4200 m altitude. In Germany Zeiss was 

building a 3.5-m telescope for the Max-Planck-Institut für Astronomie; 

though ultimately placed on Calar Alto in Spain, it had been foreseen for the 

Gamsberg in Namibia. A 3.5-m telescope was planned by the Italians for 

Castel Grande in southern Italy, though it was completed only some twenty 

years later at La Palma in the Canary Islands. Thus, ESO had lost its preeminence 

in the southern hemisphere, while in a European context it was in

ESO, La Silla, the 3.6 m Telescope 27 

Figure II, 1. Different types of telescopes. 

a – prime focus with only one reflection on a concave mirror; 

b – Cassegrain with two reflections on a concave primary and a convex secondary; 

c – Nasmyth, with a flat tertiary mirror sending the light through one of the axes; 

d – coudé with a number of flat mirrors which allow the focus to be at a fixed location 

while the telescope moves. A representative light-ray is indicated in red, while the 

mirrors are shown in white and the focal position as a green dot. The Nasmyth focus 

is particularly suited for an alt-azimuth telescope. The number of flat mirrors in the 

coudé depends upon the layout. At each reflection on aluminum coated mirrors about 

15% of the light is lost at visible wavelengths. 

competition with several equivalent national projects. Why have a costly 

European venture at a level attainable by the major countries in Europe by 

themselves? 

Initially the 3.6-m telescope project had been placed in the hands of 

a well qualified engineer, W. Strewinski. However, neither he nor ESO’s 

management had appreciated the magnitude of the task. By 1970 alternative 

solutions were looked for, and this led to the creation of the ESO Telescope 

Project Division on the CERN campus with a generous contingent of CERN 

personnel temporarily added to the ESO staff. This finally resulted in 1976 

in the successful installation of the 3.6-m telescope (Figure II, 2) at La Silla 

some 500 km north of Santiago de Chile. As a consequence of its history, 

a 

b 

c 

d


Figure II, 2. The 3.6-m telescope at La Silla. From bottom upwards the Cassegrain 

cage inside which spectrographs or other instruments are located, the primary mirror 

(invisible), the declination (celestial latitude) axis attached to the horseshoe like 

structure at the end of the polar axis on the right, and near the top the Cassegrain 

secondary with some baffles or the prime focus cage. Initially, an observer was 

present in one of the two cages, but subsequently remote controls were installed. 

it was of conservative design and had cost a great deal of money (68 MDM 4) 

or 78 M€ in 2004 value, including its housing and personnel costs). Hardly 

any instrumentation for the effective use of the telescope had been developed. 

All the 3.5–4-m telescopes constructed during the seventies share this 

conservatism. Some relatively small differences in the mechanical design 

occur, but globally all follow the overall pattern set by the 200-inch telescope


on Mt. Palomar. A prime focus cage accommodating an observer, a Cassegrain 

cage behind the primary mirror and a fixed coudé focus for heavy auxiliary 

equipment reached after extra reflections, the telescope rotating around 

an axis pointing towards the celestial north or south pole so as to track the 

daily motion of the stars with a rotation around this axis. Only the astronomers 

in the USSR had had the courage already in 1960 to adopt an altazimuth 

(one horizontal and one vertical axis) design for the 6-m telescope. 

To some extent they were forced in this direction by the large weight of the 

6-m mirror. From a mechanical point of view there is much advantage to 

have the telescope tube move only in a meridional plane on a rotating 

platform, thus avoiding the complex mechanical stresses of the polar mount. 

This leads to important cost savings (see chapter III). Also heavy equipment 

may be mounted easily and accessibly at the two Nasmyth foci. The inconvenience 

is the fact that the telescope has to be driven in two coordinates at 

varying rates, which at the time of more primitive computers was not a trivial 

matter. However, when refraction and telescope flexures are taken into 

account, even a polar mounting requires more than just an axial rotation. 

More serious is the image rotation in an alt-azimuth mount which has to be 

compensated. 

At ESO not much discussion seems to have taken place on a possible 

alt-azimuth mounting 5) . There was a general feeling that the American engineers 

knew what they were doing and that one should not deviate too much 

from their designs which had been proven to function well. Of course, this 

implied that the technology was not necessarily the newest. A certain conservatism 

was perhaps justified by the fact that the observatory, as specified in 

the convention, looked very much like a one shot affair to provide a European 

observing capability. If one would have considered the convention program 

as a first step in a long range enterprise, the need for an independent 

European capability in telescope technology would have been clear. Of course, 

in all of this one has to take into account that ESO came into being at a time 

of very rapid developments in computers and detectors and that many aspects 

were still not clear at the time decisions were made. Nevertheless, it remains 

surprising that cost-to-benefit considerations were so largely absent. Perhaps 

the ample availability of money in those days provides an explanation. 

Progress on ESO’s 3.6 m telescope had been slow, but instrumentation 

developments were in a catastrophic state. The only instrument being 

designed was a 4-color photometer/polarimeter. Though the instrument, 

developed by Alfred Behr, was excellent, it was hardly the most urgent one 

for a large telescope. Following numerous test nights, it was in operation for 

only 24 nights before being decommissioned. Much discussion had taken 

place about the construction of a large coudé spectrograph. To maximize the 

optical path the building plans at some stage had become quite fantastic: 

below the round dome the coudé floor would be square. Along the diagonal 

this would increase the available length by 2. Finally, fear for the image


quality as a result of this awkward aerodynamical shape led to its abandonment 

6) ; undoubtedly this also reduced costs. Because of the high cost of 

the coudé spectrograph, it had been decided to construct next to the 3.6-m 

telescope a 1.4-m Coudé Auxiliary Telescope (CAT). During the time that the 

large telescope would be used for other purposes, the CAT would allow the 

spectrograph to be used for the observation of brighter stars. The coudé focus 

also had a major impact on the telescope design with three large flat mirrors, 

needed to bring the light from the moving telescope to the stationary focus. 

By the time the 3.6-m telescope was completed, classical coudé spectrographs 

were being abandoned in many observatories since more compact and 

efficient Cassegrain instruments had been developed. In fact, only two of the 

three flats have been installed in the telescope and the classical coudé focus 

has never been implemented. 

When I came to ESO in 1975, it was evident that there was no real 

plan to effectively use the 3.6-m telescope for contemporary science. There 

also would be no suitable instrumentation to attach to the telescope. All of 

this reflected the absence of any scientific identity of ESO. In particular the 

French had been insisting that ESO be an “Observatoire de mission” with 

only the staff needed to run the telescopes. Instrumentation would be decided 

by an Instrumentation Committee and built largely in the national institutes, 

while scientists residing in their home institutes would decide what programs 

to execute. This approach was inadequate in giving the instrumentation the 

necessary coherence and realism. In December 1972 my predecessor, 

Adriaan Blaauw, had tried to get the ESO Council to agree to the creation of 

a small “scientific group” in Geneva, which I would be heading. Instead, 

Council offered a visiting appointment to discuss with the member countries 

the instrumentation issues. This did not seem a particularly attractive job. 

The issue came again to the fore in 1974 when a new Director General 

had to be found. Council had begun to realize that things were not going well 

and so became more receptive to a change of policy. Still a long period of 

wrangling followed which lasted more than a year. This began when I was 

to be appointed. I had made the creation of an in-house scientific group a 

condition for taking the position. Council met in closed session to discuss 

the appointment and was expected to come to a rapid conclusion, but for 

several hours nothing happened. Inside the meeting room, however, the 

situation was dramatic. The French President had received the agreed view 

of Council as to what he would tell me. At some moment during this process, 

he felt that his honor had been questioned by the German Vice-President. 

In true gallic tradition he resigned as President. The Vice-President automatically 

became President, but immediately also resigned. Since some 

decision had to be taken, J.H. Bannier as the most senior member of Council 

assumed the presidency, and finally the appointment was made in a provisional 

way. Several weeks later three Dutchmen: the Director General 

A. Blaauw, the interim President J.H. Bannier and I met to see how to


proceed further. At the December Council meeting I was to present a 

complete plan for the future of ESO with proposals for both Chile and 

Europe. If these were acceptable to Council, then my appointment would be 

confirmed. No one seems to have wondered what to do four weeks later if 

no agreement were reached. However, everything went smoothly, because 

several issues were left hanging. Half a year later the disagreement with the 

French came again to the fore, with an implied threat that they might leave 

the organization if outvoted. As a delegate of one of the small countries said, 

they would support me entirely except if this threat were to become fully 

serious. Some discussions between a few delegations took place outside, and 

the final result was an agreed resolution scribbled on a sheet of paper. Before 

this came to a vote, someone wondered if one should not ask the Director 

General’s opinion. If only because of the way in which that resolution had 

come about, it was obviously unacceptable. Following this, Bengt Strömgren, 

the President of Council, took the piece of paper with the resolution in his 

fist and crumpled it. An absolute silence followed with everyone waiting to 

see what would happen. Strömgren’s prestige was such that no one dared to 

say anything, and he simply resumed the discussions. The final result was 

that a beginning of a scientific group was agreed, while Jean-François Denisse 

would travel to Chile with me to evaluate the situation there. That visit was 

decisive. He saw there that the drastic remedies I was proposing were fully 

justified. Moreover, he discovered that the French complaint of a lack of 

French staff was unfounded: people like Jacques Breysacher and 

Daniel Hofstadt turned out to be French rather than German! Soon after this 

visit a final compromise was reached. In the subsequent twelve years I 

enjoyed excellent relations with all delegations in Council, which finally led 

to the unanimous approval of the VLT project. It shows the importance of 

forcing the issues early, rather than having them fester on unsettled for a 

long time. 

When I arrived at ESO, it was clear that to effectively use the 3.6-m 

telescope for contemporary science the absolute necessity was to have a 

simple spectrograph for the observation of faint galaxies, nebulae and stars. 

Since no time was available for an optimized design, a ready made 

Boller & Chivens spectrograph was purchased. The Instrumentation 

Committee had little love for this spectrograph, claiming that the optics were 

not optimal. However, it was the only instrument that could be acquired 

rapidly. Because of the lucky absence of some members at the decisive 

meeting, the IC finally agreed. For some 6 years this remained the only spectrograph 

at the 3.6-m suitable for observing faint objects. Especially with the 

newer detectors it was quite successful. 

During 1976 a new instrumentation plan was developed (largely based 

on a proposal of Johannes Andersen at Copenhagen and Daniel Enard at 

ESO) which in addition to the low resolution spectrograph contained a crossdispersed 

échelle Cassegrain spectrograph for resolutions of the order of


30,000. Furthermore, a high resolution (λ / ∆λ ≈ 100,000) coudé échelle 

scanner (CES) would be constructed for use with the 1.4-m CAT exclusively. 

This allowed the 3.6-m and CAT telescopes both to be used 100% of the time 

and to “postpone” the extensive work needed to implement the coudé focus 

of the 3.6-m, which still had many adherents. This liberated the personnel 

needed for more urgent instrumentation. The instrumentation plan also 

foresaw the introduction of new electronic detectors as an essential part of 

all instruments, replacing photographic plates. 

The Boller & Chivens spectrograph served the ESO community well for 

nearly a decade. However, its reflecting optics caused significant light losses, 

though it was necessary for covering a large wavelength range. In the 

meantime new glasses had been developed by Schott in Mainz which made 

it possible for Enard to design an all-transmission spectrograph containing 

only lenses and prisms. With the ESO Faint Object Spectrograph and Camera, 

EFOSC, the sum of all the light losses amounted to less than 25%. In addition, 

the lenses were so arranged that the optical beam was parallel over a certain 

distance and here filters and dispersive elements could be placed. These were 

mounted on remotely controlled wheels. By rotating these one could obtain 

images or spectra with different characteristics. This very much enhanced the 

overall efficiency. Instead of losing valuable telescope time while changing 

from imagers to spectrographs or mounting different dispersing elements to 

change the spectral resolution, a few computer commands sufficed to change 

modes in a matter of seconds. Improved versions of EFOSC were later developed 

by Sandro D’Odorico. 

The detector area had some political sensitivities. A. Lallemand in 

France had developed an electronic camera that was far superior in performance 

to photographic plates, but cumbersome to use. After a dozen exposures 

had been taken, the vacuum seals had to be broken, the exposed 

emulsions taken out and the camera rebuilt. At the time the 3.6-m was being 

completed, a Grande Caméra Électronique with a sensitive area of 80 mm 

diameter had been constructed, and it had been envisaged to use this object 

of national pride as a detector at the 3.6-m. However, the new solid state 

detectors that were becoming available in the US were much easier to use 

and they could communicate directly with a computer. So the installation of 

the electronic cameras at La Silla would be a major wasted effort. After the 

initial period up to 1984, in which image tubes, image dissector scanners, 

reticons and digicons had been used, the quality of the Charge Couple Devices 

(CCDs) had become so excellent that they became the detector of choice for 

almost all instruments, be it for imaging or for spectroscopy. Their efficiency 

in yellow light was coming close to values around 80%, i.e. a factor of fifty 

better than photographic plates. 

Infrared astronomy was still in its infancy. The main problem was that 

at wavelengths longer than 2.5 µm everything, including the atmosphere and 

the telescope itself, begins to radiate prodigiously at ambient temperatures.


To detect the faint extraterrestrial sources, rapid switching techniques are 

needed in which the source is compared repeatedly with the “empty” sky. 

Because the atmosphere is rather variable, the switching between source and 

background has to be done dozens of times per second. Moreover, to reduce 

the background due to the infrared instrument itself, the detector and the 

critical optical elements have to be cooled to temperatures of a few K above 

absolute zero. Under the leadership of Alan Moorwood some infrared photometers 

were constructed for the 3.6-m telescope, followed in 1985 by an 

advanced cryogenic infrared spectrograph based on a small solid state 

detector array. 

As a result of the new instrumentation, the ESO 3.6-m / CAT combination 

was changed from a late-comer of the previous era into a fully up-todate 

combination. Instead of having to adapt photographic instruments to 

the new world, the instruments were designed from the beginning for the 

new detectors. Of course, the CAT remained a small telescope (1.4-m) and 

only relatively bright stars could be observed. Later, when efficient optical 

fibers became available, the coudé échelle spectrograph was coupled directly 

to the 3.6-m telescope and the CAT was closed down. Later additional instrumentation 

for the 3.6-m telescope would also include a multiple object spectrograph, 

allowing numerous objects to be observed at the same time, an 

adaptive optics imager (chapter VII) and a very precise radial velocity meter 

for planet detection (chapter XV). 

The La Silla Telescope Park and its cost 

At the end of 1971, construction of the 3.6-m telescope was still to 

begin, but at La Silla smaller telescopes had been springing up like mushrooms: 

a 1.5-m for spectroscopy, a 1-m for photometry, four 40–60 cm telescopes 

(partly in cooperation with institutes in the ESO countries) and a 

1-m Schmidt telescope for photographing the whole southern sky. While 

these telescopes could certainly be justified scientifically and politically, the 

multiplicity of efforts may well have been detrimental for the progress of the 

main project, the 3.6-m telescope. Instrumentation for these telescopes also 

represented much effort. Although this was supposed to create valuable experience 

for the instrumentation of the 3.6-m telescope, hardly anything had 

been built for the latter when it was completed. Later a 2.2-m and a 1.5-m 

telescope were also added (Figure II, 3). 

All these activities came at a considerable cost. Blaauw 7) estimates that 

when the 3.6-m telescope became operational, the (3.6-m) Telescope Project 

Division had been responsible for only 28% of the cumulative ESO expenditure. 

While to this should be added the part of the infrastructure needed 

for the 3.6-m at La Silla, it shows that the cost of the smaller telescopes was 

far from negligible. Later in the 1986 ESO Annual Report, I presented an


analysis of the operational cost of the various telescopes at La Silla. Costs 

incurred in Garching were appropriately apportioned, including those for 

instrumental development, Visiting Astronomers and administrative 

overhead. During 1986 the cost for the 3.6-m telescope came to 4.6 M€ 

Figure II, 3. La Silla in 2003. In the lower part are offices and dormitories. Then 

come some small telescopes, followed by the 1.5-m, the GPO, the 1-m, the 1.5-m DK, 

the 2.2-m and the 1-m Schmidt. Higher up are the NTT and the 3.6-m/CAT and to 

the right the 15-m SEST. Near the bottom is the 15-m inflatable dome for VLT experiments.


(2004 value), that for all the others (except for the 2.2-m) to 6.3 M€. The 

2.2-m is not included here, because its installation was too recent and the 

cost for its initial instrumentation still high. The light collecting power of each 

telescope is proportional to the area of the primary mirror; so the cost per 

m 2 is an appropriate indicator of financial efficiency. For the 3.6-m the 

annual cost amounted to 450 k€/m 2 , that for the others on average 

780 k€/m 2 . Thus, the large telescope was cheapest for collecting a given 

amount of light. While small telescopes may have their uses for special, well 

focussed projects (see Gamma-Ray Bursts in Chapter XI) or for long time 

monitoring of interesting objects, in most cases their cost effectiveness is too 

low to operate them on an isolated site at 10,000 km distance. The economic 

situation is very different in the vicinity of a university campus where a low 

cost operation with students is possible. In fact, by now the small telescopes 

at La Silla have been largely closed down (Table II, 1). 

Table II, 1. The La Silla Telescopes. Subsequent columns give the diameter, the name or 

the national partner, the first and last years of use. For some of the smallest telescopes 

the closing dates are ambiguous, since there was a gradual winding down. The 1.5-m 

Danish is no longer used by ESO. 

2.2-m (MPG) 1983 – 2006? 0.6-m Bochum 1972 – 1998 

3.6-m 1976 – 1.0-m Schmidt 1972 – 1998 

3.5-m NTT 1989 – 0.9-m NL 1979 – 1999 

2.2-m (MPG) 1983 – 2006? 0.6-m Bochum 1968 – 1989 

1.5-m 1968 – 2002 0.5-m 1971 – 1997 

1.5-m DK 1979 – 2006? 0.5-m DK 1969 – 2003 

1.4-m CAT 1981 – 1998 0.4-m GPO 1968 – 1992 

1.2-m CH 1998 – 

1.0-m 1966 – 2001 15-m SEST 1987 – 2002 

In 2004 ESO operated only the 3.6-m, NTT and 2.2-m telescopes. 

From the budget 2004 it appears that the La Silla operating costs amount 

to 5.9 M€. Including also the other cost elements, I estimate a total cost of 

7 M€ for La Silla, corresponding to 300 k€/m 2 for the three telescopes, about 

a third less than 18 years earlier. So the largest cost reduction at La Silla 

during the last decade has been due to the closing of the smaller telescopes. 

These cost figures do not include the capital costs of the construction 

of the telescope. If we assume the 3.6-m continues to function till 2010, its 

78 M€ cost would correspond to some 2.3 M€/year. For the NTT, also with 

a 33 year lifetime, the corresponding figure would be only 0.7 M€/year. So 

the capital cost of these telescopes is below the integrated operating cost 

during their lifetime. Adding the capital and operation costs of the three


remaining telescopes, we find that the average cost of one clear night at these 

telescopes amounts to some 13 k€. 

In political circles sometimes the complaint has been made that astronomers 

are good at inaugurating new telescopes, but not at closing old facilities. 

In fact, when a telescope is to be closed down, it will be said by many 

astronomers that there is still much useful work that can be done with it. 

However, this misses the point. The real issues are the cost-to-benefit ratio 

becoming too high and could the funds needed to operate an older telescope 

be used more advantageously on newer instruments. From Table II, 1 it is 

seen that ESO’s record in this respect is rather favorable. From 15 telescopes 

at La Silla only 5 are still operating, and that number is likely to further 

diminish. The average lifetime of the 10 obsolete telescopes has been 25 years. 

ESO Operations in Chile and in Europe 

Coming to ESO, I found one other aspect that needed radical change, 

the operations in Chile. Here there was an astronomical-technical establishment 

in Santiago far too separated from its raison d’être, the observatory 

at La Silla. Productivity in the agreeable colonial atmosphere of Santiago was 

not very high, and in any case it was not ESO’s role to finance an astronomical 

center there. There was also too large an administrative establishment 

that found unnecessary roles for itself. So I decided to move almost everyone 

to La Silla: astronomers, engineers, technicians and much of the administration, 

leaving only a small office in Santiago. This necessitated the 

construction of more working and living space on the mountain and the transportation 

of the staff members living in Santiago or La Serena to La Silla and 

back at a reasonable frequency. 

Here the solution involved the airstrip that had been constructed for 

emergency purposes at Pelícano, in the plain below La Silla. The astronomers 

in Santiago, who feared the end of their cozy existence, had arranged for one 

of their friends who owned an airplane to fly me to La Silla so that I could 

see how easy it would be to stay in Santiago and to pay visits to La Silla when 

needed. Ironically, this provided the solution in the opposite direction: everything 

could be moved to La Silla, and the required Santiago-based staff 

would work at La Silla on a schedule of eight consecutive days of work, 

followed by six days of rest at home, the transfer being made by air. After 

some initial grumbling most of the staff rapidly got used to the scheme and 

many found the six days vacation every two weeks a positive benefit. Thanks 

to the efforts of Peter de Jonge who managed the difficult transition phase 

very well, it took less than a year for the new setup to be fully implemented. 

The whole arrangement contributed much to the efficient functioning of 

La Silla, also by a much more effective interaction between engineers and 

astronomers. The administration now was closer to the users of its services,


and a smaller number of international staff was far more effective. This arrangement 

functioned well until ESO developed the Paranal site for the VLT. With 

operations at two observatory sites a different structure was needed. 

Managing the mountain was not so simple from the human point of 

view. The enforced togetherness outside working time gave ample opportunity 

to exchange and amplify grievances. The mix of international staff and local 

Chilean staff with different financial conditions also created problems. The 

basic ESO philosophy was straightforward. In professions for which no 

suitable staff could be found in Chile, international staff was employed; to 

find such staff, rather generous payment was required. In professions that 

could be filled by Chileans, staff was recruited locally and paid according to 

the scales of the more favorable Chilean enterprises. How to place individual 

jobs in that scheme remained contentious, and the efforts of the administration 

to design a detailed job classification on the basis of abstract criteria 

were not very helpful 8) . Even though few of the Chilean staff members left 

voluntarily, because better paymasters were not to be found, their large 

number on the mountain led to increasing discontent and, finally, to a strike. 

While this strike led to a number of small measures favorable to the Chilean 

staff, the long term effect was more negative: to avoid the recurrence of a 

situation where La Silla could be completely paralyzed, more and more use 

was made of manpower provided by Chilean companies. 

By 1978, La Silla was a well functioning observatory with an excellent 

large telescope much used by visiting astronomers from the member countries 

and with a slowly growing complement of up-to-date instrumentation. 

Several smaller telescopes were in routine use (1.5-m, 1-m, Schmidt and 

some in the 50-cm class). Soon to come was the 1.5-m Danish telescope, with 

50% of the time available to ESO. For several years this would be the most 

solicited telescope after the 3.6-m, but its initial history was not auspicious. 

In order to save money the 1.5-m mirror was to be polished at an institute 

in one of the ESO countries. Of course, at the end of the polishing its quality 

had to be tested, and I was informed by the two astronomers responsible for 

this that this would be done not by the old outdated methods of ESO, but 

by marvellous new technology involving interferometers. They declared the 

mirror to be excellent and it was shipped to Chile. Upon installation in the 

telescope it was found to have images with 8 arcsecond astigmatism. 

B. Strömgren at Copenhagen saved the day by raising the necessary funds 

to bring the mirror back, to have it polished by a reputable professional 

company and to have it returned to La Silla, albeit with a delay of two years. 

Upon investigation it turned out that these highly modern testers had 

assumed in their method that the mirror was axisymmetric! One of them still 

had the nerve to show up at the next meeting of the IC with a proposal for 

a novel, rather special instrument for the 3.6-m telescope. Nowadays technical 

matters concerning large optics are generally better left to optical 

engineers rather than to scientists.


While ESO operations in Chile were drastically reorganized, important 

changes also took place in Europe. The Telescope Project division at CERN 

in Geneva gradually switched its emphasis from work on the telescope to the 

realization of the instrumentation plan. This also increased the need for a 

stronger interaction between engineers and scientists. In 1975 a “scientific 

group” had been established. Its functions were to increase contacts between 

ESO and the scientists at the member country institutes, to allow young scientists 

to spend time in the ESO environment, to interact with the engineers, 

and to perform research especially in areas of European weakness. Very 

soon this group was also to play a role in data analysis and in particular in 

image processing which was becoming a prerequisite for the effective use of 

the new detectors. The first ESO image processing system, IHAP, was developed 

single-handedly by a young assistant, Frank Middelburg. For a decade, 

it was used extensively inside and outside of ESO. Following his untimely 

death and the appearance of a new generation of computers, a new system 

“MIDAS” gradually took over. 

A further great change in ESO’s European operation came as a result 

of the move to Garching. ESO’s first Director General, O. Heckmann, had 

been the director of the Hamburg observatory at Bergedorf. So looking for 

some space to start the ESO activities, he found it more or less in his own 

backyard. When later the telescope project was transferred to the CERN 

campus, the administration remained behind and the German delegation 

watched carefully that there would be no change in this. In fact, the Germans 

hinted in 1973 at an offer to provide space for the ESO headquarters, but the 

French were reluctant to move the larger part of ESO from Geneva. However, 

while Germany was paying a large share of the budgets of international 

scientific organizations (in ESO’s case 1/3), it had no such organizations on 

its territory. It already had been reluctant to approve CERN II (LEP) in 

Geneva. Moreover, Switzerland was not a member of ESO and taxes (albeit 

at a reduced rate) were levied on ESO salaries. And finally Germany was 

offering to pay for a Headquarters building, while none of the other countries 

would. At the end of 1975, an agreement was reached that ESO would 

retain its European headquarters in Germany. Before coming to Geneva I had 

expected to be able to keep ESO there on the CERN campus. With CERN 

excellent relations in science and technology were beginning to develop. 

CERN was an organization run by physicists for physicists and the intellectual 

environment was most stimulating. Moreover, Geneva is an ideal place for 

international staff families. However, after six months in office I realized that 

this would lead to a political disaster endangering the whole organization. 

So, to the surprise of the staff, I soon became an enthusiastic supporter of 

the move to Germany. 

The choice of the location within Germany was left up to me. An 

appropriate scientific environment was needed, and so the realistic choices 

were Hamburg, Bonn with the Max-Planck-Institut für Radioastronomie and


München with in particular the MPI für Astrophysik (theoretical) and the MPI 

für Extraterrestrische Physik (largely space research). Both from the scientific 

and the environmental point of view München appeared the most 

suitable. The final result was that Reimar Lüst, President of the Max-Planck- 

Gesellschaft, on behalf of the German Government made an offer to construct 

a 3000 m 2 building in Garching to house all ESO’s European activities. After 

some further political hassles, the ESO Council at its meeting in December 

1975 accepted the offer. To celebrate the event, the German delegation took 

the Council to the Munich opera where it so happened that there was a performance 

of Verdi’s La Forza del Destino! As ESO’s requirements were further 

analyzed the building grew to 7000 m 2 , which Germany generously agreed 

to finance. In September 1980 the building 9) was ready for occupation 

(Figure II, 4) and the staff was transferred, though about one third chose to 

quit and remain in Geneva. This led to substantial delays in the completion 

of instruments. New staff had to be attracted and some lost experience 

regained. However, the effects of this shake up were perhaps not entirely 

negative. Technologically in future projects a break with the past was necessary. 

With the partial replacement of the staff this was much easier to achieve. 

There was one more important transaction with the MPG which 

concerned the 2.2-m telescope. In the sixties the MPI für Astronomie had been 

founded to operate observatories equipped with one 3.5-m and two 2.2-m 

telescopes for use by the whole German community. The idea had been to 

Figure II, 4. The elegant ESO headquarters building in Garching near Munich 

designed by the architects Fehling and Gogel. Since this photograph was taken, the 

building has been further enlarged.


place these at Calar Alto in Spain and on the Gamsberg in South West Africa 

(Namibia). Because of political problems with the latter site, the 3.5-m and 

one of the 2.2-m telescopes had been placed at Calar Alto, while the remaining 

2.2-m was stored awaiting better days. However, the political situation 

remained unchanged and having an expensive telescope lying about unused 

and ageing became an embarrassment. Hence an approach from the President 

of the MPG to discuss the possibility of placing it at La Silla. Since the attitudes 

of the MPIA and ESO at the time were rather different, it seemed clear 

that this could only work if ESO would gain full control of the telescope and 

its modernization. After some difficult negotiations an agreement was reached 

under which ESO would receive the telescope on long term loan and have 

the exclusive responsibility for its upgrading and operation. In return the 

MPIA would receive 25% of the observing time. This provided an excellent 

2.2-m telescope at La Silla, suitable for programs that did not require the 

3.6-m, but for which the 1.5-m Danish was inadequate. After the telescope 

began to function successfully the relationship with the MPIA became smooth 

and cordial. 

Other European 4-m Class Telescope Projects 

In 1961 the UK had definitely abandoned participation in ESO and 

decided to have a joint project with Australia for a 3.9-m telescope. The 

telescope was to be as much as possible a copy of the Kitt Peak (Arizona) 

150-inch national US telescope. It was finally completed in 1974 and placed 

on the Siding Springs site near Coonabarabran (NSW) which belonged to the 

Australian National University. While this site was free from the light 

pollution that had plagued the ANU observatory at Mt. Stromlo near 

Canberra, it was only moderately suitable because of its low altitude. 

However, the excellent quality of the telescope, and especially of its computer 

control system, made up for this drawback, and it has been very productive. 

Now that the UK has joined ESO, it is expected that its participation in the 

AAT will diminish. 

The UK – later joined by the Netherlands with 20% participation – 

also developed major facilities on La Palma in the Canary Islands, where it 

now operates 4.5-m and 2.5-m telescopes. The site is excellent for optical 

telescopes, but was considered not optimal for the infrared. So, a 3.8-m IR 

telescope was also built, the UKIRT, at 4200 m on Mauna Kea (Hawaii). It 

is now also part of the UK – NL cooperation. Due to the high altitude atmospheric 

transmission is very favorable and excellent results were obtained even 

in the 300 µm window. 

Also the French were anxious to construct a national telescope. Site 

tests in France and southern Spain gave unsatisfactory results. So they joined 

(initially at 42.5%) the Canadians and the University of Hawaii in the


construction of a 3.6-m telescope on Mauna Kea, a most fortunate choice. 

In the beginning the telescope suffered from an excess of instrumentation. 

This led to frequent instrument changes. Since it takes some time before a 

newly installed instrument functions optimally, this resulted in a significant 

loss of effective telescope time. After this had been corrected, the CFHT 

became very successful, in part because of its excellent site. Today it is 

equipped with a 400 Megapixel CCD camera built in Saclay (F) which allows 

more than one square degree of the sky to be imaged all at once with high 

resolution and sensitivity. 

Italian plans for a national telescope led to the selection of a site near 

Castel Grande in southern Italy. However, thereafter the project stalled. 

Renewed activity began when Italy joined ESO and the plan was made to 

model the telescope on the NTT. It took, however, till 1999 before the 3.5m 

Galileo Telescope became operational at La Palma, the inferior Italian site 

having been largely abandoned in the meantime. 

In Germany it had been difficult to find a suitable organisation to take 

charge of a major observatory. Because the universities belonged to the 

numerous state governments they did not have the capacity for this. Finally, 

the German government funded telescopes to be built by Zeiss, and the Max- 

Planck-Gesellschaft founded the Institut für Astronomie in Heidelberg, which 

opened in 1969 and which was to operate the telescopes. Site surveys in 

Greece and southern Spain resulted in the selection of Calar Alto near 

Almeria, where there are now 3.5-m and 2.2-m telescopes, as well as some 

smaller ones. Unfortunately, the quality of the site is not optimal. From 2005 

onwards Calar Alto will become a joint venture of the MPG and the Spanish 

Research Council. Adding it all up (Table II, 2), we see that Europe has some 

seven 4-m class telescopes at its disposal, about the same number as the U.S. 

A smaller European venture needs to be mentioned – the 2.5-m Nordic 

Optical Telescope (NOT, 1989) at La Palma. This joint venture of Denmark, 

Finland, Norway and Sweden, later joined by Iceland, has been very 

successful because of the excellent image quality.


Table II, 2. The 3.5–6 meter Astronomical Telescopes in the World. 

Country/ Diameter Altitude Usual 

Year Organisation (m) Location (m) Name 

1949 USA 5.1 + Mt. Palomar, 1700 Hale 

California 

1973 USA 4.0 + Kitt Peak, 2100 Mayall 

Arizona 

1974 UK/Australia 3.9 + Siding Springs, 1100 AAT 

Australia 

1975 USA 4.0 + Co. Tololo, 2200 Blanco 

Chile 

1976 Russia 6.0 + Zelentchuk, 2000 

Caucasus 

1976 ESO 3.6 + Co. La Silla, 2400 

Chile 

1978 USA 4.5 + Mt. Hopkins, 2400 MMT 

Arizona 

1979 UK/NL (20%) 3.8 + Mauna Kea, 4200 UKIRT 

Hawaii 

1979 Can/F/USA 3.6 + Mauna Kea 4200 CFHT 

1985 D (MPG) 3.5 + Calar Alto, 2200 

Spain 

1987 UK/NL (20%) 4.2 + La Palma, 2400 W. Herschel 

Canaries 

1989 ESO 3.5 + Co. La Silla 2400 NTT 

1994 USA 3.5 + Apache Pt., 2800 ARC 

New Mexico 

1995 USA 3.5 + Kitt Peak 2100 WIYN 

1999 I 3.5 + La Palma 2400 Galileo 

2004 USA/Brazil/Chile 4.1 + Co. Pachon, 2700 SOAR 

Chile 

+ Alt Azimuth mounting.

III. 

Origin of the VLT Project; The NTT 

Part of the task is done and part remains. Here let us 

rest and moor our boat. 

Ovidius 1) 

By 1978 the 3.6-m telescope had been installed at La Silla, visiting 

astronomers were regularly observing there, the instrumentation plan was 

being executed and the ESO organization functioned smoothly. The member 

states contributed 32.5 MDM (32 M€ 2004 value) annually to the organization 

and some expected that a reduction would be possible, since the main 

aim had been achieved. But though the progress made was very satisfactory, 

there was still much in the Universe that was out of reach even with a 3.6-m 

telescope: galaxies at large redshifts essential to cosmology, the chemical 

composition of stars far away from the disk of our Galaxy and many others 

could be mentioned. Still larger telescopes would therefore be needed in the 

future to analyze problems that could be only dimly perceived with telescopes 

in the 3.6-m class. And while it was most satisfying that Europe now had its 

own large telescopes and that its scientists could begin to compete at world 

level, it was clear that this happy state of affairs could not last forever. If ESO 

did not look for future opportunities others certainly would, and European 

scientists would soon again be at a competitive disadvantage. 

The situation is very similar to that in particle physics. To create new 

and heavy particles or to search for rare decay modes, ever higher energies 

or more intense beams are needed. The result has been that accelerators have 

become bigger and technologically and financially more challenging. This is 

not a quest for bigness per se, but the unfortunate fact that the exploration 

of new areas tends to be ever more demanding. In exactly the same way the 

observation of ever fainter objects requires telescopes of increasing flux 

collecting power. Thus, in California the 60-inch telescope (1908) was 

succeeded by the 100-inch (1917) and the 200-inch (1949) telescopes. Each 

of these allowed major new discoveries to be made.


Construction of the 200-inch telescope was followed by a period of 

stagnation in telescope sizes until the U.S.S.R. 6-m telescope was completed 

in 1976. However, its mirror was so massive that thermal equilibrium with 

the surrounding air could not easily be established, while its long focal length 

required a very large dome. Both had negative effects on the image quality. 

The other large telescopes constructed in the seventies and eighties all were 

in the 4-m class. Nevertheless, much progress was made in the detection of 

fainter objects. The reason was that the efficiency of detectors had increased 

spectacularly. The light detecting capability of a telescope is proportional to 

the total light collected multiplied by the fraction that is actually detected. 

Thus, a 10-m telescope equipped with a detector with 1% efficiency detects 

as much light – as many photons – as a 1-m telescope with a detector that 

has 100% efficiency. The photographic plates used with the 60-inch telescope 

probably had an efficiency of no more than 1% (and because of reciprocity 

failure probably even less for very faint objects). With present day CCD 

detectors efficiencies of up to 80% have been attained. Thus, in a global sense, 

the 60-inch telescope equipped with today’s CCD is equal to a 14-m telescope 

with the photographic plates of a century ago. Of course, this analysis is too 

simple-minded, and other factors have to be considered in the comparison. 

But it is clear that while telescope size remained more or less stationary, the 

effective light gathering power increased very substantially. Now that 

detectors have reached efficiencies close to 100%, no further progress in light 

gathering ability is possible without increasing the telescope size - at least 

when direct imaging is considered. Other reasons to increase telescope size 

relate to angular resolution, which we shall consider later. 

It was clear then that the construction of a telescope larger than the 

3.6-m would be advantageous from a scientific point of view. It was also 

important to start considering such a possibility rather soon. Much technological 

development would be needed. Moreover, if there would be no new 

project, the ESO budget would decline; politically it is much easier, especially 

in an international organization, to maintain a constant budget than to have 

one that first goes down and then has to be increased later. And finally the 

Americans were not sitting still, with first ideas about telescopes of up to 25 m 

diameter being discussed. 

A large telescope does not necessarily have to be made as one unit 

(Figure III, 1). One can also build an array of telescopes and combine their 

output optically or the output of their detectors digitally. In fact, optical 

combination was already being implemented in the multi-mirror telescope 

(MMT), a set of six 1.8-m telescopes of the University of Arizona. The light 

gathering power was therefore nominally that of a 4.5-m telescope, though 

losses in the reflections of the combining mirrors made it somewhat less. At 

the MMT 2) the six telescopes were located in a common mounting, but in 

principle also the light of an array of fully independent telescopes could be 

combined at a common focus, though the combining optics would be more

Origin of the VLT Project; The NTT 45 

a b c 

Figure III, 1. Three ways to build a large telescope. a – A segmented mirror composed 

of a number of hexagonal (or otherwise shaped) appropriately figured segments 

which are accurately supported so that the overall surface has the required form. The 

individual segments should be thick enough to be rigid, but the overall thickness to 

diameter ratio, and therefore the weight, remains low. b – A multimirror telescope 

in which a number of mirrors are placed in a common mounting and the light is 

combined optically. c – An array telescope in which the mirrors have separate mounts. 

Again, the light may be combined optically. A solution of type a has been implemented 

in the two 10-m Keck telescopes in the US and in the Spanish 10-m Grantecan, 

solution b (with only two mirrors) in the 2 × 8 m LBT (US, D, I) and solution c in 

the 4 × 8 m ESO VLT. 

complex. Arrays of this type are required for interferometry, and at the time 

an array of two small telescopes had been constructed by A. Labeyrie 3) in 

France, while large arrays of 1-2 m class telescopes were being advocated by 

M. Disney 4) in the UK. 

So what could be the next ESO telescope project? It seemed to me that 

it should represent a large step compared to what had been done before; it 

was no longer a question of catching up with the rest of the world, but of 

taking the lead. Otherwise it would be difficult to obtain the necessary 

support. A 16-m telescope might be within reach or, more probably, an array 

of telescopes with a total collecting area equal to that of a 16-m. The reasoning 

was simple. ESO had built a very complex 3.6-m telescope at a cost of some 

68 MDM or 78 M€ (2004 value). With an alt-azimuth mounting, a very 

simple building, no exchangeable parts and a highly simplified coudé focus, 

a cost of 20–30 MDM would appear not unreasonable, and newer technology 

might well allow the lower figure. In the preceding decade, the European 

countries had invested in total more than 200 MDM in large telescope 

projects. Hence, with a comparable investment in a large ESO project some 

ten 3.6-m telescopes could be acquired. But if one constructs a large number 

of identical objects, the unit price goes down. With 10 identical objects the 

cost might be about halved. So then some twenty 3.6-m telescopes could be 

financed, corresponding to the area of a 16-m telescope. This estimate


neglected the problems associated with the combination of the light from the 

telescopes and the cost of the instrumentation. But it showed that it was not 

an excessively ambitious aim to build a 16-m equivalent telescope. I made 

the first proposal to do so at the ESO conference “Optical Telescopes of the 

Future” held in Geneva, December 1977 5) . At this conference many interesting 

ideas were presented which also helped to further crystallize our own. Of 

course, the model of twenty 3.6-m telescopes was not a particularly attractive 

option, but it could easily be costed. A more ambitious project with larger 

unit telescopes was called for, but needed more analysis. 

At the time I listed just five illustrative examples of what such a 

telescope would do. They were the following: 

1. Abundances of elements in globular cluster stars. Composition variations 

were believed to be due to differences in the elemental abundances of the 

gaseous medium from which such stars formed, but since only evolved stars 

could be observed effects of stellar evolution could also play a role. But 

adequate analysis of unevolved stars was hardly possible because they 

were too faint for 4-m class telescopes. Actually the VLT has been used 

extensively to study the abundances of cluster and halo stars. 

2. The motion of globular clusters in other galaxies informs us about their 

masses and about their “dark matter” content. 

3. Cosmological studies involving faint galaxies and quasars would be of 

much importance. While the faintest objects might best be detected with 

the Hubble Space Telescope, more detailed spectroscopy of somewhat 

brighter objects would be the domain of the 16-m telescope. This complementarity 

has been very much in evidence with the VLT. 

4. Correlative optical studies of radio and X-ray sources. In fact, extremely 

faint counterparts to X-ray sources have been found at the limit of what 

the VLT can observe. 

5. High time resolution photometry of X-ray sources. Today one would have 

replaced this by observations of remote supernovae to determine the 

structure of the Universe. 

Of course, many other topics could have been listed, in particular also 

in the infrared. 

To me it seemed highly premature to go in one step to a 16-m telescope. 

ESO had constructed a moderately satisfactory 3.6-m. The USSR 6-m 

telescope was the largest in the world. It was a heavy monster. Just scaling 

up these telescopes to 16-m was not going to work. The step to 16 m was too 

large. If something would go wrong, the loss would be total. On the other 

hand, the optical combination of a large number of small telescopes would 

lead to important light losses, which could defeat the aim of efficient photon 

collection. And if all of these would be individually instrumented, the cost 

of the instruments might become a large part of the total. While such an array 

might yield high angular resolution on bright objects when used in an interferometric 

mode, for the imaging of very faint objects it would be far from


optimal. With galaxies and quasars at large redshifts and distant halo stars 

looming as the dominant scientific topics of the future, this was an essential 

point. In a very general way an array of 8-m telescopes would have several 

advantages. Each of these would represent a significant advance in telescope 

technology and scientific capability compared to the 3.6-m telescope. With 

such an array one would have the choice to use the 8-m telescopes, when 

required, as an array, but they could also be used as four large telescopes for 

different projects and perhaps also be instrumented differently. This 

argument was slightly delicate, since if the integrated array concept were too 

much deemphasized very soon funding for only one telescope of 8 m would 

be obtainable. And if the array concept would turn out to be successful, additional 

possibilities would open up – like interferometry. 

Immediately after the conference I asked our technical staff to make 

a first study of three options: one 16-m telescope and arrays of four 8-m and 

sixteen 4-m telescopes. All three would have the same collecting area. With 

this specification I had little doubt that the result would be that one would 

see the disadvantages of the two extremes and therefore settle on the intermediate 

solution. In fact, the solution with 4-m telescopes did not find 

much favor with anyone. It would require complex and expensive combining 

optics if the telescopes would be coupled optically and a large amount of 

instrumentation if each telescope would be instrumented separately and the 

outputs combined electronically. For the infrared larger unit telescopes 

would have significant advantages. Some in the infrared community favored 

one 16-m as this could have an advantage in angular resolution, but there 

was no unanimity about this. There was also the suggestion to place the 16m 

telescope on a very high site with low atmospheric water vapor which 

absorbs IR radiation and, because of the physiological problems associated 

with this, to have it operated by technicians rather than by astronomers. 

Apparently some engineers did not think much of the endurance of their 

astronomical brethren! 

All these studies had been done with an inadequate level of effort, since 

most of the staff was very busy with work on the 3.6-m and CAT telescopes 

and their instrumentation. Moreover, ESO’s departure from Geneva was 

approaching, part of the engineering staff were looking for alternative 

employment, and replacements still had to be found. 

Not surprisingly, there were quite a few astronomers who had other 

ideas of what to do when money would become available. This made it 

dangerous to push the project too much before proper technical studies had 

been made. So, on the one hand, it was important to keep the project alive 

so that it became part of the astronomical consciousness in Europe, but, on 

the other hand, not to stress it too much and too prematurely so that not 

too much opposition would arise. The opportunity to build the New Technology 

Telescope with the entry fees of two new member countries facilitated 

this and allowed the required technologies to be developed.


Italy and Switzerland 

In 1980 ESO’s horizons were suddenly enlarged and wonderful opportunities 

to push telescope development arose. For some years discussions had 

been taking place with Italy and Switzerland concerning eventual membership 

in ESO. The great majority of Swiss astronomers had been interested in 

joining ESO. The Geneva Observatory had obtained permission to place a 40cm 

photometric telescope at La Silla, and its director Marcel Golay pushed 

very hard for membership. From ESO’s side it had been noted that the 

agreement to place that telescope at La Silla was made in the anticipation 

that full membership would follow. Also in Basel much support was given. 

However, the well known solar astronomer M. Waldmeier in Zurich was 

strongly opposed and held up the matter for a long time. So the Swiss authorities 

turned down the proposal. When it became clear that Italy was going 

to join, it was evident that ESO would be the European organization in 

astronomy and the Swiss proposal was successfully revived. According to the 

convention, new member countries would have to pay an “entrance fee” for 

their share in the investments made by the other countries. The negotiation 

about the sum to be paid was essentially political, but had to be justified in 

terms of the assets of the organization and the depreciation thereof. A sum 

of DM 6,000,000 was asked for, which was not quite acceptable for the Swiss. 

Finally, I proposed a compromise on the basis of CHF 5,000,000, which at 

the time was some 10% less than the DM amount, but by the time it was 

paid in 1982 was actually slightly more. 

The negotiations with Italy had been going on for some years, pushed 

forward by Franco Pacini and Giancarlo Setti. Between the two of them they 

covered the most essential parts of the Italian political spectrum in 

parliament. The frequent changes in government had made it difficult to 

progress; in fact, some five subsequent ministers or state secretaries had been 

involved! The decisive push came when Consigliere U. Vattani, at the time 

the Chef de Cabinet of Research Minister Scalia, took a personal interest in 

the matter. A final negotiation took place in Taormina where after some 

discussion our positions were still rather far apart concerning the entrance 

fee. When Minister Scalia arrived and was informed of the situation, he said: 

“My region (Sicily) may be a poor region, but when we arrive at such a 

situation, we usually divide the difference in two” – and so it was done, 

somewhat to the distress of Cons. Vattani who believed that ESO ultimately 

would have been satisfied with less. 

An interesting aspect was that 3 MDM in money would be replaced, 

if technically feasible, by a slice of the 3.5-m disk of fused silica that the 

Italians had acquired earlier for their national project. Since ESO was now 

planning to build a thin mirror telescope and the Italians a copy of this, in 

principle it seemed possible to slice that disk in two. After the agreement had 

been reached, some speeches were held at dinner, and it turned out that the


political people believed that the disk would be cut into two half circular 

pieces! Later it appeared that the distribution of bubbles in the disk made 

the slicing impossible. However, by that time the political negotiations had 

produced a result that was irreversible, and this did not create further 

problems. In Italy it may take many years to obtain parliamentary ratification 

of international agreements. However, Consigliere Vattani, by that time chef 

de cabinet of the prime minister, succeeded to place it on a fast track. By 

1981 Italy was a de facto member and the year thereafter all formalities had 

been completed. Also in 1982 the Swiss parliament ratified the ESO 

Convention, although some deputies complained that ESO membership was 

funded, while a proposal for support of the Rhaeto-Romanic language was 

not. 

According to the ESO Convention (article VII; 4), the entrance fees paid 

by new member states should be used to reduce the contributions of the other 

member states, unless the Council would unanimously decide otherwise. 

Observing time was already in short supply, and with an increase of the user 

community by some 35%, the situation would become untenable. Council 

therefore readily agreed to my proposal to use the entrance fees to build a 

simple 3.5-m New Technology Telescope (NTT) to improve the situation. In 

1982 the budget for this was set at 24 MDM. Upon completion of the NTT, 

a surplus of 3.4 MDM remained, which could be used to instrument the 

telescope. So the cost of the NTT amounted to 21 MDM or some 18 M€ (2004 

value). If we include the uncertain in-house personnel costs, the total becomes 

25 M€ (2004), or only 32% of the cost of the 3.6-m telescope, a remarkable 

progress in some 13 years. 

The annual contribution of the ESO member countries had remained 

fixed from 1976-1981 at 32.5 MDM. By 1982 this constant level would have 

represented a loss of 31% in real terms. The adhesion of the new countries 

made it possible to remedy the situation in a painless way. The contribution 

level in 1982 was raised to 40 MDM. Through partial inflation correction it 

became 49.5 MDM (equivalent to 38 M€, 2004 value) six years later. A rapid 

increase followed to pay for the VLT and thereafter for ALMA. In 2004 it 

amounted to 100 M€. 

While the new member countries were important in increasing the 

financial resources of ESO and allowing a new telescope project to be 

started, perhaps the most significant aspect was that it provided a new 

political legitimacy to ESO as the organization for astronomy in Europe. 

If new countries bothered to join, the organization must have a certain 

importance, and a whole new dynamics arose which gave it the necessary 

momentum and confidence to later start the VLT project. However, at the 

time that the NTT was decided, Council considerably watered down the 

resolution I had proposed in which the NTT was stated to be the prototype 

of the VLT. Anything that looked like a commitment to the VLT was still 

far off.


The NTT 

When in 1980 it seemed that Italy and Switzerland would join ESO, 

it was essential to have a telescope project ready to have a specific destination 

for the entrance fees. While this did not have to be a fully developed design, 

it should at least give a believable cost estimate. Since the available time at 

the 3.6-m telescope would now be shared with an enlarged community, it 

should also be realizable quickly so as to enlarge the pool of observing time. 

With a slice of the Italian mirror being part of the deal, the diameter was 

fixed at 3.5 m. And even though officially there was no connection to the VLT, 

the new telescope should serve as a demonstration of various technologies 

which later could make the case for that project more convincing and show 

that it could be constructed at an acceptable cost. Thus, cost and speed 

became the dominant design criteria for the NTT. 

The 3.6-m telescope had had a high cost because it was mechanically 

awkward with its polar mount and multiple focus options based on exchangeable 

top units, because it was heavy and because it was enclosed in a very 

large building, which accounted for some 40% of the total cost. The building 

was 30 m in diameter. It was 30 m high, with a 30 m diameter dome on 

top, because it had been believed that the atmospheric turbulence would be 

reduced far above the ground. However, it was beginning to be clear that the 

large volume of the telescope enclosure did much harm with turbulence 

created by warm areas in the building degrading observing conditions. At Las 

Campanas, 50 km from La Silla, the Carnegie Institution had built a 2.5-m 

telescope and because of its limited budget it had been placed in a low 

building. No harmful effects were in evidence. So to bring down the cost of 

the NTT, the general guidelines were simplicity, weight reduction and a 

small building volume. More specifically the following items were considered 

important 6) : 

(1) The NTT would have an alt-azimuth mounting. The more straightforward 

mechanical structure would weigh less and have lower cost. 

(2) The alt-azimuth design provides, rather naturally, two Nasmyth foci 

where heavy instruments may be placed on platforms rotating with the 

telescope (Figure III, 2). The light is deflected by a flat mirror at an angle 

of 45˚ with respect to the optical axis (Figure II, 1). To go from one 

Nasmyth focus to the other the mirror must be turned by 180°, a relatively 

simple operation. As a result, one may switch very rapidly from an 

instrument at one focus to another at the other focus. This makes 

instrument changes very much less cumbersome than at the Cassegrain 

focus of the 3.6-m, where one instrument has to be removed to make 

place for another, which in practice cannot be done during the night. It 

is also considerably more efficient than the complicated coudé setup 

which has additional reflections in most versions and a small field of view. 

The Nasmyth flat mirror takes away some 15% of the light, and so there


Figure III, 2. Model of the NTT. The telescope rotates around a vertical axis (the 

azimuth axis) on a large bearing; the telescope tube can rotate from horizontal to 

vertical on the elevation axis. The housing of the direct drive motors is visible on this 

axis. The light of a celestial object first falls on the 3.5-m mirror at the bottom of the 

tube, returns to the secondary at the upper end and then is directed by the third, flat, 

Nasmyth mirror sideways through the elevation axis to either the left or the right 

Nasmyth focus where instrumentation may be placed. In this model, the Nasmyth 

platforms have not yet been mounted. The black baffle shields the Nasmyth mirror 

from stray light. 

were some wishes to also have a Cassegrain focus. However, this would 

have required a mechanism to take the flat mirror out of the optical path 

and a prolongation of the fork to accommodate instrumentation. This 

would have added a significant cost to which I could not agree. 

(3) The length of the telescope tube is largely determined by the focal length 

of the primary mirror. A low focal ratio (focal length / mirror diameter) 

allows a short tube. This reduces the size of the enclosure housing the 

telescope. However, a mirror of low focal ratio (usually called a “fast” 

mirror) was more expensive to manufacture , and in general the optical 

tolerances are tighter if the mirror is very fast. From such considerations 

an optimal focal ratio 27% smaller than that for the 3.6-m was adopted.


As a result of this and of the compact alt-az design, the mean diameter 

of the enclosure was 19 m, instead of 30 m for the 3.6-m telescope. 

(4) The height of the building would be much smaller than in the case of the 

3.6-m telescope (Figure III, 3). The top of the dome of the latter was more 

than 40 m above the ground. The highest point of the enclosure of the NTT 

was only at 17 m, and its total volume only one fifth of that for the 3.6 m. 

(5) Since the telescope rotates around the azimuth axis, all connections between 

it and a stationary building (cables, pipes, etc.) have to be made in a rather 

special way. At the MMT of the University of Arizona it had therefore been 

decided to let the building rotate with the telescope, and this same solution 

was adopted for the NTT. This had another major advantage. Since with 

respect to the building the telescope moved only in elevation, walls could 

be placed on either side. This allowed all heat sources to be away from the 

telescope and thereby to eliminate much of the dome turbulence that had 

plagued the 3.6-m. In addition, no classical dome was needed and the 

telescope enclosure could be designed in a more cost effective way. 

(6) The telescope drive also would contain a major innovation – the use of 

large torque motors. Keeping a telescope pointed to the same point in 

the sky to within a fraction of an arcsecond requires a very finely tuned 

drive system. This had generally been achieved in large telescopes by a 

set of gears which diminished the requirements on the precision of the 

motors by a substantial factor. However, in the meantime, very large 

torque motors had been manufactured in the USA, which could be directly 

Figure III, 3. The relative sizes of the enclosures of the 3.6-m (black), the VLT 8.2-m 

unit telescope (green) and the 3.5-m NTT (red). Since the latter two are not circularly 

symmetric, they would have somewhat different shapes when seen from different 

directions.


mounted on the telescope axes. In fact, at the 1.4-m CAT such motors 

were already in use and functioned well. However, much bigger motors 

were required to steer the larger mass of a 3.5-m telescope. The great 

advantage is that the backlash in the gears is eliminated and the overall 

control system is simplified. 

7) The greatest innovation would be the use of active optics, pioneered by 

Ray Wilson at ESO 7) . In conventional telescopes mirror deformations 

under the changing orientation of gravitational forces had been minimized 

by making the mirror thick – typically with thickness / diameter 

about equal to 1/6. Such a mirror is heavy – of the order of 10 tons for a 

3.5-m mirror. But even a thick, heavy, stiff mirror will experience serious 

deformations due to gravity when the telescope moves. The mirror is 

therefore placed in a “mirror cell” in which it is supported by an appropriate 

set of levers that should compensate the varying gravitational forces. 

If the mirror is thick enough a rather simple setup is sufficient. For large 

telescopes the weight of a thick mirror becomes prohibitive, and other solutions 

are needed. Active optics holds the key. 

If a mirror is deformed from its perfect shape, the image of a star 

becomes distorted too. With an “image analyzer” the nature of the deformation 

may be ascertained. By exerting appropriate forces on the mirror the 

deformation may be removed and the image quality restored (Figure III, 4). 

Figure III, 4. Active Optics. The light of a star is reflected first by the primary mirror 

supported by a large number of motorized levers which determine its shape. Subsequently, 

it is reflected by the secondary mirror, the position of which can also be 

adjusted by motors, and finally brought to the focus by a third, flat, mirror. Some of 

the light is analyzed by a wavefront sensor coupled to a computer which determines 

the corrections to be made to the shape of the primary and the position of the secondary 

for optimal imaging and which sends the appropriate instructions to the motors.


The image analyzer may, for example, be based on a “Hartmann screen”, a 

screen with a regular array of holes placed in the parallel beam or closer to 

the focal plane. When a photographic plate is placed some distance from the 

focal plane, a set of spots is seen. If the mirror is distorted by large scale 

deformations, the positional pattern of the spots is also deformed. When the 

photographic plate is replaced by a solid state detector (CCD) with the readout 

directly fed into the computer, the spot positions may be determined on 

line. 

The mirror is supported by motorized levers or pistons that exert 

forces on the mirror (Figure III, 5). After having calibrated the relation 

between the magnitudes of these forces and the deformations of the mirror, 

it becomes a simple matter to have the computer translate its knowledge of 

the deformation of the mirror into instructions to the motors so that the 

required forces are applied to undo the deformation. 

Figure III, 5. Support system for a 1-m mirror active optics experiment at ESO. Each 

support is adjusted by a motor which in turn is computer controlled. The instructions 

of the computer are based on the measurements of the wavefront sensor which 

determines the corrections needed to the shape of the mirror to compensate for its 

deformations.


To control the 3.5 m diameter mirror of the NTT 78 axial levers are 

required (Figure III, 6) and for the 8.2 m VLT mirrors 150, but enough 

computing power is nowadays available to control these appropriately. In the 

same way also the position of the secondary mirror in a Cassegrain system 

may be controlled. Since a sufficiently bright reference star may not be available 

near to the object, in practice the active optics measurements are made 

only from time to time and the levers adjusted in between by extrapolation 

based on previous experience. 

Active optics also relaxes the specifications for mirror polishing and 

thereby may reduce cost and allow the correction of errors. A thick mirror 

has to be polished to high specifications to avoid image deformation. With 

a thin actively controlled mirror errors in shape can be partly corrected. The 

problems of the Hubble Space Telescope (wrong focus of the primary) could 

have been corrected remotely if it had had an active optics system. Of course, 

small scale roughness cannot be corrected. With a system of levers only errors 

on at least the scale of the separation between levers can be dealt with. 

Figure III, 6. The main mirror cell of the NTT. The 78 actuators are placed in four 

rings. Above the mirror cell is the main massive support structure between the two 

wheels that steer the telescope in elevation. The support structure for the secondary 

mirror is partially visible at the top.


With active optics the primary mirror could be thin. If the mirror 

weight is smaller, the telescope tube can also be less heavy, and finally the 

whole telescope will have less weight and thereby less cost. The concept 

seemed very promising, but it had not yet been tried in a real telescope. I 

therefore concluded that one should not go to the extremely thin mirror that 

this technology allowed, but keep the mirror thick enough that even with the 

classical support systems acceptable images would be obtainable. After all, 

it would be a disaster for the prospects of the VLT if the NTT would not 

function correctly within a reasonable time. At the same time, the 3.5-m 

mirror should be thin enough to test the active optics scheme. The aspect 

ratio (thickness/diameter) was finally set at 1:15 to be compared with 1:6 for 

the 3.6-m telescope. As a result, the weight was only 40% of that of the latter. 

A very preliminary mechanical design by Wolfgang Richter, based on an altazimuth 

mounting, sufficed to estimate its cost. 

As soon as the Italian and Swiss parliaments had ratified the ESO 

Convention, a small NTT project group was set up at ESO. Initially it was headed 

by Ray Wilson who had developed the active optics concepts. However, he did 

not find project management very congenial and at his request was succeeded 

by Massimo Tarenghi who later also would successfully manage the VLT. This 

led to a tight management which, though essential for the project, did not please 

everyone. Evidently during the conceptual phase it is best to “let a thousand 

flowers bloom”, but once contracts have been concluded, changes should be 

infrequent and deadlines should be met. If not, the cost rapidly escalates. 

While ESO had made the conceptual design, a detailed design as the 

basis for a construction tender had to be done and after the move from 

Geneva ESO’s manpower was inadequate to do this in-house. A tender was 

given out and several offers were received; included were a very satisfactory 

offer by Krupp-MAN that was selected, and a technically totally inadequate 

offer from a firm in another country at only 40% of the price. This led to 

some political upheaval, and it took much effort to have the contract approved 

by the ESO Finance Committee. While price is a relatively simple criterion 

to compare contracts, quality is necessarily more ambiguous. 

Another problem was how to acquire a disk for the mirror. It had been 

found that the idea of slicing the Italian disk, which had played a very useful 

role in the political discussions, was not feasible. Initial contacts with Schott, 

the maker of Zerodur, did not yield a satisfactory price. So it was decided to 

talk in Moscow about a possible disk in astrosital, another low expansion 

material. The concern here was that this would have too much internal 

tension since it was to be cut out of pieces of a cracked 6-m disk. Discussions 

took place on how to test such a disk in East Germany, since gaining 

full access to the factory in Moscow proved difficult. I had expected that 

Schott would not wish to have competition from astrosital in western markets. 

In fact, rather soon a much more satisfactory offer for a Zerodur disk was 

made by Schott and accepted by ESO.


Some ideas had also been developed about mirrors in aluminum or steel, 

and some experimental studies were being performed at ESO. These experiments 

were continued for some time in case problems would be encountered 

with the acquisition of mirror blanks for the VLT, but for the NTT it seemed 

preferable to stay with the proven Zerodur. Though this was disappointing to 

the optical engineers who looked forward to an interesting innovative mirror 

experiment, the approach of the VLT decision necessitated the most rapid 

completion of a system that was guaranteed to work. In 1986 the Zerodur disk 

was delivered and sent to Zeiss for polishing. By mid-1988 the polishing had 

been completed and a test of the complete active optics system was made, 

which showed the high quality of the mirror and the successful implementation 

of the active optics concept. Later that year the mirror joined the 

mechanics (Figure III, 7a) and enclosure erected at La Silla (Figure III, 7b). 

Figure III, 7a (left). The NTT. Below the floor is the azimuth bearing and the base of 

the fork-like structure. Behind the walls on the sides are the Nasmyth platforms. So 

the telescope is shielded from most sources of heat which could cause turbulence in 

the air in or above the tube of the telescope and degrade the image quality. In the 

upper ring is the support structure for the secondary mirror whose position is computer 

controlled. In the square structure is the support for the Nasmyth mirror which can 

send the light to the left or to the right through the elevation axis. Below this the 

primary mirror and its support structure are seen. 

Figure III, 7b (right). The enclosure of the NTT. The telescope rotates in azimuth on 

a high precision hydrostatic bearing, while the enclosure rotates along on a simpler 7m 

roller bearing. The metallic structure of the enclosure is of much lower cost than a 

conventional building plus dome.


Finally, on the night of 22 March 1989 the first direct CCD images were taken; 

by luck that night also the atmospheric turbulence was low and the images 

were probably the best ever taken by a ground-based telescope. 

The successful completion of the NTT showed that ESO now had the 

engineering competence for innovation in telescope technology. While the 

3.6 m telescope had been one of the last of the previous generation of large 

telescopes, the NTT was the first of a new generation of telescopes based on 

active optics, new control concepts and rationally designed enclosures which 

suppressed dome seeing. The success of the NTT gave the ESO countries the 

confidence that the VLT had become a realizable dream. 

One last question remained to be settled when the telescope mechanics 

were shipped to Chile. Where should the NTT be placed? By 1986 the 

excellent qualities of the Paranal site had become clear, though the site 

testing was far from terminated. While the Paranal peak itself had been 

reserved for the VLT, there was a small hill somewhat lower and usually 

upwind from Paranal that would provide an excellent place. Some tests were 

made there which indicated that the quality of what became to be known as 

“NTT hill” could be expected to be excellent. While I was very much tempted 

to place the NTT there, the total absence of any infrastructure at Paranal 

would be difficult. Since the NTT was a highly innovative telescope, it was 

not excluded that there would be problems that would be much easier to solve 

at La Silla. The risk was too great, and serious problems with the NTT would 

have endangered the VLT. So, the NTT was placed at La Silla. If the NTT 

had been in the Paranal area, subsequent considerations about the future of 

La Silla and its relation to Paranal might have been much simplified.

IV. 

Technological, Financial 

and Scientific Planning of the VLT 

Ein bis dahin unbekannter, beinahe politisch zu 

nennender Gemeingeist hat eine Organisation 

entwickelt, die auf ein wissenschaftlich ganz neues 

Niveau hinstrebt. 

Otto Heckmann 1) 

On 1 September 1980 ESO’s scientific-technical establishments moved 

from CERN, Geneva, to Garching near Munich. Nearly half of the technical 

staff did not follow ESO and so their personal priorities became rather 

different from those of ESO. Moreover, the staff who moved to Garching had 

to get settled there, contribute to the recruitment of new staff and introduce 

the newcomers to the various projects. As a result, the move delayed ESO’s 

projects by a year. By the time the new ESO establishment was inaugurated 

on 5 May 1981 by the President of the Federal Republic of Germany, most 

of the scars from the rupture had been removed and the organization again 

began to function normally. 

There were at that time still several major instrumental projects for 

the 3.6-m telescope at La Silla which had to be completed urgently if that 

telescope were to be competitive. As a consequence, the technical staff hardly 

could devote much time to projects for the more distant future, including the 

VLT. Moreover, the development of the NTT already stressed the available 

manpower. Still advances could be made by involving a number of scientists 

from the ESO countries in discussions of some critical issues. I therefore set 

up a “VLT Study Group” under the chairmanship of Jean Pierre Swings of 

Liège, with a core membership of about a dozen scientists and engineers 2) 

and with additional contributions by a number of interested persons. About 

twenty meetings of the Study Group took place. This led to a workshop with 

46 participants, two thirds from institutes in the ESO countries and the others


from ESO, held in Cargèse, Corsica, 16-19 May 1983 2) . Among the conclusions 

reached there were a reaffirmation of the 16-m equivalent diameter, a 

strong inclination towards an array of three or four telescopes with monolithic 

mirrors, and a lukewarm emphasis on interferometry with the large 

telescopes. The latter resulted from studies by Pierre Léna 3) and François 

Roddier 4) which indicated that the gain in limiting magnitude with larger 

telescopes was rather small due to the effects of the earth’s atmosphere. For 

interferometry more numerous smaller movable telescopes seemed preferable 

to the large fixed ones. 

This created a dangerous situation from the political point of view. In 

particular for the French, interferometry was a high priority. And it could 

easily be argued that four eight meter telescopes would be very nice, but that 

with three one could do already a great deal and then the cost reduction could 

be used to build an interferometric array of smaller telescopes. Of course, 

the three 8-m telescopes could easily become two and then one at even 

greater savings. 

I had always considered interferometry an interesting option for the 

VLT, but without much confidence in its early realization. True enough, one 

had already measured the diameters of some bright stars by interferometric 

methods; but until one would be able to make images and to reach faint 

objects, the scientific benefits seemed insufficient. The solution to the problem 

was to add two (now four) small mobile telescopes to the VLT. If more efficient 

ways to do interferometry with the large telescopes could be developed, 

then perhaps an integration of the whole setup would become worthwhile. 

Another reason to combine the VLT and the small telescope interferometry 

was that for a project of the financial size of the VLT it would pay to look 

for the world’s best site. Since interferometry was extremely sensitive to the 

“seeing” quality of a site, placing it at the best possible site was imperative. 

Thus, the proposal became to enlarge the VLT project of four 8-m telescopes 

by including some mobile 1.5-m (finally 1.8-m) auxiliary interferometric 

telescopes. This combination now looks optimal, indeed. A start has been 

made with a modest interferometric program, and the large telescopes have 

been successfully combined in some experiments. With the successful implementation 

of adaptive optics in the individual telescopes, the interferometric 

option now looks more promising. 

By the end of the Cargèse meeting a large part of the European 

community had become convinced that an array of something like 3–4 

telescopes in the 8–10-m class was what was needed for the future. So in 

May 1983 a qualitative consensus on the scientific rationale and on the technological 

philosophy of the VLT was largely in place. Now it became necessary 

to convert these vague ideas into a project with a clear architecture and cost. 

While the Swings study group had done an admirable job in shaping an idea 

that enjoyed wide support in the community, this next phase clearly needed 

a much stronger engineering input. This could not be done on the basis of

Technological, Financial and Scientific Planning of the VLT 61 

the part-time involvement of a few people. A full time VLT project group was 

needed which was soon set up, headed by Daniel Enard, with initially five 

full time persons, but also support from other parts of ESO. Since the VLT 

would become a major industrial project, this group needed a dedicated 

budget with which to award study contracts to industry to explore technical 

feasibility and cost. Furthermore, to continue the close connection with institutes 

in the ESO countries and to supplement the activities of the project 

group, a VLT Advisory Committee was set up with five working groups: Site 

Selection, High Resolution Spectroscopy, Low Resolution Spectroscopy, 

Infrared Aspects and Interferometry, in which 32 outside scientists participated, 

again under the overall chairmanship of Swings. 

Very early in the VLT studies it had appeared that while there would 

be many problems in mechanics and controls, the critical item, both technically 

and financially, would be the acquisition and polishing of the 8-m mirrors. 

The only European manufacturer of suitable mirror material was Schott in 

Mainz, which had developed “Zerodur”. This is a glass ceramic of excellent 

uniformity and polishability with a very low thermal expansion coefficient. So 

a mirror of Zerodur does not change its focal length when the temperature of 

the telescope changes. This is archieved by having on the microscopic scale a 

mixture of glass with a positive expansion coefficient and crystalline material 

with a negative one. At the appropriate temperature ( 800 – 1000 °C) the 

glass slowly crystallizes; in the case of the 8-m mirrors the right balance would 

be obtained after about eight months. First, however, the glass disk has to have 

more or less the right shape. While for smaller mirrors, like the 3.5-m for the 

NTT, this may be achieved by machining away the necessary material, for large 

thin mirrors this would be very uneconomic. Hence, Schott proposed to use 

spin casting which they had previously used in other contexts. The molten 

material would be poured into a form having the shape of part of a sphere. 

When this form would be rotated, the centrifugal forces would give the upper 

surface also a concave shape. Upon cooling this shape would remain and 

thereafter the ceramization process would be started. 

So by the time the VLT proposal was written, the way to an 8-m blank 

was technologically clear. However, the existing facilities at Schott were 

inadequate and a new factory building would have to be constructed, which 

would add to the cost. Some informal discussions about a possible contract 

had taken place before the approval of the project, but neither the technical 

nor the financial viability had been unambiguously established. It was 

therefore necessary to study other possibilities in case unforeseen technological 

problems would arise and also to maintain a competitive pressure on 

the price. One alternative was to use fused silica. In fact, procedures had been 

developed by Corning in the USA for fusing silica pieces together, and this 

technology had no apparent size limits. 

A radically different possibility was to use metal mirrors 5) . These had 

been extensively used in the nineteenth century but abandoned because of


the high thermal expansion and also problems with polishing and corrosion. 

An attempt at resurrecting aluminum mirrors had been made in the sixties, 

but had been unsatisfactory because of warping at the edges. However, this 

problem may have been more a consequence of the thin rimmed vase-like 

shape given to these mirrors than of the use of aluminum per se. Since the 

thermal expansion problem did not seem prohibitive if active optics were 

implemented, it seemed worthwhile to start a program of studies of metal 

mirrors. Actually the high thermal conductivity of metals might be an 

advantage in allowing a fast control of the temperature of the mirror to 

prevent turbulence in the air in the telescope tube above it. Aluminum had 

many attractive properties, but the drawback that it could not be polished. 

Thus, it had to be coated with a layer of harder material – actually canegen, 

a nickel alloy. The long term stability at the interface of the two materials 

was a source of concern. It therefore seemed attractive to look at harder 

metals that could be produced in large disks, and here steel offered itself as 

a low cost possibility. Among the specialty steels polishable materials could 

be found. Some steel disks were fabricated and initial tests were satisfactory 

(Figure IV, 1). 

Since the steel mirror tests involved only 50 cm disks, a substantial development 

program would still be needed for the metal option. The long term 

characteristics of the metal mirrors remained uncertain, while much experience 

existed with Zerodur. So it was decided to go for Zerodur in the VLT project 

plan, although for some time the metal option was kept alive, just in case. 

Figure IV, 1. A 50-cm experimental steel mirror. At a time when it was uncertain 

that affordable Zerodur 8-m mirrors could be made, experiments were started at ESO 

with steel and aluminum mirrors.


The metal development phase was concluded in 1990 with the 

successful fabrication and testing of two 1.8-m aluminum mirrors which 

were subjected to stringent thermal cycling, showing a good long term 

stability. By that time, however, a contract had been concluded with Schott 

which was completing the construction of a new facility for casting 8-m 

Zerodur disks. Since ESO had its hands full with the execution of the VLT 

project, it was not possible to invest further effort in more long term technological 

mirror developments. However, now that new, larger telescope 

projects are beginning to be discussed, it might well be worthwhile for technological 

institutes or universities to further study metal mirrors. 

Another important issue concerned the polishing of the mirrors for 

which a major new industrial facility would have to be constructed. This 

would include not only a computer controlled polishing machine, but also a 

tower of substantial height to house the necessary optics to test the mirrors. 

The tower was to be evacuated of the atmospheric air or perhaps to be filled 

with helium so as to avoid problems with variations in temperature with 

attendant optical refraction. This was particularly important because of the 

unusually tight tolerance imposed on the optics –80% of the light within a 

circle of 0.15 arcsecond diameter, almost a factor of three better than the 

specification of the 3.6-m telescope. While in the past the atmosphere had 

in practice limited image diameters to 0.5 arcsecond or more, speckle interferometry 

(the effective superposition of short exposures to reduce the effects 

of atmospheric turbulence) could do better, and the realization of the dream 

of compensation for atmospheric effects by adaptive optics was beginning to 

be clearly visible on the horizon. 

Two study contracts were given to Zeiss in Germany and to REOSC in 

France, the two companies in Europe with experience in the polishing of 4-m 

class mirrors. The results of these studies confirmed that the polishing of thin 

8-m mirrors would be feasible and that the cost might be manageable within 

the VLT budget. Such thin mirrors are very delicate and have to be handled 

with care to avoid breakage. For example, lifting a thin mirror with only 

support at the edges would lead to a catastrophe. Another issue concerned 

transport, which would mainly occur over waterways. So the possibility for 

transport from the factory to the nearest waterway was studied. It was found 

that for an 8-m mirror there would be no problems, but for a 10-m serious 

difficulties would occur. After all it would not be very good to get stuck under 

a bridge! 

The issue of the mirrors is important for the technical aspects and the 

cost of the whole project. If the mirrors are heavy, the metal tube of the 

telescope has to become stronger and heavier and this weight increase propagates 

through the whole structure which has to be supported by more 

powerful bearings. Thus, the thinner the mirror the better. However, there 

are limits if the mirror is not to become too fragile and also because of the 

fabrication process. It is simplest to figure a mirror with a relatively long focal


length. But if the focal length is long, the secondary has to be far away from 

the primary mirror, the telescope tube becomes long and heavy, etc. Also, 

the longer the telescope tube the larger the enclosure has to be, and this again 

augments the cost. The determination of the optimum characteristics of the 

mirrors to obtain the lowest cost is therefore a complex process. Finally a 

focal length 1.8 times the mirror diameter was chosen. 

Another issue was the housing of the telescopes. In the case of the 

3.6-m telescope dome and building had accounted for nearly 40% of the total 

cost, which for the NTT had been brought down to 20%. The much reduced 

building cost would be accompanied by a significant improvement of telescope 

performance, since “dome seeing” associated with thermal disequilibrium of 

the air in the dome was much reduced. The question then was whether 

further improvements and cost reductions would be possible by operating the 

telescope in open air and having a simple housing to protect it during the day 

time or in bad weather. In this spirit a solution was explored where the four 

telescopes would be placed on a straight line, with during the night only a 

wind screen and during the day an inflatable dome as protection 6) . Such inflatable 

structures had been used in various places in the world to protect 

radar dishes. A 15-m diameter inflatable dome was ordered and placed at La 

Silla for experimental purposes. Of course, these inflatable domes were more 

complex than those for radar domes, since they should be opened every night. 

A model of the VLT (Figure IV, 2) with the inflatables was made and extensively 

used for familiarizing the scientific community and governmental 

representatives with the VLT. Since this created the image de marque of the 

VLT, it seemed dangerous to change it before the project was approved. 

However, in the “VLT Proposal” it was made clear that this was “only the 

presently nominal solution within a general concept”. Perhaps not surprisingly 

wind tunnel experiments later showed that cylindrical structures with 

a natural but controlled air flow were superior to the open air operation, especially 

when the wind was relatively strong. Also the linear telescope array 

seemed non optimal for interferometry, and the four telescopes were finally 

placed in independent enclosures in a somewhat different configuration. 

The mirror disks, the polishing and the enclosures together were estimated 

to account for half of the telescope cost. At the same time they 

created most of the uncertainty. There were, of course, many other issues 

of importance to be considered. The mechanical structure (Figure IV, 3) had 

to be optimized to avoid vibrations, the design of the active optics system 

and the mirror cells had to be refined and scaled up from the NTT design 

and the control system had to be upgraded with newer computers. In the 

early developments the software aspects took second place, but in order to 

obtain a working telescope a major software effort would be needed. All of 

this was essential for the functioning of the VLT, but one had enough knowledge 

to see how this could be done and to determine the cost with some 

confidence.


Figure IV, 2. The first VLT model. The four 8-m telescopes were placed on a common 

platform in inflatable shelters. Observations would be made in open air, and to 

reduce the effects of wind, a screen would be mounted on the side of the prevailing 

wind. At the bottom of the telescopes the pipes are visible that would bring the light 

beams from the unit telescopes to the interferometric laboratory in the middle to the 

left. The linear arrangement was not optimal for interferometry, and there was 

concern about turbulence created by the wind screen. So later the telescopes were 

placed individually in protective enclosures. 

A difficult issue arose with the secondary mirror. Since in the infrared 

beyond two microns there is strong background radiation due to the atmosphere 

and the telescope, it is essential to continuously monitor the background 

when measuring the flux from a weak source. The optimal way to do this is 

to wobble the secondary – to move it back and forth between two positions 

as frequently as possible – and then to measure the difference signal between 

the source position and the background reference position. But in an 8-m 

telescope the secondary mirror is a large (1.2 m), massive object and to move 

this back and forth some ten times a second is no small matter. It is therefore 

important to reduce the weight of the secondary as much as possible.


Figure IV, 3. Early model of an 8-m unit telescope. The support structure for the 

elevation axis is placed on the large circular azimuth bearing. The two yellow boxes 

contain instruments with the light entering through the elevation axis. The light beam 

to the coudé focus and to the interferometric laboratory passes through the white tube. 

The Nasmyth mirror which directs the light into the elevation axis is just visible At 

the time no Cassegrain focus was foreseen, because it would necessitate an increase 

in the height of the elevation axis and a mechanism to remove the Nasmyth mirror 

out of the Cassegrain beam with significant cost implications. In later designs of the 

telescope tube (Figure V, 4) fewer tubular structures of greater strength and a solid 

center piece replaced the numerous small elements to improve the stiffness of the tube. 

While a tolerable result could be achieved with a zerodur mirror, a substantial 

weight reduction would very much enhance the performance. The possibility 

of beryllium as a mirror material was therefore explored. This material is not 

easy to handle being quite poisonous as a powder. Some experience had been 

gained in space applications, though only with smaller mirrors. Ultimately 

beryllium mirrors were chosen, but serious problems were encountered before 

full success was attained. Of course, the wobbling secondary also had to be 

made compatible with the active/adaptive optics system.


One issue led to controversy: should the unit telescopes have only the 

two Nasmyth foci that naturally go with the alt-azimuth mounting or should 

there also be a Cassegrain focus? Not surprisingly the scientists wanted this, 

since it reduced the number of reflections from three to two with a 15% 

reduction in light losses. In addition, it would have a much improved polarization 

performance. However, the technical implications were serious. For 

the light to reach the Cassegrain focus the Nasmyth mirror would have to be 

removable out of the light path. Moreover, to have space for the Cassegrain 

instruments, the altitude axis would have to be moved higher with consequences 

for the mechanical structure and the enclosure. It was clear that all 

of this would have a significant cost impact, and so it seemed dangerous to 

include it in the baseline VLT proposal; however, the Cassegrain option 

could be reviewed later. A year thereafter, when a new Director General had 

taken over, that review led to the inclusion of the Cassegrain. It was approved 

by Council without much discussion of the increased costs that would be 

incurred. Not surprisingly it was later claimed that the VLT proposal had 

underestimated the costs. A realistic analysis ten years later showed that the 

extra costs incurred were largely the consequence of such extra requirements 

(see chapter V.). 

The VLT project group, which between 1983 and 1987 gradually 

increased from 5 to 10 persons, made a very complete preliminary design, 

outlining also choices that could be made following more detailed studies. 

The resulting proposal, including the cost estimates, inspired confidence. 

Particular care was taken to remain consistent: The 16-m equivalent diameter 

never varied, the four telescope array concept was there from the beginning, 

though the exploration of alternatives was necessary to establish that this was 

really the optimal solution. And most importantly for gaining support from 

the governments in the member countries, the overall financial envelope 

remained the same during the ten years leading up to the proposal in 1987. 

Galileo had made the first telescopic observations of stars and planets 

in Venice. So it was only appropriate that ESO presented the VLT design to 

the European astronomical community in Venice at the end of September 1986 

at a workshop at the beautiful property of the Cini Foundation on the Isola 

di San Giorgio (photograph overleaf). Some 80 scientists participated, and a 

consensus of the great majority was achieved. In March 1987 the complete 

proposal (dubbed the “Blue Book”) was presented to Council. Much of the rest 

of the year was used for the resolution of the last political problems. In some 

countries these centered around the issue of what national projects should be 

reduced or abandoned. Finally, in December 1987 Council unanimously 

approved the project with a total budget of 388.2 MDM (1986), corresponding 

to 300 M€ (2004), including instrumentation and interferometry. Only six 

member countries could guarantee their participation. However, in 1988 also 

Belgium was able to join, followed by Denmark in 1989. The largest project 

ever undertaken in ground based astronomy was on its way.

68 Europe’s quest for the Universe

V. 

Construction of the VLT 

Could we handle that dumb thing or would it handle us? 

I felt how confoundedly big, was that thing … 

Joseph Conrad 1) 

While many aspects of the realization of the mechanics, electronics and 

enclosure would require much effort at ESO and in industry, there were no 

unsurmountable problems in view. The mechanics had been well studied and 

even though no fully optimized design existed yet, the design one had made 

met the minimum specifications for flexure and resonant frequencies. 

Computers and electronics in general were in a state of flux with every year 

important industrial advances being made. ESO had constructed the NTT and 

even without further technological improvements it could, if need be, be 

adapted to meet the requirements of the 8-m telescopes. Experiments had 

been made with the inflatable shelters and the results were encouraging, even 

though not everyone thought this was the way to go. But the design of the 

NTT enclosure could easily be scaled up. 

The situation was much less clear with regard to the optics. No one 

had cast an 8-m mirror blank and no one had polished one. This had been 

the reason to explore other possibilities during the design phase. However, 

since 3.6-m Zerodur blanks had been cast in Europe with a good record of 

thermal stability and polishability, there was an obvious preference for this 

material. Thus, soon after approval of the project discussions were started 

with Schott about a contract for the delivery of four 8-m mirror blanks. Since 

the existing factory at Mainz was inadequate, a new building would have to 

be constructed, which obviously would add to the cost. 

The negotiations with Schott were difficult. An initial informal Schott 

offer was not accepted by its board of directors. As a result, an offer from 

Corning in the US was 22% cheaper with a schedule at least a year shorter. 

Since ESO preferred the Zerodur option because of the excellent uniformity


of the material and because it came from European industry, further negotiations 

followed which finally led to a price reduction of about 20% though 

increased with future inflation corrections 2) . After many more discussions 

about the details, the contract at 47.5 MDM + cost variation (~ 35 M€, 2004) 

was signed in September 1988. However, permits for the construction of the 

new factory had to be obtained and the new factory had to be built. The firing 

of the new furnace took place in October 1990. The first three blanks 

cracked 3) , which was not unexpected, since no such large pieces of Zerodur 

had ever been made, and so a learning process was needed. As a result, significant 

delays were incurred and the first blank was delivered in June 1993 

(Figure V, 1), about 2 1/2 years later than foreseen in the Blue Book. This 

delay continued throughout the whole project, though the fourth blank had 

been delivered on schedule at the end of 1995, and the polishing also went 

faster than anticipated. 

In the meantime discussions took place with the two firms in Europe 

that would be able to develop the tools for polishing 8-m mirrors. This led 

in July 1989 to the award of a contract for 33.75 MDM (~ 25 M€, 2004) to 

REOSC near Paris for polishing the four 8-m mirrors 4) . Again, this involved 

construction of a new building with a high test tower and the development 

of a new computer-controlled polishing machine. With the two critical 

Figure V, 1. The disk of Zerodur for the first 8-m mirror at Schott. The yellow color 

of the rather transparent material is noticeable. The disk was still to be ceramized 

for eight months at temperatures of 800 – 1000 °C.

Construction of the VLT 71 

contracts for the mirrors concluded, at a price below that foreseen in the Blue 

Book, it was clear that the VLT as an industrial project was on its way. 

In mid-1993, the first 8-m blank arrived at REOSC after a week long 

travel through European waterways. The grinding and polishing operation 

could begin. In 1995 the last blank was ready at Schott, and the polishing of 

the first one was completed at REOSC. Four years later four outstanding 

mirrors had been completed (Figure V, 2), and the first two were mounted 

in their telescopes to produce some stunning images which demonstrated 

their high quality. The investment at REOSC paid off well. Subsequently, it 

won the contract for polishing the two eight meter mirrors for the Gemini 

Project, a U.S. led consortium, including the UK. 

Though the mirrors were the most critical part of the VLT, the amount 

of work that needed to be done at ESO was quantitatively relatively limited. 

Once the optical specifications had been made, ESO had to check that they 

had been met, but no further design work was needed. It was very different 

for the overall structural design in which ESO had a more direct involvement; 

it had to ensure that the many other mechanical parts would be integrated 

in a coherent way. 

In 1990 ESO tendered for the main mechanical structure of the four 

telescopes. Several offers were received, the lowest one from an Italian 

consortium Ansaldo/EIE/SOIMI. This appeared to be an entirely suitable 

offer. Even though ESO does not follow a juste retour scheme to distribute 

industrial orders proportional to the national contributions, it seemed a very 

lucky circumstance that the three big countries each had obtained a large 

Figure V, 2. The 8-m mirror being polished at REOSC. 

On the right a polishing tool is seen attached to the computer-controlled machine.


contract in the VLT. Moreover, ESO had had a positive experience with 

Ansaldo during the construction of the NTT. However, one of the unsuccessful 

companies complained and the Finance Committee did not approve the 

contract; instead the suggestion was made to hold a meeting of all the 

bidders, ESO management and Finance Committee to discuss “technical and 

juridical points of the contract” 5) . This certainly was an unusual notion, 

which reflected national greediness on the part of some delegates. As a result, 

a 5 months’ delay was incurred and much time wasted by ESO staff before 

construction of the mechanics could start. The contract was finally concluded 

in September 1991 for 79 MDM (~ 54 M€, 2004) 

Two other mechanical items were particularly critical. The mirror 

cells with all the electro-mechanical active supports for the thin 8-m 

mirrors were determinant for the optical quality of the telescopes. The cells 

should give a sufficiently rigid support to the 150 axial supports (pushing 

in the direction parallel to the telescope tube) and 64 radial supports, but 

at the same time be as light as possible since a weight increase would 

propagate through the whole telescope structure (Figure V, 3). In addition, 

attached to the cell would be the Cassegrain instrumentation as well as the 

support structure for the (removable) Nasmyth tertiary mirror. Two parallel 

design studies were contracted out for nearly 8 MDM each to two different 

firms, and one of these, GIAT in France, thereafter fabricated these units 

for about 40 MDM (~ 25 M€, 2004). In fact, the total cost of these units 

significantly exceeded the cost of the polishing of the 8-m mirrors. An interesting 

aspect of the active optics system is that the changeover from the 

Nasmyth to the Cassegrain focus may be made without a change of the 

secondary mirror as in conventional telescopes. By modifying the curvature 

Figure V, 3. The mirror cell. The thin 8.2-m mirror is supported axially 

by 150 motor controlled pistons which are part of the active optics system.


of the primary mirror which is possible because of its thinness, one may 

switch between the two foci. 

Equally difficult and costly was the secondary mirror unit. Made of 

beryllium, the polishing was a delicate operation (REOSC) while the 

mechanics (Dornier) were complex since the 1.2 m mirror should wobble at 

frequencies over 10 cycles per second and also be part of the active optics 

setup. While these two items led to a significant cost overrun (Table V, 2) 

over the Blue Book, they have much contributed to the excellent performance 

of the telescopes (Figure V, 4). 

Thermal control of the telescopes and their environment was of prime 

importance. If the primary mirror is warmer than the air in the telescope 

tube, convection will arise which deteriorates the image quality. On the other 

hand, on humid days a cold mirror could suffer from condensation. So a back 

plate on the mirrors had to control their temperature precisely. Also turbulence 

in the enclosures could pose a serious problem. The design of the appropriate 

air conditioning system therefore was critical. In the Blue Book design 

the telescopes were enclosed in inflatable shelters which appeared to provide 

a particularly low cost solution. Night time operation would be in the open 

with the wind blowing away the turbulent air. Experiments were made with 

a 15-m inflatable dome placed at La Silla and wind tunnel tests were 

conducted. Fear of problems with wind forces on the 8-m mirrors led to the 

decision to place the telescopes in more conventional, but well ventilated, 

rotating metallic enclosures. 

A formidable task remained. A large number of smaller and larger 

motors and sensors was needed to control the movable parts, more than 200 

for the active optics systems in each telescope alone. Electronic hardware was 

needed to connect these to the control computers. Software had to be developed 

to ensure that everything would function coherently and automatically. 

This represented an enormous effort under the leadership of Manfred Ziebell. 

In the past much of the software for telescope control and operation had been 

developed at ESO. However, with many standardized, reliable commercial and 

industrial packages now available, it was preferable to use these as the basic 

software building blocks. In the beginning the NTT software had been considered 

as a prototype for the VLT. In the end the opposite happened and the 

improved VLT software was retrofitted onto the NTT. In addition, the instruments 

at the twelve foci had to be integrated with the telescopes and their 

output had to be displayed and archived conveniently. 

At the end of 1990 Paranal had been chosen as the site for the VLT 

(chapter VI.) 6) . It then became necessary to determine the layout. Some 

28 m of rock were blasted away from the top of Paranal to create a large 

enough platform (Figure V, 5). This had to be done cautiously in order not 

to fracture the rock on which the telescopes would be placed. In the Blue 

Book design the four 8-m telescopes were located on a straight line. However, 

the linear array was not optimal for interferometry. It was replaced by a


Figure V, 4. One of the four finished 8-m telescopes. Note the much simpler structure 

with fewer, but stronger elements than in the first design (Figure IV, 3). Just below the 

center piece the location of the Nasmyth mirror is visible which directs the light beam 

through the elevation axis. When it is removed the light can pass through the hole in 

the primary mirror to the Cassegrain focus below. Around the primary mirror the edge 

of the mirror cell is visible with the wiring that connects the actuators supporting the 

mirror. At the top is the secondary mirror made of beryllium. It can oscillate between 

two positions at a high frequency during observations at infrared wavelengths.


Figure V, 5. The four telescopes at Paranal in the early evening. Some of the shutters 

in the enclosures have been opened to let the cool air freely circulate. The octagons 

in front are supports for the movable 1.8-m auxiliary interferometric telescopes. The 

building to the right is the upper part of the interferometric laboratory, where the 

light from the different telescopes may be combined. Just to its left the first 1.8-m 

auxiliary telescope is visible and behind it the housing of the 2.5-m VLT Survey 

Telescope. 

crescent-shaped arrangement which is more advantageous for interferometry. 

A maze of tunnels would connect the four telescopes and the 1.8-m mobile 

auxiliary ones to the central interferometric laboratory. 

At a distance from the telescope area other elements of the infrastructure 

would be located: workshops, a residential building, an electricity 

generating plant and a water reservoir. The latter would be replenished by 

water regularly trucked in from Antofagasta, since no local water wells were 

to be found in the dry desert. The most critical item was the mirror washing 

and aluminizing plant made by AMOS (B) and Linde (D). The vulnerable 

8-m mirrors were transported to this plant and placed in the vacuum chamber 

in a series of highly automated operations. The old Panamericana (unasphalted) 

connected the Paranal area with Antofagasta, but the local roads in 

the Paranal area had to be made. Construction of the infrastructure started 

in 1991 and continued into 2002 when the temporary huts for lodging the 

staff were replaced by the elegant Residencia, complete with swimming pool 

and even several palm trees (Figure V, 6a). Most areas of the Residencia are 

climate controlled, since the extreme desert air is too dry for long term


comfort. The building is largely underground with a 35-m semitransparent 

dome ensuring a luminous aspect. Of course, during the night precautions 

are taken to ensure that no light escapes to the outside. The 175 m long 

façade, with behind it the rooms for the staff and with small windows to avoid 

the strong glare, blends perfectly into the surrounding desert (Figure V, 6b). 

Figure V, 6a. The Residencia. In the central area a garden gives some greenery to 

the staff in an otherwise extreme desert environment. The completely air-conditioned 

building is mostly located underground, but natural light may enter through the 

35-m dome. Provisions have been made to ensure that at night no unwanted light 

pollution is produced. 

Figure V, 6b. The façade of the Residencia, behind which are the rooms for the staff 

and visitors.


The design of the building was the result of an international competition won 

by the architects Auer & Weber (Stuttgart). Most of the basic design was done 

by the architect D. Schenkirz, while the interior aspect of the building owes 

much to Daniel Hofstadt, ESO’s representative in Chile. The 11 M€ Residencia 

has contributed significantly to make life of the staff liveable in the harsh 

desert. 

From this brief description of the various activities relating to the 

realization of the VLT, it might seem that most things went rather smoothly. 

However, along the way some obstacles were encountered which led to delays 

which, as always, also had cost consequences. Two of these stand out. 

Less than a year after the approval of the VLT project Council became 

concerned about ESO’s management and expenditures. As Pierre Léna said 

in Council 7) , the French astronomers had had to agree to close some national 

facilities to obtain VLT approval. A parallel effort on the part of ESO would 

be desirable, with a stronger focus on the VLT. Of course, in some of the other 

member countries the situation was no different. As the concern of Council 

increased, Council set up a VLT management review board which reported 

in May 1990. Among other items the board was concerned about significant 

morale problems among the staff and recommended the appointment of a 

VLT program manager 8) . ESO involved a costly high powered management 

consulting firm, which identified 131 potential candidates 9) . Finally someone 

was appointed, who left nine months later after having introduced much additional 

bureaucracy. A few years thereafter, for the position of Head of Administration, 

the experience was repeated with another consulting firm 10) with 

an equally distastrous result. Whatever their merits in other circumstances, 

business consultants apparently do not have much of a feeling for the requirements 

of an international, scientific/technological organization. Immediately 

after the departure of the new project manager, Massimo Tarenghi, 

who had already brought the NTT project to a successful conclusion, was 

appointed as his successor 11) . 

The situation in the ESO Council remained difficult, with several times 

the three large countries outvoted by the five small ones. While it is true that 

according to the ESO Convention each country has an equal vote, it is also 

evident that an organization cannot be run against the will of its principal 

paymasters. So a change was needed, and Council appointed Riccardo 

Giacconi as the new Director General as of January 1993. A period of 

American style management followed. While this did not please everyone, it 

created the conditions under which the VLT project could be brought to a 

fully successful conclusion. Council received a clear view of the problems and 

their solutions. But the management problems had set the project back by 

the better part of a year. 

In the meantime, a serious issue had arisen in the relations between 

Chile and ESO which were governed by the “Acuerdo” concluded in 1963. In 

the beginning everything went very smoothly, and relations between ESO and


the Chilean government, as well as with the small astronomical community 

and with ESO’s local staff, were excellent. In 1972/73 economic conditions 

in Chile became difficult and a black market appeared which created opportunities 

for some and difficulties for others. Then at the end of 1973 came 

the Pinochet coup. Relations between European countries and Chile became 

very cool, with ESO being in the middle. Obviously, it was important for ESO 

to continue to have positive relations with the government in power, and 

equally obviously some governmental delegates in the ESO Council could not 

agree to this too openly. In a confidential session of Council I said: “If you 

live in hell, you treat with the devil”, and this argument led to a tacit understanding 

allowing us to continue our relations with the government at the 

required level. Relations with the community and local personnel were not 

helped by ostentatious consumption by some European staff. Since cars 

could be imported tax free and sold on the Chilean market two years later, 

a curious traffic arose with even medium level personnel owning or driving 

top of the line Mercedeses or Maseratis. Evidently, this created resentments, 

which were not diminished when the Pinochet government donated the land 

around Paranal for a gigantic European project. 

With the election of a democratic government in December 1989, 

some of these resentments came to the fore. The Chilean astronomers claimed 

observing time at ESO, the staff wanted improved conditions, and the original 

owners, the inheritors of the La Torre family, claimed the land of Paranal. 

Though worthless desert, multi million dollar claims were made. A Chilean 

astronomer consultant for the claimants made complex calculations partly 

based on the documents I had presented to Council in which the astronomical 

excellence of the site had been described. He arrived at a sum of some 

30 MUS$! The issue of guaranteed observing time for Chilean scientists had 

been raised already early in 1988 by the foreign ministry in Santiago 12) . 

Although this was repeated several times thereafter, it had not been taken 

sufficiently seriously by ESO 13) . 

During 1994 negotiations took place between the Chilean government 

and ESO, and in November of that year an agreement was initialed. Unfortunately, 

this provisional agreement had not yet settled the ownership of the 

land. A century earlier it had been a reward for heroic deeds during the war 

with Bolivia and Peru. This gave the issue an even stronger patriotic flavor. 

The Chilean parliament also entered into the fray, and soon a local judge 

violated ESO’s diplomatic immunity and ordered a halt to the work at 

Paranal. Fortunately the Chilean foreign minister J.M. Insulza gave strong 

support to ESO and a final agreement was signed in April 1995. Towards the 

end of the year the Chilean government settled matters with the La Torre 

relatives for a substantial sum. It is undoubtedly the first time in history that 

such a sum has been paid for a piece of real estate exclusively on the basis 

of its value for astronomy. In September 1996 the Chilean senate followed 

congress in ratifying the “Interpretative, Supplementary and Complementary


Agreement” to the 1963 Acuerdo. This gave Chilean astronomers rights of 

up to 10% of the observing time at ESO telescopes and also contained provisions 

aligning the statute of the Chilean workers closer to the Chilean labor 

law. It is not evident that the latter was to their advantage, but it satisfied a 

strong sentiment. While this new acuerdo appears to have solved all 

problems, the activities on Paranal had been set back by about half a year. 

Subsequently, the relations between Chile and ESO rapidly improved and now 

are very positive and cordial. So on 4 December 1996 the “Foundation 

Ceremony” for the Paranal observatory could take place in the presence of 

the President of Chile, Eduardo Frei Ruiz-Tagle, and many other dignitaries. 

Relations with the Chilean astronomical community also became much more 

positive. 

When ESO came to Chile there were few astronomers, mainly at the 

Cerro Calan observatory of the Universidad de Chile in Santiago. Programs 

included a radio survey at 7 m wavelength which has yielded an excellent 

map of the southern sky. Some photometry was done and also astrometry, 

the latter subsequently in part with an astrolabe in cooperation with ESO. 

Some four decades later astronomical activity in Chile is expanding rapidly, 

with greatly invigorated departments at the Universidad de Chile and at the 

Universidad Católica, also in Santiago. Moreover, new programs in astronomy 

were started at universities in Concepción, La Serena and Antofagasta 14) . Of 

course, the instrumental opportunities at ESO and at the US sponsored 

observatories played a role in this, as did increased governmental funding, 

augmented by some support from ESO. The move of ESO astronomers back 

to Santiago facilitated interaction between the two communities, fostering 

joint research projects, colloquia, etc. The general improvement of the universities 

and technological institutes also created a steady stream of competent 

engineers and technicians which allowed ESO to recruit locally an increasing 

fraction of its staff. In fact, at Paranal and La Silla well above 75% of the 

technical staff is now Chilean. 

The events at Paranal had a precursor at La Silla. There ESO had 

bought the land from the government for 45,000 Escudos (8,000 US$). 

Some time thereafter a person appeared who claimed ownership of part of 

the land. Since a court case would have held up the start of activities at 

La Silla for a long time, ESO paid another 15,000 Escudos to deal with this 

claim 15) . Unfortunately, the sum at issue at Paranal was so much larger that 

the same approach was not possible. 

Subsequently, activities at Paranal proceeded at a rapid pace. By the 

end of 1996, parts of the structure of the first unit telescope arrived, followed 

a year later by the first 8-m mirror. On 25 May 1998 “first light” was achieved 

at the completed telescope, followed at 10 months intervals by Unit Telescopes 

2 and 3. Finally, UT 4 saw first light on 3 September 2000, thereby 

completing the VLT as such. It had taken 23 years since I had first proposed 

that ESO construct a 16-m equivalent telescope and nearly 13 years following


project approval. Of course, much work remained to be done before every 

last adjustment would have been made. However, it is a tribute to the quality 

of ESO’s staff and of their industrial partners that soon thereafter the VLT 

was fully functional according to its specifications without significant mishaps 

appearing along the way. 

The four 8-m telescopes are only part of the VLT project. Each 

telescope has to be equipped with instrumentation – imagers and spectrographs 

for different wavelength regions. Already in the Blue Book it was clear 

that ESO could construct in-house only a small part of the instrumentation; 

most of it should be contributed by institutes in the ESO countries. This had 

the further merit of making the VLT project a community wide effort: ESO 

would provide much of the necessary funding for the acquisition of hardware 

and industrial contracts, while the institutes would design and develop the 

instrumentation and would obtain in exchange a certain number of observing 

nights. From the experience with the 3.6-m telescope, it was clear that work 

on the instruments should begin as soon as possible. So in 1990 the first 

instrumentation plan was developed and two years later the first contracts 

were concluded with institutes in the member countries. Instrumentation is 

discussed in chapter VII. 

The other aspect of the VLT is interferometry. In the Blue Book provisions 

had been made for adding two mobile auxiliary telescopes of about 1.5 m 

in diameter to improve the interferometric image quality obtainable with the 

four stationary telescopes. Subsequently, the MPG in Germany and l’INSU 

(CNRS) in France suggested that they could provide a third auxiliary telescope 

in exchange for observing time 13) . However, ESO’s financial problems led to 

the elimination of the interferometry from the near term financial plan. Some 

years later, interferometry was successfully brought back into the planning 16) 

and a contract was concluded with the MPG and l’INSU 17) . Subsequently 

Belgium offered to pay for most of a fourth telescope and with support from 

some other countries it could be acquired. The increase of the diameter to 1.8 m 

and of the number of small telescopes from two to four are of great benefit to 

the whole program. A further increase to six would be very much worthwhile. 

The layout and various subsystems were completed or on their way when in 

1998 the contract for two, later increased to four mobile 1.8-m telescopes was 

signed with AMOS in Liège at about 5 M€ per telescope. The last of the four 

should be completed in 2006. Work on instrumentation for the VLTI also 

progresses at various institutes (see chapter VII). In the meantime successful 

interferometric observations have been made with the large telescopes. 

Planning and Reality 

In December 1987 the Council approved the VLT project as presented 

in the “Blue Book” with a budget of 382.2 MDM (1986 value), corresponding


to 272 M€ in 1999 according to ESO’s inflation calculation, which is based 

on some kind of weighted average of inflation in the relevant European 

countries, where ESO makes its purchases. In 1999, when about 90% of the 

total had been spent or contracted, it was found that the actual cost amounted 

to 313 M€, 15% in excess of the 272 M€ in the Blue Book. 

In Table V, 1 a comparison is given in more detail (where we have 

omitted the 20 M€ for the interferometry which has become very much open 

ended), from which it appears that the extra costs came from three items: 

the cells supporting the 8.2-m mirrors and the Nasmyth mirror units, the 

secondary mirror units and the costs of Paranal developments. An important 

part of these cost increases is due to additions made to the project after its 

approval. The most evident of these are the Cassegrain foci for all four telescopes. 

Access to the Cassegrain focus requires removal of the Nasmyth unit 

out of the light beam. Not only did this very much complicate the mirror cell 

and the M3 unit, it also caused cost increases in the telescope structure; the 

height of the altitude axis had to be increased to make space for the Cassegrain 

instruments. So overall weight increased. Furthermore it required additional 

focal plane instrumentation (adapters/image rotators/etc.) at the 

Cassegrain focus. It is difficult to reliably determine the extra cost incurred, 

but I would estimate it to be in the 15–25 M€ range. Of course, there is no 

doubt that from a scientific point of view the implementation of the 

Cassegrain foci has been very much worthwhile. 

Table V, 1. Comparison of the VLT budget approved in 1987 (Blue Book), updated 

to 1999 values, with actual spending (90%) through 1999 + foreseen thereafter (10%). 

All values have been converted to M€ . The contingency (20 M€) in the Blue Book 

has been distributed over the various items. Major additions to the scope of the project 

are indicated by + or ++. These include the four Cassegrain foci and the four beryllium 

secondaries. Interferometry is not included in the table, since its scope had not yet 

been decided. 

Item Blue 

book Actual Difference 

8.2-m mirrors 65 57 – 8 

M1 cells + M3 units 15++ 32 + 17 

M2 units 7++ 26 + 19 

Main telescope structures 43 43 0 

Other telescope items 31+ 28 – 3 

Infrastructure / buildings / enclosures 58 80 + 22 

Instruments 33+ 27 – 6 

TOTAL 252 293 + 41


The question of the wobbling secondary for IR observations was left 

rather open in the Blue Book, with some doubt expressed about its necessity. 

As a result, a rather modest sum was foreseen for this item, though mention 

was made of a sophisticated system based on beryllium mirrors, which had 

been used in some space applications. Later it was decided to implement such 

mirrors at all four telescopes, which led to a quadrupling of this budget item. 

Finally, also the cost of Paranal development increased substantially. In part 

this was related to additions made beyond the perhaps somewhat too 

primitive setup initially foreseen. Since life in the Atacama desert has its difficulties, 

the more comfortable surroundings created for the scientific technical 

staff are certainly beneficial. 

In conclusion, it appears that the estimates made in the Blue Book were 

essentially correct. The cost overrun of 15% is largely the result of increased 

demands made on the VLT following its approval. The same conclusion was 

reached already during the program audit in 1994. The audit committee 

wrote then 18) : “We cannot argue that the increases are only due to the 

increased scope of the project, errors in the initial estimates may also play 

a significant rôle, but the correspondence between the most significant cost 

increases and the areas of project modifications is striking.” Of course, the 

contingency included in the original budget was there to deal with possible 

errors in the initial estimates and not for covering an enlargement of the 

project. 

In the Blue Book also the schedule of the project was specified. The 

first 8.2-m blank was to be fabricated in three years, by the end of 1990, and 

to be polished three years after that. However, as explained before, the first 

blank was completed 30 months late. Other delays resulted from the management 

problems in Europe, from the contract difficulties for the mechanical 

structure and from the political problems in Chile. The first unit telescope 

suffered most and had a delay of about four years, the last one of only 2 1/4 

years. But what counts is that at the end of the construction process, Europe 

had completed the world’s most powerful telescope as planned and placed 

it on the world’s clearest site. 

Other 8-m class telescopes 

Not surprisingly, other countries have also decided to construct large 

telescopes. By the end of 2006 the total number should be fifteen, including 

the four of the VLT (Table V, 2). In addition there are two large telescopes 

of more limited steerability and optical quality for spectroscopic purposes. 

The two 10-m Keck telescopes, built with private and NASA money, may also 

be used interferometrically, but, of course, only one baseline (85 m) between 

the large telescopes is available. This somewhat restricts the potential, because 

“phase closure” techniques cannot be used, since these require at least three


telescopes. However, it is planned to add also some smaller auxiliary interferometric 

telescopes. By 2004 the necessary permits had still not been 

obtained because of eco-religious claims on Hawaii. 

The 10.4 m Spanish Gran Telescopio de las Canarias (GRANTECAN, 

Figure V, 7) with a segmented mirror is essentially a copy of the Keck telescopes. 

Funding came in part from the EU which has programs to support 

Table V, 2. The world’s 8-m class telescopes. 

Alt 

Diameter Name Country Year Location (m) Type 

4 × 8.2 VLT ESO 1998/00 Paranal 2700 Z 

Chile 

2 × 9.8 Keck US 1993/96 Mauna Kea 4200 S, Z 

Hawaii 

2 × 8.4 LBT US, D, I 2004/05 Mt. Graham 3200 BSC 

1/2 1/4 1/4 Arizona 

10.4 GRANTECAN ESP, … 2006 La Palma 2400 S, Z 

Canaries 

8.2 Subaru Japan 1999 Mauna Kea 4200 ULE 

Hawaii 

8.0 Gemini N US (1/2), 2000 Mauna Kea 4200 ULE 

UK (1/4), Hawai 

Can … 

8.0 Gemini S US (1/2), … 2002 Pachon 2700 ULE 

Chile 

6.5 Magellan I US 2002 Las Campanas 2400 BSC 

Chile 

6.5 Magellan II US 2003 Las Campanas 2400 BSC 

Chile 

6.5 MMT + US 2002 Mt. Hopkins 2600 BSC 

Arizona 

with limitations 

9.2 HET US … 2000 McDonald 2100 

Texas 

9.2 SALT SA, 2005 Sutherland 1800 

S. Africa 

S: Segmented; Z: Zerodur (Schott); BSC: Borosilicate Ceramic (U. of Arizona); ULE: 

UltraLow Expansion (Corning).


Fig. V, 7. Model of the 10-m GRANTECAN on La Palma. 

activities in less developed regions in Europe. Placed at La Palma, it may 

also help to determine the suitability of that site for even larger future 

telescopes. 

The two 8-m Gemini telescopes – one in the northern and the other 

in the southern hemisphere – represent a cooperation between the US 

(~ 50%) and the UK, Canada, Australia, Argentina, Brazil and Chile. Funding 

is governmental. The solid 8-m mirrors have been polished by REOSC. Optimization 

for the IR has been stressed. 

The most innovative of these new telescopes is the Arizona (1 / 4)/Germany 

(1/4) / Italy (1/4) / other US (1/4) Large Binocular Telescope, originally called 

the Columbus Telescope, which was later considered “politically incorrect” 

in the US. It has two 8-m telescopes in a common mounting. This has the 

advantage that interferometry between the two is possible over a relatively 

large field, but, of course, there is not much choice in baselines. The LBT 

has suffered major delays because of native Indian and ecological claims 

about the site at Mt. Graham in Arizona. While the red squirrels were still 

being hunted in various places, it was said that the telescope construction 

would risk the extinction of the subspecies on the mountain. Actually, their 

numbers appear to have increased after construction began! The first mirror 

was installed in 2004, the second should follow a year later. Perhaps the most 

innovative feature is the thinness (1.6 mm) of the 91-cm secondary mirrors.


Supported by (or rather hanging on) 672 actuators, they allow the adaptive 

optics to be implemented without auxiliary optics and so to avoid the corresponding 

light losses. Rather contradictory statements about the cost of the 

LBT have been made with values around 140 MUS$ (excluding instrumentation) 

being plausible. 

The more limited HET and SALT have composite mirrors made of 

numerous spherical segments. Moreover, these telescopes can only track in 

azimuth which limits observing time on any object to less than an hour. 

However, they have a large collecting area (70 m 2 ) at low cost (25–30 MUS$). 

They should be particularly suitable for spectroscopy of objects of intermediate 

brightness. 

With GRANTECAN, LBT and Gemini N, the European countries have 

the equivalent of 2 1/4 telescopes of the 8–10 m class in the northern hemisphere 

to supplement the four of the VLT in the south.

VI. 

Sites for Telescopes 

The only remedy is a most serene and quiet air such as 

may perhaps be found on the tops of the highest mountains, 

above the grosser clouds. 

Isaac Newton 1) 

The earth’s atmosphere has negative effects on astronomical 

observation. Clouds, haze and dust absorb the light from celestial sources. 

Turbulence in the atmosphere causes small temperature variations which lead 

to small scale variations in the atmospheric refraction (the bending of light) 

which smear out images of astronomical objects. Thus, a stellar image which 

should be essentially point-like is smeared out over a “seeing” disk of typically 

an arcsecond or less in diameter on good sites and more than that in 

poorer places. Some of the turbulence is caused by layers of varying wind 

speed rather high in the atmosphere (some km), some occurs close to the 

ground by the effect of the surface features on the wind driven air and some 

results from convection when the lower air is too warm for a stable atmospheric 

structure. With the advent of infrared astronomy the total atmospheric 

water vapor content has become important since water vapor absorbs 

incoming radiation and itself emits infrared radiation which gives the IR sky 

a luminous glow which makes it difficult to detect celestial sources. Submm 

radio waves are also subject to much absorption from water vapor. 

Newton already suggested that it would be advantageous to place a 

telescope on a high mountain, where one would have left some of the ill effects 

of the atmosphere below. However, according to Piazzi Smyth 2) Newton’s 

“very simple and probable piece of speculation” had “dropped out of notice” 

and when he was going to put it to the test “a few voices even loudly 

proclaimed that high mountain tops, all the world over, are invariably loaded 

with clouds and mist and sleet and tormented forever with impetuous storms”. 

This led him in 1856 to mount an expedition to Teneriffe where he found that 

stars four magnitudes fainter could be observed from a site 2700 m high on


the Teíde volcano than at sea level (Figure VI, 1). It is interesting that the expedition 

was made possible by Mr R. Stephenson, a member of the British 

parliament, who provided his own yacht, because “his early experiences on 

South American cordilleras had long since led him to look with favour on 

Newton’s mountain method of improving astronomical observations”. More 

than a century later his experiences were amply confirmed. 

In the tropics humidity is high and atmospheric convection strong. At latitudes 

around 50˚ the jet stream generates strong turbulence, while cloudiness 

is relatively high. As a result, most high quality astronomical sites are found at 

subtropical latitudes. A notable exception is the high central Antarctic plateau. 

It is high, very cold, extremely dry and in contrast to the Antarctic periphery 

without strong winds. However, it is no simple matter to build and operate a 

telescope there, though some specialized instruments have been erected. 

Over land temperatures are rather variable and this creates instability. 

Above the oceans the air flow tends to be much more stable, in particular 

when cold currents cool the oceanic surface. Then a temperature inversion 

(temperature increasing upwards) occurs which inhibits convection. At the 

boundary of this layer, typically a km high, low clouds are common, but 

higher up the atmosphere is calm. Thus, high island or coastal sites bathed 

in cold water have long been believed to be particularly favorable for astronomical 

observation. However, at sufficient altitude the coastal advantage 

seems to be less strong. 

Figure VI, 1. The Teíde Observatory (2390 m) on Tenerife. In the background is the 

Pico de Teíde (3700 m) which last erupted in 1798. The volcano is still slightly active 

today and the observatory has been built on its shoulder. To the right is the 90 cm 

French-Italian solar telescope THEMIS, and to the left the German 40, 45 and 60 cm 

solar towers, the Spanish 1.5-m infrared telescope and an ESA-Spanish optical ground 

station (1-m) for tracking space debris and space communication experiments.

Sites for Telescopes 89 

Because of the rotation of the earth, cold currents coming down from 

upwelling circumpolar waters tend to occur on the east side of the oceans. Of 

course, geographic constraints also play a role. In the northern hemisphere 

cold currents along the coasts of California and West Africa have created favorable 

conditions, in particular on the Canary Islands in front of the African 

coast. Here the island of La Palma with its 2400 m high volcanic rim is an 

excellent site (Figure VI, 2). The Pico de Teíde on Tenerife at 3700 m is unsuitable 

because of volcanic activity, but seeing conditions on its lower flanks are 

excellent, in particular for solar observations. Thanks to Francisco Sánchez, 

major observatories have been developed on both islands. Conditions in 

Figure VI, 2. The Roque de Los Muchachos Observatory (2400 m) on La Palma some 

140 km NW of Teíde. A large number of telescopes has been placed close to the upwind 

rim of an extinct caldera. These include the 2.5-m Nordic Optical Telescope, here just 

visible on the rim, the 1-m, 2.5-m and 4.2-m telescopes of the UK-NL cooperation, a 

Liverpool University 2-m, a Flemish 1.2-m and the 3.5-m Italian “Telescopio Nazionale 

Galileo”, as well as 96-cm Swedish and 45-cm Dutch solar telescopes. The 10-m Spanish 

“Gran Telescopio de las Canarias” is currently nearing completion. The La Palma 

Cosmic-Ray Observatory observes the Cerenkov light produced by cosmic gamma-rays 

of very high energy with MAGIC, seen here in front, a 17-m diameter segmented telescope. 

Since no high optical resolution is required, a place in the wind shadow was acceptable.


southern Spain, where the German Calar Alto observatory, with its 3.5-m 

telescope, was placed, are less favorable 3) . 

The best place in the northern hemisphere is probably Mauna Kea at 

4200 m on the big island of Hawaii. Because of its high altitude and stable 

oceanic environment, water vapor column density is low and seeing conditions 

are as excellent as at La Palma. Several US telescopes, including the 

two 10-m “Keck telescopes” are placed here. Also the UK (now joined by the 

Dutch) placed here the 3.6-m infrared telescope UKIRT, while France participates 

(now at 45%) in the 3.6-m Canada-France-Hawaii telescope. In 

addition, the 15-m submm JCMT radio telescope is operated by the UK in 

collaboration with the Netherlands. As several of the best places on 

Mauna Kea and La Palma have been taken, other northern hemisphere sites 

have been looked for. At sufficient altitude the difference between oceanic 

and continental sites may well become smaller. In fact, Germany and Italy 

– each at 25 % – participate with the US in the Large Binocular Telescope 

(2 × 8 m), the first half of which became operational in 2004 on Mt. Graham 

in Arizona at 3200 m. Also optimistic speculations are being made about high 

sites in central Asia, but only limited reliable data are available to date. 

Turning now to the southern hemisphere, we find cold currents along 

the western rims of three continents. In Western Australia there are no high 

mountains. In South Africa ESO found relatively modest conditions, but 

further north at the Gamsberg in Namibia – a table mountain 2350 m high 

– conditions have been claimed to be comparable to those at La Silla. Because 

of political problems, German attempts to place telescopes there have come 

to naught. An earlier expedition by the Smithsonian Institution to Fogo 

(2700 m) in the Cabo Verde islands and to six peaks in Namibia concluded 

that the sites were all unsuitable for measuring the solar radiation intensity, 

which requires a very pure sky with high IR transparency and therefore a 

low column density of water vapor 4) . By far the strongest cold current – the 

Humboldt current – flows along the South American coast and brings cool 

conditions even to the equator. When Humboldt reached the Peruvian coast 

in 1802, he measured a temperature of 16 °C – more than 10° lower than 

normal so close to the equator 5) . Close to the coast, frequently at no more 

than 100 – 200 km, the Andes rise to above 6000 m and form a barrier 

against humidity coming from the Atlantic. The result is an extremely dry 

coastal strip, with the Atacama desert being one of the driest areas on earth. 

As a consequence, some of the world’s finest sites for optical and for submm 

telescopes are found in Chile. 

Early Astronomical Sites in Chile 

The early history of Chilean astronomy has been well described by 

Keenan, Pinto and Alvarez 6) . The first organized astronomical activity in


Chile was the Gilliss expedition of the US Navy (1849–52) for observations 

of stellar and planetary positions. Subsequently, his observatory in Santiago 

was taken over by the Chilean state with the founding of the National 

Observatory. In 1893 a solar eclipse was observed near the town of Vallenar 

(50 km north of La Silla), where several expeditions had gone to profit from 

the clear skies. In 1903 Lick Observatory placed a 92-cm telescope on San 

Cristobal, close to Santiago, where during 26 years the radial velocities of 

southern stars were measured with the Mill’s spectrograph. From here 

H.D. Curtis in 1909 made an expedition to the region NE of Copiapo and 

reported the night sky to be “very transparent and clear”, estimating that 

some 300 nights per year might be cloud-free 7) . 

From 1920 to the early fifties C.G. Abbot from the Smithsonian Institution 

conducted a program at Cerro Montezuma to measure the intensity of 

the solar radiation (the “solar constant”) 4) . According to Abbot, this site at 

-22.5 ˚ latitude near Calama was the best place he had found in the southern 

hemisphere for his observations which required high IR transparency. It is 

interesting that the excellent sites found by ESO are all close to the one Abbot 

found without all the modern data and equipment available now. 

In the late fifties F. Rutlland, the director of the Chilean National 

Observatory, induced G.P. Kuiper – one of the great astronomical entrepreneurs 

– to consider the possibility of an observatory in Chile. In 1959 J. Stock 

arrived to make detailed site surveys first in the vicinity of Santiago, but 

rapidly moved north where clear skies appeared to be more frequent. Stock 8) 

extensively studied Cerro La Peineta near Copiapo and Cerro Tololo further 

south, which was subsequently chosen by the Americans for their observatory. 

From Stock’s results it appeared that the Chilean sites were substantially 

better than those in South Africa, where ESO had been studying several 

places 9) . In December 1962 A.B. Muller then visited La Peineta and Tololo 

for a total of 27 nights, and in 1964 ESO selected Cerro La Silla (Figure II, 3) 

100 km north from Tololo situated between La Serena and Vallenar 

(Figure VI, 3). The ESO Council had made the choice contingent on water 

being available near the site, and subterranean water was found in 1965 in 

one of the old river beds below La Silla. 

The choice of La Silla had also more political aspects. There had been 

a growing concern in ESO circles about developments in South Africa, and 

the discovery of the superiority of the Chilean sites therefore came as a 

relief 10) . There then were discussions about joining the Americans on or near 

Tololo 11) . While in particular the more American oriented Dutch were very 

favorably inclined to such an association, others were more concerned about 

the independence and visibility of the European entity. In retrospect, the 

decision to go to an independent mountain was certainly the right one. 

Different ways of doing things would have led to problems, and ESO with 

its limited experience would have been very much the junior partner. 

Relations between the observatories always remained very cordial.

Figure VI, 3. Map of northern Chile. Squares indicate cities; circles indicate observatory 

sites, filled circles those currectly active with telescopes of 2-m or more.


O. Heckmann, who became ESO’s first Director General, found easy 

access in Chile due to the strong element of German descent in that country. 

With K. Walters, an international lawyer who had handled many delicate 

matters during the war and who had a very extensive set of friends and acquaintances, 

Heckmann negotiated a treaty between Chile and ESO as an intergovernmental 

organization, which gave ESO many immunities and considerably 

facilitated future operations. Without waiting for Council approval, he signed 

the treaty, an act of independence which, though not applauded by everyone 

at the time, much speeded up ESO’s installation in that country 11) . At the same 

time, ESO’s quasi-diplomatic status complicated relations with Tololo and an 

independent site became even more necessary. While without further site 

surveys it was clear that the various mountains between La Serena and Copiapo 

should have excellent conditions, it remains remarkable that no local survey 

at all was conducted before the selection of La Silla. In retrospect, this may 

have been all to the good in accelerating the construction of the observatory. 

While ESO could be satisfied to have escaped the deteriorating political 

situation in South Africa, its optimism about Chilean politics was less 

justified. In this seemingly so peaceful country several violent revolutions and 

coups d’état had taken place since independence, and the next one was to 

come in 1973 12) . In these troubled times the “acuerdo” negotiated by 

Heckmann proved to be of great value. 

Also the astronomers from the USSR were attracted by the Chilean skies, 

and in 1967 a small astrometric observatory was built on Cerro Roble, some 80 km 

north of Santiago 6) . Site surveying for a larger observatory came to an abrupt halt 

after the 1973 coup. Finally, in 1970 the Carnegie Institution of Washington built 

its observatory at Las Campanas, 50 km north of La Silla. By the late seventies 

large telescopes had been installed at Tololo, La Silla and Las Campanas. The 

high quality of the three sites was confirmed and many scientific results were 

obtained. However, these sites were not as excellent in the IR as Hawaii at 

4200 m altitude because of a higher atmospheric water vapor content. 

In the meantime, the Astronomy Department of the Chilean University 

had begun in 1966 to take a new look at the north. J. Stock who by then was 

based at the National Observatory gives a brief description of the conditions 

there 13) : “There are a number of mountains of sufficient elevation south of 

the town of Antofagasta and very close to the coast. The abrupt rise from the 

Pacific Ocean on one side, and a large flat plain, more than 1000 m lower, 

on the other side give these mountains rather special conditions. High 

stability, that is, good seeing, is expected for night time conditions. 

Furthermore, the extremely low humidity makes this area very suitable for 

astronomical work in the infra-red. Since this area is absolutely arid, water 

supply for an observatory will be difficult and costly. Underground currents 

may exist, but most likely at a prohibitive distance and depth.” 

Since water sources had been a major concern in the location of the 

various observatories, Stock thought that sites further to the East, where


abundant water falls on the high Andes, would be preferable. Accordingly, he 

selected a site for further study at 20 km from San Pedro de Atacama, the 

flattish summit of Cerro Chaupiloma at 3300 m altitude. According to Stock 

a nearby river had sufficient flow for a hydroelectric power plant! Somewhat 

later, in 1971, astronomers from the USSR started measurements also on this 

mountain as well as on Cerro La Peineta 14) . Moreover, in 1967, the National 

Observatory reported that sites for a radio telescope had been looked for at 

the Salar de Atacama and that a suitable 6 × 3 km area had been found at 

20 km from San Pedro 15) . After the coup in 1973, the Chilean activities of the 

Academy of Sciences of the USSR came to a sudden end, the Americans and 

Europeans were busy with the construction of their observatories, and for the 

Chileans other concerns predominated. Interest in the North largely vanished. 

The New Push Northward 

During 1977 I initiated plans for a future large telescope at ESO. 

Technical studies were made, and it became clear that the Very Large 

Telescope would be expensive – well above a hundred million euros. It also 

seemed probable that the VLT would be constructed as an array of several 

large telescopes and that there was no suitable place at La Silla for such an 

array. These two factors together implied that a new site had to be looked 

for, and that site quality might be more important than low cost, at least as 

long as that cost was small compared to that of the telescope array. 

Within the ESO territory two mountains seemed to offer possibilities of 

comparable quality: Cerro Duran to the north halfway to Las Campanas, and 

Cerro Vizcachas closer to La Silla to the southeast. A visit to Cerro Duran showed 

a suitably shaped free standing summit. However, the layout of a road to La Silla 

was far from evident. In any case, the time needed to drive from one site to the 

other would be too long to have a common infrastructure. Cerro Vizcachas was 

easier to reach and a provisional road was constructed for testing. The top had 

enough space to accommodate the VLT. While there was some concern that this 

site was relatively close to the southern border of ESO’s territory and, therefore, 

of the area protected from mining, overall it seemed the most attractive in the 

La Silla area. So this became the reference site for comparison with others. 

To the east of La Silla much higher mountains could be found. One of 

these, Cerro Peralta, was clearly visible on the sky line as a free standing 

4500 m high summit. An expedition there by D. Hofstadt and myself showed 

access to be very difficult. Much running water was found on the lower slopes, 

the result of frequent summer rains which appeared to be related to thunderstorms 

drifting in from Argentina. Towering clouds can frequently be seen 

over these high mountains which only rarely reach La Silla. While it may well 

be that winter nights with extremely low water vapor content can be found 

there, the overall level of cloudiness would be higher than at La Silla.


It therefore seemed that if more exceptional sites were to be found we 

would have to go northward (Figure VI, 3, 4). From La Silla to the north cloudiness 

slowly diminishes as may be seen from Stock’s data near Copiapo who 

found there 20% more clear night hours than at Tololo. Partly because of 

stronger winds the site had not been selected by the Americans. Much further 

to the north at the cosmic ray station at Chacaltaya (5400 m, near La Paz, 

Bolivia) measurements had been made which showed much more cloudiness 

and for its altitude a relatively high atmospheric water vapor content 16) . In 

between there should be an optimum. 

Figure VI, 4. Satellite image of northern Chile taken by the ESA astronaut Claude Nicollier 

on his way to the Hubble Space Telescope. North is towards the lower left. The curving 

coast line north of Arica and the anvil like figure at Antofagasta are easily recognized. Along 

the coast clouds above the Humboldt current stabilize the atmosphere, but remain well 

below the level of Paranal. Further to the east of Antofagasta one can see the eastward 

curve in the main chain of the Andes with the whitish Salar de Atacama, an ancient dried 

up lake with below the surface brines which contain much of the world’s exploitable lithium. 

Somewhat further to the NW the plume of the copper smelter at Chuquicamata, near 

Calama, is visible. To the east of the Salar de Atacama, in between the first mountains, is 

the Llano de Chajnantor – site for ALMA, the Atacama Large Millimeter Array. On this 

image the blocking of humidity from the Atlantic and the general increase of the cloudiness 

towards the more tropical areas of Bolivia is also in evidence.


A visit was made to La Peineta, the 3000 m high mountain near 

Copiapo, by A. Ardeberg and myself; we found the road to the top very 

damaged (by rainfall), and since Stock had already investigated the site at 

some length some years earlier, it did not seem worth the effort to set up a 

site testing station there. All of the sites which had been studied till then were 

relatively far inland. But for astronomical sites the more stable oceanic air 

has a great advantage. So when one evening I looked again at a large map 

of Chile, it struck me that there was, in fact, a rather unique high mountain 

very close to the coast, Cerro Paranal at 2700 m. Later I realized that it was 

located in the general area south of Antofagasta that Stock had referred to. 

So why not have a look? 

Soon thereafter, in March 1983, I mounted an expedition (Figure VI, 5) 

during which the extreme dryness, the purity of the sky, the general suitability 

of Cerro Paranal (Figures VI, 6, 7) and the relatively easy access along 

the old Panamericana were seen from land and from the air 17) . By September 

Arne Ardeberg had set up a meteorological station where every two hours 

the general condition of the sky and also the integrated atmospheric water 

vapor content were measured in addition to the standard meteorological 

quantities. The local dryness was so extreme that at times it was thought that 

the hygrometer had gotten stuck at zero! This station, under the direction of 

Marc Sarazin, has remained in operation for more than two decades with 

increasingly sophisticated instrumentation - including also a seeing monitor, 

the Differential Image Motion Monitor which he built. It was temporarily 

dismantled when the top of the mountain was removed for the VLT 

construction. 

Following the establishment of the monitoring station at Paranal, 

Ardeberg made repeated visits to some other mountains in northern Chile, 

transporting in particular a second apparatus for measuring total 

atmospheric water vapor. Carrying such a 25 kg instrument on foot from 

5500 to 6000 m at the top of Cerro Tacora was no mean feat! The 

conclusion of Ardeberg’s work was that only at substantially greater altitude 

could lower atmospheric water vapor be found and that the high sites east 

of San Pedro sometimes suffered from cirrus clouds, which would be unfavorable 

for optical observations 18) . 

Once seeing measurements were started at Paranal by Sarazin, the 

exceptional qualities of the site were confirmed. Not only was the frequency 

of clouds half of that at La Silla, but seeing was significantly better with the 

light of a point source smeared out over an area on average 25% smaller. 

Furthermore, during the nine driest months water vapor content was substantially 

less that at La Silla. So after six years of cloudiness measurements and 

two years of seeing measurements, in 1990 Paranal was chosen as the site 

for the VLT 19) . 

In retrospect the issue of the availability of water, so important in 

earlier site selections, seems curious. If no local water is available, it can be


Figure VI, 5. The first expedition to the Paranal area. From left to right: Gerhard Bachmann, 

Hans-Emil Schuster, the author and André Muller, photographed by Ulla Demierre. In the 

background is the escarpment which terminates the higher area around Paranal. 

Figure VI, 6. Image of the 

Paranal area taken from 

SPACELAB with the University 

of Munich camera. 

The summits of these 

mountains are exceedingly 

dry which is very important 

for observations in the 

infrared. Because of large 

climatic fluctuations from 

year to year, it was necessary 

to continue the ESO 

studies of atmospheric 

conditions in this region 

for seven years, before a 

definite decision about the 

VLT site was made. Conditions 

were monitored in 

particular at Cerro Paranal 

(2700 m) close to the 

Pacific coast and occasionally 

at Cerro Armazoni (3000 m), the isolated mountain half way up along the right 

side of the picture. The old Panamericana highway passes just east of the north–south 

escarpment in the middle. The scale is 6 km/cm. North is up.


Figure VI, 7. The Paranal area photographed by C. Madsen and H. Zodet. In front 

of the Pacific, Co. Paranal connected by a road to the NTT hill and to Co. La 

Montura on the right. The VISTA optical/infrared wide field telescope will be placed 

on the NTT hill, so named because I considered placing the NTT there rather than 

at La Silla. 

brought in by truck at a cost that is manageable. The same is done at several 

Chilean copper mines. And it is interesting to note that for the city of Antofagasta 

with 300,000 inhabitants much of the water is transported from the 

east by a pipeline, since none is available locally. Even during the darkest 

political periods, nobody has seriously disrupted that water supply. In the 

meantime a desalination plant has also been built. Today all the water for 

Paranal is bought near Antofagasta and trucked to the mountain. 

Millimeter Sites 

The very high sites in the main chain of the Andes had been inspected 

rather casually during the VLT site surveys. Numerous high mountains, with 

altitudes up to 6000 m, were found in the latitudes considered. Low water 

vapor column density was found, substantially lower than at Paranal, but the 

relatively high frequency of cirrus clouds made the area less attractive for 

optical telescopes and so no measurements of seeing had been made. Since 

such cirrus is composed of small ice crystals it does not affect mm radio waves 

which are absorbed only by water vapor. Also large areas were excluded by 

the smoke from the Chuquicamata copper smelters, which could be traced 

visually for more than 100 km to the east. 

In between the mountain peaks high plateaus are found, and these have 

drawn the attention of radio astronomers looking for a site for a large submm 

interferometer for which large flat areas with very low water vapor column 

density are required. The Nobeyama Radio Observatory (Japan) has been


testing an area (Río Frío at 4200 m) 180 km SE of Antofagasta in the 

Cordillera Domeyko, while the Europeans visited the nearby Pampa San 

Eulogio, a flat area 20 × 20 km at 3700 m altitude. 

The US National Radio Astronomical Observatory has extensively 

studied a higher site at 5200 m, the Llano de Chajnantor, 300 km east– 

north–east of Antofagasta, 60 km from the picturesque village of San Pedro 

de Atacama and conveniently just a few km from the road to Argentina 

(Figure VI, 8). This site appears to be exceptionally dry and has been selected 

as the location for ALMA, the Atacama Large Millimeter Array – which will 

combine the American, European and Japanese projects (see Chapter IX) 20) . 

It remains to be seen how many scientists and engineers are able to work at 

this altitude. In my (qualitative) experience most people are able to cope with 

the conditions at 4000 m but at 5000 m this is much more difficult to do. 

However, with an operational facility at 2900 m where most engineering activities 

will take place, the situation should be manageable. The 12-m radio 

telescopes can be transported there for refurbishment. 

Figure VI, 8. The 5000 m high Llano de Chajnantor. Scattered over an area 10 km 

in diameter, the 64+ submm telescopes of 12-m diameter of the Europe-Japan-US 

ALMA project should be in place here by the end of 2011.


Climatic Variability 

Some observatories have been placed in the wrong spot on the basis 

of site testing of inadequate length. Almost every site has substantial yearto-year 

variations, and a short campaign will tend to lead to the selection of 

a place that had an above average quality during that time, even though on 

a long term basis it could be inferior. To avoid such problems, the site testing 

for Paranal continued for more than six years before a decision was made. 

Since then the conditions at Paranal have been monitored for a period 

three times longer (Figure VI, 9). According to Sarazin 21) , for the 20 year 

interval 1984–2003 photometric nights (with clear sky for at least six consecutive 

hours) averaged 76%, slightly below the 80% of the first six years, but 

remained well above conditions at observatory sites elsewhere. The La Silla 

average was 61%, essentially the same as the the 62% found there during 

1966–75. In both places there seems to be some tendency for above or below 

average conditions to persist for several years in succession. Seeing conditions 

also have varied. At Paranal the 0.7 arcsecond mean seeing of the years 

1987–1997 quite suddenly deteriorated to values around 0.9 arcsec for 

1998–2003. The more fragmentary La Silla data also show a deterioration 

at about the same time. At both sites 2002 was the cloudiest year ever. Note 

that the seeing values are mean values. Median values are typically 10 better. 

Also these data come from the seeing monitor which appears to overestimate 

the image diameter measured by the VLT telescopes by some 10% in the 

visible and up to 30% at 2.4 µm 21) . 

The climate in the eastern Pacific appears to be subject to cyclical 

variations on various time scales. The variable El Niño – La Niña cycles of 

typically half a decade are, of course, well known to be associated with 

climate events over a good part of the earth. Recently a 50 year cycle has 

been found 22) . During the cooler half of the cycle in the eastern Pacific 

anchovies were abundant, to be replaced by sardines during the warmer part. 

The transition between the two appears to be rather abrupt. The fish catches 

have enabled two such cycles to be identified during the twentieth century. 

The last warm phase began in the mid-seventies and ended in the mid to 

late nineties. Rather remarkably, at La Silla and Tololo the annual number 

of photometric nights diminished significantly around 1976, only to recover 

some twenty years later – with the exception of the catastrophic year 2002. 

Large fluctuations possibly associated with the higher frequency El Niño– 

La Niña cycles superposed on the longer term trends are not unexpected. 

Changes on even longer time scales have also occurred. Anecdotal 

evidence was provided by locals at Pelícano near La Silla who stated that half 

a century earlier tall grass was growing where now not much vegetation is 

to be found. The Pelícano river, ESO’s source of water, went underground 

and only reappeared for a few months during the nineties. Also the derelict

1.0 

0.9 

0.8 

0.7 

0.6 

0.5 


0.4 

1980 1985 1990 1995 2000 2005 

0.6 

0.7 

0.8 

0.9 

1 

1.1 

1980 1985 1990 1995 2000 2005 

Figure VI, 9. Evolution of annual mean conditions at Paranal (■) and at La Silla (■). 

The upper graph gives the fraction of photometric nights, the lower graph the mean 

diameter of the seeing image in arcseconds. Incomplete data are indicated by open 

symbols. The horizontal bar in the upper graph represents the average for the La Silla 

data for 1966–1975. For 1993 and 1999 the incomplete La Silla seeing data have been 

combined with those for the preceding year to obtain 12 months of data appropriately 

distributed through the year. The figure is based on monthly data provided by M. Sarazin 21) .


irrigation ditches in the La Silla area suggest a wetter past climate. More 

quantitatively at La Serena the rainfall appears to have diminished over the 

past century by 63% 23) . It is perhaps not surprising that the La Serena – 

La Silla area would be particularly sensitive to climate changes. Over the 

300 km distance between Copiapo and La Serena average annual rainfall 

during the 1971–1984 period varied from 11 to 78 mm 24) , to increase a further 

factor of 4.5 over the 400 km to Santiago. With such strong gradients relatively 

small changes in the location of the pressure systems can have very 

large local effects. In that respect Paranal is better situated within a wide 

latitude range with rainfall below 10 mm per year. Latitude shifts of a few 

hundred km of pressure systems would be expected to cause less change at 

Paranal. Of course, rainfall and astronomical conditions are not quite the 

same. In particular, seeing may depend on more subtle effects. In fact, 

Sarazin has noted that the deterioration of the seeing at Paranal over the last 

years appears to be related to a change in the large scale pressure distribution 

which shifted the winds more to the NE. 

On much longer time scales, some recent studies seem to show that 

the climate in the region east and north of the Salar de Atacama was very 

dry much of the time 25) . The very dry period during the late parts of the last 

ice age was followed by a somewhat more humid interval from perhaps 

16,000–10,000 years ago. Numerous archeological remains are found around 

ancient lake shores which date to this period. An extremely dry period 

thereafter left the area uninhabited. A certain recovery to slightly less dry 

conditions took place subsequently, but the record from different sites is 

sometimes contradictory. The last 4000 years appear to have been more or 

less as at present. In one of the lakes on the altiplano the water level never 

exceeded present values during the last 9000 years. Thus, the astronomical 

sites in northern Chile may look forward to a continuation of present day 

favorable conditions unless unforeseen effects of global warming intervene. 

Sites for future telescopes 

The quantitative comparison of sites involves a number of parameters. 

Clear sky is obviously essential. “Photometric nights” are commonly defined 

as nights with at least six consecutive hours of clear sky. When also shorter 

periods are included, the time is referred to as “spectroscopic” or “usable”. 

The additional time may be used for obtaining spectroscopic data like 

redshifts where only the wavelength of spectral features is needed. However, 

to obtain accurate photometrically calibrated spectral data, sufficiently long 

continuous periods of observation are needed. 

The second essential parameter is the “seeing” or more specifically the 

diameter of the image of a point source due to atmospheric turbulence. The 

turbulence may be excited, for example by instabilities, at the interface of


atmospheric layers moving at different speeds. The simplest way to measure 

the seeing is to take images with large telescopes. Since these are not transportable, 

other methods are needed to compare sites. Moreover, when the 

housing of a large telescope contains air at different temperatures, the local 

“dome seeing” may make site conditions seem worse than they are. 

At ESO Marc Sarazin has built the DIMM, the Differential Image 

Motion Monitor 26) . It consists of a 35-cm telescope with in front of a detector 

a mask with two small holes separated by perhaps 20 cm. The two resulting 

images are continuously moving over the detector because of the atmospheric 

turbulence. The relative motion of the two images gives quantitative information 

about the turbulence. On the assumption that the distribution of the 

turbulent elements follows a standard (Kolmogorov) law, the turbulence is 

fully characterized and the image that would be observed with a large 

telescope may be inferred. The great advantage of the DIMM is that contrary 

to earlier instruments it only measures relative motions of the images and 

so it is impervious to movements of the telescope by the wind or other 

causes. At Paranal the actual images observed with the VLT are some 10% 

smaller in the visible and, therefore, better than inferred from the DIMM. 

This is presumably related to the fact that the larger turbulent elements do 

not follow the standard distribution. The DIMM or some version thereof has 

now become a worldwide standard for seeing measurements. 

When adaptive optics systems (Chapter VII) are considered for correcting 

the turbulent effects on the images, other site parameters become of interest: 

the number of turbulent layers, their altitude and the speed at which they 

move. These may be determined by campaigns with balloon borne equipment, 

lidars, echo sounders, etc. Unfortunately, such campaigns tend to be of short 

duration. 

A third main parameter is the quantity of water vapor above the site. 

IR observations are affected both by the emission from the H 2O in the atmosphere 

and by its absorption of the radiation coming from the outside. The 

quantity of H 2O in vapor form is measured in mm of precipitable water. Ice 

crystals in cirrus clouds are largely irrelevant in the IR, though they are a 

hindrance to observations in the visible. H 2O may be measured from its IR 

emission and from its absorption of radio waves at submm wavelengths. A 

site with 1 mm of H 2O is excellent, but several mm are found at typical observatories. 

Not surprisingly, the best results are obtained at high, cold sites. 

Data for a selection of sites are assembled in Table VI, 1. Seeing measurements 

have been transformed to median values on the ESO DIMM scale. 

The table documents the remarkable frequency of clear nights at Paranal, 

which appears to be unparalelled in the world. For its altitude it is also particularly 

dry. Chajnantor is, of course, much drier, but the available information 

suggests that clouds are more frequent. Cornell University has started a site 

testing campaign on Co. Chico, about a hundred meters above the Llano de 

Chajnantor 27) . Seeing measurements yielded a median value of 0”71 compared


to 0”80 at Paranal during the same 38 nights. However, the distance of some 

300 km between the two is probably too large for reliable conclusions to be 

based on so few nights. The Cornell study indicated that a few hundred meters 

higher above the plateau the dryness may become even more extreme, but 

obviously life becomes more difficult. 

The Argentinian side of the Andes does not appear to offer advantages 

compared to Chile, and the same appears to be the case for southern Africa 

and Australia. Sarazin performed some limited testing for ESO on the island 

of La Réunion, but conditions were not particularly favorable 19) . 

Turning to the northern hemisphere, I would doubt that any US sites 

would be suitable for new large European telescopes. Some continental sites 

are good, but not as outstanding as Mauna Kea on the big island of Hawaii. 

There the fraction of clear sky is perhaps on the modest side, but seeing and 

low H 2O are excellent. According to the Keck telescope website image 

diameters have a median value of 0”55. When comparing Paranal and 

Mauna Kea, we should take into account that the median values are some 

10% smaller than the mean values given in Figure VI, 9. Moreover, the DIMM 

results are some 10% larger than the directly measured image diameters. 

Taking also into account the fraction of photometric time, the number of 

hours with sub 0”6 seeing should be comparable on the two sites. However, 

Mauna Kea begins to be rather full, and the religio-ecological problems, 

which have caused long delays both there and at Mt. Graham, make these 

sites not very attractive for a large European telescope. In that respect the 

Mexican sites, like S. Pedro Martír or Sierra Negra, are more promising 27) . 

High sites in central Asia could perhaps have been worth considering 28) , but 

political factors effectively exclude large investments there. Maidanak in 

Uzbekistan appears to have excellent seeing (0”69 median, comparable to 

Paranal intercalibrated with ESO instruments), but the 60% clear sky is 

disappointing. Hanle in the Indian Himalaya also appears to be rather good. 

The low water vapor values at St. Katherine in the Sinai 4) , combined with 

the recent easy accessibility of the Red Sea resorts, makes this perhaps an 

interesting area for further study for a regional telescope. 

For Europe the most suitable site for a large northern hemisphere 

telescope would appear to be La Palma. The median seeing of 0”65 on the 

better subsites (intercalibrated with ESO) is excellent 29); unfortunately, the 

3.7 mm median column density of H 2O is not 30) . The percentage of photometric 

nights is acceptable, but on the low side 31) . The mean seeing of 0”75 

compares well with the long term average at Paranal of 0”80, though for the 

number of photometric hours with excellent seeing the latter still has the 

edge. The La Palma site is situated in Spain and, therefore, in the EU, while 

the national and regional governments have demonstrated an admirable 

engagement for its protection. Perhaps with JWST and ALMA expected to 

be in operation early in the next decade, the H 2O problem should carry less 

weight than the excellent seeing. In any case, on the basis of presently available


Table VI, 1. Astronomical sites. Subsequent columns give the altitude in m, the 

percentage of photometric nights, the percentage of “spectroscopic” or usable time, 

the median seeing in arcsec as measured by a DIMM, the median column density of 

H 2O in mm and the longitude and latitude. Note that these data sometimes are based 

on insufficiently long observations to yield a reliable long term average. Figures 

placed between the ph and sp columns give the percentage of clear time without the 

requirement of 6 hours continuously clear. 

Alt. % ph % sp DIMM H 2O I b 

Chacaltaya (Bolivia) 5400 ( ) 1 ( ) 1 2.3 2 68W –16 

Chajnantor (Chile) 5200 (63) (81) 1.2 68W –23 

Paranal (Chile) 2700 76 91 .70 3 2.2 70W –25 

La Silla (Chile) 2400 61 82 .84 3 3.8 71W –29 

El Leoncito (Argentina) 2400 48 69W –32 

Mauna Kea (Hawaii) 4200 55 72 .60 4 2.0 155W +20 

S. Pedro Martír (Mexico) 2800 64 81 .60 115W +31 

Sierra Negra (Mexico) 4600 .73 97W +19 

Kitt Peak (Arizona) 2100 67 6.7 2 112W +32 

Mt. Graham (Arizona) 3200 64 75 2.9 110W +33 

McDonald Obs. (Texas) 2000 38 65 104W +34 

La Palma (Spain) 2400 51 73 .65 3.7 18W +29 

Oukaimeden (Marocco) 2700 65 2 8W +31 

Calar Alto (Spain) 2200 30 57 .92 3W +37 

Maidanak (Uzbekistan) 2600 60 .69 67E +39 

Hanle (India) 4500 53 71 .8 < 2 79E +33 

La Réunion (France) 2900 (38) (69) (5) 55E –21 

AAO (Australia) 1100 40 65 149E –31 

Dome C (Antarctica) 3250 >75 5 .27 5 0.25 5 123E –75 

1 average day time cloud cover 53%. 2 day time. 3 mean value × 0.9. 4 image diameter × 1.1. 5 winter 

only. 

evidence, there would be only three plausible sites for a large European 

telescope: The Paranal area (Armazoni?), one of the summits around the 

Llano de Chajnantor and La Palma. Moving the NTT from La Silla to the 

Chajnantor area might be an effective way to test its suitability for future large 

telescopes. For the other two sites telescopes of sufficient size will continue 

to provide data for a comparison. Concerning Paranal and surroundings, 

much will depend on whether the deterioration of the last six years is a 

temporary aberration or not and on whether it affects Armazoni equally. 

Finally, it might be worthwhile to further study the Mexican sites which look 

promising, but for which the data are still very limited. 

Another site that at present evokes much interest is the South Pole. 

In the interior of Antarctica winds are very weak and the atmosphere 

extremely dry and cold. The SP is not very suitable for most observations in


the visible, because it is astronomically dark (Sun more than 18 ° below the 

horizon) for only 79 days per year. Moreover, a turbulent layer at low altitude 

causes the seeing to be terrible. However, in the IR and submm domain this 

is not so much of a problem. Measurements made at 350 µm show that in 

the zenith direction the median atmospheric transmission is 0.30 versus 0.25 

at Chajnantor and 0.15 at Mauna Kea 28) . The stability of the transmission is 

particularly favorable at the SP. However, the fraction of the sky accessible 

at small zenith angles is small, while at low latitude sites like Chajnantor it 

is much larger. For special projects, like the high precision determination of 

the fine structure of the Cosmic Microwave Background, the SP appears to 

be unsurpassed, but for a broader range of programs the advantage over sites 

like Chajnantor is not evident. Moreover, the Cornell measurements have 

shown that the water vapor content of the atmosphere above the Llano de 

Chajnantor may diminish rapidly with height 27) . So conditions on the 

surrounding mountains may well be as good as at the SP. 

Conditions appear to be much more favorable at “Dome C”, a high 

Antarctic plateau (3250 m) some 15 ° from the SP. Here a French-Italian 

cooperation has constructed the “Concordia” base for a variety of purposes. 

Dark time and the area of the sky at low zenith angles are already more favorable. 

The most outstanding characteristic of Dome C is its incredibly stable 

atmosphere. Recent measurements of atmospheric turbulence correspond to 

wintertime seeing with a median of 0.27 arcsec, spectacularly better than 

anywhere else in the world 32) . Also the angular distance over which the 

turbulent patterns are correlated and the slowness of their variation appear 

to be optimal. Though a longer term data set would be desirable, it seems 

probable that both for observations in the IR and for interferometry in the 

visible Dome C would offer unique advantages. However, in the absence of 

a large base at Dome C, it would not be very realistic to try to place a 100 m 

telescope like OWL there. 

So far we have discussed only conditions in the atmosphere. A serious 

threat comes from city lights, which even at tens of kilometers distance may 

cause a significant increase in the background luminosity of the sky. Even 

at La Silla and still more at Tololo this is becoming noticeable. Fortunately, 

the authorities in La Serena and in the Atacamean region are beginning to 

impose standards on street lighting which reduce the upward flux 33) . This has 

both economic and astronomical benefits. The difficult conditions of life in 

the Atacama desert for the moment limit light pollution at Paranal, though 

mining operations pose an ever present threat. In fact, the Yumba mine SE 

of Paranal has become increasingly visible. The commercial exploitation of 

space may also pose grave dangers. Various proposals for space advertising 

have been successfully defeated for now. However, experiments have been 

made to light cities in the Arctic by solar reflectors, and the risks to ground 

based astronomy are all too real.


In Chile earthquakes pose an additional danger. While modest earthquakes 

cause no greater problem than the temporary loss of the telescope 

pointing, larger ones may do more lasting damage. From the data of 

Barrientos 34) , an earthquake stronger than 7.5 on the Richter scale may be 

expected in the Paranal region once every 250 years. Of course, the damage 

would depend very much on its precise location. So the risk is small, but real.

VII. 

The VLT Observatory: 

Adaptive Optics, Instruments, Interferometry 

and Survey Telescopes 

Die Daten der kosmischen Schöpfung sind ein nichts als 

betäubendes Bombardement unserer Intelligenz mit 

Zahlen, ausgestattet mit einem Kometenschweif von zwei 

Dutzend Nullen, die so tun, als ob sie mit Maß und 

Verstand noch irgend etwas zu tun hätten. 

Thomas Mann 1) 

The VLT array of four 8.2-m telescopes has been built, but many other 

aspects have to be taken care of before it could be a fully functioning observatory. 

The deleterious effects of the atmosphere have to be mitigated to 

obtain the full benefit of the large unit telescopes. A wide variety of instruments 

is needed to analyze the light collected. A substantial infrastructure is 

required to make use of the VLT as an interferometric array. And, finally, 

since the large telescopes can observe only a minuscule fraction of the sky, 

it would be beneficial to have wide angle survey telescopes – the successors 

to the Schmidt telescopes of the past – to discover important objects for the 

8.2-m telescopes to study in detail. 

Adaptive Optics (AO) 

The performance of ground based telescopes is degraded by the earth’s 

atmosphere, while space based telescopes are very expensive. So simple 

economics tells us that we should look for ways to reduce the atmospheric 

effects. In the ultraviolet the ozone layer is opaque, and in part of the infrared 

various atmospheric constituents block the incoming radiation. So in these 

wavelength ranges we have no choice but to observe with space telescopes.


There are also some wavelength ranges in the IR where water vapor is the 

main problem. Hence, the selection of high, dry sites is advantageous. Observations 

at some submm wavelengths may be made from places like 

Chajnantor, Mauna Kea or even better from the high, cold Antarctic plateau. 

But even in the optical/near IR spectral domain from 0.3 – 2.5 µm, where 

the transparency is good, there is a serious problem: the atmospheric turbulence 

disturbs the incoming light rays making the astronomical images 

unsharp, or in astronomical parlance causing “seeing”. Typically the seeing 

smears out the image of a point-like star over an arcsecond or more, far larger 

than the intrinsic diffraction image of a telescope a few meters in diameter. 

This was one of the reasons the 2.4-m Hubble Space Telescope (HST) was 

constructed, which gave spectacular images with much fine detail not seen 

on images from ground based telescopes. However, by now, new technologies 

are being developed – adaptive optics – which allow equally excellent images 

to be obtained from the ground, at least in the near IR. 

When different layers of the atmosphere move at different speeds, 

turbulence tends to result at the interface. Different parcels of gas – different 

cells – then move in randomly different directions and at different speeds. 

This also causes small temperature variations, as a result of which the light 

rays passing through the medium are refracted and this leads to the diffusion 

of the images. The smallest turbulent cells are only a few cm across, and the 

pattern of cells may change on millisecond timescales. 

Suppose now that we take the image of a star with only a millisecond 

exposure time. Then the turbulence will effectively be “frozen”. The image 

of the star will be deformed by the turbulent medium, but during the millisecond 

it will not change much. We then observe another star, so near to 

the first one that its light passes through the same turbulent pattern. Its 

image will be deformed in the same way. We analyze the image of the first 

star, and we can find out how it has been deformed from the point-like 

image it should have had in the absence of the atmosphere and what corrections 

have to be applied to the deformed image to recover the true one. We 

now can apply these same corrections to the neighboring star and also 

recover its image. The next millisecond we will find somewhat different 

corrections, and again we can restore the image of the second star with these, 

and so on. 

Of course, all of this only works if the first star is sufficiently bright 

so that there is enough information in the image to determine the corrections. 

But the second star can be very much fainter or it may be a more 

composite image, like a double star that due to the seeing could not be 

resolved. In principle, to make an adaptive optics system we could deform 

the primary mirror of the telescope in such a way that it corrects for the 

seeing effects in exactly the same way as the active optics system in 

Figure III, 4. Instead of making the mirror optically more perfect as in that 

case, we could introduce the imperfections needed to compensate the seeing

The VLT Observatory 111 

effects. However, the primary mirror is generally too heavy to do this on millisecond 

timescales. So a thin flexible mirror is introduced into the optical 

beam with the necessary actuators to shape it. Alternatively, it may be feasible 

to achieve the same result directly with the Cassegrain secondary mirror if 

it is made sufficiently thin 2) . 

The principle of adaptive optics is identical to that of active optics. 

However, apart from the faster response that is needed, there is one fundamental 

difference. The active optics corrections are valid in the whole focal 

plane. But since the turbulence pattern is different in different directions, the 

adaptive optics corrections are only valid in close proximity to the star from 

which they are determined. The size of the “isoplanatic patch” over which 

the corrections are well correlated depends on the wavelength. In the optical 

at 0.5 µm it is typically 2 arcsec on a good site. But in the near IR at 2.5 µm 

it would be about 14 arcsec. Also the corrections change more slowly. The 

number of actuators needed on the deformable mirror is proportional to the 

square of the diameter of the primary mirror. For an 8.2-m VLT telescope 

it is about 6000 at 0.5 µm wavelength, but at 2.5 µm only 125. So adaptive 

optics is much simpler in the near IR than at visible wavelengths. 

At ESO the first adaptive optics instrument was developed very much 

under the influence of Pierre Léna by a cooperation of ESO, ONERA in Paris 

and some French observatories. In 1990 this instrument “COME-ON” was 

placed at the 3.6-m telescope. It had 19 actuators on the flexible mirror and 

was intended to give perfect diffraction limited images at 3.5 µm. With the 

completion of the VLT, a MultiApplication Curvature Adaptive Optics 

(MACAO) program was implemented to build seven AO systems for some 

instruments and for the VLT Interferometer 3) . An example of the results from 

one of the VLTI systems is shown in Figure VII, 1. Also for the high resolution 

camera CONICA a German-French collaboration has constructed the 

AO system NAOS with 185 actuators, which gives diffraction limited images 

at 2.2 µm. Even at 1.2 µm the system worked well with 0.04 arcsec resolution, 

probably the best reached so far by any telescope on the ground or in space! 

It remains a formidable task, however, to advance to full adaptive optics 

correction at visible wavelengths around 0.5 µm. Both the fast image analysis 

and the control of the flexible mirror still pose some problems. We have not 

yet mentioned another limitation of adaptive optics. The reference star which 

determines the corrections to be applied has to be sufficiently bright. But 

within the small isoplanatic patch of an object we wish to study, there may 

not be such a star. Artificial laser stars may be the answer. 

There are two options. In the high atmosphere, about 100 km up, there 

is a layer of neutral sodium. Higher up the sodium is ionized, lower down it 

is incorporated into molecules. When we shine a laser tuned to the wavelength 

of the strong sodium D line onto this layer, some of the light is scattered back, 

creating an artificial star. Alternatively, laser light in the blue part of the 

spectrum may be scattered by nitrogen or oxygen molecules. If the laser is


Figure VII, 1. Adaptive Optics. To the left a star imaged in the K-band (2.4 µm) at 

a time the atmospheric seeing was 0.75 arcsec. To the right the same star seen after 

the adaptive optics system for the VLTI was switched on. The resulting image shows 

that the “star” is actually a close double star with a separation of 0.12 arcsec between 

the components. The first AO system at ESO was COME-ON implemented in 1990 

at the 3.6-m telescope. Not only is a more detailed image obtained, but also the sharp 

peak of light allows fainter objects to be detected above the background. 

pulsed and if we suitably select the time delay of the returning light, the 

altitude of the apparent laser star is also determined because of the finite 

velocity of light. Even though there are many complications, the advantage of 

the laser star is that by pointing the laser beam in the right direction, we can 

ensure that it is within the isoplanatic patch around the object under study. 

Instrumentation 

Each of the four 8.2-m unit telescopes has two Nasmyth foci and one 

Cassegrain focus. So at these foci one may install 12 instruments which can 

remain in place for long times. In the past, at the 3.6-m telescope with effectively 

just one Cassegrain focus, multiple instruments were used. The frequent 

instrument exchanges caused much loss of time, since new calibrations had 

to be made each time an instrument was replaced, and because malfunctions 

were most frequent when another instrument was put in place. At the VLT, 

each instrument is permanently placed until a new instrument or an upgrade 

arrives. As a result, quality and efficiency have much increased. The only 

exception is the “visitor focus” where astronomers from the community may 

place an experimental – or a niche – instrument they have developed. 

The construction of instruments for the VLT is a major undertaking. 

So it was neither feasible nor desirable for ESO to build all the instruments 

in-house. Instead, with some exceptions, most have been contracted out 

(competitively) to institutes, or more usually consortia of institutes, in the


member countries: ESO would provide the funding for the industrial 

hardware and the institutes would provide the necessary personnel. In 

exchange, the institutes would receive a specified amount of privileged 

observing time outside the normal time allocation channels. After this time 

has been used up, the persons who have participated in the building of an 

instrument still have the advantage of a better knowledge of its potential and 

therefore a certain advantage in the preparation of proposals for the normal 

time allocation process. The participation of many institutes in the instrument 

building has created a much stronger sense of participation in the VLT by 

the community and fostered European cooperation in multinational consortia. 

We note that the ESO procedures are different from those at ESA, where the 

total cost of instruments is (in principle) assumed by the institutes of the 

member countries and their space agencies; correspondingly, the return of 

privileged observing time is also larger at ESA. However, in the meantime 

the situation at ESO has become more mixed. To ensure uniformity, also in 

later maintenance and data handling, ESO has taken more responsibility for 

the area of detectors and associated electronics. On the other hand, hardware 

expenses have also sometimes been assumed by the national institutes to 

speed up the construction. And, of course, ESO staff always has a role in 

ensuring that the instruments can be properly integrated at the telescope. 

The total cost and effort involved in the instrumentation is quite large. 

For example, UVES built at ESO cost some 2.5 M€ in money and in addition 

40 man/years of effort. For the MIDI interferometric instrument the 

consortium members invested 1.8 M€ in hardware and 4.2 M€ in personnel 

costs. I would estimate that in total the instrumentation cost for ESO and 

the national institutes to-date is some 20% of the cost of the VLT itself. This 

is not very different from the situation at ESA where the national payload 

support (for instruments) during the nineties amounted to 24% of the 

spending of the Science program, the latter essentially used to build and 

manage the satellites. 

When a few decades ago ESO received instruments from astronomical 

institutes, the quality sometimes was modest. Loose wires would be hanging 

around, electronic interfaces or components would be incompatible with 

La Silla standards and data handling software limited. The situation now has 

changed. Most instruments built so far are of the highest engineering quality, 

and only in two cases did ESO have to cancel a contract. The improved quality 

of the work of the institutes is in part the result of their participation in the 

space program. An instrument built for a satellite has to undergo stringent 

tests and to meet certain deadlines. If not, the satellite may leave without it. 

The resulting attitudes towards quality control have benefitted ESO and also 

the participating industries. 

The selection of the 11 facility instruments has been preceded by much 

consultation with the community. Some instruments have been functioning 

for six years, others have just been finished. At the same time, plans for


second generation instruments have been made. In Figure VII, 2 and 

Table VII, 1 the instruments located at the four unit telescopes are identified. 

Around full moon the sky is too luminous to observe faint objects at visible 

wavelengths, but in the IR this is less of a problem. Also observations of 

brighter objects at very high spectral resolution are not much affected. So 

each unit telescope has at least one instrument in these categories. 

Six of the instruments are imagers. With filters broad or narrow wavelength 

ranges may be selected. The near IR imagers are provided with 

adaptive optics. Different angular resolutions may be obtained, with the 

corresponding field of view determined by the size of the detector. The better 

the resolution, the smaller the angular field of view. Even though it does not 

have a real adaptive optics system, ISAAC has yielded excellent images which 

Figure VII, 2. The VLT and its instruments. From left to right, the four unit telescopes 

with their Mapuche names. UT1: Antu, the Sun; UT2: Kueyen, the Moon; UT3: 

Melipal, the Southern Cross; UT4: Yepun, Sirius. In front, the stations where the auxiliary 

interferometric telescopes may be placed. Schematically, the subterranean tubes 

are shown through which the light reaches the VLTI laboratory, which houses the 

delay lines (Figure VII, 7), the beam combiners and the interferometric instruments. 

Between UT3 and UT4 the 2.6 m VLT Survey Telescope, VST, is visible. VISTA is a 

4-m IR survey telescope on NTT hill.


Table VII, 1. Instruments at the VLT. The columns from left to right give the year of 

completion, the unit telescope and the focus Nasmyth or Cassegrain, the acronym, the 

wavelength range in µm, the characteristics with im for imager and the maximum 

spectral resolution for spectrographic modes, the largest field of view in arcminutes, the 

smallest number of arcsec per detector pixel indicative of the angular resolution and the 

eventual combination with adaptive optics, the maximum number of spectra taken in 

multiple object spectroscopic mode and the presence of an integral field unit (IFU) or 

of a long slit (ls), the number of pixels on the detector in units of a million, and a reference 

to an article in the ESO Messenger. It is important to note that the field of view 

is smaller if the angular resolution is high and that at high spectroscopic resolutions multiplicity 

of objects is smaller. For a more complete review of the instruments, the articles 

in the “Messenger” or the ESO web pages should be consulted. 

max 

max FOV min 

Year UT Name λ (µm) res (arcm) arcs/pix MOS Mpix ref 

1998 1 C FORS1 0.3–1.1 im, 1800 7 0.1 19 4 a 

1999 2 C FORS2 0.3–1.1 im, 5000 7 0.1 100 4 a 

1999 2 N UVES 0.3–1.0 115000 0.2 0.5 7 ls 16/8 b 

2002 3 N VIMOS 0.4–1.0 im, 2500 15 0.2 1000, IFU 8 c 

2002 2 N FLAMES 0.4–1.0 47000 25 0.5 125, IFU 8 d 

1998 1 N ISAAC 0.9–5 im, 3000 2.5 0.15 ls 1 e 

2001 4 N NAOS-CONICA 1–5 im, 2000 1.2 0.013 AO ls 1 f 

2004 4 C SINFONI 1.1–2.5 4000 0.13 0.025 AO IFU 4 g 

2004 1 N CRIRES 1-5 100000 0.8 0.1 AO ls 4 h 

2004 3 C VISIR 8–25 im, 25000 1 0.075 ls 0.06 i 

2006 N HAWK-1 0.9–2.5 im 7.5 0.1 AO? – 16 j 

2007 C X-shooter 0.3–1.9 7000 0.2 0.6 ls 8/1 j 

2010 N KMOS 0.9–2.5 4000 7.2 0.2 AO? IFU j 

References: a. ESO Messenger 94, 1, 1998; b. 99, 1, 2000; c. 109, 21, 2002; d. 110, 1, 2002; e. 95, 1, 

1999; f. 107, 1, 2002; g. 117, 17, 2004; h. 114, 5, 2003; i. 117, 12, 2004; j. 115, 8, 2004. 

frequently show very different features from those seen in the visible. In many 

heavily absorbing nebulae ISAAC can penetrate the absorbing dust and study 

star formation. Also interesting multicolor observations in the solar system 

may be obtained. In the case of Jupiter different wavelengths show different 

features because of the different absorption by methane and other molecules 

(Figure VII, 3). 

Particularly spectacular results on the center of our galaxy have been 

obtained with NAOS-CONICA (Figure VII, 4) 4) . In visible light it is unobservable 

because of very heavy interstellar absorption. However, in the near 

IR numerous stars shine through (left figure). One of these is extremely close 

to the radio source Sagittarius A* which is believed to be coincident with the 

black hole at the Galactic Center. In fact, repeated observations, first with


Figure VII, 3. False color 

combination of several 

broad and narrow band 

images of Jupiter in the 

3.2–4.1 µm spectral 

range. The auroral oval 

is well visible. The energetic 

particles which 

create the aurorae interact 

with the atmosphere 

and generate the 

“blue haze” which is 

spread around in longitude 

by the strong 

zonal winds. 

Figure VII, 4. The Galactic Center imaged by NAOS-CONICA. To the left the orbit 

of the star (S2) closest to the radio source Sagittarius A*, which describes an elliptical 

orbit with 15.2 year period around it. This effectively demonstrates that Sag A* 

is coincident with the 2.6 million solar mass black hole at the Galactic Center. At the 

moment of closest approach Sag A* was hidden by the star. To the right are two exposures 

in the IR of the area of the Galactic Center taken later in 2002 after Sag A* 

became again observable. In the image at t = 0 no emission was visible at its location, 

but 39 minutes later (t = 39) it had erupted, presumably due to some matter spiralling 

into the black hole.


the NTT and later with the VLT, have enabled to determine the highly elliptical 

orbit of this star around Sag A* (left figure). It has a period of 15.2 years 

and passed closest to Sag A* in April 2002 at a distance of about 0.015 arcsec 

or 17 light hours with a speed of 8000 km/sec. The origin of this star and 

others close by is baffling. But these results show the incredible power of a 

large diameter high quality telescope with Adaptive Optics. At the moment 

of closest approach Sag A* was hidden by the star. As this star began to move 

away, Sag A* became observable again. Hour long bursts of IR radiation were 

detected which were precisely coincident with this object. Also XMM-Newton 

(Chapter XI) has detected X-ray bursts from the area of the Galactic Center. 

However, its angular resolution is inadequate to prove that the X-rays come 

from Sag A*, though that is the most likely interpretation. 

A typical spectrograph consists of a slit through which the light enters, 

a dispersing element (prism, grism, grating), some further optics and a 

detector. With a relatively long slit the spectra of more than one star or of 

a slice of an extended object like a galaxy may be determined. But if, for 

example, we wish to measure the redshifts of the numerous faint galaxies in 

a field of view, it is unlikely that more than two or three will be located exactly 

on the slit. It is here that the Multiple Object Spectrographs (MOS) come in: 

numerous slitlets are placed in the focal plane at the positions of stars or 

galaxies to obtain their spectra. Two ways to do this are employed in the VLT 

instruments. The simplest is the metal mask with small slits cut in. First, an 

image of a certain field is taken and the positions of the objects of interest 

determined. Subsequently, the slitlets are cut at these positions. At first this 

was done mechanically, now a laser cutter is used which does this much 

faster. The most extreme MOS is VIMOS which allows up to 1000 slitlets in 

one go (Figure VII, 5). Of course, for each new field a new mask is to be made. 

The alternative is to use fiber optics. Small lenses coupled to optical fibers 

are mounted on arms so that they may be placed anywhere in the field. 

Through the fibers the light reaches the slit of a long slit spectrograph. In 

the case of FLAMES, 125 fibers allow 125 spectra to be stacked above each 

other. It is necessary to design the system of fibers so that they cannot 

collide or become entangled. 

An alternative type of spectrograph is the Integral Field Unit. Here a 

two-dimensional array of contiguous lenslets images a certain area. Subsequently, 

the light of all these lenslets is projected on a slit spectrograph. In 

the case of SINFONI, the array consists of 32 × 32 lenslets, and so 

1024 spectra are taken at the same time. Thus, a star cluster or a galaxy can 

be completely analyzed all at once. 

At very high resolutions more conventional single slit spectrographs 

with échelle gratings have been constructed. In the échelle format different 

segments of the spectrum are stacked above each other on the detector. So 

a large stretch of spectrum at high spectral resolution can be obtained. In 

the case of UVES, the segments are separated by 12 arcsec and so there is


Figure VII, 5. Some 220 stellar spectra taken simultaneously by VIMOS with a spectral 

resolution of 250. With VIMOS up to 1000 spectra may be taken at the same time. 

space for the spectra of some other objects in between. A mode has been developed 

in which UVES at one Nasmyth focus of UT2 is coupled to FLAMES 

at the other focus with 50-m long fibers; this allows seven stars to be observed 

at the same time. 

Three new instruments are being planned. HAWK-1 will be an imager 

and KMOS an Integral Field Spectrograph, both for the near IR and both 

covering as large an area as possible. When adaptive optics on the secondary 

mirror are implemented (as on the LBT, Chapter V), this would further 

enhance the performance. X-shooter would be a spectrograph that allows 

simultaneous coverage of the visible and most of the near IR. 

Irrespective of the details of their construction, all spectrographs share 

a very much increased efficiency. Through mirrors or fibers the spectra are 

stacked in such a way that most pixels of the detectors obtain useful data; 

nothing is wasted. The VLT has become very much one integrated facility. 

Observers for all telescopes are located in the VLT control center. By activating 

remotely controlled mirrors, they may switch in seconds from one 

instrument to another and in each instrument between different imaging and 

spectroscopic modes. During routine observation, manual intervention on the 

spot should not be needed. Unless something goes wrong, it is not necessary 

to touch the instruments since they all have their fixed place. In fact, most 

observers need not see their telescope at all!

Interferometry 


A high angular resolution requires a large telescope. However, it is not 

necessary that all of the mirror surface be covered with reflecting material. 

In fact, if a number of small reflecting areas are suitably chosen, much of 

the image resolution is preserved, but, of course, the light collecting power 

is diminished. If now these reflecting areas are mounted individually, the 

situation is no different. Hence, instead of building a 10-m telescope, one 

could build a number of 1-m telescopes and obtain a comparable angular resolution. 

This is the principle of the interferometer where light is combined from 

a number of independent telescopes scattered over an area large compared 

to the areas of the individual telescopes (Figure VII, 6). 

There is, however, one difference. In a single surface telescope the 

optical path length to different parts of the mirror is the same, no matter 

what the orientation of the telescope is. In two separately mounted mirrors 

this is no longer the case, and the path length difference depends on the 

direction of the object being studied. To compensate for this, “delay lines” 

are introduced which allow the optical path to the different telescopes to be 

equalized. Since the optical path length should be stable to a fraction of a 

wavelength, the delay lines represent high precision optomechanical systems 

(Figure VII, 7). Of course, the positions of the mirror surfaces should be 

equally stable. Vibrations of the telescope mechanics and of the soil on which 

they rest should be minimized. In interferometry the atmospheric turbulence 

is also a major obstacle and with large telescopes adaptive optics is essential. 

At the VLT the four telescopes have fixed locations, and this is insufficient 

to obtain complete interferometric images. To improve the situation, 

four mobile 1.8-m telescopes are being added to the interferometer, so that 

by positioning these in various places a better approximation to a large 

telescope may be realized. While in this way the image quality may approach 

that of a 200-m telescope, the limiting brightness corresponds to that of a 

1.8-m telescope. Still the angular resolution of a milliarcsecond at 1 µm 

wavelength should allow very detailed observations of numerous interesting 

objects. 

Since the tolerances of the optomechanical systems are proportional 

to the wavelength and since AO is required, the VLT interferometer has 

been initially restricted to the nearer infrared. Observations at longer wavelengths 

are also foreseen, but since the atmosphere radiates rather strongly 

in the “windows” around 10 and 20 µm, even on as dry a site as Paranal, 

very faint objects cannot be observed. For most interferometry in the midand 

far-infrared space based interferometers are required. Both ESA and 

NASA are planning such interferometers, but the technological challenges 

are daunting. 

Several facility instruments are being constructed for the beam combination 

in the VLTI laboratory 5) : MIDI 6) (2003) is a mid IR (8–13 µm)


Figure VII, 6. Interferometry with two independent telescopes of the VLT array. 

Several flat mirrors bring the light beams from the moving Nasmyth focus to the 

stationary coudé focus. Since the light waves from a star will reach the two telescopes 

at variably different times, delay lines (essentially moving mirrors, see Figure VII, 7) 

are inserted to ensure that the optical path length remains the same. Then the two 

beams can be made to interfere in the Beam Combination Lab, resulting in an image 

composed of bright and dark stripes – the interferometric fringes. 

instrument which combines the beams of two telescopes and provides a 

spectral resolution of 300. AMBER 7) (2004), a near IR instrument 

(1–2.4 µm), can combine three beams. This is important because then 

“closure phase” techniques (developed by radio astronomers) may be used 

which improve the image quality. It provides spectral resolutions of 10,000.


Figure VII, 7. The VLT interferometric tunnel with the delay lines. These have to be 

extremely straight and accurate to ensure that differences in optical path length 

remain much less than one wavelength. 

In 2005 the near IR instrument PRIMA should arrive. While the drawback 

of the other instruments is the small field of view (2 arcsec), with PRIMA 

two such fields separated by up to an arcminute may be observed simultaneously. 

With a star in one field as a reference, the positions in the other 

may be determined with a relative accuracy of 10 microarcsec. This is particularly 

interesting for planet searches (Chapter XV). An experimental 

instrument, GENIE, is being developed in an ESA-ESO collaboration, which 

is to serve as a prototype for the Darwin nulling space interferometer aimed 

at finding earth-like exoplanets (Chapter XV). 

Much indirect evidence has led to a picture of active galaxies in which 

a black hole nucleus and its environment are surrounded by a dusty absorbing 

torus which would generally be too small to be directly observed. With MIDI 

for the first time a glimpse of such a torus has been obtained at 10 µm wavelength 

8) . Emission from warm dust at about 320 K temperature was detected 

from a region with dimensions of only 7 × 13 light years around the nucleus 

of the well known Seyfert galaxy NGC 1068. This result shows the great 

potential of the VLTI. Further upgrades would appear to be justified.


Survey Telescopes 

In the past, Schmidt telescopes were used to photograph large parts of the 

sky. These allowed interesting objects to be found for more detailed studies with 

the larger telescopes. However, the photographic plates did not reach very faint 

objects. Even though the fields that may be surveyed are much smaller, the depth 

and accuracy reachable with CCD detectors have led to the closing of many 

Schmidt telescopes, including the 1-m at La Silla. Still large scale surveys remain 

important. A 2.6-m VLT Survey Telescope has been built by the Capodimonte 

Observatory in Napoli to be placed at Paranal. Unfortunately, during transport 

to Chile the mirror has been destroyed. A new mirror arrived in 2004. The VST 

has a CCD camera with 256 million pixels 9) , allowing it to image one square 

degree with a resolution of 0.22 arcsecond. An observation of 4 hours through 

five filters should reach quite faint objects (25th magnitude). However, it still 

would take half a century to survey the whole southern sky, and so suitable areas 

have to be selected. The quantity of digital data generated will be enormous. 

A 4-m survey telescope, VISTA, is being built by the UK at a cost of 

51 M€ and will be transferred to Paranal in 2007 as part of the entrance fee 

the UK had to pay as a compensation for the investments made earlier by 

ESO. VISTA should make surveys in the near IR to 2.4 µm with a 64 million 

pixel camera. Its enclosure is being built on the “NTT Hill” (Figure VI, 7). 

The Virtual Observatory 

The incredible data flow coming from the world’s optical, radio and space 

based observatories necessitates the implementation of suitable archiving procedures. 

In the past observatories archived their photographic plates, and when 

a scientist was looking for a particular item there generally was someone who 

could locate it in a plate catalog or from memory. With the expansion of the 

number of instruments and their increased efficiency, this is no longer possible. 

Moreover, if every institute decided on its archival format, access would be 

difficult. So it is important to make the archives follow certain rules and also to 

ensure that one can conveniently discover what has been done before. Hence, 

the International Virtual Observatory Alliance which manages the Virtual 

Observatory. The European version of it is the Astrophysical Virtual Observatory. 

The AVO has as partners ESO, ESA, Astrogrid (UK), the Institut d’Astrophysique, 

the Université de Strasbourg, Jodrell Bank Observatory, and the Centre 

de Données Astronomiques de Strasbourg which in Europe pioneered data 

archives. The AVO is partly funded by the EC. Once the system is complete, it 

should become very easy to combine different data sets. As an example, ultimately 

one should be able to superpose on a VLT image the X-ray sources that 

will be detected by the Japanese ASTRO-E, the IR sources found by NASA’s 

Spitzer and also to find all the available spectroscopic data for these objects. For 

the VO to be fully useful, it will be important to include only fully validated data.

VIII. 

Ground and Space Based Optical Telescopes 

HST 

By sparing neither labor nor expense, in constructing for 

myself an instrument so superior that objects seen 

through it appear magnified nearly a thousand times … 

Galileo Galilei 1) 

In 1946 Lyman Spitzer described the great advantages that could result 

from placing a large telescope in space. Not only would this give access to the 

ultraviolet, hidden from our view by ozone in the stratosphere, but it also would 

eliminate the deleterious effects of atmospheric turbulence on image quality in 

the visible part of the spectrum and the effects of the faint atmospheric airglow. 

Years later, in 1971, NASA would initiate planning for building the Large Space 

Telescope, which finally resulted in the 2.4-m Hubble Space Telescope. In 

1979 the total cost of the program to NASA was estimated at 440 MUS$ 2) (equivalent 

to 1000 M$ in 2004 value), including 90 M$ for designing, building 

and testing the scientific instruments. The telescope was to be launched late 

in 1983 by the Space Shuttle into Low Earth Orbit, which would make it 

possible to visit it again at a later date to make repairs or upgrade instruments. 

In those days of shuttle optimism visits every 2–3 years by astronauts and a 

return to earth and relaunch every 5 years were envisaged 3) . Five instrument 

locations were foreseen, four of which would be occupied by a wide field 

imager, a low and a high resolution single aperture spectrograph and a high 

speed photometer (Table VIII, 1). The launch of HST took place in April 1990, 

following a long delay due to an earlier shuttle accident. 

In 1977 ESA joined the project as a 15% partner; it would provide the 

fifth instrument, the Faint Object Camera (FOC), the solar panels and a 

contingent of some 15 scientists at the Space Telescope Science Institute 

(STScI) in Baltimore. In return, European scientists could apply for observing 

time on all instruments with a guarantee of at least 15% of the total. Actually 

European principal investigators obtained about 19%.


Table VIII, 1. Instruments at HST and foreseen for its successor JWST. From left to 

right the columns give the acronyms, the years of operation, the principal functions 

(imaging, spectroscopy, high speed photometry), the wavelength range, the spectral 

resolutions and the field of view. Spectral resolution may be obtained for all objects 

in the field with filters (f), grisms (prism with on one of the surfaces a grating so that 

at the central wavelength the position of the spectrum and the direct image are coincident) 

(g), prisms (p) and in addition for selected objects from spectrographs with 

slits; grisms have typical resolutions of the order of 100, while the STIS prism has a 

resolution ranging from 26 at 0.32 µ to 1000 at 0.12 µ. The spectral resolution range 

is not necessarily available over the whole wavelength range. Several imagers also have 

higher angular resolution cameras with smaller FOV’s. 

HST instruments 

wavelengths spectral FOV 

years function (µm) resolution (arcsec) 

WFPC 1) 1990-2007? im 0.12–1.1 f 3 × 75 × 75 

FOC 1) 1990-2002 im/sp 0.12–0.6 f, g, 1000 7 × 7 

FOS 1990-1997 sp 0.12–0.8 250, 1300 0.3 

GHRS 1990-1997 sp 0.12–0.3 20000, 90000 0.3 

HSP 1990-1993 hsph 0.12–0.8 f 

STIS 1997-2004 sp/im 0.12–1.0 f, p, 400–100000 50 × 50 

NICMOS 1997-2007? im/sp 0.8–2.5 f, g 50 × 50 

ACS 2002-2007? im 0.12–1.0 f, g 200 × 200 

JWST instruments 

NIRCam 2011- im 0.6–5 variable f-100 140 × 280 

NIRSpec 2011- sp 1–5 100–3000 180 × 180 

MIRI 2011- im/sp 5–27 f, 100, 3000 100 × 100 

1) Data for WFPC 2 (1993) which was adapted to the telescope optics and for FOC + 

COSTAR (1993). FOC also had a less used 14 × 14 arcsec camera. 

The FOC was to be the imager with the highest angular resolution. It 

also contained a spectrographic mode which allowed long slit spectroscopy. 

While the two other spectrographs could only obtain a spectrum at one 

point, the FOC could also study spectral variations at different points along 

the slit. The FOC was a very complex, but powerful instrument, though it 

could only image a rather limited field. Larger fields were the domain of 

another instrument, the Wide Field and Planetary Camera (WFPC). 

The Space Telescope Science Institute was to ensure that the instruments 

functioned optimally and that the users of HST could obtain all the 

necessary information and assistance. It also was responsible for organizing

Ground and Space Based Optical Telescopes 125 

the time allocation process. The 15 ESA scientists were rapidly fully integrated 

into the institute staff and fulfilled a useful role for the project in general 

and the European users in particular. However, there remained a concern 

that the European scientific community was insufficiently prepared to make 

effective use of the HST and to submit competitive observing proposals. So 

it was decided by ESA, following some pressure from the scientific 

community, to have a small group in Europe devoted to HST operations – 

the ST/ECF, the European Coordinating Facility for the Space Telescope. It 

was to promote awareness of the potential of HST, information for prospective 

users and assistance with the analysis of data when needed. The ECF 

was foreseen as a cooperative venture between ESA and a host institute of 

high scientific quality. ESO and a few other European institutes responded 

to ESA’s Announcement of Opportunity. While it was perhaps unfortunate 

to have ESO in competition with institutes in its member countries, it was 

also clear that it was the most suitable organization from many points of view. 

The services which ESO already provided to scientists in the member countries 

were of the same nature as those required for HST. Thus, in 1983 an 

agreement was concluded between ESA and ESO for the joint operation of 

the ECF at ESO in Garching. This first significant agreement between the two 

organizations has had a very positive effect on the development of European 

astronomy, in particular in the areas of image processing and archiving, but 

also more in general in bringing ground and space based astronomy closer 

together. The excellent cooperation between the ECF and the STScI in 

Baltimore was essential to the success of the former and beneficial to the 

friendly relations between the European and American astronomical 

communities. 

It should be noted that the creation of the ECF did not give full equality 

to European scientists. After obtaining data from HST, funds for equipment 

and assistants needed for the analysis had to be applied for nationally by the 

investigators. The American scientists generally obtained NASA funding 

immediately after they had been awarded the observing time. 

On April 24, 1990 HST was launched. Soon thereafter it was discovered 

that the primary mirror had not been figured according to specification, 

owing to an error in testing. As a result, it did not fit very well to the 

secondary and the image quality of the telescope was degraded. While this 

was reducing the effectiveness of all instruments, it was particularly damaging 

for the FOC which had been specifically designed to obtain the very highest 

possible resolution. Following months of intensive analysis and consultation, 

it was decided to construct corrective optics (COSTAR) for the FOC and the 

spectrographs, and to build a new WFPC, optically adjusted to the characteristics 

of the primary mirror. During a visit by the shuttle in December 1993, 

the old WFPC was replaced and the high speed photometer taken out to make 

room for the correcting optics. However, by that time the FOC had developed 

some electronic problems which somewhat reduced its usefulness.


Three further shuttle missions to HST took place in February 1997, 

December 1999 and February 2002. During the first one the two spectrographs 

were removed and replaced by a much more powerful Imager/Spectrograph 

STIS optimized for the ultraviolet, and a Near Infrared Camera and Multiple 

Object Spectrograph (NICMOS) which extended the spectral range of HST 

to 2.4 µm. The NICMOS detectors had to be cooled, but the block of solid 

nitrogen evaporated faster than foreseen. The 1999 mission was for repairs, 

maintenance and orbital lifting. In the 2002 shuttle visit a mechanical cooler 

was installed which brought NICMOS back to life. The FOC was removed and 

replaced by the Advanced Camera for Surveys. From then on there was no 

ESA hardware on HST, but the ESA contingent continued its work in 

Baltimore, while ESA and NASA were negotiating a new agreement which 

also included a 15% share in the successor telescope JWST. Plans were being 

made for one or two additional refurbishment missions, but for the moment 

the second shuttle accident put an end to these. Since HST needs an orbital 

lift from time to time, this would imply that it may end its life in 2007 or 

2008, unless pressure from the US scientific community and the general 

public causes NASA to change its plans. In the meantime STIS failed with 

little chance of it being revived. Also proposals have been made for a robotic 

repair mission at such a high cost that other future missions might have to 

be significantly delayed. 

ESA’s participation in HST has been very much worthwhile for the 

European scientific community. The total cost to ESA in 2004 euros has been 

of the order of 600 M€. The overall cost of the whole HST project including 

operations may be estimated at 6 G$, with the largest items five shuttle flights 

and 18 years of spacecraft operation. In round numbers this corresponds to 

a million US$ per day. 

It has frequently been said that the HST experience demonstrates the 

usefulness of manned space flight. True enough, without the shuttle visits 

it would have been impossible to make the repairs and instrument 

exchanges. But the telescope was more expensive than it could have been 

because it had to be safe for human intervention, while the cost of the shuttle 

flights far exceeded that of the telescope itself. Moreover, the low earth orbit 

required for shuttle access was operationally expensive and scientifically far 

from optimal. In fact, less than half of the total time could be used because 

of earth occultation effects. Probably for the same amount of money, three 

or perhaps more STs could have been built and placed into better orbits with 

conventional rockets. It is also true, however, that it might have been 

difficult to maintain the political support for such a program, while the 

glamor of the various visits by astronauts has benefitted the overall space 

program. In the future when telescopes are placed at L2, beyond lunar 

orbit, robotic repair missions might be needed. However, some thought is 

also being given to the development of a more suitable vehicle for astronauts 

to go there.

HST and VLT 


The question has been asked, why we still should build the VLT when 

the Hubble Space Telescope provides such beautiful images of celestial objects 

which are unsurpassed by telescopes on the ground? Alternatively one could 

ask, why, with the VLT having such superior light gathering power, would 

we still build a successor to HST in space? The answers are partly scientific 

and partly economic. At some wavelengths the atmosphere is opaque and 

observations are only possible from space. But when both space and ground 

based observations are feasible, the latter are much cheaper. For the same 

amount of money a more powerful instrument could be constructed on the 

ground. Hence, what can be done from the ground, should be done there. 

New technological developments, in particular adaptive optics, are dramatically 

changing the capabilities of ground based telescopes. But also space 

telescopes could improve their performance by moving out of low earth 

orbit. So the balance between the two has to be revisited and the answers 

that were given some decades ago may no longer be valid. 

Let us first compare the cost of collecting a certain amount of light 

with the VLT and the HST. The four 8.2-m telescopes of the VLT with their 

instrumentation will have cost some 1000 M€ after 17 years of operation. 

This figure includes personnel costs at ESO and in the institutes of the 

member countries which are contributing instrumentation. The cost of HST 

is more difficult to estimate, but in the preceding paragraphs we found a 

figure of the order of 6000 M$ if the costs of the shuttle flights for maintenance 

and upgrading of instrumentation are included. In the further 

discussion we shall take euro and dollar as equal, which is appropriate as an 

average over the last decade. 

The 2.4 m HST has a light gathering surface 47 times smaller than the 

VLT. Since in visible light the atmosphere absorbs or scatters on average some 

10% of the incoming light, the effective light gathering power of HST is 

42 times smaller than that of the VLT. One more factor needs to be taken 

into account: the annual amount of observing time. Even at Paranal, the 

world’s most favorable site for low cloudiness, some 15% of the time is lost 

or not very useful. Of the remainder the sun is up half of the time, and the 

percentage of real dark time is only 37% of the 24 hr day. Thus, finally only 

31% of the total time can be used. In the visual part of the spectrum the full 

moon makes some observations difficult or impossible, but in the near IR 

the situation is more favorable. Also spectroscopic work at high resolution 

is not much affected. So we shall neglect the lunar problems in the comparison. 

We have seen that HST in its low earth orbit has an effective observing 

time about half of the total or less. With HST being six times more expensive 

and having an effective light gathering power some 42 times smaller than 

the VLT, we conclude that the cost of detecting a certain amount of light is 

some 150 times higher for HST.


However, this is not the whole story. When we observe very faint 

objects, we become less efficient because the diffuse background light may 

exceed the light received from the object under study. This background light 

may be due to the earth’s atmosphere, to the zodiacal light resulting from 

the scattering of light from the sun in interplanetary space and to sources 

further away. Eliminating the terrestrial component of the diffuse background 

light, we roughly halve its intensity in the visual part of the spectrum. 

A further important factor is the angular resolution. Without adaptive optics 

at the best sites a stellar image on the ground is spread out over some 

0.6 arcsec by atmospheric turbulence. As a consequence, more background 

light is sampled than in the case of HST where the image spread is closer to 

0.1 arcsec. 

If the brightness of the background underlying the image of a star is 

much larger than the brightness of the star, the latter is determined by 

subtracting the background from the image of star + background. Since 

these then are nearly equal, a very precise determination is needed so that 

the difference may be established sufficiently accurately. In practice this 

means that the amount of time needed to observe a faint star is multiplied 

by l’/l where l’ is the brightness of the background underlying the image and 

l that of the star. Thus, if we observe a star 100 times fainter than the background, 

we have to spend a 100 times longer time than in the absence of a 

significant background to obtain a (statistically) equally precise result. So the 

cost advantage would be reduced correspondingly. Furthermore, the background 

under the stellar image may include sometimes unresolved faint 

stars which may cause the observation of the target star to be in error. With 

the better resolution of HST that risk is smaller. Moreover, time variations 

and inhomogeneities in the atmospheric night glow provide intrinsic limitations 

to the accuracy with which stellar brightness may be measured from 

the ground. The conclusion is that for very faint stars the HST has a qualitative 

superiority. For the moment HST is the telescope of choice to reliably 

detect the faintest stars in visible light. 

The situation is modified by adaptive optics, but it is difficult to make 

quantitative predictions. Since the intrinsic resolution of a diffraction limited 

8.2-m unit telescope is 8.2/2.4 times better than that of HST, the effects of 

the background would be drastically reduced if full compensation for atmospheric 

turbulence could be obtained. Then we would sample the background 

under the stellar image over an area of only (2.4/8.2) 2 times that with HST. 

Even for faint objects the advantage would be overwhelmingly in favor of the 

VLT. However, existing adaptive systems work only in the IR; AO is much 

more difficult in the visible. Moreover, such systems tend to concentrate part 

of the light in a sharp central peak, but some remains in a more diffuse image. 

So the gain is certainly not as large as a simple minded calculation would 

indicate. The photometric precision obtainable with AO also remains to be 

explored.

HST and VLT are complementary. Because of the exquisite angular 

resolution HST is the most suitable for detecting objects much fainter than 

the background. But because it is rather small it does not collect enough light 

to obtain a spectrum that could show the nature of faint objects. For this the 

VLT with its large light collecting power is much more suitable. So the 

combination of the two is producing results that could not have been obtained 

with each telescope alone. 

In Figure VIII, 1 are shown the time needed to observe stars of a given 

visual magnitude with HST, a VLT unit telescope, with and without adaptive 

optics, a 40-m telescope and the 100-m OWL, both with AO. The curves are 

for a measurement with 10% accuracy, for a total efficiency (throughput) of 

the optical system of 1/3 and for a 0.1 µm wide segment of the spectrum. If 

the desired accuracy is a times better, if the throughput is b times smaller 

and if the spectral segment is c times narrower, the time needed becomes 

a 2 × b × c times longer. 

JWST and OWL 


HST and VLT have been immensely successful and continue to 

generate a high quality data stream on the widest variety of objects in the 

Universe. Both have stretched financial resources almost to the breaking 

point. Should we then consider these two as the endpoint of telescope development 

in space and on the ground or are they just an intermediate stage 

to be followed by even more powerful instruments? 

In 1995 HST was pointed to the same area of the sky for ten days. The 

result was the “Hubble Deep Field” image in which numerous faint galaxies are 

visible. Three years later followed the southern counterpart the “HDF-S”, where 

many spectra have been obtained with the VLT. With the new ACS an even 

deeper “Hubble Ultra Deep Field” was completed in 2004 (Figure VIII, 2). But 

even in these deep fields the faintest but intrinsically bright spiral galaxies 

(similar to our own or the Andromeda Nebula) have redshifts not much larger 

than z = 1. However, most galaxies must have formed at redshifts of perhaps 

z = 4–6 or even more. So we still have sampled only a small part of the Universe, 

and our direct knowledge of the formation and early evolutionary phases of 

galaxies like our own is very slight. It is, of course, true that already we now 

see the most luminous galaxies or quasars at redshifts up to z = 6. But these 

are only rare very bright objects. It is as if in a forest we would only see the 

tallest trees, while the thousands of others escape our view: we would know 

very little about the ecology of the forest as a whole. 

HST has had only a limited capability in the near IR. But when we 

look at galaxies at a redshift z = 6, all wavelengths have been shifted by a 

factor 1 + z = 7. Thus, spectral lines which we observe in our Galaxy at 0.6 µm 

are displaced to 4.2 µm, well into the IR. The first galaxies must have formed


Observing time in powers of 10 (s) 

-4 

-2 

0 

2 

4 

• 

•••• 

6 

15 20 25 30 35 40 

even earlier, and to obtain cosmological information a telescope optimized 

more towards the IR seems required. Since the angular resolution becomes 

poorer in proportion to the wavelength, it is important that the telescope 

mirror be as large as possible. Such considerations led NASA to the planning 

for the Next Generation Space Telescope, in which European scientists were 

also involved. The diameter of the NGST started out at 4-m and then, because 

. 

• •••••• 

. . 

Magnitude of a star at intermediate ecliptic lattitude 

Figure VIII, 1. The sensitivity of HST —, VLT unit telescope with AO — and without 

AO •••, a 40-m on the ground with AO — , and OWL —. Along the vertical axis is 

the observing time in powers of ten in seconds and on the horizontal axis the V 

magnitude of a star at intermediate ecliptic latitude, with 5 mag. representing a 

factor of 100 in luminous flux. The curves presented are based on the observation, 

with 10% accuracy, of a 0.1 µm wide spectral band centered at 0.55 µm with a 

telescope/instrument combination with throughput of 1/3. Note that at present no 

full adaptive optics system in the visible has been built. However, AO in the near IR 

is currently being implemented at the VLT. The relative shapes of the curves at 1 µm 

would not be very different. The curves with AO are drawn on the assumption that 

only half of the light is in the corrected image.


Figure VIII, 2. Part of the Hubble Ultra Deep Field 

with a total HST exposure of 1 Msec. 

of the enthusiasm of the head of NASA and the optimism about “faster, 

cheaper, better”, was doubled to 8-m. Equally optimistic industrial studies 

suggested a cost of some 1000 M$. Following the loss of some Mars missions, 

the “faster, cheaper, better” philosophy lost some of its glow, while industry 

became more cautious in its cost estimates when firm contracts were to be 

signed. So gradually the diameter shrunk and the cost went up to become 

1600 M$ for a telescope with a collecting surface of 25 m 2 , equivalent to that 

of a 5.6-m diameter telescope with a circular mirror. To this were added 

contributions by ESA and Canada, bringing the total project cost to around


Figure VIII, 3. The sensitivity of JWST and OWL. The two lines show the lowest flux 

that can be detected at 10% accuracy in 100,000 sec for a star at the ecliptic pole in 

spectroscopy at a resolution of 50; 1 Jy = 10 -26 watt m 2 Hz -1 . In blue is the model 

spectrum of a primeval dwarf galaxy at a redshift z = 10, with a million solar masses 

in an active star forming phase which leads to strong hydrogen and helium emission 

lines at an epoch when heavy elements had not yet been synthesized. Many such 

galaxies may have been later incorporated into bigger systems. A comparison between 

JWST and other mid-IR missions is given in Figure XI, 7. The OWL curve is only 

applicable in the IR windows. 

2000 M$. Past space missions had frequently the names of famous scientists 

(Hubble, Einstein, etc.) or mythological figures (Ulysses), but before 

many people were aware of it and without consultation, NASA named it after 

an earlier Administrator, James Webb, and NGST became JWST. 

JWST 4) (Figures VIII, 3, 4) is to be launched with an ESA provided 

Ariane V rocket and placed at L2, the second Lagrangian point, some 

1.5 million km from earth in the antisolar direction. Around L2 quasi stable 

orbits of spacecraft are possible which may be maintained with a very small 

expenditure of gas. The great advantage of a telescope placed at L2 is that 

the view is not restricted by earth occultation, and so almost all time may 

be used for observation, rather than the 50% in low earth orbit. Moreover, 

with Sun, Earth and Moon all in more or less the same direction, their IR 

radiation is far less troublesome than it was, for example, in ISO.


Figure VIII, 4. Layout of the JWST 5) . Since the telescope is to operate in the near 

and mid-IR, a large shield protects it from heat sources. The primary mirror of 25 m 2 

area is made of light weight beryllium petals that will be deployed in orbit. The light 

reflected by the petals reaches the secondary mirror which reflects it back to the 

science instruments. The surfaces above the sun shield are covered by special coatings 

which allow the telescope to radiate heat efficiently into space and so reach temperatures 

around 30 K, necessary for the mid-IR observations. Below the shield are solar 

panels, communication equipment and some electronics. 

Since a 6-m telescope cannot be fitted into the launcher, the primary 

mirror will be composed of 18 segments (made of beryllium for low weight) 

that will be deployed to form the mirror surface once in orbit. Also the 

secondary will be placed in position at that time. An active optics system will 

ensure that the telescope is diffraction limited at 2 µm wavelength. To avoid 

strong radiation from the telescope itself, it will be cooled to around 30 K. 

The cooling will be passive, with special coatings favoring heat loss by 

radiation into space, while minimizing radiative heating by an effective sun 

shield. 

JWST should be equipped with three instruments which cover the 

wavelength range 0.6–28 µm: NIRCam, a wide field camera covering 

0.6–5 µm in wavelength, NIRSpec, a multiobject spectrograph for the range 

1–5 µm, and MIRI, a camera-spectrograph for the mid IR range 5–28 µm 

(Table VIII, 1). NIRCam will be a NASA responsibility, while Europe will 

provide NIRSpec. MIRI will be a joint US – European undertaking.


Canada will also participate in the project with the “Fine Guidance Sensor” 

which will ensure the continuous precise pointing of the telescope, and which 

also has an astrometric capability. 

JWST should be diffraction limited upwards from 2 µm, HST from 

0.6 µm. Below these wavelengths the angular resolution does not change, 

because it is determined by the imperfection of the fine structure of the mirror 

surface. With the diameters differing by a factor of 2.5, the two should have 

the same angular resolution at 0.8 µm, but JWST will collect nearly six times 

as much light. So a deep JWST field may show even more numerous remote 

galaxies than the deepest HST fields. 

Some of the very faintest galaxies or quasars seen by JWST may be at 

large redshifts, but to be sure it is necessary to take their spectra. Because 

in a spectrum the light is spread out over many pixels, a larger telescope 

would be needed. This is one of the numerous motivations for constructing 

Extremely Large Telescopes (ELTs), the largest of which would be OWL 6) 

(Figure VIII, 5), the OverWhelmingly Large telescope, a 100-m behemoth, 

currently under study at ESO. The projected cost is some 940 M€. 

Figure VIII, 5. Artist impression of sunset over OWL. The 100-m spherical primary 

mirror is visible low down. The secondary is in the upper left, and the complex central 

structure contains additional mirrors. The mechanical structure is made from sets of 

identical components for cost reduction; also the mirror is a composite of identical 

segments. To the left are the rolloff roof for protection during the day and a smaller 

structure containing instruments.


Mechanically there does not seem to be an unsurmountable problem 

to construct a 100-m telescope. After all, radio telescopes of such a size have 

been constructed before. However, with the wavelength for an optical 

telescope being more than a thousand times smaller, the tolerances are 

proportionally more rigorous requiring highly sophisticated controls. It hardly 

seems possible to effectively protect such a telescope from the wind by a 

building, since it would need an opening quite a bit larger than 100 m. So, 

like the radio telescopes, it would operate in the open air and undergo significant 

wind stresses which have to be compensated. To protect the telescope 

from storms and rain, a rollover structure is needed. 

In principle, the optics also seem to be feasible. However, several 

issues remain open. One proposal is to have a spherical primary, with a cost 

advantage in polishing. But the consequence is the need for a more complex 

image correction, requiring in one design six mirrors in total, causing significant 

light losses at visible wavelengths. 

The main unsettled issue pertains to the adaptive optics. The power 

of a diffraction limited 100-m telescope is largely due to its angular resolution 

and the consequent reduction in sampling background light. But this requires 

a very effective suppression of atmospheric image diffusion. It is necessary 

to deal with more than one atmospheric turbulent layer (multi conjugate AO). 

In fact, it is estimated that half a million active elements would be needed 

to achieve this at visible wavelengths. Since at present adaptive optics is 

beginning to be operational at 8-m telescopes only in the near IR where the 

tolerances are much more relaxed, it will be some time before such a system 

can be demonstrated. It is perhaps an interesting question if chaotic behavior 

may arise if the system becomes too complex. Since much of the science for 

OWL would be in the infrared, it might perhaps be acceptable to start with 

an AO system at 1 µm, especially if there were a reasonable prospect of 

extending it later to shorter wavelengths. 

The power of OWL would certainly be impressive. Cepheid variables 

for direct distance determination of galaxies could be measured nearly till a 

redshift z = 1, and so the global Hubble constant for the Universe could be 

obtained directly. Every type I supernova that has exploded in the Universe 

could probably be observed – and probably the same is the case for most 

type II’s (exploding very massive, young stars) which are intrinsically fainter, 

but relatively strong in the uv. The type I could possibly give a very clear 

picture of the geometry of the Universe, while type II would inform us about 

star formation and element synthesis history from very early time onwards. 

Quasars could be observed to high redshifts at sufficient spectroscopic resolution 

to see the absorption of intergalactic gas even at low density and to 

study its dynamics. The formation of galaxies would come within our reach. 

More in our immediate neighborhood very faint neutron stars could be 

observed. The center of our Galaxy could be studied in exquisite detail, and 

so could star and planet forming processes. Perhaps it could even be possible


to obtain spectra of earth-like planets. And, of course, anything detectable 

by JWST in the optical and near IR could be studied spectroscopically by 

OWL. The principal limitation of OWL is the inaccessibility of much of the 

mid-IR. It would most effectively function in the range of 0.4–2.4 µm. At a 

redshift z = 9 this would correspond to the (far) uv for the emitted radiation. 

Some observations might be possible in the 10 µm and 20 µm windows, but 

because of the background due to the atmosphere and to the warm telescope 

the sensitivity would fall far short of that of JWST, at least for the faintest 

objects. But for higher resolution spectroscopy it would be superior. 

The cost of OWL is still very uncertain. Three decades ago the rule of 

thumb was that the cost of a telescope varies as the diameter to the power 

2.6. With the 16-m equivalent VLT having a capital (industrial) cost 

(excluding VLTI and instrumentation) of 300 M€ (2004 value), OWL would 

come in at 32,000 M€! However, the VLT has shown that the situation is 

much more favorable than this. The NTT and the VLT have been built in 

rather similar ways. The industrial cost of the NTT (updated to 2004) was 

around 18 M€. In comparison with the VLT cost, this shows a variation with 

d 1.8 rather than d 2.6 . So a larger mirror area has become cheaper on a per m 2 

basis – at least in this example. Nevertheless, scaling this way the cost of 

OWL would still be nearly 8000 M€. The cost of the NTT was some three 

times lower than that of the 3.6-m telescope at the same diameter. This was 

possible because of improved technology. The challenge for OWL is greater. 

Whether its cost can be brought down a further factor of 10 per unit area 

remains to be seen. Initial industrial studies are encouraging. 

The conclusion of the foregoing is clear. The OWL project is well 

worth detailed design studies. Before it can be built, three essential questions 

need be answered: 

(1) Is it possible to build the active optics system required for its diffraction 

limited performance, and at what wavelengths can it operate? 

(2) Can the cost be brought down to an acceptable level? 

(3) What is an acceptable cost level? 

More modest proposals for ELTs are under study in several places. At 

the 2003 meeting of the International Astronomical Union no less than nine 

proposed projects in the 16–50 m class were reported, though not all of them 

of equal realism. Sweden (Lund University) and institutes in SF, Ei, ESP and 

the UK are designing EURO 50, a straightforward 50-m telescope with a 

mirror composed of 618 segments at an estimated cost of 600 M€ 7) . A US- 

Canada cooperation is designing the TMT, a 30-m segmented mirror 

telescope, while another US group plans to build the GMT, a 21-m multimirror 

telescope with seven 8.4-m mirrors, corresponding to a collecting area 

1.8 times that of the VLT. So if Europe would rest too long on its VLT 

laurels, it could soon lose its first place. 

The siting of these telescopes is still an open question. For Europe there 

seem to be two plausible options: La Palma or northern Chile. In both good

seeing conditions prevail; the latter has the advantage of a very dry atmosphere, 

but the drawback of being more earthquake prone. 

There remains one problem not addressed by either OWL or JWST, 

the access to the ultraviolet. Once HST will have been terminated, there will 

be no uv telescope left. It had been foreseen to install at the next shuttle 

mission to HST the Cosmic Origins Spectrograph with a powerful uv capability. 

It has been built at a cost of 90 M$, but if no further refurbishment 

of HST is made, this very expensive instrument will remain in storage. In 

the Russian “Spectrum” series there were plans for “Spectrum uv”, a 1.7-m 

telescope of which some parts have been made. Lack of funds has prevented 

its completion. Some scientists in the community wish to revive this project 

(sometimes as a “world space observatory”), but no plausible sources of 

funding have been identified. 

Some smaller uv telescopes have been launched by NASA: FUSE 8) , a 

spectroscopic satellite for the 0.09–0.12 µm spectral region (with French 

participation) in 1999 and the Galaxy Evolution Explorer 9) in 2003. With its 

50 cm telescope it is making a sky survey in the uv. The Indian satellite 

ASTROSAT, scheduled for launch in 2008, will have two 38-cm uv telescopes 

for observations in the 120–300 nm domain. 

Astrometry 


Atmospheric effects also limit the precision of the determination of 

stellar positions. In addition to the image diffusion by seeing, refraction in 

the atmosphere creates further problems. These may be overcome in case 

relative positions of not too widely separated stars are measured. If absolute 

positions over the whole sky are needed, the fitting together of results from 

observatories with access to different parts of the sky becomes difficult. The 

only really satisfactory solution is to go into space. In 1989 ESA launched 

the Hipparcos satellite. The spinning satellite registered the times at which 

100,000 stars transitted over its detector. It was a major effort from these 

data to determine the positions of all of these. The satellite continued to 

observe for four years. Thus, it could also measure changes in position and 

so obtain annual parallaxes, due to the motion of the earth around the Sun, 

from which the stellar distances immediately follow. From the distances the 

physical properties of the stars, like the luminosities, may be obtained and 

stellar models thereby refined. Also the proper motions – the real displacements 

over the sky – could be obtained which is of interest in studies of the 

dynamics of our Galaxy. 

Hipparcos obtained positions with a precision of about 1 milliarcsec, 

yielding stellar distances out to a few thousand light years. The success of 

the mission led to various proposals for a follow up: at NASA FAME and in 

Germany DIVA, with the aim of an improvement of an order of magnitude


in precision. In the meantime, both have been cancelled. ESA is planning 

GAIA – Galactic Astrophysics by Imaging and Astrometry – which should 

be launched in the 2010–2012 time frame 10) . GAIA should obtain results a 

hundred times more precise for 10,000 times more stars than Hipparcos 

(Table VIII, 2). Distances should be measurable through most of our Galaxy, 

allowing a full three-dimensional picture to be obtained of the whole system. 

Spectral distributions should also be measured for all stars and radial velocities 

for many. Very accurate motions should be obtained for many millions 

of stars. This should lead to a determination of the gravity field in the Galaxy 

and thereby also of the distribution of dark matter. GAIA will undoubtedly 

be quite important in studies of stars and of the dynamics of our Galaxy. 

GAIA should also detect half a million quasars, of interest for establishing a 

cosmological reference frame, 100,000 supernovae, 30,000 exoplanets and 

numerous asteroids and trans-Neptunian objects. It also should measure the 

gravitational bending of light by the Sun with high accuracy. It follows a 

European tradition of the study of large statistical samples in astronomy. 

Table VIII, 2. Comparison of Hipparcos and GAIA, two ESA astrometric missions. 

Hipparcos Gaia 

Faintest magnitude 12 20 

Complete till magnitude 7 20 

Number of stars 120 000 1 000 million 

Precision in µarcsec 1 000 4 (at mag 10) 

10 (at mag 15) 

200 (at mag 20) 

Orbit earth L2 

In 2005 new complications surfaced 11) . The manufacturer of the JWST 

demanded a substantial extra payment, and with other items this caused a 

cost overrun of nearly a 1 000 million US$. So now there are proposals to 

further reduce the size of the mirror, to restrict the wavelength range and to 

limit the lifetime to 5 years. If these were to be implemented, it would be 

advisable for Europe to reconsider its participation. Joining the Japanese 

SPICA mission (Figure XI, 7) might be and attractive alternative.

IX. 

Radio Astronomy; ALMA and SKA 

At length a universal hubbub wild 

Of stunning sounds and voices all confused 

Borne through the hollow dark assaults his ear 

John Milton 1) 

Visible radiation constitutes only a very small part of the electromagnetic 

spectrum, while most of the IR and X-rays are unobservable from the 

ground because of atmospheric absorption. However, radio waves can penetrate 

the atmosphere at most wavelengths from around 1 mm to 30 m, where 

the ionosphere provides a barrier. 

Radio Astronomy 2) was born in 1932 when Karl Jansky at Bell Telephone 

reported his discovery of a mysterious source of radio noise which 

waxed and waned with sidereal rather than solar time. So the source had to 

be located outside the solar system. Subsequently, his data at 15-m wavelength 

showed that the strongest signal came from the area of the sky where 

the center of our Milky Way Galaxy is located. Since no radiation from the 

Sun had been observed, this could hardly be due to the accumulation of stars 

at the center. Actually, the radiation is “synchrotron radiation” due to energetic 

relativistic electrons gyrating in interstellar magnetic fields. Such 

radiation nowadays is well known in terrestrial synchrotrons where it is used 

to generate intense sources of light for the study of materials and biological 

structures. Since the magnetic fields in the interstellar medium are very 

much weaker, the Galactic emission emerges largely at radio wavelengths. 

In the meantime, a whole high energy universe has emerged, complementary 

to the visible universe of stars. Synchrotron radiation has been observed in 

stars, galaxies (Figure IX, 1), quasars and prodigious amounts of energy 

have been involved in the acceleration of these electrons. In our Galaxy the 

energetic electrons responsible for a large “halo” of radio emission are part 

of the cosmic-rays (Chapter XIV), and the study of the two has become very 

much intertwined. At decimeter wavelengths radio emission from


Figure IX, 1. VLT image of the nearest radio galaxy Centaurus A. On the scale of 

this image, the radio emission (synchrotron radiation) extends over more than 10 

meters, demonstrating the presence of magnetic fields and cosmic-ray electrons more 

than a million light years from the galaxy. 

warm (10 000°) ionized interstellar matter is also observed. In addition, the 

spin flip line of atomic hydrogen at 21-cm gives very detailed information 

about the diffuse interstellar gas. Since this line has a fixed intrinsic wavelength, 

velocities of the gas can be measured from the Doppler effect. Much 

of the information about the motion in galaxies is obtained in this way from 

which inferences about the presence of “dark matter” have resulted. However, 

at large distances the angular diameters of the galaxies become very small

Radio Astronomy; ALMA and SKA 141 

and a high angular resolution is required. The same is the case for the study 

of remote quasars and radio galaxies in which the jet-like structures made 

of relativistic particles give information on the energetic processes taking 

place there and on the surrounding intergalactic medium. 

While the 21-cm line is a rather isolated feature in the radio spectrum, 

at mm wavelengths a plethora of emission lines appears due to molecules in 

the cool (10–1000 K) interstellar gas. In addition to lines of common molecules 

like CO at 3 mm and at shorter wavelengths, very complex molecules 

have been found in dense molecular clouds. As a result, cosmic chemistry 

has become an active branch of the astronomical sciences. Intricate chemical 

reactions take place on the surfaces of interstellar dust grains and in the 

atmospheres of cool supergiant stars. The resulting large molecules may play 

an important role in the formation of planets. Some scientists also believe 

that their presence on early earth may have been a factor in the origin of 

life. 

At very long wavelengths simple antennas made of some wires have been 

used, but most radio telescopes at decimeter to millimeter wavelengths follow 

the same model as optical telescopes – Cassegrain or prime focus. However, 

there are two important differences. The angular resolution given by 

θ 200 000 λ / d arcsec 

with λ the wavelength and d the diameter of the telescope, is evidently much 

poorer at radio wavelengths. Thus, at 10 cm even a 100-m telescope has a 

resolution no better than 200 arcsec, inadequate for most purposes. So 

except at mm wavelenghts radio astronomy is done mainly with interferometers. 

The other point is that in order to have a good image quality and 

sensitivity, the collecting surface of the telescope should reproduce the theoretical 

form (usually a paraboloid) with an accuracy of the order of λ/20. 

Thus, at 10 cm deviations from the perfect shape of as much as 5 mm are 

entirely acceptable. So a radio telescope is very much cheaper than an optical 

one of the same diameter; fully steerable 100-m telescopes have been built. 

Of course at (sub)mm wavelengths radio telescopes also become more costly. 

The only way to obtain subarcsec resolution in the radio domain is to 

build an interferometer. While in practice the interferometric combination 

of optical telescopes has been a rather difficult undertaking, the long wavelengths 

in the radio spectrum greatly simplify this. Various techniques exist 

to amplify signals and to combine them coherently. Arrays of tens of telescopes 

have been built, scattered over areas tens of km in diameter. In the 

expression for the angular resolution d is now the separation of the most 

distant telescopes. 

The signals coming from the different telescopes may be transported 

through wires, radio links or fiber optics cables to a common place where the 

correlation takes place. In fact, it is not even necessary to connect the telescopes 

in these ways, one can also register the signals of each telescope on tape and 

then a posteriori combine the contents of the tapes in a computer. To be able


to do this, a sufficiently accurate (atomic) clock at each site is needed to 

synchronize the tapes. This is the principle underlying the VLBI (Very Long 

Baseline Interferometry) which has made it possible to combine the signals of 

telescopes on different continents. Thus, in the expression for the angular resolution 

d is now of the order of the diameter of the earth. With d = 10 000 km 

at a wavelength of 1 cm a resolution of 0.0002 arcsec (0.2 mas) may be reached. 

Still larger baselines with d = 20 000 km have been obtained by correlating the 

signals of the space based 8-m radio telescope HALCA of the Japanese Space 

Agency with those from ground based arrays. 

Large single telescopes 

Two large fully steerable radio telescopes were built in Europe early 

in the development of radio astronomy: a 76-m at Jodrell Bank near 

Manchester in 1957 (Figure I, 2), and a 100-m at Effelsberg in Germany in 

1972 (Figure IX, 2). Both have been subsequently upgraded, and at present 

the 76-m is usable at 3 cm wavelength and the 100-m at 3 mm, albeit with 

reduced effective area. A 64-m telescope, also functional at 3 mm, is currently 

under construction in Sardegna. While these national telescopes have their 

separate scientific programs, they are particularly useful in the context of the 

EVN, the European VLBI Network. Two other large telescopes exist in the 

Figure IX, 2. The 100-m Effelsberg telescope of the MPG; 

the solid central part is now usable to 3 mm wavelength.


world: the 64-m Parkes (Australia) telescope built in 1961 and a 100-m 

completed in 2002 in West Virginia. 

Several less flexible large telescopes have also been built of which the 

305-m Arecibo (Puerto Rico) has been the most successful. It has been 

constructed in an appropriately shaped mountain valley. So the spherical 

primary mirror is immobile, but by moving the instrument cabin at the 

prime focus a rather large area of the sky may be accessed. In Europe, at 

Medicina near Bologna a cross antenna (Figure IX, 3) was built in 1964 with, 

in its final form, NS and EW arms about 600 m long, yielding an angular 

resolution of some 4 arcminutes at a wavelength of 75 cm. The total collecting 

area is 30 000 m 2 , some 40% of that of the Arecibo dish. A 200 × 35 m transit 

instrument at Nançay (near Orléans), also with a fixed mirror, has recently 

been upgraded. For most purposes interferometric telescope arrays have 

now taken over if superior angular resolution and shorter wavelengths are 

desired. 

Figure IX, 3. The “Croce del Nord” at Medicina near Bologna. With 600 m long arms 

it combines good angular resolution and sensitivity at 75 cm wavelength. Installation 

of fiber optics could allow a greater bandwidth and, thus, a higher sensitivity. To the 

right is the more recent 32-m telescope which is used for VLBI observations. 

Interferometric Arrays 

Two-telescope interferometers have been constructed in various places 

to improve angular resolution. At Cambridge (UK) much of the technology 

was developed and early results on the structure of radio galaxies obtained. 

In particular the synthesis methods were pioneered, in which the rotation of


the earth changes the orientation of the line connecting the telescopes with 

respect to the source, so as to obtain resolution in two dimensions. A large 

linear array along these lines was constructed in 1970 in Westerbork (NL) 

which today consists of 14 telescopes of 25-m each. A decade later it was 

superseded by the Very Large Array in New Mexico. The VLA consists of 

27 mobile telescopes of 25-m distributed in Y shape with longest baselines 

between telescopes of 36 km (Figure IX, 4). The advantage of the Y shape is 

that one has immediately two-dimensional image information over the whole 

sky. The earth rotation based synthesis methods are not usable close to the 

celestial equator. The radio astronomy community is much more apt to share 

facilities than the optical, where telescope access tends to be more strictly 

proportional to the investment made. As a consequence, European astronomers 

have frequently observed with the VLA as US astronomers had done 

at Westerbork. A major 60 M$ upgrade is planned with the addition of 

several telescopes, increased sensitivity and angular resolution, and wavelength 

coverage down to 3 mm 3) . 

In the meantime, operations also began in 1980 at the Multi-Element 

Radio Linked Interferometer in the UK. MERLIN is now composed of six 

25 m class telescopes (including one recently added of 32 m) and the 76-m 

Figure IX, 4. The VLA in New Mexico. With 27 mobile 25-m telescopes distributed 

in Y shape 36 km across, it combines high sensitivity and excellent angular resolution. 

The future SKA could be 30 times larger and with an 80 times larger collecting area. 

Frequently European scientists have obtained valuable data with the VLA.

at Jodrell Bank. Baselines range up to 217 km. An upgrade (e-MERLIN) will 

see the radio links replaced by fiber optics cables. This allows the receiver 

band width to be augmented and, thus, the sensitivity increased by up to a 

factor of 30. Expansion of MERLIN with an Irish telescope has been 

discussed. In the southern hemisphere there is the Australia Telescope, 

composed of 6 telescopes of 22-m, which was recently upgraded to operate 

at 3 mm wavelength. As the dominant radio astronomical facility in the 

southern hemisphere, the AT also plays an important role in collaborative 

programs with the ESO telescopes in Chile. For longer wavelengths India has 

built an array of thirty 45-m telescopes usable above 20 cm. It has an unprecedented 

sensitivity and angular resolution above a wavelength of 50 cm. 

Japan has constructed an array of a 45 m and six 10-m telescopes for observations 

at wavelengths of several millimeters. It may be usable down to 1 mm, 

though the humidity of the Nobeyama site is an obstacle. 

VLBI 


Very Long Baseline Interferometry has frequently been performed on 

an ad hoc basis between radio telescopes in various parts of the world. By 

now, however, VLBI has become more organized and an important part 

takes place in organized networks. In the US a dedicated VLBI network was 

built, the Very Long Baseline Array (VLBA) composed of ten 25-m telescopes 

at sites ranging from Puerto Rico to Hawaii – a distance of about 8000 km. 

Operations down to 3 mm should be possible, corresponding to a resolution 

of some 0.08 milliarcsec. 

The first VLBI observations in Europe were made in 1976 with radio 

telescopes at Onsala (S), Dwingeloo (NL) and Effelsberg (D) participating. A 

more formal cooperation, the European VLBI Network (EVN) was set up four 

years later. The need for a more institutional framework to construct a large 

16-telescope correlator and to more properly organize the operations led in 

1993 to the creation of the Joint Institute for VLBI in Europe (JIVE) in 

Dwingeloo. An initial investment of some 7 M€ was contributed mainly by 

the Dutch, while the EU also made a small contribution. Most of the radio 

telescopes in the EVN (Table IX, 1) had been in existence before the VLBI 

network was organized and, as a consequence, the location of the telescopes 

was perhaps somewhat less optimized than in the VLBA. However, with 

some new telescopes added, this is no longer a problem. In fact, the availability 

of north–south baselines in addition to those oriented east–west greatly 

improves the image quality, while several very large telescopes in the EVN 

lead to a high sensitivity. European baselines being limited, it was important 

to extend the EVN into Asia. The inclusion of two telescopes in China now 

yields baselines of up to 9000 km. In the meantime, the telescopes at Arecibo 

and at Hartebeestpoort (South Africa) have also become associated with the


EVN (Figure IX, 5) further increasing the baselines. The main drawback in 

the EVN is that most telescopes are also used for other programs and the 

total time available has been no more than 1000 hours per year. Some of 

this time was used for joint operation with the VLBA or with the Japanese 

satellite HALCA 3) with its 8-m telescope. 

Space VLBI 

Table IX, 1. The European VLBI Network (EVN). 

Location Diameter (m) min. λ (mm) 

Jodrell Bank (UK) 76* 30 

Five telescopes in UK ~ 25* 13 

Cambridge (UK) 32* 7 

Westerbork (NL) 94 + 30 

Effelsberg (D) 100 3 

Wettzel (D) 20 30 

Yebes (ESP) 14 3 

40 3 

Onsala (S) 20 3 

25 60 

Metsähovi (SF) 14 3 

Torun (PL) 32 7 

Medicina (I) 32 7 

Noto (I) 32 7 

Sardegna (I) 64 ++ 3 

Seshan (PRC) 25 13 

Nanshan (PRC) 25 13 

* These telescopes form the MERLIN (Multi Element Radio Linked Interferometer) 

array. An upgrade to fiber optics links is in progress. + Actually a 

14 × 25 m tied array. ++ Completion in 2007. 

The size of the earth limits the resolution that may be obtained with 

ground based VLBI arrays. So it was only natural that suggestions were 

made to incorporate in the global arrays some space based element. Several 

proposals were made to ESA from 1979 onwards, but these have not been 

selected in the competition with other missions. This may have been due to 

a feeling that this was niche science which would allow improved resolution 

on a relatively small number of sources and also to the relatively weak radio 

community in the overall space research setup. However, the case for the

science remains compelling. We still have only limited understanding of the 

radiation mechanisms that allow extreme brightness temperatures to be 

reached in quasars and other sources. 

In Russia the 10-m RADIOASTRON project seemed promising, but 

funding difficulties have delayed its realization (till 2007?). The only successful 

mission to-date has been the HALCA satellite within the Japanese VLBI Space 

Observatory Program (VSOP). The satellite carries an 8-m radio telescope, 

operating at 1.6 and 5 GHz (20 and 6 cm). The orbit has an apogee of 21000 

km, yielding a maximum resolution of 0.3 milliarcsec. The cooperation with 

the ground based arrays has been very successful and demonstrated the 

validity of the concept. An improved version is being planned. VSOP-2 will 

have a 12-m telescope. In the US there is a project for a 25-m orbital telescope, 

usable till 86 GHz, which could be realized later in the decade. 

(Sub)Millimeter telescopes 


Figure IX, 5. The sites of the EVN, the European VLBI network. 

As noted before, telescopes should have a collecting surface with shape 

errors less than 1/20 of the wavelength or at 1 mm errors of less than 50 

µm. Considerable care is needed to achieve such a precision for telescopes 

operating in the open air. The Sun, wind and temperature variations in 

addition to deformations due to gravity may create problems. Moreover, the 

atmosphere becomes less transparent at short wavelengths with water vapor 

being the main culprit. So it is important to place mm/submm telescopes on 

high dry sites. This is even more critical for interferometers where variations


in the water vapor above different telescopes may be fatal. In Table IX, 2 are 

listed the large telescopes that can function effectively at or below 1 mm. It 

is seen that Europe has been doing rather well in this domain. 

In the early seventies both French and German astronomers were 

considering possible ventures in (sub)mm astronomy. While the latter wanted 

to build the largest possible reflector for maximum sensitivity, the former felt 

that the angular resolution would be inadequate and opted for an interferometer. 

Both projects suffered from difficulties in obtaining sufficient technical 

personnel within their organizations, while at the time funding was less 

of a problem. The solution was found by founding a new entity, l’Institut 

Radio Astronomie Millimétrique, on a fifty-fifty basis between the MPG and 

INSU which would operate a single dish of 30-m diameter at the Pico Veleta 

(2900 m) near Granada in Andalusia and an interferometer of 15-m telescopes 

on the Plateau de Bure near Grenoble in the French Alps. Headquarters 

would be in Grenoble. In the meantime, the number of 15-m 

telescopes has grown to six and Spain has joined IRAM. The Pico Veleta 

location was financially favorable, because a nearby skiing area provided relatively 

easy access. The Plateau de Bure at 2500 m was more difficult, and a 

special cable cart had to be constructed to transport people and equipment. 

In 2001 a terrible tragedy happened when a cable broke. Soon afterwards, 

when transport was assured by helicopter, a crash caused further disaster. 

Table IX, 2. Radio Telescopes with min λ 1 mm. 

Organization/ 

Altitude location/Name Diameter Countries 

2900 m Pico Veleta (ESP) 30-m IRAM 

2500 m Plateau de Bure 6 × 15-m IRAM 

4000 m Hawaii/JCMT 15-m UK/NL/Can 

2400 m La Silla/SEST* 15-m S/ESO 

5000 m Chajnantor/APEX 12-m D (MPG)/S/ESO 

3200 m Mt. Graham, Arizona/H. Hertz 10-m D (MPG)†/Arizona 

4600 m Sierra La Negra, Mex/LMT+ 50-m Mex/US 

2100 m Kitt Peak, Arizona 12-m US 

4000 m Hawaii/Caltech 10-m US 

2600 m ++ California/Caltech 6 × 10-m US 

2600 m ++ California/BIMA 9 × 6-m US 

4000 m Hawaii/SAO 8 × 6-m US/Taiwan 

* Operations discontinued in 2003. † Participation terminated. + Not yet 

completed. ++ In 2004, was lower before being moved. The two arrays are 

now combined into the CARMA array.


A total of 24 people perished in the two accidents. Following a difficult 

period, the interferometrer has resumed full operations. 

Important results have been obtained with the two facilities. The 

30-m, completed in 1985, has remained the world’s largest submm telescope 

for nearly two decades. It has mapped molecular clouds, detected new lines 

from molecules and found very faint sources associated with quasars. More 

recently with the MAMBO2 117 element detector surveys for sources have 

been made at 1.2 mm. The interferometer with baselines of up to 300 m 

(Figure IX, 6) has yielded angular resolutions of better than an arcsec at 1 

mm. As a result, it was able to begin to resolve stellar envelopes, star and 

planet forming regions and some gas rich galaxies at large redshifts. Importantly 

it found that substantially higher resolutions would be needed to 

analyze such objects properly and so pointed the way towards ALMA. Both 

at IRAM and at the other European mm telescopes much engineering work 

was done on improving submm and mm receivers for increased sensitivity. 

While IRAM has been a great success, climate at the European sites 

has limited submm observations and especially the access to the important 

0.3 mm window. The same has been the case for the 10-m Heinrich Hertz 

Figure IX, 6. The IRAM interferometer on the Plateau de Bure near Grenoble. With 

the six 15-m telescopes angular resolutions better than 1 arcsec have been attained 

at 1 mm wavelength.


telescope at 3200 m altitude on Mt. Graham in Arizona. It was built by 

the Max-Planck-Institut für Radioastronomie and operated conjointly with 

the University of Arizona. During summer conditions are very poor. In the 

meantime, the MPIfR has abandoned the telescope in favor of APEX. 

Undoubtedly the best location so far is the area near the top of Mauna 

Kea, Hawaii, at 4100 m, where the UK in cooperation with the Dutch and 

the Canadians has placed the 15-m JCMT (James Clark Maxwell Telescope). 

With the SCUBA detector array at 0.85 mm highly interesting observations 

have been made of sources associated with obscured galaxies with stunningly 

high rates of star formation 4) . These have again shown the promise 

of larger telescope arrays at still better sites. 

SEST and APEX 

In the early eighties large submm telescopes were still lacking in the 

southern hemisphere. But it is here that the most interesting objects for investigations 

at mm wavelengths are situated: the center of our Galaxy and the 

areas around it with dense molecular clouds, the Magellanic Clouds with 

interesting areas of star formation, and Centaurus A (Figure IX, 1) the nearest 

radio galaxy which also contains much molecular gas. Occasionally the ESO 

3.6 m telescope was used to study CO at 3 mm wavelength. However, the 

telescope was far from optimal for this and also lacked the necessary angular 

resolution. Moreover, it was a bit of a waste to use its excellent optical 

surface for observations at long wavelengths where a rougher surface would 

suffice. Nevertheless, these early observations indicated what a more suitable 

telescope would be able to do. 

At Onsala, near Göteborg (S), much expertise in radio receivers for mm 

wavelengths had been built up in conjunction with two 20-m class telescopes 

there. So it was natural for its newly appointed director, Roy Booth, in 1984 

to initiate steps to build a southern submm telescope. Since IRAM had 

started the construction of its six 15-m telescopes, it seemed most effective 

to construct an extra one appropriately modified for a fixed pedestal, an idea 

enthusiastically embraced by its director, Peter de Jonge, who previously had 

headed the telescope operations and technical services at La Silla. At La Silla 

there was ample space to place the telescope. Since the Swedes had only half 

the necessary funds and since others in the ESO member countries were interested, 

the project finally became the Swedish ESO Submillimeter Telescope 

(SEST). Initially there was some concern in the Council about ESO going into 

radio astronomy. But after I had pointed out that radio waves below 1 mm 

could be considered part of the IR, there were no further problems. 

The SEST project came at a favorable moment. Italy and Switzerland 

had just joined, and so some new funds were available. While the VLT was 

looming in the future, it was too early to use these funds for it, and Council


was unwilling to take any action that might imply a commitment. On the 

other hand, it is dangerous to have too much uncommitted money lying 

around, and so SEST fitted in very well. With the unique scientific opportunity 

of the first large submm telescope in the southern hemisphere being 

recognized, approval came easily and SEST was installed at La Silla late in 

1987 at a total cost of 9 M€ (in 2004 €). 

Prior to the installation it seemed desirable to measure the wind speed 

during the winter months at the selected site, so as to be sure that the specifications 

for survival were sufficient. A high mast with an anemometer was 

placed there. During one of the storms it was destroyed after having registered 

186 km/hour, and we shall never know the maximum wind speed. Since 

the nominal limit of 200 km/hour for the telescope contained some extra 

safety factors, and since insufficient time was left for further measurements, 

we decided to take the risk that higher speeds would occur. A more serious 

disaster occurred during the assembly of the telescope. The reflector was 

pointing to the zenith; it had high reflectivity also in the visible. Since at 

midsummer the Sun passes at only 6° from the zenith, enough energy was 

concentrated on the secondary to start a fire. The La Silla fire brigade energetically 

extinguished the fire, which caused burning pieces to fall on the 

primary. A fair amount of damage resulted as well as some delays in the 

completion. Following this, however, no further mishaps occurred, and during 

the next 16 years the telescope functioned well. 

Among the noteworthy results of SEST were the following 5) : the discovery 

of the coldest gas in the Universe in the Boomerang Nebula where CO is seen 

in absorption against the 3 K microwave background. Such gas can only be 

cooled to such a low temperature because it is expanding rapidly; the discovery 

of some 600 mainly molecular lines, many of which remain unidentified in the 

absence of adequate laboratory data; the discovery of dense gas in a so-called 

Bok globule, opaque to visible radiation, in which curiously no stars are being 

formed as might have been expected because of the high density; studies of 

detached circumstellar envelopes, very thin structures of short lifetime 

(< 10,000 years) which are expelled by evolved low mass stars during periods 

of explosive helium burning; observations of molecules in comets, including 

among others CO, OH, H 2S and HCN. In addition, large scale maps of CO in 

the Magellanic Clouds and in the Galaxy were obtained. Some of these maps 

should be very valuable to find interesting regions for further study by ALMA. 

CO is important because it provides a tracer for molecular hydrogen, which 

itself is much harder to observe because of its unfavorable molecular properties, 

but which accounts for most of the mass of dense interstellar matter. SEST also 

has been used for experimental VLBI in the mm domain. 

La Silla is a good site for mm observations but still has too much 

atmospheric water vapor to be an optimal submm site. With the development 

of the 5000 m high Chajnantor site for ALMA a far better opportunity arose 

(Figure IX, 7). Since the surface of SEST is not very suitable for the shorter


precipitable water 

H2O 

1.0 mm 

0.5 mm 

0.5 mm 

frequency 

300 GHz 400 500 600 1000 1500 

1 µm 0.8 0.6 0.4 0.2 

wavelength 

Figure IX, 7. The transparency of the atmosphere at submm wavelengths. The blue 

areas represent wavelengths at which the transparency is better than 50% or in the 

lowest strip 10%. The amount of precipitable water corresponds to 1 mm equivalent 

in the upper strip and 0.5 mm in the other two. At La Silla 1 mm H 2O would be highly 

exceptional. At Chajnantor values in the 0.5–1.0 mm range prevail some 50% of the 

time. 

submm wavelengths and since the cost of moving it would be quite high, a 

new 12-m submm telescope has been erected at Chajnantor, where in some 

years’ time the 64 telescopes of ALMA will be placed. This Atacama 

Pathfinder EXperiment, APEX (Figure IX, 8) 6) , will also serve as a test of the 

conditions and operational problems at this rather difficult site. 

APEX is a collaboration of the Max-Planck-Institut für Radioastronomie 

(MPIfR) in Bonn (50%) with the two SEST partners, ESO (27%) and 

Onsala (23%). Because it was difficult to finance both telescopes, normal 

operations at SEST have been terminated mid-2003. APEX should become 

operational in 2005, initially with the 1.3 mm receiver from SEST and soon 

thereafter with others. It is planned to equip APEX with receivers covering 

the atmospheric windows from 1.5 mm to 0.3 mm and to test the possibility 

for observation at even shorter wavelength. Of course, the angular resolution 

is far inferior to that of ALMA, but at 0.3 mm it is still 5 arcseconds. With 

its relatively large field of view it is well suited for mapping projects to 

search for early star forming galaxies and protostars in our Galaxy in addition 

to spectroscopy of many molecular lines important in astrochemistry. APEX 

will be operated by a staff of 18, largely by remote control from a base 

constructed by ESO at about 2500 m altitude in the village of San Pedro de 

Atacama. 

50 % 

50 % 

10 % 

atmospheric transparency

ALMA 


Figure IX, 8. APEX, the 12-m Atacama Pathfinder Experiment, a cooperative venture 

of the MPIfR, Sweden and ESO. In the very dry atmosphere of Chajnantor it should 

be fully functional down to 0.3 mm and perhaps obtain useful results at even lower 

wavelengths. 

The IRAM interferometer data have shown that many structures observable 

at submm wavelengths are quite small in angular measure. Examples 

include the disks around stars where planets are forming or dense regions 

in the interstellar or circumstellar gas where conditions for chemical reactions 

are favorable, as well as the structures in galaxies far out in the Universe. 

To adequately study these a resolution better than 0.1 arcsec is needed which 

requires interferometers with baselines of several kilometers. But the 

radiation is feeble, and in objects resolved by such an interferometer the 

amount of flux in one beam area is small. Hence, a large collecting area is 

needed to be able to profit from the high angular resolution. In fact, in many 

cases an angular resolution of 0.1 arcsec is only useful if the total collecting 

area is of the order of 10,000 m 2 . 

The first ideas about a European Large Southern millimeter Array 

(LSA) arose in discussions among radio astronomers around 1991. The IRAM 

interferometer on the Plateau de Bure had shown the power of mm interferometry, 

and it was time to reflect on the next step. Early on it appeared that 

a southern site was preferred because of the greater richness of the southern


Galaxy and because particularly suitable dry sites exist in the Chilean Andes. 

Moreover, a southern site would be optimal if the results of observations at 

radio and optical wavelengths were to be combined, the latter to be obtained 

with the VLT. ESO had already become involved in the SEST project, so it 

became an early partner in the LSA discussions. 

Some initial studies were made by IRAM, ESO, the Onsala Space 

Observatory in Sweden and the Netherlands Foundation for Research in 

Astronomy, and a document outlining the project 7) was presented in late 1995 

to a workshop held at ESO 8) . The LSA was to be a mm array optimized for 

maximum sensitivity at 3 mm and 1.3 mm wavelengths, but ultimately 

covering the atmospheric windows from 7–0.8 mm. The total collecting area 

was to be 10,000 m 2 to ensure the required sensitivity at a resolution of 0.1 

arcsec. A dry site above 3000 m was being looked for. 

This still left the diameter of the individual telescopes to be decided. If 

the telescopes are very small, their number becomes very large. But each 

telescope has fixed costs independent of its diameter: receivers, links to the 

central area and infrastructure. Also the problems associated with the correlation 

of the outputs of the telescopes rapidly increase with their number. On the other 

hand, if the telescopes are large, their field of view becomes small, and so does 

the area that may be mapped by the interferometer. Moreover, problems with 

wind forces and other environmental problems are aggravated. The conclusion 

was that the optimal array would consist of 50 × 16-m telescopes or possibly 

100 × 11-m. The cost of the LSA was estimated at some 270 M€ . 

Also in the US a project was being developed, the MMA (MilliMeter 

Array). It would have a smaller collecting area of 2000 m 2 and be composed 

of 40 × 8-m telescopes operating down to 0.3 mm. The emphasis on (sub)mm 

science led to the relatively small unit telescopes. With larger telescopes the 

field of view was thought to be too small at the very low wavelengths. It also 

required a very high, dry site. The Llano de Chajnantor at 5100 m was being 

investigated as a possibility. Even though the MMA and the LSA had 

somewhat different objectives, the idea of having two large arrays in northern 

Chile with substantial costs for infrastructure seemed wasteful. So it was 

finally decided to merge the two projects into ALMA – the Atacama Large 

Millimeter Array. ALMA 9) would be a joint project on a fifty-fifty basis 

between the US+Canada on the one hand and Europe on the other. After 

some clumsy initial arrangements in Europe, the situation was simplified 

when the UK joined ESO. Thus, ESO now represents Europe in the ALMA 

cooperation, with Spain having concluded a separate agreement with ESO of 

which it is not yet a member, though negotiations about a possible 

membership have taken place from time to time. 

ALMA should consist of 64 telescopes of 12-m diameter for a total 

collecting area of 7240 m 2 (Figure IX, 9). It will cover the atmospheric 

windows from 0.3–10 mm wavelength. The initial set of receivers should 

cover the wavelength ranges 3.6–2.5, 1.4–0.81 and 0.50–0.42 mm. Additional


Figure IX, 9. ALMA. With 64 telescopes of 12-m diameter an excellent sensitivity is 

achievable. The longest baselines of 14 km will provide an angular resolution better 

than 0.02 arcsec at 1 mm wavelength. 

receivers could be implemented later, but of course every time 64 copies are 

needed which makes this rather costly. It is one of the advantages of APEX 

that receivers can be installed singly so that the returns can be evaluated 

before a major commitment has to be made. Placed on the Llano de 

Chajnantor (Figure VI, 8), ALMA will have maximum baselines of up to 

14 km, corresponding to angular resolutions of 0.004–0.15 arcsec according 

to wavelength. The telescopes of the array can be moved on big trucks, so as 

to have either a compact array with very high sensitivity to resolved objects 

or an extended array for maximum resolution. 

Also in Japan there were plans for a large mm array of 50 × 10-m telescopes. 

A site close to the Llano de Chajnantor was under study. Unfortunately, 

financial problems initially prevented Japan from joining the ALMA cooperation, 

but these have now been solved. Additional telescopes will be integrated 

into the array, making it even more powerful. 

Construction of ALMA has now been started. The full array should 

be completed by the end of 2011, but some observations with part of the


array could perhaps begin as early as 2007. The agreed cost envelope for 

Europe and N. America is 552 MUS$ (year 2000). So the cost to Europe 

is some 250 M€ (2004) of which ESO will pay 92.5% and Spain 7.5%. The 

project has one director serving under a board composed of equal numbers 

of N. American and European representatives. Of course, Chile as the host 

country is also very much involved in the project, providing the site and 

other facilities. In projects of this magnitude, issues of industrial return 

play an important role. The construction of the individual telescopes is a 

substantial item in the overall budget. As a first step, industrial companies 

from both sides of the Atlantic have been invited to manufacture a 

prototype. The resulting two prototypes have been shipped to the VLA site 

in New Mexico for comparative tests. Depending upon the results, one will 

have to proceed cautiously to equilibrate the total contributions from both 

sides. Perhaps more worrisome, the financial envelope was set on the basis 

of estimates of the telescope costs before prototypes were constructed. If 

the final unit costs were to exceed these estimates, there would be little 

choice but to reduce the number of telescopes. The alternative of 

increasing the financial envelope seems very difficult on both sides of 

the partnership. So it is fortunate that Japan is bringing in additional 

telescopes. 

Undoubtedly, with this first 50-50 trans-Atlantic large scientific project 

disagreements will occur. Success in dealing with these will very much 

influence future cooperations of this kind. However, the presently foreseen 

administrative arrangements are not entirely promising. Possibly the full 

Japanese integration in ALMA, making it a truly tripartite venture, could in 

some ways simplify matters. 

As mentioned before, MPIfR, ESO and Onsala are placing a first, 

somewhat modified, ALMA type 12-m telescope at Chajnantor, so as to gain 

a number of years of submm observing before ALMA comes on line. The 

Atacama Pathfinder EXperiment, APEX, will also serve as a valuable test of 

operating a telescope at such high altitude. With APEX and ALMA the 

European community will have access to the most advanced submm facilities 

in the world. Also Japan is placing a 10-m submm telescope, ASTE, nearby 

at 4800 m on the Pampa La Bola 10) . 

ALMA should have a broad impact on many domains of astrophysics. 

Its exquisite angular resolution will allow the study of star and planet 

formation in detail. In its wavelength range numerous lines of sometimes 

quite complex molecules are found and the astrochemistry of their formation 

can be studied. The circumstellar envelopes where dust and molecules form 

are also a prime target. Interesting data on molecules in comets and 

planetary atmospheres may be expected. The dust emission from very early 

galaxies should be measurable with ALMA as will be molecular gas in 

galaxies and quasars at a wide range of redshifts. Many other topics could 

be enumerated.


SKA – The Square Kilometer Array 

ALMA will have subarcsec angular resolution at mm wavelengths. To 

have the same resolution at decimeter wavelengths, an array would have to 

be spread out over an area 1000 km across. It is, of course, true that the 

VLBI networks achieve even better resolutions, but because their telescopes 

are so sparsely distributed, the image quality is rather limited and the sensitivity 

frequently inadequate. The collecting areas of the VLBI networks and 

their prospective enhancements amount to less than 50,000 m 2 . Taking into 

account a dose of financial realism, radio astronomers around the world have 

set an aim to have a million m 2 – hence the Square Kilometer Array. At the 

IAU meeting in Sydney in July 2003 a memorandum of understanding was 

signed by scientists from Australia, Canada, China, D, India, I, NL, PL, S, 

UK and the US to collaborate on the design, search for funding and 

construction of SKA. 

It would have been very simple if the results of the decimeter observations 

could also be obtained at mm wavelength, where ALMA has the 

necessary resolution. However, in the mm range one observes the cool gas 

in the galaxies, while at decimeter wavelengths hot gas and synchrotron 

radiation from cosmic-ray electrons predominate. Moreover, at large redshifts 

important lines, like the CO line at 2.6 µm, are beyond the range of ALMA, 

which in any case at longer wavelengths would have inadequate angular 

resolution. In addition, at 21-cm the ubiquitous spin flip line of hydrogen is 

observed which usually comes from regions so tenuous that few molecules 

are present. So ALMA and SKA address entirely different areas of science. 

The specifications of SKA 11) are simple: 1 km 2 collecting area, baselines 

up to 3000 km or more, a flat, quiet site with low artificial radio noise and 

as large a field of view as possible. A Y-shaped layout, like the VLA, or 

perhaps a spiral-like arrangement is envisaged, but the telescopes will not 

be mobile. Observations should be feasible at wavelengths from at least 3 m 

to around 1 cm, with an imaging field of view of a square degree at 21-cm. 

With these specifications the wavelength coverage of SKA + ALMA extends 

continuously from 3 m to the atmospheric limit around 0.3 mm, with an 

angular resolution everywhere better than 0.2 arcsec and with a field of view 

that gradually narrows from square degrees to 30 arcsec 2 at the shortest 

wavelengths. 

Suitable locations for SKA exist in Western Australia; other sites may 

be found in China, South Africa and Argentina. With ALMA in the southern 

hermisphere, it would be important to have SKA also there so that the 

complementarity of the two may be fully utilized. 

A typical 100-m telescope usable to 1 cm should cost at least 25 M€. 

If the SKA were to be made up out of 127 such telescopes, the total cost would 

amount to some 3000 M€ for the telescopes alone. The replication savings 

of manufacturing many telescopes at the same time would substantially


reduce this sum, but when all the other items are added it probably would 

be difficult to bring the total cost far below the 1000 M€ mark. However, 

entirely different technologies involving phased arrays may be used. Here very 

cheap detector elements view a large area of the sky at once. Extensive 

computer processing then picks out from all the signals, those coming from 

a particular area in the sky. While this would be a very attractive option, the 

computer requirements are enormous. So for now it is difficult to estimate 

what the total cost will be. Other proposals for SKA involve an array of 

Arecibo-like fixed dishes for which a certain area of China would be 

promising. But in whatever way SKA is finally constructed, it is likely to have 

a cost in the 500–1000 M€ range. 

The scientific potential of SKA 11) is enormous. As an example, consider 

the “epoch of reionization” when the neutral gas in the Universe began to be 

ionized by the uv radiation from the first stars and quasars in the newly 

forming galaxies. The 21-cm line of hydrogen observed at redshifts of 7–15 

(i.e. at wavelengths of 1.7–3.4 m) would give much information about conditions 

in the Universe at that crucial time during which the outline of the 

present day world became visible for the first time. Also the 2.6 mm line of 

CO molecules could be observed with SKA at redshifts above 3–4. So it 

should be possible to detect the very beginning of the formation of elements 

like C and O. We also note here the complementarity of ALMA and SKA. With 

ALMA higher order lines of warm CO and other lines at smaller wavelengths 

may be observed at high redshifts as well as the dust continuum emitted by 

typical star forming galaxies. Again, SKA can study the 21-cm emission in 

galaxies at lower redshifts and ALMA their CO emission. A complete view of 

the evolution of the gaseous component of galaxies at modest redshifts could 

be obtained. 

Magnetic fields have been detected (from the Faraday effect, the 

rotation of the plane of polarization in an ionized magnetic medium) in 

many galaxies and also in clusters of galaxies. Nothing is known about their 

evolution, their first origin or the cosmological effects they may have 

produced. 

A very complete inventory of pulsars, radio sources pulsing with 

periods of 0.001–10 seconds, in our Galaxy could be obtained. Typical pulsars 

are rotating magnetic neutron stars that emit narrow beams of electromagnetic 

radiation. Several pulsars are known in binaries, orbiting another 

neutron star. Rare cases are expected to be discovered of pulsars orbiting 

black holes which would give much information on the properties of spacetime 

around these. Of course, there is much more to SKA than these items: 

quasars and galaxies with bursts of star formation at high redshifts, stellar 

atmospheres and circumstellar flows, supernovae and gamma-ray bursts, 

exoplanets and many others. 

The Dutch project LOFAR 12) (LOw Frequency ARray) will make use of 

the phased array technology. LOFAR would observe the long wavelength part


of the radio spectrum in the range 30–1.4 m, that is at frequencies of 

10–220 MHz. While the technology is simpler at longer wavelengths, the 

ionosphere creates serious problems. LOFAR could be constructed on a five 

year time scale at an estimated cost of the order of 150 M€. Extensive technology 

development is needed which also has commercial implications. With 

the antenna elements distributed over a 300 km diameter area, the angular 

resolution at 30 m would be some 20 arcsec, and around 1 arcsec at 1.5 m. 

Because of the long wavelengths and of the ionospheric problems, progress 

in this wavelength domain has been slow until now. LOFAR should open up 

the field. 

LOFAR would be completed long before SKA. Some of the scientific 

aims are not very different from those SKA has set and may later achieve 

with superior resolution and sensitivity. However, most of the 3–30 m wavelength 

domain will not be accessible to SKA. Unique results could be obtained 

on sources of coherent radio emission, pulsars, quasars with very steep 

spectra, exoplanets with Jupiter-like radio emission, as well as in ionospheric 

studies, observations of coronal mass ejections from the Sun with the 

resulting “space weather” and the detection of radio waves from the air 

showers of extreme cosmic ray events. 

The history 13) of LOFAR shows some of the pitfalls of international 

collaborations in which the siting plays an essential role. In the early nineties 

it was discussed as a relatively cheap NL–US project with possibly also 

Australian participation. With costs escalating and disagreements about the 

site and about the scientific optimization, the collaboration fell apart. Now 

there are four projects: The LOFAR of the Dutch, with German participation, 

is still by far the largest. A US project, the Long Wavelength Array, will be 

placed in the SW US, a US–Australia project – the Mileura Telescope in 

W. Australia, and a Canada–China–US project, the Primeval Structure 

Telescope in China. Different US groups participate in the different projects. 

Part of the problem has been that funding available on one site was not transferable 

to another. Similar problems could be faced by SKA. 

Note added in proof: 

Because of the increased prices of steel and carbon fiber, the cost of 

the ALMA telescopes came in higher than expected. As a consequence, the 

number of 12-m telescopes has been reduced from 64 to 50.

X. 

Europe in Space: ESA’s Horizons 2000 

Le risque de surdépendance vis-à-vis des États-Unis ne 

doit cependant pas être ignoré, et il convient de faire en 

sorte que la part de notre activité scientifique qui dépend 

de décisions américaines, prises à partir de considérations 

qui ne sont pas nécessairement les nôtres, ne 

devienne pas prépondérante… Dépendance. Indépendance. 

Interdépendance et surdépendance. Voilà un beau 

sujet de dissertation et pas seulement dans l’espace. 

H. Curien 1) 

Following a schedule very similar to that of ESO, European space 

science came into being in Paris on 14 June 1962 with the signing of the 

convention for the European Space Research Organization (ESRO). It took 

effect on 20 March 1964 upon ratification by nine countries (A, B, DK, F, D, 

NL, S, CH and UK), soon joined by Italy. A month earlier the European 

Launcher Development Organization (ELDO) had been founded, which 

turned out to be a preprogrammed failure: different countries were responsible 

for different parts of a rocket, and not surprisingly the interface 

problems could not be properly handled. As a minister remarked after one 

of the launches of its “Europa” rocket, it seemed that the organization was 

involved in deep sea research! ESRO was more successful; by 1980 a dozen 

relatively small satellites had been placed in orbit, albeit with American 

rockets. 

Most of ESRO’s satellites were for studies of the earth’s magnetosphere, 

aurorae, the ionosphere and the nearby interplanetary medium, but three 

were concerned with science outside the solar system: TD-1 (1972–74) 

obtained data on stars in the ultraviolet, COS B (1975–82) very successfully 

mapped the sky in gamma-rays, and IUE (1978–96) – the International


Ultraviolet Explorer – carried a small (45 cm) telescope equipped with a spectrograph; 

IUE was a cooperation of ESA, the UK and the US. More than any 

other mission it succeeded in integrating space data into mainstream 

astronomy. In total, some 3000 articles in refereed journals have been based 

on the 110,000 spectra obtained by IUE. Till the end it remained in heavy 

demand by a broad astronomical community. The aging spacecraft was deliberately 

turned off in 1996 because its cost-to-benefit ratio diminished, while 

the participating agencies had financial problems. 

After these successful beginnings ESRO began planning for larger 

missions which soon exceeded its financial and technological means. With 

ELDO a failure and ESRO’s future uncertain, a fundamental reorganization 

was needed. In 1975 the convention creating the European Space Agency 

(ESA) was signed by the ESRO member states, minus Austria, but including 

Spain. In 1987 Austria, Ireland and Norway became full members, followed 

by Finland in 1995, Portugal in 2001, and Greece and Luxembourg in 2004. 

ESA would be responsible for research, launchers, space technology and its 

applications. Its headquarters were placed in Paris, the European Space 

Technology Centre (ESTEC) in Noordwijk (NL), the European Space Operations 

Centre (ESOC) in Darmstadt (D) and the European Space Research 

Institute (ESRIN) in Frascati near Rome. The function of the latter was 

variable and not always clear, except that politically it had to be continued 

in Italy. In the meantime also a center for managing astronomical missions 

has come about in Villafranca near Madrid. This was started for dealing with 

the European part of the International Ultraviolet Explorer and continued 

with ISO and XMM-Newton. When the gamma-ray mission INTEGRAL came 

along, ESA very rationally put the data center as an “instrument” and, in fact, 

the Swiss were successful in obtaining this, with a greatly reduced cost to 

ESA. This sent alarm bells going off in Madrid, with the result that ESA 

decided to place the data centers for all future astronomy missions in 

Villafranca. An outside observer might wonder why pay for something one 

could have got partly for free, but this is not the way Europe functions. 

The development of an independent European launcher capability was 

an essential part of the agreements, with Kourou in French Guyana as the 

launch site. Space Science was a relatively small part of ESA, representing 

of the order of 10% of the total budget. While there is no argument that 

Europe needs an independent launcher capability, the unfortunate effect was 

that the science program had to use the Arianes and could not freely negotiate 

a favorable price. This changed only after the first Ariane 5 disaster when 

in the case of the Cluster reflight a Russian launcher could be used. After a 

commercial arrangement was concluded between Ariane Espace and the 

Russian Space Agency for the former to market the Soyuz rockets, it became 

possible for the science program to obtain these launchers, which for smaller 

missions were much more cost effective. For large missions, like Rosetta, 

XMM-Newton or Herschel-Planck, the Ariane 5 is an excellent launcher.

Europe in Space: ESA’s Horizons 2000 163 

An important aspect of the ESA Convention is that it specifies the 

science program as a separate mandatory program. All countries who are 

members of ESA have to participate and contribute generally in proportion 

to their GNP. From time to time the Council of Ministers establishes the 

overall financial envelope. While that envelope is far from satisfactory, the 

separate nature of the program has had a protective effect. It made it impossible 

to transfer science funding into other branches of the organization 

when shortfalls occurred there. 

By 1980 the ESA Convention had been appropriately ratified by the 

parliaments of the member countries, and it became time to start defining a 

coherent long range plan for space research. Serious work on this began when 

Roger Bonnet became director of the ESA Science Program. It was his decision 

that this would not be a plan devised by some wise men, but it would be created 

by the community. So in 1983 a sollicitation went out to the wider scientific 

community for mission “concepts” which resulted in 67 responses, of which 37 

were for solar system research. A survey committee was set up, chaired by 

Johan Bleeker, composed of 15 scientists supported by 21 scientists in “topical 

teams” with the task of constructing the outline of a program for the period 

1985-2004. The program would be based on the input from the community, 

and its elaboration would take into account, apart from scientific quality – the 

sine qua non, flexibility, continuity, balance between disciplines, technological 

content and financial realism. Some missions – Giotto to Halley’s comet, 

Ulysses to study the solar wind, Hipparcos to measure accurate stellar distances, 

ISO, the Infrared Space Observatory and participation in the Hubble Space 

Telescope – which had previously been approved were included in the overall 

program “Horizon 2000”. It was clear from the beginning that a budget increase 

was needed to realize Horizon 2000. In fact, an annual increase of 5% above 

inflation was agreed to by the ESA member countries from 1985 onward till 

1994 – leading to a cumulative increase of around 60%. Unfortunately, the 

diminishing willingness of some of the ESA countries, in particular first the 

UK and subsequently Germany, to invest in space and in science led to a decline 

of 3% per year immediately thereafter. As in the English nursery rhyme: 

“The Duke of York 

with all his thousand men 

he marched them up the hill 

and marched them down again.” 

By 2004 the science program had lost 21% in real income compared 

to 1995 to arrive at a budget of 371 M€, only a quarter more than the totally 

inadequate budget of 1983. The contrast with the US situation is pathetic. 

The NASA budget for space science in 2004 is 3971 MUS$ corresponding to 

3300 M€, with the proposed 2005 budget 4.2% higher again, well above 

inflation. The sum of the NASA items “Astronomical search for origins” and 

“Structure and evolution of the universe” are twice as large as the total 

European spending on space science (see Note 2).


The Horizon 2000 program 3) (Figure X, 1) was based on four “cornerstones”, 

large missions with long lead times of much importance in their 

respective disciplines, as follows: 

– XMM, a large MultiMirror X-ray telescope optimized for X-ray spectroscopy, 

now “XMM-Newton” 

– FIRST, a Far InfraRed Space Telescope, now “Herschel”; 

– Rosetta, a mission to the nucleus of a comet, including a lander; 

– STSP, the Solar Terrestrial Science Program, composed of two parts: 

Cluster, an array of four magnetospheric satellites, and SOHO, the Solar 

and Heliospheric Observatory. 

The STSP was an artifact which allowed the concept of four cornerstones 

to be maintained without forcing a choice between the solar and the 

magnetospheric communities. In reality it consisted of two medium sized 

missions. In addition, the program included medium sized missions – in part 

those already previously approved and in part missions to be selected later 

so as to retain flexibility. The cornerstones were to be fully autonomous 

European missions, though SOHO became a joint ESA-NASA enterprise. 

A typical cornerstone would be cost capped at twice the plateau of 200 MAU 

(1983 value) foreseen for the annual budget of the Science Program † . The M 

(medium sized) missions were to cost one such annual budget, the program 

to end with as yet unspecified four (or perhaps five) missions M1 – M4. By 

the end of the 1985–2004 nominal period of the Horizon 2000 program most 

missions foreseen had been executed, though the FIRST/Herschel cornerstone 

and the Planck M3 mission had been delayed to 2007. Also M4 had 

not been implemented, but in a way became Cluster II, following the 

destruction of Cluster I on the maiden flight of Ariane 5. The high cost ISO 

had effectively become a cornerstone. Several missions were extended beyond 

their nominal two year duration (Figure X, 2), which had a negative impact 

on the financial situation, though it greatly increased the scientific returns. 

There are not many 20-year programs in science that have been executed so 

faultlessly through a variety of misfortunes. 

An update of Horizon 2000 for the next ten years was requested by 

the 1992 Council of ESA at ministerial level. This led to Horizon 2000-Plus 4) 

– a roll-forward of the earlier program. This time 101 mission ideas were 

generated by the scientific community, 39 in solar systems science, 32 in 

astrophysics and 30 in physics in space. The survey committee, which 

I chaired, and its associated working groups totalled 75 scientists from 

outside ESA. This time three new cornerstones were selected: 

– A mission to Mercury, now named Bepi Colombo; 

– LISA, a Large Interferometric Space Antenna to study gravitational waves; 

† The AU (Accounting Unit) was an ESA financial construction which via the ECU was 

replaced by the Euro.

Figure X, 1. The Horizons 2000 Program as adopted in 1995. The Mercury cornerstone 

is now envisaged as a cooperation with ISAS (Japan), and the gravitational wave observatory 

LISA with NASA. The Interferometry Observatory will be the astrometry mission 

GAIA, but could also include a share in an infrared interferometer (DARWIN) aimed at 

the direct detection of earth-like planets. The M-missions – now in part “flexi-missions” 

at reduced cost – include “Planck” (Cosmic Microwave Background), Mars express, Venus 

express, ESA share in JWST (next space telescope), and Solar Orbiter. The small missions 

include now SMART-1 (technology demonstration + lunar science), a share in the French 

COROT (exoplanets) and Microscope (test of equivalence principle), and Double Star, a 

magnetospheric mission with China. The IR and X-ray observatories were “green dreams” 

for an undefined future. Recently, Horizons 2000 has been rebaptized “Cosmic Vision”.

CLUSTER 

DOUBLE STAR 

1 

9 

9 

0 

2 

0 

0 

0 

2 

0 

1 

0 

MAGNETOSPHERE 

ULYSSES HELIOSPHERE 

SOHO 

SOLAR ORB 

GIOTTO 

ROSETTA 

HUYGENS 

MARS EXP 

VENUS EXP 

BEPI COLOMBO 

SMART-1 

PLANCK 

HERSCHEL 

ISO 

ODIN 

JWST 

HIPPARCOS 

COROT 

GAIA 

HST 

IUE 

ROSAT 

XMM-NEWTON 

BEPPO SAX 

INTEGRAL 

AGILE 

LISA 

MICROSCOPE 

Year 

SUN 

COMETS 

PLANETS 

IR 

VISIBLE 

UV 

X-RAYS 

γ-RAYS 

GRAVITY 

Figure X, 2. European Astronomy in Space. Missions in various scientific areas are 

indicated as follows: — ESA satellites; — ESA missions in cooperation with U.S., 

Russian (INTEGRAL), Japanese (B. Colombo) or Chinese (Double Star) space 

agencies; — major non ESA European satellites; — ESA cooperation with national 

European missions. Duration of current and future missions have not necessarily been 

formally decided. Qualitative indications of the main subjects are on the right hand 

side. The present program still appears to exceed current resources and so some delays 

in future missions are possible.


– An interferometry mission, either astrometric (GAIA) or infrared for 

high angular resolution studies of astronomical objects, including the search 

for earth-like planets, the latter now named Darwin. While GAIA was given 

a slight edge, a priority decision would be taken some years later after further 

studies. 

M3 and M4 the two still undefined M-missions of Horizon 2000 would 

be supplemented by another four of the same class. 

In the Horizon 2000-Plus survey committee much discussion took 

place on possible planetary missions. At the time of the development of 

Horizon 2000 the situation had been very different. Both the US and the 

USSR had been engaged in a substantial and costly program of planetary 

exploration: The US had launched sixteen and the USSR an even larger 

number of planetary missions, though with a higher failure rate. The main 

targets had been Mars and Venus. A few missions had aimed at Jupiter and 

beyond, while also Mercury had once been visited. A very large number of 

missions had been sent to the moon. So it had been concluded that for 

Europe there were only limited opportunities in the planetary area except 

perhaps in certain niches. One such niche concerned comets and a flyby of 

comet Halley in 1986 had already been decided. Thus, in Horizon 2000 

another cometary mission, Rosetta, had been included. In the meantime, 

consultations with the US had resulted in the M-1 mission Huygens to Titan, 

the major satellite of Saturn, as an adjoint to the large NASA mission Cassini 

to the planet. Apart from the difficulty in seeing where a European planetary 

mission could fit in, undoubtedly also scientific attitudes played a role. As a 

report of the European Science Foundation and the US National Research 

Council 5) states: “A mission on the scale of Marsnet or Intermarsnet might 

not have attracted sufficient support in Europe as a cornerstone because of 

the inbred commitment of a majority of European space scientists to experiments 

on small bodies, particles and fields, and dust.” Moreover, “Averaged 

over all of Europe, the European astrophysics community is considerably 

stronger and more cohesively organized than its planetary science 

community”. 

In the meantime the planetary programs of both Russia and the US 

had developed much more slowly than foreseen. In Russia the political transformation 

reduced the importance of the space program. In the US the very 

high costs of the Galileo (to Jupiter) and Cassini missions, the shuttle disaster 

in 1986 and the cost of the Space Station very much diminished funding for 

other planetary ventures. So new opportunities opened up for European 

scientists who wanted to be part of the planetary exploration programs. 

When the Horizon 2000-Plus committee discussed the future plans for 

ESA, the issue of planetary research came again to the fore. It was clear that 

missions to Jupiter and beyond could hardly be considered. The solar energy 

flux at 5 AU would be too feeble for effective electricity generation by photocells, 

while suitable RTGs (Radioisotope Thermoelectric Generators) had not


been developed in Europe. Moreover, their utilization would risk much ecolopolitical 

fallout. So the issue became which of the terrestrial planets to 

choose. The most attractive choice seemed to be Mars. As the committee 

stated 6) “There is worldwide consensus that gives Mars the highest scientific 

priority among the inner planets, due to its outstanding interest for comparative 

planetology. The planet is smaller than the Earth, but nevertheless 

shows enough similarity for many geological and atmospheric processes to 

provide interesting comparisons and tests for theories regarding terrestrial 

processes.” Nevertheless, the majority of the committee selected a mission 

to Mercury as the next planetary cornerstone! 

The ostensible reason was that 7) “the loss of NASA’s Mars Observer in 

1993 and the programmatic uncertainties both at NASA and in the Russian 

program cast much doubt on the realization of the plans made some years 

ago” and that “In such a fluid situation, it is impossible to specify a well 

defined ESA Mars mission; in any case international cooperation will be 

required. All that can be done at this time is to specify a priority for a 

meaningful substantial participation when the opportunity arises. This 

priority should be such that other items in the ESA planetary-science program 

may have to be rearranged.” Is Europe unable to specify a major Mars 

mission on its own, especially when the misfortunes of the others had left 

the field wide open? Following a brief discussion of the fact that relatively 

little was known about Mercury, the committee went on to propose a 

cornerstone mission to that planet. It was the only issue about which it had 

been necessary to have a vote; on all other items a consensus could be 

reached. Apart from concerns about where an ESA mission to Mars could fit 

in, the advantage of Mercury was that it was a planet with a magnetosphere. 

So there was something in it for two communities. Moreover, no new missions 

in the terrestrial magnetosphere were foreseen, so for that still powerful 

community it was Mercury or nothing. 

There is no doubt that a mission to Mercury had a high scientific 

interest * . But it does not have the much broader appeal of the Mars missions: 

climatologists, geologists and biologists all would benefit from the study of 

Mars. Moreover, one has seen several times the incredible enthusiasm of the 

general public for Mars missions. While one cannot base a science program 

on this, it is, nevertheless, a significant fringe benefit. Support for science 

requires funding and public support is helpful in obtaining this. The unfortunate 

consequences became evident very quickly. Both the French and the 

Italians decided to seek participation in the NASA program. So, instead of 

having a vigorous European program of Mars exploration, Europe would 

again be dependent on priorities set elsewhere. In 2000 the French CNES, 

* In the meantime NASA has launched in 2004 the Messenger mission to Mercury which 

should from 2011 onwards map the uncharted part of the surface and measure its magnetic field. 

Is the ESA mission with arrival in 2016 still equally interesting?


prodded by research minister C. Allègre, announced the plan to place in 2007 

(in cooperation with eight other countries) four small landers on Mars for 

seismological, mineralogical and climatological observations. However, in 

April 2003 (coincidence?) NASA suddenly pulled out of the venture 8) . A 

month later, France cancelled the whole project and also withdrew its support 

for the unrelated US gamma-ray mission GLAST 9) . The French also announced 

that future Mars exploration would take place only in the ESA context. In 

part the French decisions resulted from a long overdue analysis of the CNES 

finances. The uncertain prospects for space funding in Italy have also made 

its participation in NASA’s 2009 Mars missions quite uncertain. 

In the meantime, other factors led to the renaissance of a European Mars 

program. Many laboratories had been building instruments for the Russian 

Mars-96 mission, which unfortunately ended in the Pacific Ocean. Spares of 

several instruments were available, and so a relatively cheap and fast mission 

was in ESA’s reach. This became Mars Express, successfully launched in 2003. 

Moreover, with spending on the Space Station tapering off, ESA began to also 

consider what to do next in manned space flight. The result was “Aurora”, to 

investigate the possibility of placing a European on Mars. While the question 

may be asked what that European would do there, this could lead to more 

vigorous preparatory missions to Mars. “Aurora” was formulated some two 

years before the corresponding widely publicized US proposal in 2004. It is 

presently outside the Science Program of ESA and thus depends on non 

mandatory financial contributions from the ESA member states. So it seems 

that the recent political tensions and more accidental factors may finally lead 

to a more unified, coherent European Mars program. However, much will 

depend on the funding decisions for “Aurora” during the coming years. Of 

course, cooperation with Japan, Russia and the US in the Mars program is also 

a good thing, but only if there is first a clearly formulated program in Europe. 

In the meantime the US program on the Moon and Mars is beginning 

to take on gigantic proportions, with the expectation that this will necessitate 

the end of the Space Station. If so, what have the Europeans gotten out of 

their participation in the latter? Several thousand million euros down the 

drain without any return? It never looked a cost effective venture from any 

point of view, neither scientifically nor industrially. But a unilateral decision 

to terminate it would also show that Europe should not enter again in such 

a large project with the same partner. Why not learn one’s lesson and develop 

a sophisticated, technologically challenging robotic program? The spin off to 

industry could be very large. And when finally the first American stands on 

Mars in 2030 waving a flag, while worrying about his return, Europe could 

have a considerable remotely controlled presence there at a fraction of the 

cost. The astronaut could even be welcomed by a robot waving a flag with a 

circle of 12 stars. 

Following the adoption of Mars Express, a mission to Venus also found 

its way into the program. Since much of the spacecraft would be the same


as for Mars Express, such a mission would be relatively cheap. Nevertheless, 

Venus Express went through a cycle of approval, cancellation and resurrection 

all within a year. Launch is now foreseen at the end of 2005. 

The Space Station also figures in the Horizons 2000 program. Proposals 

have been made to place there EUSO, an instrument to observe radiation 

from very energetic cosmic rays hitting the earth atmosphere, and Lobster, 

an all sky X-ray monitor. However, the future of the Space Station for scientific 

research is now so uncertain that serious planning is difficult. It had also 

been envisaged to assemble a large X-ray facility, XEUS, at the Space Station 

and subsequently to place it in an independent orbit. In the meantime XEUS 

is envisaged as an independent mission to be placed at L2. 

The result of the two exercises, referred to as “Horizons 2000”, was 

to cover the period till 2017 (Figure X, 1). The Horizon 2000-Plus program 

was based on a constant budget (corrected for inflation) through 2000, 5% 

annual increases in the years 2001–2005, followed by constant budgets at 

the 2005 level. The ministerial Council of ESA in 1995 approved the Horizon 

2000-Plus program, but deleted the increases for the 2001–2005 period. 

Instead it imposed the budget reduction of 3% per year mentioned before, 

followed by a flatter budget a few years later. As a result, the approved 

program was seriously out of balance. As the financial circumstances deteriorated, 

this led to a number of reshuffles of the program. The final result, 

however, preserved all the elements of the program: The six unallocated 

M-missions became Planck – to study the cosmic microwave background – 

Mars express, Venus express, the JWST participation, Solar Orbiter and the 

reflight of Cluster. The interferometric cornerstone was transformed into 

GAIA (no longer interferometric). The small missions became the technology 

demonstration mission dubbed SMART-1, and ESA contributions to two 

French missions, now internationalized, COROT for asteroseismology and to 

look for planets and Microscope to test the Einsteinian principle of equivalence, 

and Double Star, an ESA cooperation with China in magnetospheric 

research. In a wave of optimism the reserve medium mission Eddington, 

which was to study asteroseismology and occultations of stars by exoplanets, 

was added to the program but removed again less than two years later much 

to the chagrin of the community that had just been built up around the 

project. Perhaps it will be revived in the future. 

It may seem surprising that with diminished resources the full program 

could still be executed. However, a number of factors have allowed significant 

cost reductions in both cornerstones and M-missions. Grouping of missions 

to have commonality of the space platforms and other resources, new technologies 

and international cooperation all contribute to this. The Mercury 

mission now will have a Japanese component and LISA will be a joint 

ESA-NASA mission. New technology reduced the projected weight of GAIA, 

allowing a launch with a Soyuz-Fregat, which is also the launcher of choice 

for several other missions at substantial savings. While it has been possible


to squeeze the various missions into the Horizons 2000 program with a 

reduced budget, this has increased the dependence on international partners, 

taken all flexibility out of the program and left little room for adjustments 

for contingencies. The time lines of the major elements of the program are 

shown in Figure X, 2. A few large national missions are also included in this 

figure. More detailed descriptions of individual missions are provided in 

chapters VIII and XI - XV. A new director of the ESA Science Program 

having arrived, Horizons 2000 had to get a new name: “Cosmic Vision”. 

It may be asked if the budget driven cost reductions are realistic. At 

NASA the “faster, cheaper, better” was pushed very far, and the results have 

been mixed. Some cheap missions were very successful, but others ended in 

failure. New technology is helpful, but, nevertheless, there are limits as shown 

by the Next Generation Space Telescope. As it went from early design to 

hardware contract, the diameter was reduced and the cost increased substantially. 

Until now the ESA scientific satellites have had a nearly perfect record, 

and a valid case may be made that a significant cost reduction with the 

increased risk of an occasional failure gives the best cost-to-benefit ratio. The 

success of the Mars Express orbiter and SMART-1 contributes to confidence 

in the realism of the overall program. An indication of the updated costs of 

the ESA missions is given in Figure X, 3. The precise meaning of the inflation 

corrections is open to argument, especially over periods of more than a decade. 

ESA’s science budget is in reality smaller than it seems because of 

various constraints built into the system. The most serious of these is the 

principle of “juste retour”. Each member country obtains industrial orders 

in proportion to its contribution. It is understandable that in the very 

beginning, when space industry was not yet developed in some countries, one 

would have given favorable treatment to the “have nots”. But by now it is a 

rather inefficient system. At every ministerial meeting the situation is further 

aggravated by a further increase in the minimum cumulative return 

percentage. The result is that one has to place industrial orders that one 

knows to be uncompetitive, and that the offers from the major enterprises 

include inefficient subcontracts for the sole purpose of having the right 

industrial return percentage. In view of the continuing effort of the European 

Union to combat anticompetitive practices within the Union, the whole arrangement 

seems anachronistic. It is generally thought that “juste retour” adds 

some 20% to costs, but I believe this may be an underestimate. It also may 

affect the effective rate of inflation. 

An important difference between the nature of ESO and CERN on the 

one hand and the ESA science program on the other should be noted. The 

former are built around one dominant project. For ESO during the last 

decade the VLT was the absolute priority, scientifically and financially. Similarly 

at CERN everything else has to make way for the Large Hadron Collider. 

Budgets for these projects have been set at the beginning and determine 

future overall spending by these organizations. At ESA it is different.


Figure X. 3. Major ESA Science Missions launched or planned after 1980. Costs in 

M€ have been updated to 2004. They include capital costs and operational costs 

during the mission. Completed missions are indicated in red, current missions in green 

and planned missions in blue; in cooperative missions, only ESA costs are included. 

Instrumentation costs borne by the member countries are not included. 

It executes a program of missions within a certain financial envelope. So there 

is competition between the solar, planetary, infrared, optical, X- and gammaray 

communities which each obtain a spacecraft from time to time with long 

intervals inbetween. Balance is the key word in the ESA Horizons program, 

while ESO and CERN are concentrated around one aim at a time. As a 

result, they have a much stronger scientific identity. 

One other aspect of the ESA Horizons program is important. While 

ESA provides the spacecraft, interfaces and mission operations, almost all 

scientific instruments are made in institutes in the member countries and 

paid for by those countries out of national space budgets. In the nineties, 

this payload support typically has amounted to 50–70 M€ annually, corresponding 

to some 20% of the budget of the ESA science program, with part 

of the personnel expenses still to be added. However, more recently it has 

become lower, with some of the member countries even asking ESA to choose 

between an inadequate payload and a partial ESA financing for its realization! 

Most instruments are constructed by multi-institute cooperations headed by 

a Principal Investigator (PI) (Table X, 1), whose country usually pays a

Table X, 1. PI countries on ESA missions. One PI is indicated by +, two or three by ++, and more by +++. 

Mars 

Venus 

Huygens 

Smart-1 1) 

Giotto 

Rosetta 

Ulysses 

D ++ ++ + + +++ +++ ++ + ++ + + 

F ++ ++ ++ ++ +++ ++ +++ + + 

I ++ ++ + ++ 2) + 

UK + + + ++ ++ + ++ + + ++ 2) + + 

A + + + 

B ++ 

Dk + 

SF + + + 

Ei + 

NL + + + + 

ESP + 

S + + ++ + 

CH + + + + ++ + 3) 

Hun ++ 

Rus + + 3) 

US + + ++ ++ +++ + ++ 

1) Only science instruments. 2) One originally I, later changed to UK because PI assumed other function. 3) CH: Science Data 

Centre, Rus: proton launch, Russian data center. 

Note: European institutes have also made instrumental contributions to non ESA missions. Among the larger ones we 

mention the French SIGMA and FREGATE to Russian – respectively NASA γ-ray missions, the German COMPTEL and the 

Dutch-German LETG (spectroscopy) to NASA γ-ray respectively X-ray missions, the UK Bragg Crystal Spectrometer and the 

Large Area Proportional Counter to the Japanese Yohkoh (solar) respectively Ginga X-ray missions. The Swiss contribution 

to RHESSI (solar X-rays) and the French one to FUSE (uv spectroscopy) also were important. In addition, a variety of European 

institutes contributed to magnetospheric and heliospheric missions by other agencies. Instruments for national missions in 

Europe have included the UK EUV camera and the NASA high resolution imager for ROSAT (D), and the Dutch wide field 

X-ray cameras for BeppoSAX (I). 

Cluster 

SOHO 

EXOSAT 

XMM 

INTEGRAL 

ISO 

Herschel 

Europe in Space: ESA’s Horizons 2000 173


substantial part of the cost, but the co-investigators’ countries also contribute. 

From the table the broad participation and the differing interests of some of 

the ESA countries are apparent. On average, the instruments on the solar 

system missions have been more numerous and less expensive than those of 

the astronomical observatories. In solar system missions the tradition has 

been that the scientists who have constructed an instrument are the “owners” 

of the data it produces. In the astronomical observatory missions the 

instrument providers obtain a certain fraction of the observing time – typically 

30% initially, and somewhat less later on. The remainder is distributed 

to scientists who propose observing programs which are evaluated competitively. 

This is entirely appropriate since the cost of the instruments is generally 

substantially less than the cost of the mission as a whole, which is borne 

by the whole ESA community. Sometimes different procedures are followed; 

for example in Hipparcos the complete satellite was provided by ESA, since 

a meaningful separation of instrument and spacecraft was not possible. 

However, two large consortia of scientists performed the complex analysis 

of the data and thus also had a first look at the data. 

Conclusion 

The Horizons 2000 program has been an undisputed success. It has 

given a relatively stable frame to European space research with the scientists 

in the various subdisciplines knowing what to look forward to on a 

decadal time scale and to prepare themselves adequately for maximizing the 

returns of the missions. Of course, the long term planning also has a negative 

aspect: reduced flexibility. It was thought that some of the flexibility could 

be provided by the national programs, and in the nineties this was, in fact, 

the case. However, the reductions in national spending have largely put an 

end to this complementarity. It is not only the flexibility that risks being lost, 

but also the intervals between the missions have become so long that it is 

difficult to have enough continuity, especially for students and postdocs 

wishing to work in these fields. 

X-ray astronomy is an example. After the end of EXOSAT in 1986, 

it took 14 years before XMM-Newton started taking data. That European 

X-ray astronomy was not more seriously affected is the result of the national 

missions of ROSAT and BeppoSAX which bridged the gap. When the national 

missions become less frequent, such gaps in the ESA program will become 

still more damaging.

XI. 

European Space Missions: 

IR, X- and Gamma Rays 

But time is short and science is infinite – how infinite 

only those who study astronomy fully realize - and 

perhaps I shall be worn out before I make my mark. 

Thomas Hardy 1) 

The visible–near infrared radiation observable from the earth’s surface 

represents only a very narrow slice of the electromagnetic spectrum (Figure I, 4). 

The IR above 2.5 µm is largely unobservable from the ground, though there 

are some limited “windows”. Below 0.3 µm the atmosphere is opaque. Astronomers 

have been lucky that common stars, like the Sun, emit most radiation 

in the 0.3–2.4 µm accessible interval. So stars and galaxies could be observed 

from the ground and a certain picture of the Universe obtained. However, 

many essential aspects remained hidden. Much of the energy of galaxies is 

emitted in the far IR, the cosmic microwave background is mainly around 

1 mm, and also, for studies of the interstellar medium, star and planet 

formation only in the IR can the all pervading dust absorption be overcome. 

X- and γ-rays contain much of the information about the hot, high energy 

Universe, on the largest mass concentrations – the clusters of galaxies – and 

on black holes. So just a view of the Universe in visible light would remain 

terribly incomplete or even erroneous. Most observations of the IR, X- and 

γ-rays have been obtained with satellite based instruments. Useful observations 

may also be made with high altitude balloons or with week long shuttle 

flights. It would lead us into too many details to discuss all of these here. 

In this chapter we briefly review recent and future European space 

science missions in the Infrared, X- and Gamma-Rays. Optical and near IR 

space telescopes are discussed in chapter VIII, missions in the Solar System 

in chapters XII and XIII, studies of Cosmic-Rays and Gravitational Waves


in chapter XIV, and searches for Exoplanets in chapter XV. In several 

chapters related ground based activities are also included. 

Infrared / mm 

From the ground observations are possible from the visible to 2.5 µm 

and again upwords from 1 mm. While there are some “windows” in between 

(Figure XI, 2), the atmosphere is nearly completely opaque from 30 to 

300 µm. Moreover, telescopes and mirrors at ambient temperatures are 

powerful radiators over much of the IR, and so is the atmosphere. The 

resulting background very much reduces sensitivity. While for some purposes 

it is possible to observe from the 4 km high plateaus at the center of 

Antarctica or from high flying aircraft and balloons, the only fully satisfactory 

solution is to go into space and there to cool everything that may radiate into 

the detectors. 

The first cryogenic satellite devoted to IR astronomy was IRAS – the 

InfraRed Astronomical Satellite, a US-NL-UK cooperative venture. In 1983 

it made a six month survey of 97% of the sky. IRAS resulted from plans in 

the Netherlands in 1974 for a successor to the ANS satellite (Astronomical 

Satellite of the Netherlands) and from an Announcement of Opportunity for 

an Explorer class mission by NASA. With its 57-cm telescope and some 

60 detectors cooled to 3 K it performed photometry in broad bands centered 

at 12, 25, 60 and 100 µm wavelength. Some 250,000 sources were catalogued, 

mainly stars but with nearly 10% galaxies. IRAS also had a low resolution 

spectrometer. 

Some earlier observations of known optical objects had been made in 

the mid-IR with balloons and rockets. The importance of IRAS was that it 

made an unbiased survey which allowed it to discover sources that were 

strong in the IR, but inconspicuous in the visible. Most notable among these 

were galaxies that radiate in the IR up to a thousand times as much energy 

as our Galaxy radiates at all wavelengths. Such galaxies have very high rates 

of star formation, but dust prevents most of the visible radiation from 

reaching us. 

While IRAS detected many sources, its four broad band detectors were 

insufficient to gain detailed spectroscopic information. So already in 1978 

some scientists made a proposal to ESA for a 1-m cooled IR telescope. Ultimately, 

this led to ISO 2) (Figure XI, 1), the Infrared Space Observatory, 

which was launched on 17 November 1995. With its 60-cm mirror it was no 

larger than IRAS, but its instrumentation was far more powerful, with 

imaging cameras and spectrographs of various angular and spectral resolutions 

(Figure XI, 2). The ISO instruments covered the wavelength range 

2.5–240 µm. At the shortest wavelengths the angular resolution was a few 

arcseconds, but at 200 µm the diffraction at the small mirror limited it to

Figure XI, 1. The ISO satellite. The liquid helium, which slowly evaporates, cools the 

telescope to 3K above absolute zero temperature (– 270 °C) and some of the detectors 

to 2 K. Just behind the 60-cm primary mirror of the Cassegrain telescope is a pyramidal 

reflector which sends the light into one of the four instruments. The star 

tracker keeps the telescope pointed towards the target. The service module contains 

units for telemetry and other housekeeping tasks. 

R 

10 6 

10 4 

100 

1 10 100 µm 1000 

wavelength 

Figure XI, 2. Spectral resolution (R) and wavelength ranges of the instruments of ISO 

(–), Herschel (–) and the NASA SIRTF (–). The main wavelength ranges inaccessible from 

the ground are indicated by grey areas in the upper part of the diagram; however, in the 

three windows between 3 and 12 µm the atmospheric background is too strong for very 

sensitive observations. The windows beyond 300 µm may be observed with APEX and 

ALMA (chapter IX). The HIFI instrument on Herschel may be used at resolutions from 

10 6 down to 10 3 . The duplication between ISO and Herschel in the 80–230 µm range is 

only apparent, since the angular resolution of the latter is six times better.


about 3 arcminutes. The four instruments of ISO were multifunctional and, 

as a result, quite complex (Figure XI, 3). However, they functioned almost 

faultlessly. Contributions to their construction were made by laboratories in 

most ESA countries. There were two imagers (with also spectroscopic 

options), ISOCAM (F) and ISOPHOT (D), and two spectrographs, SWS (NL) 

and LWS (UK), with the principal investigators from the countries indicated; 

these also paid for the larger part of the costs of the instruments. All instruments 

were extensively used : ISOCAM 28% of the time, ISOPHOT 30%, SWS 

24% and LWS 18%. During the operational phase of ISO, contributions were 

also made by Japan and the US, which increased the total observing time by 

making additional ground station facilities available. 

ISO presented a number of difficult technological problems. All the 

mechanisms for moving wheels with filters and other items had to function 

in the extreme cold environment. But probably the most difficult was to 

obtain the required very sensitive, low noise, detectors. Thanks to its 

enormous military budgets, industry in the US has generally had a significant 

advance over Europe in detector technology and production. This was particularly 

so in the infrared where night vision devices were in much demand. 

While these detectors were available to US scientists, they usually could not 

be exported. The game played by the Americans was to see what was made 

in Europe and then “declassify” something just a bit better. This served to 

discourage European industry, except when governments (especially in 

France) took matters in hand to avoid too strong a dependence. As a result, 

Figure XI, 3. The layout of ISOCAM. The light beam enters the camera through the 

entrance wheel, which in some positions has polarizing optics. It is then reflected by 

mirrors on the selection wheel and subsequently passes through filters and lenses on 

other wheels. These allow the selection of different wavelength ranges and image 

scales. Many different combinations are possible.

European Space Missions: IR, X- and Gamma Rays 179 

the ISOCAM camera, built in France, for the 2.5–17 µm range had two 

detector arrays of 32 × 32 elements, while substantially larger arrays already 

existed in the US. Sensitive detectors at the longest wavelengths became available 

very late during the development of the ISOPHOT cameras built in 

Germany, so that not much time remained for testing. In orbit it turned out 

that while the sensitivity to infrared light was excellent, the same was the 

case to charged particles. Though ways were found to mitigate these effects, 

it remained an unpleasant problem. 

ISO may well have been the most expensive mission in the ESA science 

program. Updating costs to year 2004 euros and including national contributions 

for instrumentation, I would estimate that the overall cost amounted 

to nearly 1000 M€, with the instrumentation accounting for 20–30% of the 

total. The costs were high, but the results impressive. The mission lasted more 

than two years until the helium was exhausted. During this time some 

26,000 observations were made for projects involving 550 scientists as PI’s. 

Targets ranged from the planet Mars to the most distant galaxies in the 

Universe. Results included the discovery of water throughout the Universe, 

from the atmosphere of Saturn’s moon Titan to distant galaxies. The composition 

of the dust disks around numerous stars was analyzed and similar dust 

properties were found in comets and around some stars, reinforcing the 

belief that planets may be forming in these disks. Ices of water, CO2, CO, 

methane and others have been studied in the cold envelopes of very young 

stars. Characteristic PAH (polycyclic aromatic hydrocarbon) bands due to 

small dust particles (a few hundred molecules) were extensively observed and 

in galaxies seem to be associated with star formation. Molecular hydrogen, 

a dominant constituent of interstellar matter, was also studied in many 

places; this is important since usually the H 2 abundance was inferred from 

the intensity of the CO lines in the radio spectrum with an assumed H 2/CO 

ratio. The interstellar gas is heated by stars and cooled by emission lines, 

the most important being the ionized carbon line at 158 µm, fully within ISO’s 

reach. In dust rich galaxies the structure becomes much clearer in the mid- 

IR (Figure XI, 4). Emission lines of highly ionized elements indicate the 

presence of quasar-like nuclei hidden in galaxies by dust (Figure XI, 5). 

Deep surveys in selected regions have taught us much about galaxies in the 

distant, high redshift, Universe. Both galaxies and quasars of high luminosity 

were more abundant, presumably because encounters between galaxies were 

more frequent in the higher density Universe. 

A number of lessons have been learned from the ISO experience. 

Initially, the overall software effort needed in the Scientific Operation Center 

had been grossly underestimated. This had been based partly on the EXOSAT 

experience. However, that X-ray satellite was far less complex, suffered fewer 

orbital constraints and had observations of much longer duration. As a result, 

early in 1994, well before operations began, the projected manpower requirement 

had to be almost tripled. The SOC had both ESA manpower and staff


Figure XI, 4. The Whirlpool Nebula M51. At visible wavelengths the spiral arms are 

very thick and dust absorption occurs almost everywhere, complicating the interpretation 

of the image. In the ISO image around 15 µm dust absorption is no longer 

important and the spiral arms are very clearly defined. The emission is mainly due 

to dust heated by very active star formation. Tidal effects due to the associated galaxy 

NGC 5095 (to the left of M51) perturb the outer arms of M51. 

provided by the participating institutes. This mix of people who had been 

involved in the construction of instruments and others who interfaced with 

the users, functioned very well. 

All instruments were multimode. While each mode had a certain scientific 

justification, it required a non negligible software effort for its implementation. 

So even with the increased manpower, the number of modes 

offered had to be reduced to 24. However, at the end of the mission it 

appeared that 9 modes in ISOPHOT had been used in total for only 2.5% of 

the available time. A stronger concentration on the most essential modes 

could have saved money, increased reliability and allowed a more efficient 

use of the available manpower. 

The ISO orbit (1000–70 000 km high) involved many constraints. The 

sun, the moon and the earth had all to be avoided by a fair angle so as to 

avoid stray light. This limited the accessible part of the sky at any particular 

moment, which complicated the scheduling process. The observing time 

proposals had received quality ratings of 1, 2, or 3 in the evaluation process.


Figure XI, 5. ISO spectrum of the nearby Circinus Galaxy. Spectral lines due to singly 

ionized silicon, neon and others are emitted by gas ionized by a recent burst of star 

formation. But lines of eightfold ionized silicon (Si IX) demonstrate that a quasarlike 

nucleus is hidden inside the galaxy. Photons with an energy of 303 electronvolts 

(0.0041 µm) are required to ionize the Si. Stars hardly emit any such photons. 

Frequently, these operational constraints made it necessary to fill the time 

with priority 3 proposals. Future satellites placed at L2, at 1.5 million km 

from the earth in the antisolar direction will avoid these troubles. 

ISO was a great success as the world’s first observatory mission in the 

IR. However, at longer wavelengths its angular resolution was very poor due 

to the small diameter of its mirror. The next ESA mission in the far IR should 

improve on this and also cover the remaining wavelength range beyond 

200 µm. The Far Infrared Space Telescope, Herschel 3) (earlier baptized 

FIRST), to be launched in 2007, will have a mirror of 3.5 m (Figure XI, 6). 

Both the telescope and the mirror will be made of silicon carbide, a material 

with a favorable strength over weight ratio. At the longer wavelengths 

radiation from the telescope and mirror is a lesser problem, and it will be 

sufficient to passively cool these to some 80 K. This can be achieved by the 

radiative heat loss towards space because Herschel will be placed around L2, 

where the heat radiated by earth and moon is unimportant, while a shield


prevents heating by the Sun. Cameras and spectrographs will cover the wavelength 

domain of 60–670 µm. The detectors again will have to be cooled to 

below 2 K by superfluid helium. Beyond 300 µm ground based observations 

become possible at some wavelengths, and here ALMA with its superior 

sensitivity and angular resolution will begin to take over, though between 300 

and 670 µm many gaps remain where only Herschel has access (Figure IX, 6). 

Figure XI, 6. Herschel (left) and Planck (right) are to be launched in 2007 with one 

Ariane-5 rocket. Herschel will be an observatory for the 60–670 µm domain with 

imagers and spectrographs (Figure XI, 2), while Planck will scan the sky to determine 

the intensity distribution and polarization of the Cosmic Microwave Background, the 

relic radiation from the Big Bang. It will observe the sky in 9 channels at wavelengths 

from 0.35–10 mm. The instruments of Herschel will be cooled to 1.7 K, some of those 

of Planck to 0.1 K. Both will be placed at L2. So the Sun, earth and moon are close 

together in the sky and the opposite hemisphere is free from their IR radiation. In 

the upper part of the left image the 3.5-m Cassegrain telescope is seen, behind it the 

cryostat filled with liquid helium which envelops the instrument, and below the 

housekeeping unit. Planck’s 1.5-m mirror is seen on the right in an arrangement which 

minimizes star light.


Herschel in space and ALMA on the ground are very much complementary 

missions. The two main areas of research of both are the same, but 

at different wavelengths different aspects come to the fore. The cost of the 

two is comparable: of the order of 600–700 M€. But, of course, after a few 

years the helium in Herschel will be gone, while ALMA may continue to 

function for decades. 

Herschel will have three instruments : PACS (D), SPIRE (UK) and HIFI 

(NL) with the PI countries as indicated. Again, important contributions are 

made by laboratories elsewhere. PACS is a broad band imager for the 

60–210 µm spectral region and SPIRE for the 200–670 µm domain. Both 

also have a spectrometer for low to medium resolution spectroscopy. HIFI 

is a very high resolution instrument based on heterodyne techniques and able 

to attain spectral resolutions of up to 1,000,000 in some bands in the 

100–600 µm region. Through the Doppler effect this corresponds to a velocity 

resolution of 0.3 km/sec. 

During its 3–4 year lifetime Herschel is expected to observe a wide 

variety of celestial objects - in particular young galaxies in the early Universe 

and regions of star and planet formation in our own Galaxy with the associated 

chemical processes. Young galaxies and quasars in the early Universe 

should still be very rich in gas and dust which will obscure and absorb their 

visible radiation and reradiate it in the far IR. Herschel will be well equipped 

to find such objects, to determine the energy they radiate and to study the 

conditions in and the motions of the gas in these galaxies, which may give 

us an idea of how our own Galaxy must have looked in its early days. 

The formation of stars and planetary systems from the interstellar gas 

and dust is still rather poorly understood. In a general way, in denser regions 

the interstellar medium begins to contract due to its own gravity until it 

becomes finally hot enough for nuclear reactions to occur and a star is born. 

Along the way dust particles may stick together into bigger and bigger clumps 

which by their gravity attract more matter and become planets. During these 

various phases in the evolution, chemical reactions take place which lead to 

the formation of complex molecules which are believed to have played an 

important role in the evolution of planetary atmospheres and perhaps even 

of life. Both the dust and the molecules provide many diagnostic features in 

the spectra of the star forming regions which Herschel should be uniquely 

able to study. 

At wavelengths of several hundred µm there is a diffuse glow over the 

whole sky which is believed to be due to numerous massive galaxies in the 

early Universe. It is one of the tasks of Herschel to track down the origin of 

this radiation in detail. However, around 1 mm there is a still more energy 

rich glow left over from the early hot phase of the Universe – the Big Bang. 

The Cosmic Microwave Background has the spectrum of a perfect (black 

body) radiator at about 2.7 K. The CMB is extremely uniform with temperature 

fluctuations of no more than a few parts in 100,000. These variations


are related to small density fluctuations in the gas out of which much later 

galaxies began to form. These fluctuations also contain information on much 

earlier times, close to the origin of the Universe. 

The first satellite to detect the fluctuations in the CMB was NASA’s 

COBE. With its angular resolution of 7° only the broadest features could be 

discerned, but still much progress was made 4) . Subsequently, much better 

angular resolution was obtained with BOOMERANG 3) (I + US with Canada 

and UK), a balloon borne instrument flown over Antarctica. Structures down 

to 0.2 degrees were measured in a limited area of the sky which showed three 

peaks in the correlations due to sound waves in the early Universe resulting 

from initial inhomogeneities dating back to very early phases of the Universe. 

Further results with balloons were obtained with ARCHEOPS 3) (F, I) launched 

from Kiruna (S) and with MAXIMA in the US. Also some ground based 

instruments operating at the long wavelength end of the CMB (~ 10 mm), 

including a UK – ESP cooperation at Teneriffe, have provided useful data. 

An 8-m submm telescope at the South Pole is being planned by the US. The 

next NASA satellite WMAP 3) followed in 2001. It has five wavelength bands 

between 3 and 14 mm with angular resolutions from 18–54 arcminutes and 

is also able to obtain polarization information. In a year it reached a sensitivity 

of 35 µK, corresponding to a fluctuation in brightness temperature of 

one part in 100,000 per 18 × 18 arcmin 2 pixel. 

ESA’s Planck mission 3) aims for still higher sensitivity and angular resolution. 

With its 1.5-m telescope it will observe the CMB around its spectral 

maximum at 1 mm with a resolution sufficient to measure the smallest 

features expected. It will have nine sets of imaging arrays in the wavelength 

range of 0.35–10 mm, four with HEMT radio receiver arrays and six with 

bolometer arrays. These have one overlapping channel at 3 mm. The bolometers 

will have to be cooled to 0.1 K above absolute zero, certainly an ambitious 

goal in space. The broad wavelength range will allow an excellent 

separation between the CMB and emission from our own Galaxy by both dust 

and gas. At 0.8 mm (800 µm) the best angular resolution of 5 arcmin is 

reached with a sensitivity of 40 µK per pixel. At shorter wavelengths the sensitivity 

deteriorates rapidly. At 2–3 mm the resolution is still 8–11 arcmin, and 

the sensitivity reaches 5 µK per pixel corresponding to a temperature fluctuation 

in the CMB of two parts per million. Planck also has the possibility 

to measure polarization. This will enable us to determine the “epoch of reionization” 

when the first stars formed and ionized the intergalactic gas. Scattering 

by the resulting electrons produced low levels of polarization in the 

CMB. The Planck spacecraft is spinning to provide all-sky coverage at a 

uniform rate. With its low angular resolution (compared to Herschel) it is 

not the ideal instrument to study point sources. However, thousands of 

clusters of galaxies should be detected, which may be further studied with 

XMM-Newton and with the VLT. Planck and Herschel are to be launched 

together with an Ariane-5 rocket in 2007.


Two other European ventures in the IR should be mentioned. In 2001 

the Swedish (with SF, F, Can) satellite Odin 3) was launched with 50% of the 

time available for astronomy and the other 50% for aeronomy. It contains a 

1.1 m telescope with instruments which may obtain observations around 

0.53, 0.6 and 2.5 mm wavelengths. Spectral lines of H 2O, NH 3 (ammonia) 

and O 2 could be observed. The latter was not detected and unexpectedly low 

limits have been placed on its abundance. A smaller 60 cm telescope, SWAS 3) , 

for similar observations was launched by NASA two years earlier. Because 

of its larger telescope Odin has nearly twice the resolution of SWAS; its sensitivity 

is ten times better for point sources, and its velocity resolution up to 

12 times higher. The latter was important in observations of comets where 

water outflow from the nucleus was mapped with 80 m/sec velocity resolution. 

Germany participates at a 20% level in a NASA project, SOFIA 3) , for 

a Boeing 747 plane with a 2.5-m telescope and a suite of instruments. While 

even at 13 km altitude the residual atmosphere presents many problems, a 

wide range of spectroscopic observations may be made. Of course, the great 

advantage is that instrumentation can be continuously updated and liquid 

helium to cool the detectors can be added as long as needed. The telescope 

was provided by Germany, which also contributes two of the nine initial 

instruments. Instrumentation includes cameras for the 1–240 µm wavelength 

range and spectrometers with resolutions up to 10 5 or 10 6 for 

5–600 µm. SOFIA is expected to be fully functional at the end of 2005. Some 

160 flights with 6 hours at altitude are expected annually. The US and 

Germany will separately allocate their part (80% respectively 20%) of the 

observing time. 

In 2003 NASA launched SIRTF 3) – the Space InfraRed Telescope 

Facility, now named Spitzer. It is similar to ISO, but with newer, better and 

larger detector arrays. With the usual hype this is advertised across the 

Atlantic to be infinitely superior! However, its 85-cm telescope gives it an 

angular resolution not much better than ISO, while it lacks the higher spectral 

resolutions. But the 256 × 256 pixel camera is some 45 times larger than that 

of ISOCAM, and its sensitivity is also higher. However, in deep surveys at 

several wavelengths confusion noise, due to overlapping images, predominates. 

Since this depends only on the angular resolution, the advantage over 

ISO is not so very great, but, of course, Spitzer arrives at the confusion limit 

faster and over its larger area. Its orbit trailing the earth with ever increasing 

distance avoids some of the operational drawbacks of ISO in earth orbit. 

It is ironic that when ISO was started, NASA told ESA that there was no point 

to it, because they would be faster and so ESA better join their project. As 

it came out, ISO was eight years earlier and obtained several important 

firsts. 

Japan is making very rapid progress in the IR. In 1995 it launched IRTS 

with a 15-cm liquid helium cooled telescope which functioned for about five


weeks, during which time it surveyed 6% of the sky. The next mission, 

ASTRO-F 3) has been prepared for launch in 2006. With its 67-cm siliconcarbide 

mirror cooled to 5.8 K it will make an all sky survey in six wavelength 

bands in the range of 6–200 µm, with a sensitivity some 30 times 

better than IRAS. After completion of the six months survey, pointed 

observations should reach much greater depth albeit in more limited areas. 

A particularly ambitious project is being studied in Japan for launch around 

2010. SPICA 3) would be a 3.5-m telescope, optimized for the 5–200 µm 

wavelength range, cooled to 4.5 K by mechanical coolers. Since the telescope 

would be launched at ambient temperature, the weight of large quantities of 

liquid helium is avoided. SPICA should have unprecedented sensitivity, 

outperforming JWST above 15 µm, albeit at 1.6 times lower angular resolution 

(Figure XI, 7). It should be placed at L2. Beyond 100 µm its performance 

would be comparable to that of Herschel, because it has the same diameter; 

IR sensitivity 

-15 

-20 

 

 

 

 

 

 

 

 

 

 

10 100 µm 1000 

wavelength 

Figure XI, 7. Schematic view of IR sensitivities. The vertical scale give log(vF v) in 

w/m 2 , which is a measure of the energy received in a broad band around wavelength 

λ indicated on the horizontal scale. For the IRAS and ASTRO-F surveys the actual 

limiting fluxes (at a signal-to-noise ratio of 5) are indicated, for the observatory type 

missions those corresponding to a 1 hour observation. Source confusion and backgrounds 

may be very different depending on the source location and affect the sensitivities. 

The missions are identified as follows: — IRAS, — and • ASTRO-F, — ISO, 

— SIRTF, — Herschel, — JWST, ••• SPICA (still undecided) and — the ground based 

ALMA.


at the long wavelengths the cooling of the telescope does not give an 

advantage, while source confusion may be the limiting factor for both. 

For the moment there is no competition in sight for Herschel. There 

were proposals to NASA for an 8-m telescope SAFIR 3) (Single Aperture Far 

InfraRed) for the 30–300 µm spectral range. In the meantime it appears to 

have been enlarged to a 10-m telescope, cooled to 4 K for the 15–600 µm 

range. If JWST is an example, it may well shrink again when the real cost 

becomes apparent. The intent would be to launch it around 2015, but nothing 

appears to have been decided as yet. It could be a valuable complement to 

JWST, the successor to the Hubble Space Telescope. 

The only future project with mid-IR capabilities after ISO and Herschel 

currently under consideration in Europe is the 15% participation in the 6-m 

JWST (see chapter VIII). It should allow observations from 0.6–28 µm. 

Surveying the overall European program in the IR, we conclude that it has 

been quite satisfactory with two important firsts: ISO and Herschel, which have 

opened up several spectral domains never surveyed before or should do so in 

the near future. However, the longer term future is less evident. A summary 

of the world’s astronomical IR space missions is given in Table XI, 1. 

Table XI, 1. Infrared space missions. From left to right the columns present the 

(expected) year of launch, the acronym of missions of Europe, joint EU-US, US, Japan, 

diameter of primary mirror and smallest and largest wavelengths, followed by c for 

telescopes cooled to liquid helium type temperatures. IRAS lasted 10 months, COBE 

4 years, IRTS 5 weeks and ISO 28 months. MSX was a military mission that produced 

a published Galactic plane survey. The others are in orbit or not yet launched. SPICA 

and SAFIR are still uncertain. More details can be found in the text. 

Launch EU US Japan d (m) λ (µm) 

1983 IRAS 0.6 12–100 c 

1989 COBE 1–9500 c 

1995 IRTS 0.15 3–800 c 

1995 ISO 0.6 3–200 c 

1996 MSX 0.35 4–22 

1998 SWAS 0.6 530–620 

2001 Odin (S) 1.1 500–2500 

2001 WMAP 3000–14000 

2003 Spitzer 0.9 3–200 c 

2005 ASTRO-F 0.7 6–200 c 

2007 Herschel 3.5 60–670 

2007 Planck 1.5 350–10000 

2010 SPICA 3.5 5–200 c 

2011 JWST 6 0.6–28 

2015 SAFIR 10 30–300 c


X- and Gamma-rays 

While the impetus for ISO and FIRST came from the astronomical 

community, the first push for X- and gamma-ray missions came from cosmicray 

physicists who were familiar with the necessary instrumentation and 

intrigued by a possible gamma-ray component in the cosmic rays. During the 

seventies some small European satellites were launched with X-ray detectors, 

including two by the UK (Ariel 5 and 6) and one by the Dutch (Astronomical 

Netherlands Satellite No 1). Also the Japanese Hakucho satellite performed 

well. Beginning in 1970, NASA launched some six X-ray satellites of ever 

increasing performance, until 1978 when “Einstein” with its focussing optics 

revolutionized the field. 

The fundamental problem of X-ray astronomy was that the types of 

telescopes that are used for visual light cannot function at very short wavelengths. 

At nearly vertical incidence the X-rays would be absorbed or scattered 

rather than reflected. However, at very low angles (~ 1 degree) the situation 

is different and appropriate metallic surfaces reflect very well. Of course, this 

means that we cannot employ Cassegrain telescopes. Instead it is possible to 

obtain images by having the X-rays reflected first by a paraboloidal and subsequently 

by a hyperboloidal mirror. An unfortunate by-product of the grazing 

incidence is that the light rays converge only slowly and so the focal length 

is large, which is not very convenient in a spacecraft. At the present time, 

gold coated mirrors may be used to about 10 keV of X-ray energy. Much experimental 

work is currently being done in Japan and elsewhere to try to 

extend this to higher energies by employing multilayer coatings. It is expected 

that this may push up the limit to perhaps 50 keV. 

X- and gamma-ray detectors tend to be sensitive also to energetic 

particles around the earth or in the solar system. The larger the detector, the 

greater this problem. In the absence of focussing telescopes, large detectors 

have to be directly exposed to the sky to detect faint sources. So the source 

signal increases with the size of the detector, but so does the particle noise, 

reducing the sensitivity. But with imagers the situation is different: the X-ray 

collecting surface may be large, but the detector need not be bigger than one 

resolution element. Hence, the signal-to-noise ratio is much improved. NASA’s 

“Einstein” was the first satellite which made effective use of such X-ray optics. 

Also gamma-ray satellites appeared early on with NASA’s SAS-2 (with 

Italian participation) in 1972, which lasted only 8 months, too short to obtain 

sufficient statistics. Three years later followed Europe’s COS B 5) which for 

seven years surveyed the sky. It mapped diffuse galactic radiation due to collisions 

of cosmic rays with interstellar gas and detected several dozens of 

discrete sources. While for more than a decade the COS B results remained 

unequalled, it was a small satellite and the angular resolution was no better 

than 5 degrees making convincing identifications with sources at other 

wavelengths difficult.


The first ESA X-ray observatory was EXOSAT, launched in 1983 6) . 

During its three year lifetime it obtained excellent observations which 

extended to higher energies than could be reached by “Einstein”. On board 

were a 1.5–50 keV hard X-ray detector and a telescope for the 0.04–2 kev 

imager/grating spectrograph. One of the original aims of EXOSAT had been 

to observe lunar occultations of X-ray sources and thereby to determine 

angular sizes. For this purpose it was placed in a very elongated orbit with 

an apogee of 192,000 km. Most of the time then would be spent far from 

the earth with a low speed with respect to the moon. With the better imaging 

capabilities of the “Einstein” (and in a more minor way EXOSAT) focussing 

optics, the occultation mode had become largely redundant. However, the 

high orbit meant that continuous observations of 72 hours duration were 

possible. This permitted the discovery of Quasi-Periodic Oscillations in the 

X-rays emitted by accreting neutron stars. These QPOs provide information 

on the interaction of the infalling matter with the magnetosphere of the 

neutron star and on the rotation of the latter. The Transmission Grating 

Spectrometer took only a few spectra because of a hardware problem, but 

these provided the data on which models of stellar coronae could be based. 

The long continuous observations also allowed the first detailed studies of 

stellar flares. An active visitor program contributed to the expansion of the 

X-ray community in Europe. Studies of quasars and galaxies took 31% of the 

observing time and black holes, neutron stars and other stellar sources 54%. 

While the next ESA mission for X-rays would not be launched before 

the end of 1999, two national initiatives, ROSAT and BeppoSAX, allowed the 

European astronomers to continue making substantial progress. First in 

1990 came the German satellite ROSAT with focussing optics and high efficiency 

till about 2.4 keV in energy 7) . In the ROSAT all-sky survey some 

100,000 sources were detected for the first time, more than half of them 

quasars and the remainder mainly stars, though also normal galaxies and 

clusters of galaxies were found. Included in the ROSAT payload were also a 

High Resolution Imager (HRI), provided by the US, and a grazing incidence 

Extreme UV telescope, contributed by the UK. With the latter an all sky EUV 

survey was made which detected more than 1000 sources in the range 

60–200 Å (200–60 eV), mainly white dwarfs and active stars. Absorption 

by interstellar gas in our Galaxy is too strong to see much of the extragalactic 

Universe at those wavelengths. As a result of the ROSAT surveys the 

numbers of catalogued X-ray and EUV sources were both increased a 

hundredfold. In the “Lockman hole”, an area of low absorption, the HRI in 

observations totalling more than a million seconds was able to reach sufficiently 

low flux levels to show that at least 70–80% of the X-ray background 

observed in low resolution observations was resolved into individual sources, 

almost all quasars and Seyfert galaxies. 

For seven years ROSAT continued to generate data on hot stellar 

coronae, supernova remnants, neutron stars, clusters of galaxies and every


variety of quasar or Seyfert galaxy. For many classes of objects inferences 

previously had been drawn from two or three examples. Thanks to ROSAT 

for the first time large statistical samples became available which provided 

a basis for reliable conclusions. As an example, before ROSAT only a few 

galactic star clusters had been observed. With the ROSAT sample of nearly 

30 clusters, it could be clearly demonstrated how the stellar X-ray luminosity 

declines with age. Several pulsars were found to be pulsing X-ray sources, 

but also non-pulsing cooling neutron stars were identified. The latter provided 

constraints on the relation between pressure and density in matter at or above 

nuclear densities. Through an ample flow of postdocs at the Max-Planck- 

Institut für Extraterrestrische Physik near München and through extensive 

collaborations with scientists elsewhere, ROSAT has much benefitted the 

whole European astronomical community. 

As ROSAT aged, the Italian Space Agency in 1996 launched its major 

X-ray satellite, BeppoSAX, with a set of instruments that could observe the 

whole range of X-ray energies from 0.1 to 100 keV 8) . After a difficult path 

towards realization it has been a brilliant success. The broad energy range 

has enabled us to obtain clear information on X-ray spectra and absorption 

in quasars and related objects, on the hard X-ray background and on a 

variety of problems involving neutron stars and black holes. 

Originally there had been two proposals in Italy: one to build an 

X-ray imager like the one on the “Einstein” satellite and one for what is now 

BeppoSAX. While SAX was chosen in 1982, the losing party both in Italy and 

in the US still tried to torpedo the project as late as two years before launch. 

Fortunately, both the Italian Space Agency and the Science Ministry were in 

the hands of scientists who understood the matter. Following a review by an 

eminent Italian scientist, the government asked the European Science Foundation 

to give an opinion. All of us in the advisory committee unanimously 

agreed that SAX should be continued. I have been amazed about the shortsightedness 

of the opponents: if they had succeeded to abort the project after 

much of the money had been spent, the credibility of the whole Italian astronomical 

community would have been lost. Now in collaboration with their 

Dutch partners, who provided two excellent wide angle X-ray cameras, they 

have collected one of the great prizes of the decade – the identification of 

the sources of the mysterious gamma-ray bursts and the determination of 

their locations in the furthest reaches of the Universe. Such bursts leave a 

faint X-ray and optical afterglow that rapidly weakens. With BeppoSAX it was 

possible to determine the position of the X-ray afterglow sufficiently fast and 

with adequate accuracy for the optical counterpart to be found, which turned 

out to be located at the edge of a galaxyy with a redshift of 0.7. Also stellar 

flares were detected and emission over the full 0.1–50 keV range was found, 

indicating that the flares were associated with gas at a temperature of 10 8 K. 

While BeppoSAX would last till 2002, the large ESA X-ray satellite 

XMM (first proposed to ESA in 1982 and now baptized XMM-Newton) began


to provide data in early 2000 9) . With three telescopes of 58 shells each of 

gold plated focussing optics (Figures XI, 8, 9) providing a high sensitivity 

and 4.2–6.6 (FWHM) arcsec angular resolution, its instruments (Table XI, 3) 

Figure XI, 8. A mirror module for 

XMM-Newton. The 58 gold plated 

shells reflect incoming X-rays by 

double reflection. 

Figure XI, 9. Artist impression of XMM-Newton in orbit. The three mirror modules 

are visible under the sunshade. The detectors are at the right at the foci of the 

modules. The focal length is about 7 m.


cover the range of 0.1 to 10 keV at spectroscopic resolutions of up to 700 at 

some energies. XMM-Newton is particularly effective in the hard 5–10 keV 

band. BeppoSAX had pioneered the detection of sources in this energy range 

and resolved some 30% of the X-Ray Background. XMM reaches a factor of 

more than ten fainter at these energies, and now 60% of the XRB is resolved 

into individual sources. As yet there is no evidence of a truly diffuse XRB of 

cosmological origin. Of course, there is more to XMM than the XRB, but the 

variety of its programs precludes giving an account here (Figures XI, 10, 11). 

In addition to the X-ray imagers and spectrographs, XMM carries an 

optical/uv monitor. 

Also in 1999 NASA launched AXAF (now “Chandra”), an X-ray mission 

with focussing optics; its principal aim was to obtain the best possible angular 

Figure XI, 10. The 30 Doradus region of the Large Magellanic Cloud seen by XMM- 

Newton. Supernova shells and point like sources (mainly X-ray binaries) are seen. 

Harder X-rays are shown in blue and softer ones in red.

Figure XI, 11. Quasars and other extragalactic X-ray sources in the Lockman Hole where absorption by the interstellar gas in our 

Galaxy is particularly low. The red sources (with a white core if strong) emit mainly soft X-rays, the blue ones hard X-rays. Some of 

the spectra obtained by XMM-Newton are also shown. The second spectrum from below on the left is rather soft. Its counterpart on 

the right is much harder with only photons above 1.5 keV. Even though the latter’s flux is only just above 10 –7 photons/(cm 2 sec kev) 

at 8 keV an adequate spectrum could be obtained thanks to the large effective area of XMM. The two spectra at the top are very soft. 

European Space Missions: IR, X- and Gamma Rays 193


resolution ( 1 arcsec). For once this was a felicitous combination of competition 

and collaboration: AXAF would obtain the finest images, while XMM 

with its large collecting area would obtain the best spectra. In particular in 

fainter objects, the diagnostically important iron line at 6.4 keV is only accessible 

by XMM. The cost of XMM including instrumentation is somewhere 

around 900 M€ , while that of AXAF appears to have been substantially more. 

XMM is expected to remain operational for a decade. 

While the overall European program represents a coherent approach 

to X-ray astronomy, of course others have also launched missions 10) . At NASA, 

the Einstein satellite (1978) had been the first with focussing optics. The US 

also provided the High Resolution Imager for ROSAT. Subsequently RXTE 

(1995), the Rossi X-ray Timing Explorer, took over where EXOSAT had left 

off, with high time resolution for hard X-ray observations. Chandra preceded 

XMM-Newton by some months. In Japan the Institute of Space and Astronautical 

Science launched a series of highly successful X-ray satellites, Tenma 

(1983), Ginga (1987) and ASCA (1993), which were to be followed by the 

powerful Astro-E just after XMM-Newton. Unfortunately, it was destroyed in 

a launch failure; a follow up is now scheduled for 2005. All these satellites 

made important contributions to the field, in particular ASCA with its optics 

usable up to 10 keV which allowed it to observe hard X-rays from many 

galactic and extragalactic sources in which the softer X-rays are absorbed. All 

in all the contributions of the EU, the US and Japan have had a rough equivalence. 

Cooperation between the three has been satisfactory. A summary of 

the X-ray missions may be found in Table XI, 2. Also India has plans for a 

substantial X-ray/uv mission ASTROSAT to be launched in 2008. In addition 

to two 38 cm uv telescopes, it should have 0.6 m 2 hard X-ray counters and 

also a 200 cm 2 effective area soft X-ray telescope with UK participation. 

Various plans are being made for future X-ray missions beyond 

Newton-XMM, Chandra and ASTRO-E, but nothing appears to be firmly 

decided. XEUS, for X-rays from the Extreme Universe Spectroscopy, started 

out in Europe as a Space Station related project. The idea was to gradually 

build up large focussing optics, which subsequently would be brought to the 

Space Station for assembly into an X-ray facility of increasing size. Once a 

large enough area would have been assembled the facility would be set free, 

since the ISS is not very suitable for very precise pointing. Subsequently, as 

more optics arrived, it would be captured again, the new elements would be 

integrated into the facility, and it would again be set free, etc. At the time 

that the organizations responsible for the ISS were looking rather desperately 

for a purpose to justify their huge investment, this seemed promising. 

However, in the meantime the future of the Space Station has become much 

more uncertain as a subsequent industrial fantasy project happens to take 

its place. Moreover, the very low earth orbit would be quite inconvenient with 

earth occultations very much reducing efficiency. Thus, in the meantime 

XEUS has evolved into an autonomous facility at L2.

Table XI, 2. X- and γ-ray missions launched after 1980 by Europe, the US and Japan. The effective collecting areas (in m 2 ), angular resolutions 

(in arcminutes) and fields of view (in square degrees) generally vary with energy, and therefore are only indicative. Representative 

values for the highest energy (in keV, unless stated otherwise) are given. More accurate descriptions may be found in the scientific literature. 

Several spacecraft also have γ-ray monitors on board which have not been taken into account in the table, unless indicated. 

Eff. Area E max Ang. Major 

EU USA Russia Japan m2 keV Resol. FOV contrib. Notes 

With focussing telescope 

1990-98 ROSAT (D) 0.05 2 0.07 3 US, UK 7 

1993-01 Asca 0.08 10 1.5 0.5 US 19 

1996-02 BeppoSAX (I) 0.015/.05 10/120 1.6 0.3 NL 8 

1999- Chandra 0.08 7 0.01 0.01 NL, D 20 

1999- XMM-Newton 0.40 12 0.09 0.2 UK, NL, D 9 

(ESA) 

2005 ASTRO-E2 0.15 12 1.5 0.1 US 21 

With collimators or coded masks 

1983-86 EXOSAT (ESA) 0.16 50 50 0.5 UK, D, NL, I 6 

1983-84 Tenma 0.10 60 150 8 22 

1983-88 Astron 0.17 25 180 9 22 

1987-91 Ginga 0.40 37 90 2 UK 22 

1987-01 Röntgen/Kvant 0.20 1000 8 3 D, NL, UK, ESA 22 

1989-99 Granat 0.25 100 6 4 F, Dk 22 

1991-00 COMPTON 0.15 30 GeV 60 2000 D 23 

1995- RXTE 0.78 200 60 1 24 

2000- HETE 0.01 400 60 5000 F 25 

2002- INTEGRAL (ESA) 0.55 10 MeV 12 80 Russ/I/F/Dk/ESP 14 

2004 SWIFT 0.52 † 150 0.3 † – I, UK 25 

2006 AGILE (I) 0.06 50 GeV 30 8000 17 

2008 GLAST 0.8 300 GeV 20 6000 I, D, F, S, J 26 

Major European instruments on non-EU spacecraft 

1989-99 SIGMA (F) on Russ GRANAT 0.08 1.3 MeV 15 120 12 

1991-00 COMPTEL (D) on US COMPTON 30 MeV 60 3000 23 

2000- FREGATE (F) on US HETE 0.02 400 – 10000 25 

† Effective area for γ-ray burst alert telescope, but angular resolution for 0.01 m 2 X-ray tel; also copy of XMM-Newton optical monitor.


There are four principal motivations for building XEUS 11) : the study of 

the hot gas in clusters of galaxies (with their large dark matter content) at 

moderate redshifts, the origin and evolution of black holes at large redshifts 

(z = 10?), the nature of space–time around black holes, and the nature of matter 

under extreme conditions, perhaps beyond those found in neutron stars. To 

explore those areas, angular resolutions down to a few arcsec, effective collecting 

areas of at least 10 m 2 and time resolutions of µsec are required. Such a 

telescope will have a large focal length (50 m?). Since it is not feasible to have 

this in one structure with the mirrors, the detectors would be in a separate 

satellite. With the same ionic thrusters as used in SMART-1 (chapter XII), the 

mm accurate relative positioning of the two satellites should pose no insurmountable 

problems. The example of BeppoSAX has shown the importance of 

observing hard X-rays up to at least 50 keV. To obtain sufficient angular resolution 

and sensitivity, it would be desirable to utilize telescopes also at high 

energies. The hard X-ray reflectivity of the mirrors may be obtained with multilayer 

reflective coatings. Since the Japanese have also built up some experience 

with such mirrors and are considering a future hard X-ray telescope (NEXT), 

an ESA–ISAS partnership might be very fruitful. At NASA the preferred future 

project has been CONSTELLATION, an array of four X-ray telescopes on independent 

satellites which would all be pointed in the same direction. Current 

planning suggests a launch after 2016 at the earliest. 

In addition to these very large X-ray missions, several survey type 

instruments are planned which would be attached to the Space Station. 

These include ROSITA, a German-ESA cooperation for a sensitive hard 

X-ray survey (> 2 keV). It would in a way replace an earlier German mission 

ABRIXAS which failed in 1999 because of an error in the power system. 

ROSITA should detect some 50,000 sources. In addition, Lobster-ISS would 

be an ESA all sky monitor which would produce an X-ray catalog of 200,000 

sources every two months so as to detect variable objects. Japan is in an 

advanced stage of building such an instrument with lower sensitivity. Finally, 

in the US EXIST is being planned for surveying the whole sky every 

90 minutes in the 6–600 keV range. All these plans depend on the future of 

the Space Station. For ROSITA a free-flyer option is also being studied. 

Gamma-ray astronomy has its own particular problems. Of course, the 

boundary between X- and γ-rays is rather arbitrary with hard X-rays 

extending up to 50 keV or more. Since no focussing optics exist, γ-ray telescopes 

have generally made use of mechanical collimators which limit the 

angle from which rays may reach the detector. Not surprisingly the angular 

resolution is poor. More recently coded masks have been developed. A coded 

mask in front of a detector hides selected parts of the field. Pointing the 

telescope in slightly different directions, different areas of the sky are occulted 

and a comparison of the results yields the location of the sources. The application 

of this technology to the French SIGMA instrument on board of the 

Russian GRANAT mission has been particularly successful 12) .


Without focussing optics the detector has to be large and the background 

due to charged particles hitting it is high, especially in the energy 

range around an MeV. Hence also the sensitivity is relatively low. The 

situation improves at much higher energies where the tracks of individual 

photons can be followed in spark chambers and other detectors familiar to 

particle physicists. So the direction of the origin of the γ-rays can be determined 

and background events become less important. 

In 1972 NASA launched the SAS-2 satellite which during its seven 

months lifetime detected high energy emission from some pulsars, but which 

accumulated insufficient statistics on most other sources. With COS B (1975–82) 

ESA made a first partial sky survey in the 0.03–5 GeV energy range which 

yielded more than a dozen sources. In addition, it mapped the diffuse γ-ray 

emission from the galactic plane which results from unresolved sources, 

from cosmic-rays colliding with nuclei in interstellar matter and from energetic 

electrons. 

In the meantime, American satellites which had been launched to verify 

that the nuclear weapons test ban treaty was obeyed, had discovered Gamma 

Ray Bursts, short spiky flashes of γ-rays with overall duration of seconds or 

less. Gamma-ray astronomy got a major boost from the launch of the NASA 

Compton Gamma Ray Observatory, a decade long mission launched in 1991. 

It contained instruments for the study of high energy γ-rays, Gamma Ray 

Bursts, hard X-rays, and also a German instrument COMPTEL (with NL, US 

and ESA contributions) intended for the difficult 1–30 MeV range. Among the 

results from COMPTEL is the discovery of emission at 1.16 MeV from radioactive 

titanium ( 44 Ti) in the supernova remnant Cas A which probably exploded 

in 1667 13) . With a half life of only 78 years it was clear that it must have been 

synthesized very recently in the supernova event. Later the result was 

confirmed by BeppoSAX from other lines. 

Already in 1985 a proposal had been made for a new ESA γ-ray mission 

(GRASP), but it had not been selected in the competition. Since usually 

several missions compete for one slot in the program, and since a balance 

has to be maintained between the different disciplines, this in no way indicated 

lack of merit. Subsequently, a new proposal was made for a very similar 

project, and this led to INTEGRAL, the INTErnational Gamma-Ray Astrophysics 

Laboratory. INTEGRAL is an ESA mission with a large Russian 

participation 14) . It was launched in 2002 with a Russian Proton rocket into 

a high orbit with apogee at 153,000 km well beyond the earth’s radiation belts 

(Figure XI, 12). The two principal instruments (Table XI, 3) for the 

15 keV–10 MeV range are a coded mask imager with 12 arcmin angular resolution 

and a spectrometer with a spectral resolution of 500–1000. These are 

supplemented by a 3–35 keV X-ray instrument and an optical monitor to 

ensure that the highly variable γ-ray sources can be observed over a wide 

range of photon energies. The γ-ray spectrometer is expected to detect a 

number of radioactive elements in the interstellar medium that have been


Figure XI, 12. The γ-ray observatory INTEGRAL. Four instruments are on board 

which are identified in Table XI, 3; the IBIS coded mask in the back with its detector 

below, next to it the two coded masks of JEM-X, and below the detectors just visible 

behind the round tube of SPI. Right next to the JEM-X masks is the OMC. The solar 

panels are 16 m across; the mass of the satellite is 4 tons, with the instruments 

accounting for half of the total. 

synthesized during the last 100 to 1,000,000 years in supernova explosions 

and Wolf-Rayet stars. Early results from INTEGRAL include the resolution 

of the γ-ray emission around the Galactic center into several dozens of sources 

(Figure XI, 13) and the discovery of some very heavily absorbed objects. 

A number of Gamma-Ray Bursts were detected. GRB are brief (msec–sec), 

extremely energetic events, possibly associated with stellar interiors collapsing 

into black holes during supernova events. They frequently leave afterglows 

also at visible wavelengths from which a more precise location may be 

obtained. Since these afterglows are also very short lived, a small telescope 

is needed that can quickly point to the area where the γ-ray source was


Table XI, 3. The instruments on XMM-Newton and INTEGRAL. From left to right 

the columns give the PI country, the energy range in keV, the energy resolution, the 

effective area in cm 2 , the angular resolution in arcminutes and the field of view in 

square degrees; E/∆E, A eff and angular resolution may be energy dependent, in which 

case a representative average has been taken. 

Ang. 

Acronym PI E (keV) E/E A eff Res. FOV 

EPIC UK 1) 0.25–12 100 4000 0.09 0.20 

RGS NL 0.35–2.4 400 100 

OM UK visible/uv 700 0.03 0.06 XMM 

↑ 

↓ 

IBIS I 15–10000 10 6000 12 80 INTEGRAL 2) 

SPI F 20 - 8000 600 500 120 250 

JEM-X Dk 3–35 8 1000 3 23 

OMC Esp visible 20 0.3 20 

1) Initially Italy. 2) The Integral Science Data Centre (CH) was also considered an 

“instrument”. 

Figure XI, 13. INTEGRAL resolved the γ-ray sources near the center of our Galaxy. 

The image covers 30° in longitude. 

detected. Two robotic telescopes have been placed at La Silla, the very fast 

(seconds) 25-cm TAROT 15) (F) for observations in the visible and RME 16) (I) 

with a slightly slower 60-cm telescope which also accesses the near IR. As 

soon as INTEGRAL or the NASA satellite SWIFT, which is more specifically 

optimized for detecting GRBs, observes an event, the corresponding information 

is fed into the worldwide network and these telescopes (and others


elsewhere) automatically move to the right position. Such small telescopes 

can only track the initial very luminous phase, but thereafter the VLT can 

take over. 

A small gamma-ray observatory at higher energies (30 MeV–50 GeV) 

is being developed by the Italian Space Agency for launch in 2006. This 

mission “Astro-rivelatore Gamma a Immagine LEggero” (AGILE) should 

image about 20% of the sky simultaneously at 30 arcminute (at 1 GeV) resolution 

17) . Because of its efficient silicon detectors AGILE will have a mass of 

only 60 kg–30 times smaller than the corresponding instrument (EGRET) 

on the NASA Compton Observatory which was based on more classical spark 

chambers. As a result the cost will also be much lower, with a target cost of 

40 M€. Even if this aim could not be quite realized, the cost reduction would 

remain quite spectacular. Around 2008 AGILE will be followed by the big 

NASA mission GLAST, with 20 times better sensitivity. However, AGILE 

remains very useful, because high energy gamma-ray sources tend to be 

variable and continuity in the observational record is important. Several 

European laboratories are participating in the GLAST instruments. 

In Table XI, 2 a semiquantitative comparison is made between the 

W. European, American, Russian and Japanese X- and γ-ray missions. Of 

course, the description is very incomplete, since the parameters for different 

instruments and energies may be very different. Nevertheless, it is clear that 

a rough equality prevails between the four. It is also clear that for this to 

remain the case, a major effort will be needed in Europe to secure funding 

for at least one future mission. The European X-ray community has survived 

the 13 year gap in ESA X-ray missions thanks to the German and Italian satellites 

and by participation in non-European missions. However, after 2005 

no major project appears to be in the pipeline, either from ESA or nationally, 

and so the future of an independent European X-ray astronomy is contingent 

on the early realization of XEUS. 

Ultrahigh Energy Gamma-Rays 

The GLAST mission will detect γ-rays up to about 300 GeV. However, 

even from the stronger sources few photons will be detected. At such energies 

the fluxes are so small that affordable detectors have inadequate collecting 

areas to obtain meaningful statistics. Since the spectra are very steep, at still 

higher energies no detections can be expected. But the most energetic photons 

are particularly interesting since they convey information about the extreme 

events in the Universe. 

Fortunately, other techniques are available to detect such high energy 

γ-rays. When such a γ-ray photon hits the earth’s atmosphere, it initiates a 

shower of electrons and positrons. Since these are highly relativistic, they will 

emit Cerenkov radiation at visible wavelengths in the form of nanosecond


duration flashes. These may be observed by large telescopes of very modest 

optical quality and, therefore, of modest cost. The larger the telescopes, the 

lower the energy that still can be detected. In practice, such telescopes are 

made of a large number of glass segments mounted in a rather simple metal 

frame. 

Following the first 10-m Whipple telescope in Arizona, a number of 

experiments have been made to utilize the large collecting areas of solar 

power plants. These included CELESTE, at a defunct solar plant in the 

French Pyrenées with 2000 m 2 collecting area, GRAAL, a German-Spanish 

experiment, and STACEE in the US. Because of their large areas, CELESTE 

and STACEE were able to detect photons with energies as low as 50 GeV. 

The solar plants have large collecting areas, but they are far from optimized 

for suppressing the strong background from cosmic-rays and to obtain 

precise positions. This is best achieved by stereoscopic observations with 

several dedicated telescopes. A first such array, HEGRA, was built by the Max- 

Planck-Institut für Kernphysik in Heidelberg and placed at La Palma. It 

consisted of six telescopes with the rather small area of 8.5 m 2 each. This 

cooperative venture of D, ESP, Armenia was in operation from 1997–2002. 

Other relatively small arrays were built by France, the UK and others. 

The first source of TeV γ-rays to be detected was the Crab Nebula. It 

is a strong source of visible radiation and of X-rays. Both are synchrotron 

radiation due to energetic electrons gyrating in the nebular magnetic field. 

So we gain information on the combination of these, but not on each separately. 

The magnetic field could be weak and then there would have to be 

many electrons to produce the observed radiation, or it could be strong and 

fewer electrons would be needed. Some of the synchrotron radiation may 

scatter against the energetic electrons, and the resulting Compton radiation 

would have energies in the GeV and TeV range. The observation of these high 

energy γ-rays allows the number of electrons to be determined, and we then 

can also determine the strength of the magnetic field. 

A few very active galactic nuclei (AGN) have also been detected, with 

photon energies as high as 20 TeV, probably also due to the Compton effect. 

At such high energies these photons may be destroyed by scattering against 

the photons of the Cosmic Microwave Background. Some evidence has been 

found that this depletes the spectrum at the high energy end. If this were 

not the case, these events could not originate from photons, but have another 

unknown origin. 

Because of the many ramifications of the detection of high energy 

γ-rays, new larger telescopes and telescope arrays have been built or are being 

constructed. The four most important ones are listed in Table XI, 4 18) . 

The stereoscopic observations of HESS have particularly good angular 

resolution, while MAGIC (Figure VI, 2) is able to observe γ-rays down to 

perhaps 20 GeV because of its large collecting area. The costs are still very 

manageable. The 17-m MAGIC telescope is said to have cost about 4.5 M€,


Table XI, 4. The four principal instruments for detecting TeV γ-rays. Several of these 

instruments may be further expanded in the future. 

Name Size Year Participants Hemisphere 

HESS 4 × 107 m 2 2004 D, F, UK ... S 

MAGIC 1 × 234 m 2 2003 D + 9 others N 

CANGAROO III 4 × 57 m 2 2003 J, Australia S 

VERITAS 4 × 100 m 2 2006 US, Ei, UK N 

while the complete future VERITAS project of seven 12-m telescopes has been 

budgeted at 35 MUS$ (2000). It has been delayed by the usual ecolo-religious 

site problems in the US, and will first be built with four telescopes. A second 

MAGIC is also likely to be implemented, and other telescopes may well 

follow in the various projects. So the first half dozen sources detected with 

the instruments of the first generation should be joined by many others 

during the coming few years. At present, there are still important disagreements 

between observations of some sources by different instruments. While 

variability plays a role in this, it also shows that it is not a superfluous 

luxury to have two main instruments in each hemisphere. With positional 

accuracies of typically ten arcminutes or less, reliable identifications with 

known visible objects should be obtainable for many sources.

XII. 

European Space Missions: The Solar System 

…that there is at long intervals a variation in the course 

of the heavenly bodies and a consequent widespread 

destruction by fire of things on the earth. 

Plato 1) 

The solar system consists of the Sun, the planets and their satellites, 

the asteroids – small rocky bodies and the icy bodies mainly in the cold outer 

reaches. The Sun and the heliosphere, the gas, magnetic fields and energetic 

particles flowing outwards through interplanetary space will be discussed in 

chapter XIII. 

The terrestrial planets (or inner planets) Mercury, Venus, Earth and 

Mars are solid bodies, with in the case of Earth and Venus substantial atmospheres. 

Their masses range from 0.82 earth’s masses for Venus to 0.11 and 

0.06 for Mars and Mercury respectively. Surface gravities in the same order 

amount to 0.88, 0.38, 0.37 times that on earth. The outer planets Jupiter, 

Saturn, Uranus and Neptune are much more massive (318, 95, 15 and 

17 earth’s masses respectively) and are largely gaseous though they should 

have rocky cores. The Moon has a mass 81 times smaller than Earth. Other 

satellites with a comparable mass are the four Galilean moons of Jupiter and 

Saturn’s satellite Titan. Numerous more negligible satellites exist. The four 

inner planets have distances of 0.39, 0.72, 1.00 and 1.52 AU (astronomical 

units), while Jupiter and Saturn are at 5.20 respectively 9.54 AU. The asteroids 

are found mainly between Mars and Jupiter, but some come close to 

Earth and on rare occasions collide with it. The most massive asteroid is Ceres 

with a mass some 70 times smaller than the Moon and the next one is 

already a factor of four less than that. 

The solar system was formed by the coalescence of many smaller 

“planetesimals” that had originated in contracting dense clouds of interstellar 

gas and dust. At the same time the Sun was beginning to radiate.


At small distances the volatile parts of the planetesimals evaporated and the 

rocky planets from Mercury to Mars ultimately resulted. Further out the more 

massive planets Jupiter to Neptune formed, which were able to also retain 

much of the gaseous matter. Far out the Sun’s radiation was too weak to 

evaporate the icy aggregates, and after the planets had formed their numbers 

were too small and their motions too fast to form larger units by sticking 

together. Thus, many of them have stayed unchanged in the outer reaches 

of the solar system. 

Comets 

Gravitational effects of the planets or of passing stars occasionally 

perturb the orbits of the remaining planetesimals and may place them on 

trajectories that pass closer to the Sun. Rapid evaporation follows. The solar 

light will be reflected by the escaping dust particles or excite the gas that 

subsequently reradiates the energy. The solar wind and radiation pressure 

interact with this matter and stretch it into a long tail in the antisolar 

direction: a comet is born. Analysis of cometary tails by earth bound telescopes 

gives some information about the composition of the comet, but only 

with spacecraft which approach much more closely are we able to see the 

nucleus in a less processed state. 

The first European venture into the wider solar system was the Giotto 

mission to comet Halley, which comes close to the Sun once every 76 years. 

Launched in 1985, the Giotto spacecraft arrived close to the comet in the 

following year passing its nucleus at a distance of only 596 km. As a result, 

for the first time detailed images of a cometary nucleus were obtained 

(Figure XII, 1) 2) . The surface turned out to be surprisingly black with some 

bright spots. Jets of escaping dust and gas emerged from some localized areas 

facing the Sun, but most of the surface was inactive. Prior to Giotto it was 

thought that a comet was a “dirty snowball” composed of ices with a relatively 

small amount of dust. Actually, there was found to be as much dust 

as ice, and the basic structure of the nucleus may well be determined by fluffy 

dust aggregates which originally condensed in interstellar space. The evaporating 

ice drags along some of the dust. Water vapor was found to be the 

dominant constituent of the gas, but CO, CO 2, CH 3OH, NH 3 (ammonia) and 

minor amounts of other substances are also observed. These findings are 

important for studies on the formation of the solar system which may have 

resulted in part from the aggregation of many planetesimals of which the 

cometary nuclei are the last survivors. Several other missions passed the 

comet at much larger distances: two USSR Vega spacecraft at 10,000 km and 

two Japanese spacecraft at 100,000 and 8,000,000 km respectively. The US 

International Comet Explorer (formerly ISEE-3) observed the comet from 

30 million km after having passed by the Giacobini Zinner comet at 7800 km

European Space Missions: The Solar System 205 

Figure XII, 1. The Giotto image of the nucleus of comet Halley at resolutions ranging 

from 100 m to 800 m. The scale is 2.2 km/cm. The nucleus is very dark except in 

places where the Sun creates hot spots from where jets of dust and gas are ejected 

in the solar direction. Ultimately, radiation pressure and the solar wind will deflect 

this matter to form a tail in the antisolar direction. 

from the nucleus. So only Giotto had the resolution needed to study a 

cometary nucleus. Following its passage by comet Halley, the spacecraft was 

directed towards comet Grigg-Skjellerup where it arrived four years later. The 

imaging camera had been destroyed by the dust particles from Halley, but 

useful data were obtained on the interaction of Grigg-Skjellerup with the solar 

wind. 

While the results of Giotto clarified some aspects of cometary nuclei, 

much remains unclear because the observations were still obtained at quite 

a distance. To make further progress in situ study of the nucleus would be 

needed. In 1984 the Horizon 2000 program already included a major mission 

to do this and to perhaps return a sample to earth. From 1986 it was studied 

jointly as a collaborative project with NASA, but by the end of 1991 it became 

clear that the implementation schedules of the two agencies did not match


and NASA withdrew. It then appeared that the sample return would be 

beyond ESA’s financial means. The in situ part of the mission remained and 

became “Rosetta” consisting of an orbiter and two landers. One of these would 

be provided by a CNES-NASA collaboration. However, in 1996 NASA also 

pulled out of the lander for “budgetary and programmatic reasons” 3) . The two 

landers then became one all European lander. The orbiter will first map the 

nucleus from distances of the order of 100 km and subsequently descend to 

a few km for detailed studies. Because of the low gravity orbital velocities 

are of the order of only one m/s, which makes the orbital manœuvers quite 

delicate. After selection of a suitable location the lander will be released and 

placed on the surface. The orbiter has instruments to make multicolor maps, 

more detailed spectroscopy of the surface, to study the composition (including 

some isotope ratios) of the gas and dust escaping from the nucleus and to 

measure magnetic fields, etc. With the lander detailed imaging and analysis 

will be made of the surface materials, while also some subsurface measurements 

and deeper soundings will be performed. 

Initally Rosetta 4) was scheduled for launch in January 2003 with the 

target being comet Wirtanen. However, the failure of a modified Ariane 5 

rocket in December 2002 made it seem imprudent to go ahead before the 

circumstances of this event had been clarified. Since the spacecraft would 

need gravity assists from several planets, the original orbit could no longer 

be implemented. Finally, it was decided to choose comet Churyumov- 

Gerasimenko which, in fact, had earlier been the preferred target, albeit for 

a mission one orbital period earlier. Rosetta was successfully launched in 

February 2004. This comet is particularly attractive since it has spent only 

a small number of orbits close to the Sun (until 1840 perihelion was at 4 AU ; 

encounters with Jupiter reduced this to 1.3 AU), and so it may be in a relatively 

pristine state, less changed from the days when the solar system formed 

than the more typical short period comets. Observations with HST and VLT 

have been made. The nucleus has a size of 3 × 5 km and a rotation period 

of 12 hours. So it is three times larger than comet Wirtanen. As a result, the 

gravity is likely to be stronger which necessitated changes in the landing gear. 

The rendez-vous of Rosetta with the comet is foreseen for May 2014, when 

it is still at four astronomical units from the Sun. The orbiter will continue 

to orbit the nucleus as it becomes more active due to its approach towards 

the Sun, while the lander should be placed on its surface in November 2014 

(Figure XII, 2). The mission will come to an end in December 2015, four 

months after perihelion passage. 

From mission conception to conclusion about 30 years will have 

elapsed. It will have taken some 16 years between the beginning of instrument 

construction and first data. Such long times cause difficulties: some of the 

investigators will have retired or developed other interests, while it is not easy 

in a university environment to engage doctoral students for such a long 

range project.


Figure XII, 2. Artist’s impression of the Rosetta lander on comet Churyumov- 

Gerasimenko. The surface is unlikely to be very smooth, and so the actual landing is 

a delicate, uncertain operation; it takes nearly an hour between the time the lander 

is observed and the arrival of a follow-up command from earth. 

Cometary landers should be prepared for surprises. Comet Schwassmann- 

Wachmann 3 had been considered as a back-up in case there were problems 

with comet Wirtanen. A few years later during perihelion passage it broke 

up into three pieces. Even more spectacular was the demise of comet 

LINEAR 5) . It was discovered in late September 1999. Its orbit showed that 

it came from the Oort cloud of comets in the outermost reaches of the solar 

system. On passing perihelion ten months later it broke up completely. An 

image taken with the VLT 11 days later shows 16 fragments (Figure XII, 3) 

which a week later had become invisible. The Rosetta comet which has been 

much longer relatively near to the Sun is very unlikely to undergo such an 

extreme event. However, the splitting of cometary nuclei is not exceptional. 

Cometary projects elsewhere include in the US the “Stardust” mission 

(1999) which is to collect dust from the coma of comet Wild-2 and bring it 

back to earth in 2005, and in 2001 flybys of two other comets. The CONTOUR


Figure XII, 3. The breakup of comet LINEAR in 2000 imaged by the ESO VLT with 

FORS I. The 16 fragements apparently originated some 11 days prior to this image 

and had vanished from view a week later. 

mission aimed at flybys of three comets failed when the spacecraft was 

destroyed. In 2005 “Deep Impact” will send an impactor to the nucleus of 

comet Temple 1 and observe the result. 

The Rosetta spacecraft will pass by two asteroids and observe their 

surface. Also some US missions are aiming to observe asteroids. 

Exploration of Planets and Satellites 

A major NASA mission (with ESA and Italy participating) to Saturn, 

“Cassini”, was launched in 1997 6) . Attached to it was the ESA provided 

“Huygens” lander which late November 2004 arrived at Titan and two months 

later descended through the atmosphere. Titan is by far the largest satellite 

of Saturn with a mass twice that of the moon. From what is known the atmosphere 

of Titan is mainly composed of nitrogen with some methane and 

hydrogen at a surface pressure at about 1.5 atmospheres. These characteristics 

are thought to be not very different from those on earth around 4000 millions 

years ago before life had oxygenized the atmosphere. Nevertheless, the similarity 

is limited in that the temperature is much lower on Titan. There is some 

evidence that at the surface there are some lakes or oceans which could be 

composed of liquid methane. In about 2 hours Huygens traversed the Titan 

atmosphere from 100 km down to the surface, while being slowed down by


a parachute. During this time, its six instruments measured temperature, 

density, composition, winds and aerosols in the atmosphere, studied clouds 

and imaged the surface. The spacecraft survived the descent and conditions 

at the landing spot could be determined. Because the light travel time between 

earth and Titan is more than 70 minutes, the whole Huygens descent had to 

be preprogrammed. The instruments on Huygens are listed in Table XII, 1. 

Of the 13 instruments on the Saturn orbiter two were European – a magnetometer 

(UK) and a dust analyzer (D). Early results from Huygens include 

the discovery of river-like surface features and some impact craters. The 

atmosphere contains nitrogen and methane. The lander appears to have 

penetrated one or two decimeters into the soil and its heat has evaporated 

some of the liquid methane in the surface layer. 

The first independent European planetary mission is “Mars Express” 

launched in 2003. While in the case of Huygens some of the conditions to be 

encountered were uncertain, much of what “Mars Express” would experience 

was well known. Numerous spacecraft have been sent to Mars: 18 by the 

Table XII, 1. Instruments on current ESA planetary missions. 

Mars Express 

ASPERA Energetic Neutral Atoms (S) 

HSRC High-Resolution Stereo Colour Imager (D) 

MARS Radio Science Experiment (D) 

MARSIS Subsurface – Sounding Radar (I, US) 

OMEGA IR Mineralogical Mapping Spectrometer (F) 

PFS Atmospheric High Resolution Spectrometer (I) 

SPICAM uv/IR Atmospheric Spectrometer (F) 

Venus Express 

ASPERA Energetic Neutral Atoms (S, F) 

MAG Magnetometer (A) 

PFS Atmospheric High Resolution Spectrometer (I) 

SPICAV uv/IR Atmospheric Spectrometer for Occultations (F, B, Rus) 

VERA Radio Occultation Instrument (D) 

VIRTIS uv – IR Imaging and Spectrometer (F, I) 

VMC Wide Angle Monitoring Camera (D) 

Huygens 

ACP Aerosol Collector (F) 

DISR Imager/Spectral Radiometer (US) 

DWE Wind Profile Measurement (D) 

GCMS Atmospheric Composition (US) 

HASI Atmospheric Structure (F) 

SSP Surface Science Package (UK)


USSR/Russia with modest success, 16 by the US with four failures, and one each 

by Europe and Japan, the latter also a failure. While earlier missions have given 

a general picture of the nature of the Martian surface and atmosphere, many of 

the essential questions remain unanswered. The main impression is that of an 

utterly dry planet, variably covered with impact craters. Since impacts were more 

frequent in the past, the density of such craters allows rough chronologies for 

different areas to be established. The most notable dichotomy with the northern 

hemisphere several km lower than the southern is not understood. The highly 

cratered terrain in the south must be very old. Elsewhere plains alternate with 

mountains and a few huge volcanoes. Olympus Mons (Figure XII, 4) rises 24 km 

above its surroundings, making it the highest volcano in the solar system. At its 

base this shield volcano measures more than 500 km in diameter. The relatively 

low density of impact craters on its surface suggests that volcanic activity has 

continued until relatively recently, if not until today. Some of the plains are so 

smooth that they have been taken to be the floors of ancient oceans or lakes. 

Elsewhere very eroded mesas are found (Figure XII, 5). 

Figure XII, 4. Olympus Mons as imaged by the Mars Express stereoscopic imager. 

The huge caldera of 60 × 90 km is the result of an eruption in the highest volcano 

in the Solar System. The volcano rises 24 km above its surroundings – three times 

as much as Mauna Kea above the floor of the Pacific. Some impact craters from a 

later date are also visible. There is evidence for more modest volcanism in recent 

times. The scale is 1 cm/10 km.


Figure XII, 5. Mesas on Mars. Erosion seems to have removed much of the surroundings 

of the 3 km high plateau area. The scale is 1 cm/2.5 km. 

Fluvial morphologies in hilly terrain have suggested to most investigators 

that water was once flowing there above or possibly below the 

surface. At present there is very little water vapor in the tenuous atmosphere, 

which has a pressure of 6 millibar, only 0.6% of that on earth. Also 

some water ice is present in the polar caps which sublimates and freezes 

according to the seasons. The fundamental question about Mars is: where 

is the water now that appears to have been there in the distant past? Either 

it has gone underground to form a layer of permafrost or it has escaped 

into space. The issue is of vital importance if future manned missions are 

planned or if terraforming, the transformation of Mars into a more hospitable 

planet, is considered. Without water Mars will be forever dead. The 

question of water is also directly related to the question of life on the 

planet. Unfortunately, the issues of water and life are of such passionate 

interest to scientists, their funding agencies and the general public, that 

the standards of proof appear to have been relaxed sometimes in the rush 

to the next press release. 

Even though the atmosphere of Mars is very tenuous, like Earth it 

presents a global circulation. Its composition contains clues about the planet’s 

past, and some trace gases may provide evidence about current volcanism 

or biological processes. Planet wide sandstorms which may alter surface 

features and other meteorological phenomena are of much interest to the 

comparative climatologist. The climate history of Mars has been very complex 

because of the chaotic character of its orbital characteristics. Even over the 

last 10 million years its obliquity (the angle between the equatorial and 

ecliptic planes) has changed over the range 15–45°, while the eccentricity of


its orbit has varied between 0 and 0.12. The much smaller variations of the 

orbit of the earth have been responsible for the modulation of the climate 

with glacial and interglacial periods. So much of the ice in the surface layers 

of Mars may have moved between different areas 7) . 

A first proposal for a European Mars mission, “Kepler”, was made to 

ESA in 1980. It was to be a relatively simple orbiter. In 1985 it was concluded 

that it would be advantageous to link it with a NASA mission that later 

became “Mars Observer”. The two parts of Mars Dual Orbiter would be independent, 

but coordination would increase the scientific value of both. 

However, in the meantime Cassini-Huygens had also appeared on the scene, 

which had been selected as M-1 in the new Horizon 2000 program. Mars 

Observer was actually launched in 1992, but failed. In 1989 a more ambitious 

Mars mission was proposed. By 1992 a phase A study had been 

completed by ESA of “Mars Net”, to be conducted jointly with NASA. It 

consisted of 3 landers. In parallel NASA had studied the Mars Environmental 

SURvey mission, MESUR, for 18 small landers. As Fred W. Taylor 

has written 8) : “One mission priced itself out of the market, while at the same 

time making the affordable mission look inadequate.” 

Subsequently, a somewhat changed version “Intermarsnet” was studied 

again, with the aim of a joint mission. It lost out in the ESA M-3 selection 

where Planck won. Intermarsnet would have consisted of three NASA landers 

and a European orbiter all launched together with an Ariane-5 rocket. At the 

time it seemed to me that NASA would have had the more interesting part 

of the deal. 

In the meantime European Mars enthusiasts participated in building 

instruments for the Russian Mars 96 mission which failed. After its failure 

into the Pacific, spares of the instruments were still available. It would be a 

waste not to use these. Combined with the strong emphasis in Horizon 

2000 Plus on the scientific value of Mars exploration, this led to Mars 

Express. It was inserted into the program without the usual lengthy selection 

procedures. It was approved at 150 M€, not including the instruments. The 

UK added a lander to the instrument package. Substantial cost overruns, 

owing to rosy predictions of money flowing in from the general public, finally 

forced ESA to put another 16 M€ into the “Beagle-2” lander with subsequent 

arguments about the status of this “loan”. The story is an interesting appendix 

to the perpetual complaints of the UK delegation during the nineties about 

the perceived inefficiency of the ESA science program. Of course, it is also 

true that they were not the only ones to expect Europe to pay for their own 

programs. 

Mars Express consisted of an orbiter and a small lander 9) . The orbiter 

has a highly elliptical nearly polar orbit with perimars at 250 km altitude. 

Aerobraking made the orbit gradually more circular. A stereo imager is 

mapping the surface with 12-m resolution. Small areas are even imaged with 

a resolution of 2–3 m. Spectacular Stereoscopie images have already been


obtained (Figures XII, 4, 5). With such high resolutions even small impact 

craters may be found which is helpful in dating different areas. The results 

document volcanic activity in the area of Olympus Mons as recently as a few 

million years ago 10) . Exciting evidence has been found for a frozen sea near 

the equator which would be as large as the North Sea 11) . However, on the 

other side of the Atlantic it is believed to be a lava flow 12) . The mapping IR 

spectrometer OMEGA for mineralogical studies with resolution of 100 m has 

made maps of the distribution of water ice and CO 2 ice in the south polar 

cap. Widespread deposits of sedimentary sulfates, like gypsum, have been 

found. At the time of their formation water must have been present 13) . Spectrometers 

have analyzed the distribution of various gases and confirmed the 

presence of methane. Since methane would be destroyed relatively rapidly 

in the Martian atmosphere, a continuing production possibly indicates 

volcanic or biological processes. However, abiogenic pathways for methane 

production also exist. The interaction of the solar wind with the Martian 

atmosphere is being studied by an energetic neutral particle analyzer, while 

the surface roughness is studied by the reflection of radio waves. Of particular 

interest is the subsurface sounding radar which should determine 

mantle structure and water content down to the level where permafrost 

occurs. The unfolding of the radar antenna is a delicate matter and has been 

postponed to late in the mission, so as not to endanger the functioning of 

the other instruments. The instruments on Mars Express are listed in 

Table XII, 1. 

The lander Beagle-2, provided by the UK, was to study the landing site 

geologically and chemically, act as a weather station and search for evidence 

of life – present or past. Of particular importance would have been its ability 

to sample the subsurface soil which has not been modified by solar radiation 

and to determine the isotope ratio 12 C to 13 C which on earth is a sensitive 

indicator of biological processes. X- and γ-ray spectrometers would have 

allowed mineralogical studies and the determination of ages of the rocks 

found. Unfortunately, the lander was never heard of again after it had separated 

from the orbiter. Its remarkably low cost may have been too extreme. 

Nevertheless, the technological experience in miniaturization remains 

valuable for the future. For example, the whole X-ray spectrometer weighed 

no more than 300 grams. 

In parallel with Mars Express currently two NASA orbiters and two 

rovers are active on Mars. The surface is being mapped with resolutions 

comparable to those of Mars Express. A γ-ray spectrometer studies water ice 

buried near the polar caps. In 2005 an additional orbiter will be launched 

to map numerous places at sub-meter resolution and to look for evidence for 

water or ice; like Mars Express it will also carry a subsurface sounding radar. 

Other missions are planned by NASA every two years, with a sample return 

mission during the next decade.


The future of ESA’s Mars missions is contingent on the funding for 

the Aurora program (chapter X). The program foresees an Exo Mars mission 

in 2011 with an orbiter and a rover equipped with a drill which will analyze 

the Martian soil and look for evidence of life. In addition, various technologies 

required for future exploration will be tested. A later mission in the 

Aurora program should include the return of a 500 gram sample for analysis 

on earth. At the moment the main contributors to Aurora are Italy and the 

UK. F, B, ESP, NL, A, P, S, CH and Canada also participate. After an initial 

refusal Germany now also has joined. The total envelope of about 42 M€ 

allows some industrial studies to be made. A substantially increased envelope 

will have to be decided at the next Ministerial Council meeting at the end of 

2005, if the 2011 mission is not to be delayed. 

The relatively cheap spacecraft for Mars Express would be even cheaper 

if a copy were made. This has led ESA to plan a second mission, Venus 

Express, for launch at the end of 2005. Though some 23 (6 failures) missions 

to Venus have been launched by the USSR and 6 by NASA, basic questions 

about the planet remain unanswered. From the absence of old impact craters 

revealed by radar mapping and the uniform distribution of the younger ones, 

it has been concluded that the surface of the whole planet has been changed 

in a relatively short period some 500 million years ago. Perhaps the heat flow 

from the interior was higher than could be transported outwards through the 

very dry crust. This may have resulted in a global melting event. Other possibilities 

have also been considered. The CO 2 rich atmosphere with its clouds 

of sulphuric acid accounts for the enormous greenhouse effect with the 

temperature at the surface above 300 °C. Trace gases about which not much 

is known must also contribute. A high altitude haze hides the surface from 

view, though some IR windows may allow direct observation of the surface. 

The nature of the haze and the chemical processes in the atmosphere remain 

to be elucidated, with volcanism undoubtedly playing a major role. Zonal 

winds at speeds of several hundreds of km/hour have remained mysterious. 

From the decision to build Venus Express to the launch date late in 

2005, only three years will have elapsed. A much longer delay would have 

reduced the benefits of the commonality with the Mars Express spacecraft. 

Insufficient time and funding were available to build a complete set of new 

instruments. So most are derived from flight spares of instruments on Rosetta 

and on Mars Express. Included are a sounding radar for (sub)surface and 

ionospheric studies, uv–IR imagers and spectrographs, instruments for 

studying the atmosphere by observing occultations of the Sun, bright stars 

and radio sources, and plasma and particle analyzers for in situ observations. 

Instruments (listed in Table XII, 1) and spacecraft had to be adapted to the 

rigorous conditions around the planet. It is interesting that Venus Express 

could be decided and realized so quickly. Dedicated Venus missions had 

figured in Horizon 2000 with one proposal and in Horizon 2000 Plus with 

none at all, except for a remark that an international Venus mission could


be of interest. Perhaps the history of Mars- and Venus Express shows that 

a more rapid turnover in the planning cycles of ESA would be advantageous. 

The SMART missions (Small Missions for Advanced Research in 

Technology) have been introduced into the ESA science program in the midnineties, 

as technology demonstrators. Very large missions could hardly take 

the risk to utilize untested technology. A cost cap of some 40 M€ was 

assumed, but SMART-1 actually cost 86 M€. While technology was the 

primary driver, some small scientific instruments could also be included, 

adding to the opportunities for a scientific community that was much 

concerned about the long waiting times between the larger missions. 

SMART-1, a lunar mission, was designed to test solar electrical 

propulsion, in which the energy collected by solar cells is used to create a jet 

of high speed ions 14) . So a small mass of a suitable material (in this case Xenon) 

produces a much larger thrust than would be possible with conventional 

rocket fuels. In principle, the same technology could be used when the power 

is derived from nuclear energy, which would make it possible to move into 

the farther reaches of the solar system where the solar energy flux is too small. 

However, at least in Europe, this could be expected to raise political problems. 

SMART-1 was launched in September 2003 into a Geostationary 

Transfer Orbit as a piggyback passenger on an Ariane 5 launch. Subsequently, 

its solar engine slowly let it spiral outwards, until it transferred into 

a lunar orbit. With the engine now thrusting in the opposite direction, it 

spiraled inwards towards an elliptical orbit with perilune at around 500 km 

above the surface. Because of the modest power (2 kW) available from 10 m 2 

of solar cells, the trip took about 15 months. 

On board of the spacecraft are a camera for imaging in four wavelength 

bands, a spectrometer for near IR mineralogical studies, and an X-ray spectrometer 

which will allow the elemental composition of the surface to be 

mapped by observing fluorescent X-rays. The three instruments have been 

successfully miniaturized with a total weight of less than 7 kg and a power 

consumption of only 25 Watt. Other instruments on board serve to monitor 

the propulsion system. 

Lunar missions have become quite popular again. Japan is planning 

a substantial orbiter for 2006, while India, China, and NASA intend to launch 

orbiters soon thereafter. ESA may participate in the Indian mission. 

The final element in the ESA planning for planetary research is the 

Mercury mission “BepiColombo”, which now is a cooperative venture with 

the Japanese Space Agency, JAXA. It is composed of two independent spacecraft 

to be launched by Soyuz-Fregat launchers in the 2010–2012 time frame. 

The direct path to Mercury would not be very long, but demanding on the 

launcher. So the gravitational assists of two flybys by Venus and two by 

Mercury will be used, supplemented by a solar electrical propulsion system. 

This trajectory will take some three years with the spacecraft arriving at 

Mercury not far from the time that Rosetta reaches its destination.


The ESA component of the mission, the planetary orbiter, will observe 

the surface of the planet from the height of 400 km and more. The JAXA 

Magnetospheric Orbiter will be a spinning satellite in an orbit with an apo- 

Mercury of some six planetary radii. 

The interest of Mercury to the planetary community is twofold. The 

mean density of the planet is 5.4 g/cm 3 , which indicates that it must have 

a large iron-nickel core with a radius 3/4 that of the planet. The planetary 

or cometary bodies in the solar system range from H 2O icy and dusty 

bodies far from the sun through mainly rocky bodies at Mars distances to 

the end of the sequence at Mercury, presumably because closer to the sun 

much of the dust and planetesimals have been vaporized and swept away, 

leaving only the most refractory elements to form the planet. The other 

aspect of Mercury is its magnetic field and associated magnetosphere. The 

origin of the field is mysterious, since it hardly seems probable that the core 

is still liquid, because such a small planet cools down rather fast. The 

magnetosphere should be strongly affected by the solar wind, which should 

be some ten times stronger than on the Earth. Moreover, the magnetospheric 

structure is different, because in contrast to the earth, Mercury is 

devoid of an ionosphere and an electrically conducting surface. 

The instruments for the Mercury mission have not yet been selected. 

Certainly there will be cameras to image the heavily cratered surface and 

determine its mineralogical composition, instruments to determine the 

elemental composition from fluorescent X-rays, magnetometers and analyzers 

of the plasma and of energetic particles in the magnetosphere. The detailed 

orbits of the two spacecraft should give information on the internal structure 

of the planet. 

Much interest was attached to the mission because 60% of the surface 

had never been observed and because of the mystery of the magnetic field. 

However, NASA has launched its “Messenger” mission in 2004 which should 

arrive at Mercury in 2009. Even though Messenger is perhaps a somewhat 

more modest spacecraft, the risk is that much of the cream will have been 

skimmed off by the time BepiColombo will be launched. It is not clear that 

this has led to a drastic review of ESA’s planning. In the meantime the 

mission has been placed on hold because of cost overruns. 

Surveying the overall program of planetary/cometary exploration, there 

is much that is very positive. The cometary studies are worthwhile scientifically, 

but the decade between launch and mission completion for Rosetta is 

very long for enthusiasm to be maintained. Mars Express and Huygens have 

been highly successful and Venus Express looks quite promising, but all risk 

to be one-shot-affairs without follow up and continuity. NASA with its much 

larger budget could afford a very varied program. One may wonder if ESA, 

with its more modest means, would have been better off by putting all its 

eggs in one basket in concentrating on one or two planets in a continuing 

program of studies that also could lead to a more active participation of a


larger community of geologists, geophysicists, climatologists and even biologists. 

The total cost of the ESA planetary/cometary program 1990–2010 is 

of the order of 2300 M€ , including the cost of instruments funded by the 

member countries. This is equal to ten Mars-Express like missions. So one 

could have had a sustained autonomous European program of every two years 

a small mission to Mars or Venus or, more reasonably, every four to six years 

a larger one. European laboratories then could have used part of their national 

funding to participate in missions by others to comets and to other planets. 

The final science mix might not be so different, but Europe would have at 

least one planetary program, fully autonomous and with good continuity. In 

fact, Mars might have become for a significant part terra europea!

XIII. 

European Space Missions: 

The Sun and the Heliosphere; 

Ground based Solar Telescopes 

Deus Sol Invictus 

The heat generated by nuclear reactions in the solar interior is 

transported outwards by radiative leakage until in the outer layers convective 

motions are induced. The dynamo action resulting from convection combined 

with rotation generates magnetic fields. The interaction of the gas flows and 

the magnetic fields leads to much complexity. In some places the magnetic 

forces dominate, in others the flow drags the fields along. A variety of hydromagnetic 

waves are generated, while in places oppositely directed magnetic 

fields meet and annihilate each other. Such processes heat the gas and/or 

accelerate charged particles to high energies. The result is that the outer 

envelope of the Sun, the tenuous corona, is at a temperature of a million 

degrees, while the photosphere – the level where most of the light is emitted – 

is much cooler at 6000 K. The precise mechanism of the heating of the corona 

is still uncertain. It is one of the subjects of active solar research. 

At the high temperature of the corona the solar gravity is insufficient 

to contain the gas which begins to stream outwards: the “solar wind”. Thus, 

the solar system is pervaded by outward moving gas with velocities of hundreds 

of km/sec and in this stream magnetic fields and energetic particles are 

dragged along. When major energetic events like solar flares or Coronal Mass 

Ejections occur, the solar wind may be enhanced. Ultimately the wind will hit 

the earth’s magnetosphere, and especially during such events the earth’s 

magnetic field is perturbed allowing energetic particles to reach lower altitudes. 

At 100 km above the surface they may excite atoms and molecules in the 

atmosphere, giving rise to the aurorae – the northern (and southern) lights. 

Less artistically they may also affect telecommunications and electricity lines.


Early space research was very much involved with the study of the 

earth’s magnetosphere and the local solar wind. Even with small satellites 

significant results could be obtained. Certainly ESA’s origins were in magnetospheric 

science. By 1980 some nine European satellites had been launched 

to study the magnetosphere and the solar wind near the earth (the US total 

was closer to 50). In addition, national European space agencies had launched 

several magnetospheric satellites or placed instruments on US satellites. 

Germany had gone far into the solar wind to 0.3 AU with the two Helios 

probes which measured temperatures and particle distributions until the 

beginning of 1980, while Swiss instruments on several Apollo flights had 

measured its composition. 

When the solar wind first interacts with the magnetosphere, a 

“bowshock” is formed, followed by the “magnetopause”, the boundary of the 

earth’s magnetic field (Figure XIII, 1). Here we shall only further consider the 

domain down to the magnetopause, leaving the rest of the magenetosphere 

Figure XIII, 1. The geometry of the upper magnetosphere. The solar wind comes from 

the left and at the bowshock interacts with the magnetic fields in the wind that pile 

up against the magnetopause where the earth’s field begins. On the other side of the 

earth in the tail the situation is more complex because oppositely directed fields are 

separated by only a thin neutral sheet. Sometimes magnetic flux of the solar wind is 

transferred and reconnected to the field of the earth. Also in the solar wind itself there 

is a neutral layer separating field lines from the solar poles. The four Cluster spacecraft 

following the red orbit can study these regions, with additional data coming from 

the two Double Star satellites an ESA collaboration with China.

European Space Missions: The Sun and the Heliosphere 221 

to the geophysicists. It is, of course, true that these separations are not 

always very precise, with particles and waves traversing the boundaries. The 

ESA satellite ISEE-2 would continue well into the eighties (1978–1987). 

NASA launched ISEE-1 at the same time and later ISEE-3. The first two 

International Sun-Earth Explorers were placed close to each other to study 

the structures near the solar wind interface. Both the bowshock and the 

magnetopause were found to be unexpectedly thin and variable, moving and 

oscillating with speeds up to 100 km/sec. Thereafter followed AMPTE 

(1984–89), a mission with three independent satellites – a US magnetospheric 

one, and one each from Germany and the UK. The latter two penetrated into 

the solar wind. A few clouds of lithium and barium were released and their 

subsequent evolution followed. During the nineties, the German Equator-S 

functioned in the high magnetosphere, but only for a few months, while the 

US launched “WIND” on which also ESA and France had instruments. Its 

apogee was beyond the lunar orbit, and so it could effectively measure the 

undisturbed solar wind. If we add it all up, then the number of earth orbiting 

satellites that reached the magnetopause or beyond during the period 

1961–1979 was 16 for the US, 4 for the USSR and 2 for ESA. During 

1980–1999 there were only 2 for the US, 3 for the USSR/Russia and 2 D, 

1 UK, 1 Japan and a Czech minisatellite, less than half that of the previous 

two decades. In addition, various deep space probes also obtained data on 

the solar wind. Much had been learned about particles, waves and magnetic 

field structures, and on how stormy conditions in the solar wind propagate 

downward with effects even at the earth’s surface. Two fundamental questions 

remained to be answered. The solar wind was observed near the earth 

in the plane of the ecliptic, which is also close to the equatorial plane of the 

Sun. But the corona looks rather different in the polar direction, and so the 

first question was how does the solar wind change with solar latitude? The 

second question related to measurements in the earth’s magnetosphere. 

Since everything there is variable in time and in space, how can we distinguish 

the spatial variations from the temporal ones? While with the two satellites 

ISEE-1, 2 some spatial information had been obtained, the rapidity of 

the variations with time made unambiguous results not easy to obtain. 

This was the origin of ESA’s Cluster project – four independent satellites 

for simultaneous observations of particles, electric and magnetic fields. 

Launched in 2000, the four Cluster II satellites (Figure XIII, 2) are flying in 

formation in the neighborhood of the interface of the magnetosphere and the 

solar wind with mutual distances varying from 200 to 18,000 km. Comparison 

of their measurements allows a very precise analysis of discontinuities 

in the magnetic fields, particle and wave distributions. Cluster I was on the 

maiden flight of Ariane-5 in 1996. While this gave a free launch, unfortunately 

the rocket exploded and destroyed the four spacecraft. Subsequently, 

ESA decided to redo the mission, making use in part of instrument spares 

which had been used for testing or kept as a reserve. Cluster II was launched


Figure XIII, 2. The four Cluster spacecraft. The various booms (some 50 m in length) 

measure electric and magnetic fields. 

in 2000 on two Soyuz rockets. A further expansion of the Cluster program 

results from “Double Star”, a collaboration with China. One satellite in an 

equatorial orbit has been launched with a Long March rocket in December 

2003 and the next one in a polar orbit followed in 2004. Half of the instruments 

on board are European, derived from Cluster, and half are Chinese. 

Both have been very successful and so a further enhancement of the results 

from Cluster may be expected. 

For the moment no future magnetospheric missions are in the ESA 

program. Perhaps, after the results from Cluster and Double Star will have 

been obtained, the scientific priority of the field will be somewhat lower. In 

fact, after the Cluster I disaster, it was said by some that Cluster II should 

be done very quickly, because otherwise much of the magnetospheric 

community would have retired. This seems certainly a remarkable motivation 

for a scientific mission! However, it remains the case that the earth’s 

magnetosphere is an intermediary between the solar wind and the upper 

layers of the atmosphere. As such it would seem important to continue monitoring 

events in the region, which would not necessarily require very large 

investments. Since the US still deploys several magnetospheric satellites and 

since minisatellites for auroral and other studies in this area have been 

within the reach of Sweden and other countries, it is not obvious that there 

is a need for ESA to develop new activities in this domain.


To answer the question about the latitude dependence of the solar wind, 

it was necessary to send a spacecraft to fly over the solar poles. It is not easy 

to do this by a direct launch from earth, but by sending the spacecraft “Ulysses” 

first towards Jupiter and then have Jupiter’s gravity change the orbit in a major 

way, taking it out of the ecliptic, success was achieved. In 1994 for a few 

months Ulysses flew over the solar south pole and a year later the north polar 

region was reached. At this time the Sun was in the quiet phase of the 11 year 

Sun spot cycle, but six years later Ulysses would again reach the polar regions, 

this time at high solar activity. Instruments on board measure magnetic fields, 

the speed and composition of the solar wind, particles and waves of various 

energies, solar X-rays and dust particles. Perhaps the most important discovery 

of Ulysses was that the solar wind is strongly latitude dependent. While near 

the equatorial plane speeds of 400 km/sec are typical, at high latitudes values 

twice as large are found. Also the composition of the gas is different in the two 

cases. The magnitude of the radial magnetic field in the solar wind was found 

to be independent of latitude – contrary to what could be expected from the 

dipole type field at the solar surface. As a result of these findings, much more 

sophisticated models of the heliosphere have been developed with implications 

also for cosmic-ray propagation and the Sun’s effect on the earth’s climate. 

Ulysses had originally been conceived as a two-satellite cooperative mission 

between ESA and NASA. Each would be responsible for one of the two and the 

orbits would be such that they would arrive simultaneously above opposite solar 

poles. A detailed agreement was concluded which unexpectedly and suddenly, 

without any consultation, was cancelled by NASA because of budgetary problems. 

So finally only the ESA satellite was launched, albeit by the NASA shuttle and 

with some US instruments on board. As described by Bonnet and Manno 1) , this 

episode had a very negative effect on ESA-NASA cooperation. 

Further studies of the solar wind are being made by SOHO, the SOlar 

and Heliospheric Observatory, which is a happier ESA-NASA collaborative 

venture. The main purpose of SOHO was the direct observation of the Sun 

in the visible, uv and extreme uv. Most of the instruments take spectra with 

good angular resolution or obtain images in broad or narrow spectral 

domains. Others measure the solar irradiance with high precision or study 

various types of solar oscillations, both in velocity and in irradiance. The solar 

irradiance, its spectral distribution and its relatively slow global variations 

are, of course, essential for the modelling of the earth’s climate. 

The rapid, but miniscule oscillations in irradiance and in velocity over 

the solar surface are evidence of sound waves in the solar interior. Since the 

velocity of sound depends on temperature and more weakly on other parameters, 

the observation of these oscillations gives very detailed information 

on the structure of the solar interior. The oscillations also give information 

about the internal rotation in the Sun. A very large number of oscillation modes 

are superimposed. These waves were first detected by ground based radial 

velocity observations. Long continuous data sets are needed to disentangle the


different wave frequencies. Following some five days of continuous observations 

by the French in Antarctica, a number of consortia, BISON based in 

the UK, Iris in France and GONG in the US, were set up which placed 

measuring equipment at sites in countries at different longitudes so that the 

Sun could be observed 24 hours a day. However, clouds may intervene from 

time to time and atmospheric transmission variations limit the accuracy. One 

of the great advantages of SOHO is that it is located at the inner Langrangian 

point L1 from where it can observe the Sun with the same instrument without 

interruption 24 hours a day for a long time. L1 is a point some 1.5 million km 

sunwards from the earth, where spacecraft may be maintained in an orbit 

without much expenditure of fuel. A list of SOHO instruments is given in 

Table XIII, 1. In ESA SOHO began as DISCO which was proposed in 1980. 

It would have included instruments for studying solar oscillations, irradiance 

variations and the solar wind. It was not selected, but six years later it would 

be revived as SOHO in an ESA–NASA cooperation. 

Table XIII, 1. The SOHO instruments. 

Twelve instruments constitute the SOHO payload as follows: 

SUMER (D) Chromospheric and Coronal uv spectra 500–1600 Å, 

spectral resolution ~ 30,000, angular resolution ~ 1”3 

CDS (UK) Coronal spectra 150–800 Å, spectral resolution ~ 3000, 

angular resolution 3” 

EIT (F) Extreme uv Imaging Telescope full disk images in 

spectral lines originating at different levels in the 

chromosphere and corona, angular resolution 2”5 

(Figure XIII, 3) 

UVCS (US) Extreme uv coronographic spectra till 10 solar radii 

LASCO (US) Coronographs and spectra till 30 solar radii 

SWAN (F) Anisotropies and variability of the solar wind from 

Lyman-alpha measurements 

GOLF (F) Large scale solar oscillation modes 

MDI (US) Small scale solar oscillation modes 

VIRGO (CH) Irradiance oscillations and “solar constant” 

CELIAS (CH) Charge, element and isotopic composition of particles 

up to 1 MeV/charge 

COSTEP (D) Energy distribution of ions (H, He) and electrons 

ERNE (SF) Energy distribution and isotopic composition of ions 

and electrons. 

Only the country of the principal investigator is listed, but most ESA 

countries participated in one or more instruments.


SOHO has produced a wealth of data. Analyses of the oscillations have 

shown that while the slower rotation of the photosphere surface at the higher 

solar latitudes persists through the convection zone, the interior rotates 

uniformly as a solid body. Flows from the equator to the pole extend down 

to at least 0.8 solar radii from the center at speeds of about a solar radius 

per year. Deeper down the flow must reverse sign if a pile up of matter at 

the pole is to be avoided. Such a flow pattern is important for understanding 

the dynamo which generates the solar magnetic field. 

“Blinkers”, half hour long flashes of extreme uv radiation in the quiet sun, 

discovered by SOHO, give evidence that magnetic reconnection and dissipation 

take place continuously in the quiet Sun. Small bipolar magnetic structures have 

been observed by SOHO to emerge randomly in the photosphere and then to 

be moving to the boundaries of the large scale supergranules. There field lines 

of one polarity cancel the existing ones, which are replaced by the field lines of 

the other polarity. In the process the connections between field lines change. In 

less than two days the whole field at the boundaries is replaced. The origin of 

these small bipolar areas is mysterious, but their dissipation is undoubtedly 

important for the processes which heat the corona. 

From the spatially resolved spectra of the Sun detailed information on 

density, temperature, composition and velocity of individual parcels of gas 

may be obtained. The electron temperature in coronal holes is too low for 

effective acceleration of the solar wind, which suggests that it is due in part 

to the direct momentum transfer from magnetohydrodynamic waves. The 

outflow of different ions has different velocities and is variable, and as a 

consequence also the composition varies in space and time. So it is no 

surprise that the composition of cosmic rays accelerated in flares may be very 

different from the overall composition of the Sun. Of much interest are the 

coronal mass ejections – huge eruptions in the corona caused by a magnetic 

instability – which later may cause magnetic storms on earth. As a result of 

SOHO, the prediction of “space weather” may become more accurate. 

H. Kreuz long ago identified a small group of Sun grazing comets which 

passed at only a million km from the Sun, well inside the corona. Among 

these the comet of 1882 was particularly brilliant and after perihelion had 

broken up in four parts, undoubtedly with many smaller fragments. SOHO 

has discovered a thousand comets of the Kreuz class which would seem to 

represent the fragments of this or a similar comet. Most of these do not 

survive their perihelion passage. 

One future solar mission is foreseen in the long term ESA program. 

Somewhere in the 2010–2015 time frame “Solar Orbiter” should be launched 

by ESA or possibly be undertaken as a joint project with another agency. The 

spacecraft would be placed into an elliptical orbit with perihelion (closest 

approach to the Sun) at some 0.21 AU or 45 solar radii. At that distance the 

solar surface may be studied with unprecedented resolution (35 km pixels, 

corresponding to 0.05 arcsec as seen from the earth). In addition near


Figure XIII, 3. The Sun observed with EIT on SOHO. The four images have been 

taken in narrow spectral bands around spectral lines emitted by gas at different temperatures 

by the Extreme-ultraviolet Imaging Telescope on the ESA-NASA SOlar and 

Heliospheric Observatory. Clockwise from the upper left are lines from: 14 times 

ionized iron Fe XV (28.4 nm), Fe XII (19.5 nm), Fe IX + Fe X (17.1 nm) and singly 

ionized helium He II (30.4 nm) corresponding to temperatures of respectively 2, 1.5, 

1.0 and 0.05 million K. The first three are typical coronal lines, while He II originates 

in the complex transition region between the hot corona and the relatively cool 

chromosphere. At the He II level the chromospheric network is visible which results 

from convective motions below the solar photosphere interacting with magnetic fields. 

Also some prominences are seen which represent cool magnetically supported gas in 

the corona. At the higher temperatures typical coronal structures with magnetic loops 

dominate the picture, as well as activity related to the dissipation of magnetic energy. 

The connection to two sunspot groups at photospheric level is clear in all four images.


perihelion the angular orbital speed of the satellite and that of the solar rotation 

match, so that the satellite hovers for some time over a fixed area on the solar 

surface and can study its evolution in exquisite detail. Moreover, the orbit would 

be tilted so that higher latitude areas may also be observed. Solar Orbiter would 

be equipped with high resolution imagers in visible and far uv light, spectrometers, 

and a magnetograph to measure magnetic fields. In addition, the solar 

wind would be studied in situ closer to the Sun than ever before. Solar 

maximum is predicted to occur around 2011–2012 and could be optimally 

observed if a launch early in 2009 were possible, which may be difficult financially. 

If not, the mission would observe the declining phase of solar activity 

unless one would wish to wait till the next solar maximum eleven years later. 

Technologically the mission is challenging since at 0.21 AU the solar radiation 

is some 23 times more intense than near the earth. So preventing excessive 

heating of the spacecraft and instruments is a major problem. An even more 

ambitious mission would be “Solar Probe” which was already proposed in 

Horizon 2000 as a “green dream” for an indefinite future. It would approach 

the Sun to within a few solar radii (0.03 AU) and make in situ observations of 

the corona in the region where the solar wind originates. While Solar Probe 

has frequently been discussed in various contexts, the technical and financial 

aspects are so forbidding that no specific plans have yet been made. 

Both the US and Japan have launched their own solar missions in the 

post 1980 period. The Hinotori satellite from 1981–1991 and especially 

Yohkoh from 1991–2001 made major contributions. The X-ray images 

obtained by the latter were spectacular and informative on flare phenomena. 

The UK made a major contribution to the Yohkoh instrumentation. A new 

Japanese mission Solar B (with US, UK) is planned for 2005. Its optical 

telescope should have a resolution of 0.2 arcsec, corresponding to 150 km 

on the Sun. Also uv and X-ray instruments are included. 

Following the Solar Maximum Mission (1980–1989) with contributions 

from UK, NL, and D, and several spacelab based short missions, NASA 

launched in 1997 the Advanced Composition Explorer which measures 

elemental and isotopic abundances from H to Ni in the solar wind and in low 

energy galactic cosmic rays. It has been placed at L1. It was followed in 1998 

by the Transition Region And Coronal Explorer which has taken images of 

the Sun in the light of spectral lines corresponding to different temperatures. 

It has a higher angular resolution than the EIT instrument on SOHO, but can 

image only a small part of the solar disk. In 2001 came Genesis, a spacecraft 

which collected solar wind material at L1 and returned it to earth for analysis 

in 2004. A soft X-ray imager on the meteo satellite GOES-12 now takes a whole 

disk image every minute. The Ramaty High Energy Solar Spectroscopic Imager 

launched in 2002 is obtaining γ-ray images of the Sun with unprecedented 

angular resolution to study flare phenomena at the highest energies. A contribution 

to this mission was made by the Paul Scherrer Institute near Zurich. 

In late 2005 NASA intends to launch STEREO, a set of two spacecraft one


ahead of the earth in its orbit and one behind. Contributions to the instrumentation 

have been made by F, D and the UK. It should obtain stereoscopic 

images of the Sun as well as threedimensional information on Coronal Mass 

Ejections. In 2007 it would be followed by the Solar Dynamics Observatory. 

The US has also launched military satellites for solar observations. 

Russia returned to the solar scene with KORONAS-I (1994–1995) and 

KORONAS-II launched in 2001. The latter, with contributions from Georgia, 

PL, D, F, UK and US, has several X-ray and uv imagers and spectrometers, 

a coronograph and photometers. For the future, Koronas-Photon is planned 

to observe γ-rays and neutrons. Also China is considering a solar satellite with 

a 1-m optical telescope and other uv and X-ray instruments. 

If we survey these programs (Table XIII, 2) it is clear that, though 

Europe has made a more than respectable showing with Ulysses and SOHO, 

it is far from being the leader in the field. With Solar Orbiter long into the 

future, this is unlikely to change. 

Table XIII, 2. The solar missions of ESA, Japan, NASA and Russia. 

EU Japan NASA Russia 

1980–89 1/2 Ulysses; Hinotori; X Solar Max; v, uv, 

solar wind X, γ 

1/2 Ulysses; solar 

wind 

1990–99 1/2 SOHO; Yohkoh; X 1/2 SOHO; v, uv 

v, uv ACE; solar wind, CR Koronas-I; 

radio-γ 

TRACE; v, uv 

2000–09 Solar B; v, uv, X Genesis; solar wind Koronas-II; 

radio-γ 

RHESSI; γ 

2 STEREO; v, uv Koronas-Photon; 

γ, neutron 

SDO; v, uv 

Ground based solar telescopes 

Ever since Galileo and his contemporaries watched the dark Sun spots 

on the solar disk, observations of the Sun with relatively small telescopes have 

continued. Because of the importance of events on the Sun to conditions in 

the ionosphere, the auroral belt and even lower down, institutes in many


countries monitor the Sun on a daily basis. While this activity has been useful, 

progress in solar physics now demands more optimized facilities. Space facilities 

have many advantages in giving access to the wavelengths that are inaccessible 

from the ground, as well as in the study of the corona. However, for 

investigations of the photosphere and its magnetic fields and for studies of 

the elemental composition of the Sun, the larger ground based telescopes 

remain essential, especially when provided with adaptive optics (AO). Since 

the photospheric magnetic fields determine much of the structure of the fields 

in the corona which are difficult to observe directly, coordinated programs 

of space and ground based solar observations have been particularly useful. 

In fact, one third of the SOHO observations were coordinated with observations 

from the ground. Here we shall only mention the most important of 

the ground based European facilities. 

THEMIS started out as a French project in which Italy now participates 

at the 15% level. Inaugurated in 1996, various problems, partly financial, 

have slowed down the progress of the 90 cm telescope placed at the Observatorio 

del Teíde on Tenerife (Figure VI, 1). It has been constructed to be 

free of instrumental polarization so that solar magnetic fields can be 

measured with maximum sensitivity. Two German telescopes, also at Teíde, 

with apertures of 70 cm and 45 cm, have been operating for almost 20 years, 

obtaining mainly high spectral resolution data. The 70-cm is being equipped 

with AO, while the 45-cm will be replaced in 2005 by a 150 cm AO telescope 

“GREGOR”, which will be one of the two largest solar telescopes worldwide, 

the other being at Kitt Peak in Arizona. Two other solar telescopes have been 

placed at La Palma. The new Swedish instrument, with a 97 cm fused silica 

lens and an adaptive optics system, aims for the highest possible angular resolution 

of about 0.1–0.2 arsec. The Dutch Open Telescope (45 cm) is testing 

a novel technology in which the wind prevents overheating. Countless other 

solar telescopes operate in Europe and in the rest of the world, with variable 

impact on the research field. While long term continuity of solar observations 

with the same instrument has a great value in providing uniform data 

sets over long periods, an overdue consolidation appears to have begun. 

For a number of years JOSO, the Joint Observatory for Solar Observations, 

conducted site selection campaigns, among others in the Canary 

Islands. A more formal organization, the LEST Foundation (Large European 

Solar Telescope), was founded in 1983 at the Royal Swedish Academy of 

Sciences. When there seemed to be a prospect of non-European participation, 

the meaning of the “E” was changed to “Earth-based”. A design study 

of a 2.4-m telescope was made. However, real funding proved elusive. The 

French were fully engaged with the underfunded THEMIS, while the US was 

starting to plan its own telescope. So the LEST program has been terminated, 

while the US now is looking for international partners for its 4-m project! 

Observations of the radio emission from the sun provide much additional 

information. At long wavelengths (~ 1 m) the radiation comes from the


corona, while at a few cm the cooler photosphere is also observed. The 

Nancay (F) radioheliograph was developed in 1967 and renovated in 1996. 

It regularly observes the corona at 10 wavelengths between 70 and 180 cm 

and is particularly suited for the detection of coronal mass ejections which 

later may perturb the solar wind and the earth’s magnetosphere. At Zurich 

observations are made in the 7-30 cm range. In the US a powerful facility is 

being planned, the Frequency Agile Solar Radio Telescope. It would operate 

over the 1.2-600 cm wavelength range with angular resolutions down to 

0.8 arcsecond at 1.2 cm and a field of view of 70° at 600 cm.

XIV. 

Astroparticles and Gravitational Waves 

Die experimentelle Begründung der Einsteinschen Gravitationstheorie 

ist also noch nicht weit gediehen. Wenn 

die Theorie aber trotzdem schon heute den Anspruch auf 

allgemeine Beachtung erheben kann, so hat das in der 

ungewöhnlichen Einheit und Folgerichtigkeit ihrer 

Grundlagen seinen berechtigten Grund. 

Erwin Freundlich 1) 

While most astronomical information comes to us through visible light 

and other electromagnetic radiation, there are additional channels through 

which information about cosmic events may reach us: energetic particles, 

neutrinos and gravitational waves 2) . The particles, the cosmic-rays (CR) were 

discovered by Victor Hess in 1912. During balloon flights he showed that a mysterious 

source of ionization increased with height in the atmosphere, indicating 

that its cause was outside. Clarity about the nature of CR was only obtained 

during the thirties when it was concluded that they are composed primarily of 

energetic protons. At first they were utilized mainly as a convenient source of 

energetic particles for particle physicists during the pre-accelerator days. Only 

in the early fifties was their astrophysical significance fully realized, in particular 

due to the work of Vitali Ginzburg and his associates in Moscow. 

Neutrinos were hypothesized by Wolfgang Pauli in the thirties to 

explain certain aspects of radioactive decays. Experimental confirmation 

came in laboratory experiments in 1955. Neutrinos have little interaction with 

matter, which makes their detection very difficult. Gravitational waves were 

predicted by Einstein on the basis of his 1916 General Relativity Theory. They 

represent waves in the fabric of space-time. The validity of the theoretical 

prediction remained somewhat uncertain until the middle of the century. 

Indirect evidence for their existence has been obtained, but direct observation 

still has eluded us.


Cosmic-rays 

The energies of cosmic-ray particles cover an enormous range from 

some MeV to values at or above 10 20 eV (~ 10 joule = 10 wattseconds). Few 

particles of the highest energies arrive on earth, perhaps one above 10 20 eV 

per km 2 per century! But they are of much interest because nobody has an 

idea what they are or where they come from. Speculation abounds that they 

may represent some new type of particle, but this need not be the case. If 

these particles of the highest energies are protons, they cannot come from 

more than a few hundred million light years away, since collision with 

photons of the Cosmic Microwave Background would have destroyed them. 

At these energies plausible (inter)galactic magnetic fields would not deflect 

them very much, and so we might be able to trace them back to their places 

of origin. 

The rarity of the highest energy particles implies that no direct observation 

is possible. However, when such a particle strikes the atmosphere it 

collides with oxygen or nitrogen nuclei. The result is an Extensive Air Shower 

(EAS) of secondary particles, principally electrons (and positrons), but also 

muons and some hadrons. The shower extends over an area of some 10 km 2 

with on average 1000 electrons per m 2 . To characterize the shower it is sufficient 

to sample it with detectors distributed here and there over a large area. 

The most important early arrays included Haverah Park in the UK and 

Volcano Ranch in the US. They have been superseded by EAS arrays at 

Yakutsk in Siberia and the very large Japanese AGASA array at Akeno which 

covers 100 km 2 . The most interesting result from AGASA are four pairs and 

two triplets of events above 4 × 10 19 eV coming (within the angular resolution) 

from the same directions. If confirmed, this would suggest that discrete 

sources are seen. However, the world total of claimed > 10 20 eV events still 

is less than two dozen. 

The small number of detected events makes everything still quite 

uncertain, and bigger arrays are needed. A large 13 country collaboration, 

including several European countries, is constructing the Pierre Auger Observatory 

(PAO), which will consist of two large arrays, one for each hemisphere. 

The southern component in Argentina consists of an array of 1600 detectors 

distributed over a 3000 km 2 plateau. It should be fully operational in 2006. 

It is planned to build thereafter a northern array in Arizona or Utah. With 

these arrays the number of high energy events detected should increase by 

an order of magnitude or more. After a few years of operation the PAO may 

detect a hundred events with energies above 10 20 eV, if they really exist. In 

any case, some several thousand events in the 10 19 –10 20 eV should be observed 

(Figure XIV, 1) and the directions from where they come measured. The size 

of the PAO has been set such as to keep the cost below 100 M€. 

Another way to detect the air showers is to optically observe their tracks 

through the atmosphere. The energetic electrons and positrons will excite the

Log 

+5 

F (>E) 

0 

-5 

-10 

-15 

Astroparticles and Gravitational Waves 233 

log [E 1.7 F (>E)] 

10 15 log E (eV) 20 

nitrogen molecules in the air. This results in nanosecond (10 -9 s) fluorescent 

light flashes which may be observed by large telescopes, which are 

relatively cheap because optical quality need not be very high. At the focus 

a multiple set of fast photomultipliers (fly’s eye) is placed to detect the 

flashes. With this method one may survey a larger area for showers than 

with the existing EAS arrays, but, of course, only during clear moonless 

nights. Fly’s Eye in Utah operates on this basis. The precise intercalibration 

of the two methods is far from trivial and the results from Fly’s Eye and 

AGASA are partly contradictory. To resolve these problems the PAO will 

be a hybrid array with four telescopes to also obtain stereoscopic images 

of the fluorescent tracks. A smaller 900 km 2 hybrid array is being built in 

20 

19 

Figure XIV, 1. The flux of 

cosmic-rays. The curve gives 

the integral, omnidirectional 

flux (particles per m 2 and 

sec, vertical scale) of particles 

with energy larger than 

E(eV) (horizontal scale). In 

the insert the steep slope has 

been eliminated by multiplying 

the flux with E 1.7 , 

which makes it easier to see 

the “knee” around 10 15 eV 

and the flattening around 

10 19 eV. Note that the scale 

for E 1.7 F(> E) indicated on 

the right hand side is different.


Utah by a Japan-US cooperation, in order to get an improved capability in 

the northern hemisphere more quickly. 

Even larger areas may be surveyed from space by a wide angle camera 

that looks down imaging a large stretch of the earth’s atmosphere. The 

Extreme Universe Space Observatory, EUSO, is a project under evaluation 

at ESA. It could be attached to the European Columbus module on the International 

Space Station at 400 km altitude. EUSO (Figure XIV, 2) would 

survey some 170 000 km 2 of the atmosphere, 60 times the effective area of 

the first half of the PAO. However, the gain would be less because of clouds 

and the need for night time observations. NASA is considering a similar 

project which would consist of two satellites at 1000 km altitude surveying 

an area still three times larger than EUSO. Both projects should detect events 

above several times 10 19 eV. 

The more numerous cosmic-rays at lower energies have been studied 

with a variety of the standard detectors of nuclear physics carried first by high 

altitude balloons and later by spacecraft. The UK satellite Ariel 6 (1979–82) 

determined abundances of heavy elements. Subsequently, NASA’s Long 

Duration Exposure Facility remained in orbit for 69 months before being recovered. 

It included solid-state nuclear track detectors, provided by Ei, F and 

UK, which reliably determined the abundances of elements around uranium. 

The bulk of the CR are almost certainly accelerated in or around supernova 

remnants, and it had been thought that such elements might be overabundant, 

being produced in the supernova process. However, the result of all of this 

work is that the abundances of most elements in the source regions of the 

CR are disconcertingly normal. Apparently, the CR are accelerated mainly in 

Figure XIV, 2. The proposed EUSO instrument. Attached to the ESA Columbus 

External Payload Facility at the International Space Station, it would observe the 

nitrogen fluorescence and the reflected Cerenkov radiation generated by very high 

energy cosmic-rays passing through the earth’s atmosphere.


interstellar space by the shock waves generated by the supernovae rather than 

in the material of the supernova itself. Isotope abundances have also been 

determined by Ulysses and in particular by NASA’s Advanced Composition 

Explorer, which was launched in 1997 and placed at the inner Lagrangian 

point L1. It measures the composition of the solar wind and of relatively low 

energy CR. 

The energy distribution of the cosmic-rays is quite steep (Figure XIV, 1). 

For every decade increase in energy there are globally 50 times fewer cosmicrays 

above that energy. Around 10 15 eV this increases to about 100, creating 

a “knee” in the steepening distribution. It is believed that at that energy the 

particles begin to leak out of the Galaxy or that the supernova shocks are 

becoming less effective accelerators. In either case it could be expected that 

the composition would begin to shift to heavier nuclei with a larger nuclear 

charge, since these are more tightly coupled to the magnetic fields. To 

determine the composition at that energy a precise analysis of all the components 

of the resulting air showers is needed, but analysis of data from arrays 

of a few hundred meters diameter suffice. The most convincing results have 

been obtained by KASCADE (D with PL, Armenia, Romania), which was 

constructed to study particles around the “knee” and consists of several 

hundred m 2 of detectors spread out over a 200 × 200 m 2 area in 252 detector 

stations. Since all three of electrons, muons and hadrons are detected, relatively 

reliable inferences on the global composition of the incoming particles 

can be made. These show that, in fact, the heavier particles with larger 

charge become more abundant after the “knee”. A similar result was obtained 

by the EAS-TOP and the MACRO cooperation. The MACRO detector was built 

under the Gran Sasso mountain in halls that were excavated for the building 

of the Rome to L’Aquila highway tunnel. A number of other physics and astrophysics 

experiments are also conducted there, since the km thick layer of 

rocks overhead shields the detectors against unwanted particles. The MACRO 

detector was operated from 1989–2000 to look for exotic particles (monopoles, 

etc.), neutrinos and muons. When a high energy cosmic ray particle 

strikes the atmosphere, the resulting Extensive Air Shower of electrons and 

positrons is detected on the ground near the top of the mountain, while the 

muons may make it to the MACRO detector. Again, comparison of the two 

components gives some information on the overall composition of the cosmicrays 

near the “knee”. 

There is one other area where it is remotely possible that cosmic-rays 

could make a significant contribution, this is the search for antimatter. In 

our neighborhood in the Universe there is matter, but no antimatter. If there 

were antimatter in our Galaxy, it would be rapidly annihilated with copious 

production of γ-rays. In the cosmic-rays there are some antiprotons which 

result from collisions between energetic CR and the interstellar gas. Such 

collisions can make antiprotons, but are too destructive to synthesize complex 

antinuclei. If there were regions of antimatter in the Universe, they could be


sources of antimatter CR. This has led to the AMS (Alpha Magnetic Spectrometer) 

experiment in which antihelium nuclei are looked for. A first 

shuttle based attempt did not yield evidence for such nuclei, and a second 

attempt should be made with a massive detector placed on the Space Station. 

Several European countries participate in this US led project. 

In conclusion, we have learned much about cosmic-rays during recent 

decades, though the precise mechanisms and places of acceleration have not 

yet been fully established. However, above 10 16 eV our ignorance is almost 

total. From this brief survey it is clear that Europe has made an entirely 

respectable contribution to the field, though it is not quite the world leader. 

Neutrinos 

While the charged cosmic-ray particles are affected by magnetic fields, 

photons and matter along their path, neutrinos can move along straight 

lines almost totally unhindered by matter or magnetic fields. As a consequence, 

the direction from where they come points directly to their place of 

origin. However, the fact that they interact so little with matter makes their 

detection very difficult. In the sources of high energy cosmic-rays, collisions 

with matter may produce energetic neutrinos which could be detected on 

earth. Enormous detectors are needed to obtain a signal. Neutrinos which 

pass through the earth interact with the rocks and produce upward moving 

muons which may be detected from light flashes they produce in transparent 

media, like water or ice. The detectors need to be placed at a large depth to 

reduce the flux of particles coming from above. Two European detectors are 

being prepared: NESTOR (GR with I, F, Rus) at a depth of some 3 km, and 

ANTARES (F, other EU) at 2 km, both in the Mediterranean near the Greek 

and French coasts respectively. In these detectors photomultipliers to detect 

the light flashes hang down from the surface of the sea on strings. Obviously, 

areas of very calm, transparent water are needed where the light may be seen 

from distances of several tens of meters. Earlier experiments were done in 

Lake Baikal, known for its pure waters. 

The US, with German participation, has built an ice based detector, 

AMANDA, at the South Pole. Strings of photomultipliers are hung in holes 

drilled into the ice. Between now and 2010, AMANDA is expected to be 

gradually upgraded to ICECUBE by a large international cooperation 

involving D (15%), S, B, NL, J and Venezuela. Upon completion a total of 

4800 fast photomultipliers on 80 strings will be mounted deep under the 

ice surveying events in a km 3 of ice. The detector will come on line gradually 

with every new string added beginning to take data almost immediately. So 

far no high energy neutrino from beyond the earth has been detected, but 

interesting data about luminescent organisms in the depths of the sea are 

being obtained!


Low energy neutrinos are produced in the nuclear reactions which 

power the sun, and they can easily escape from the solar interior. Two 

seminal ideas in the field are due to Bruno Pontecorvo, the Italian physicist, 

who fled to Moscow in 1950. He proposed in 1946 to detect neutrinos through 

the reaction neutrino + 37 chlorine → 37 argon + e – , and about a decade later 

he suggested that neutrinos could oscillate between various states. Somehow 

the second idea which resolved the “solar neutrino puzzle” was insufficiently 

appreciated at the time. The resulting goose chase has led to an avalanche 

of papers concerning the solar interior, even though the solution was so 

simple. 

The chlorine reaction was exploited in a deep gold mine in North 

Dakota. A huge tank of C Cl 4, a very cheap liquid was from time to time 

searched for the radioactive argon produced by the solar neutrinos. Some was 

found, but only about a third of the predicted amount. Since the neutrinos 

in question come from a reaction which is rather sensitive to the temperature 

distribution in the solar interior, the first thought was that something was 

wrong with the solar models. Confirmation of the observations by a different 

technique came from (Super)Kamiokande in Japan. 

Subsequent experiments involved the low energy neutrinos emitted 

during the basic energy generating reaction in the Sun. Even without a 

model one could predict that neutrino flux from the total energy radiated 

by the Sun. GALLEX, the GALLium EXperiment (I, F), installed in the Gran 

Sasso laboratories in Italy, involves 30 tons of Gallium to measure the 

reaction 71 Gallium + neutrino → 71 Germanium + e – . SAGE, a Russian-US 

experiment, using 55 tons of Gallium, in the underground laboratory at 

Baksan in the Caucasus has, after initial disagreement, confirmed the 

GALLEX result. Again it is found that the observed rate is lower than 

predicted. 

Subsequently, KamLAND, the successor to Kamiokande, demonstrated 

the existence of neutrino oscillations, by observing neutrinos from surrounding 

nuclear reactors. There are three flavors of neutrinos: ν e, ν µ and ν τ. Apparently 

the neutrinos can oscillate between the three flavors. So an experiment 

capable of detecting only one of them is likely to observe fewer than expected. 

The Sun emits only electron neutrinos. On the way to Earth they transform 

in part into ν µ and ν τ. The definitive proof has come from the Sudbury 

Neutrino Observatory in Canada (Can, US, UK). It involves 1000 tons of 

heavy water (D 2O) which allows all three flavors to be detected. In fact, the 

total flux of all three is about equal to the flux of ν e expected from the solar 

models. Incidentally these results also imply that neutrinos have mass, 

although the mass is very small, too small to be of interest as a dark matter 

candidate. In addition to those from the sun, two dozen neutrinos have been 

detected by detectors in the US and in Japan from the 1987 supernova 

explosion in the Large Magellanic Cloud. Thus, so far neutrinos have been 

detected only from two cosmic sources.


Dark matter 

The matter we see in the form of stars and gas is only a small part 

(~ 10%) of all matter in the Universe. The rest is “dark matter”. In our own 

Galaxy there is evidence for its existence because the gravity inferred from 

stellar motions is stronger than what could be expected from the visible 

matter alone. The nature of the dark matter is still entirely unknown. Among 

the possibilities are particles beyond the current “standard model” of the 

particle physicists. A variety of proposals have been made for their direct 

detection. Some of these have been investigated experimentally in Europe, 

among others in the underground laboratories under the Gran Sasso. It 

would take us too far into the domain of particle physics to discuss these here. 

Alternatively, indirect evidence might be obtained if such particles and their 

antiparticles annihilate with the emission of neutrinos or γ-rays. For example, 

WIMPs, Weakly Interacting Massive Particles, could be captured by the sun 

and there produce high energy neutrinos observable with the detectors 

already discussed. Since the thermonuclear reactions in the Sun produce only 

low energy neutrinos, a clear result could be obtained. It has also been 

suggested that the annihilation of such particles at the galactic center could 

generate a flux of energetic γ-rays measurable with instruments like HESS. 

In fact, HESS (chapter XI) has found a source there, but its spectral characteristics 

did not fit with the expectation for WIMP annihilation. 

Gravitational waves 

According to Einstein’s theory of gravity (the “General Theory of Relativity”) 

any non axisymmetric motion of matter generates “gravitational 

waves”, waves in the fabric of space–time. In fact, the existence of such waves 

has been indirectly confirmed by the orbit of the “binary pulsar”, a close 

binary of two neutron stars. The orbital energy is gradually lost owing to the 

emission of gravitational waves in quantitative agreement with theoretical 

expectations. 

Gravitational waves may be emitted in various processes. Before a 

supernova explodes, part of the star implodes. When this process is spherically 

symmetric no gravitational waves are emitted. But when the star rotates 

fast enough, the resulting asymmetries lead to gravitational waves, though 

quantitative predictions depending on the degree of asymmetry are difficult 

to make with confidence. The collapse process towards a neutron star or black 

hole is very rapid and the wave frequencies involved should be of the order 

of 1000 Hz. It should not be too complicated to detect the gravitational waves 

from a supernova in our Galaxy, but such events occur only about twice a 

century. So we may have to wait a long time! Under favorable conditions some 

supernovae might be observable out to the distance of the Virgo cluster


(~ 50 million light years) and so a higher frequency of events would perhaps 

be possible. 

Very compact stellar mass binaries typically may have periods of a few 

thousand seconds, corresponding to wave frequencies in the 0.001 Hz range. 

When such binaries are sufficiently close to the Sun these waves might be 

detectable. The energy loss in the form of gravitational waves will cause the 

two stars to spiral inwards and ultimately to merge. For solar mass stars with 

separations like that of the Sun and the earth (1 AU), this process would take 

much longer than the age of the Universe. However, some binaries are known 

which are much closer. For the “binary pulsar” composed of two neutron stars 

with a separation of 0.006 AU, this would take only some 400 Myr. So there 

should be many such systems in the Universe which achieve coalescence. An 

even stronger signal would result when two black holes merge. Neutron stars 

or black holes of stellar mass falling into supermassive black holes at the 

centers of galaxies also would give strong signals. 

The waves with frequencies of the order of 1000 Hz have wavelengths 

of a few hundred km. They may be detected by measuring with high 

precision the changes in the distance between two test masses as the waves 

pass by. Extreme precautions have to be taken to ensure that natural seismic 

or man-made noise does not perturb these test masses. Laser based interferometers 

measure the infinitesimal displacements of these masses as the 

waves pass by. Since the relative displacements are proportional to the 

length of the instruments, typical setups have dimensions of the order of 

one or more km. However, other factors also play a role in the final sensitivity, 

in particular the suppression of seismic noise. Construction has just 

been completed near Pisa of “VIRGO”, a French-Italian detector with arms 

of about 3 km at a cost of some 70 M€ (Figure XIV, 3). Seismic “super attenuators” 

ensure extreme protection against noise sources. A smaller 

German-UK project “GEO 600” has been constructed in Germany. In the 

US two 4 km long facilities (LIGO) have been completed, and in Japan a 

smaller experimental facility of 300 m, TAMA, is operational. It seems very 

uncertain that these detectors have the sensitivity required to see more than 

a few events per year. So plans for VIRGO II or LIGO II are already being 

made, with in Germany a tendency to participate in the US project. The 

LIGO upgrade alone is budgeted at 185 M$. Since false events may easily 

occur in a single detector, it is important to have a means to confirm the 

reality of what is observed. To achieve this, VIRGO and the two LIGO 

detectors exchange data in real time. If all three see the same event, it should 

be real. 

There are, however, severe limits to what may be achieved on the 

ground at lower frequencies. Small movements of the soil or even changes 

in the density of the air which are dragged along by the wind already limit 

the accuracy at frequencies around 1 Hz. The only solution for observations 

at frequencies in the mHz range is to place the equipment in space.


Figure XIV, 3. VIRGO. The French-Italian gravitational wave detector is located near 

Pisa. A laser beam is split in two and travels down the two 3 km long arms, to be 

reflected by mirrors at the ends. The beams are reflected back and forth numerous 

times before being recombined at the central station. The resulting interference 

pattern would be modified if gravitational waves pass by the facility. 

LISA, the Large Interferometer Space Antenna, was proposed as a 

cornerstone in the Horizons 2000 program of ESA. It also appears in NASA’s 

long term planning. LISA (Figure XIV, 4) would be composed of three spacecraft 

separated by about 5,000,000 km. Again the separations would change 

when gravitational waves pass by. Though the changes are minuscule, they 

could be measured with the required precision by exchanging laser beams 

between the satellites. LISA may be realized a decade from now, perhaps as 

an ESA–NASA collaboration at a total cost (optimistically?) estimated at 

perhaps 400 M€. An earlier technology mission “LISA pathfinder” is also 

planned. Since many sources will affect the orbits of the LISA spacecraft 

simultaneously, problems of source confusion may be important. In any 

case, the data analysis problem appears rather formidable. 

The gravitational wave detectors represent experiments at the limit 

between physics and astrophysics. Not only will they directly demonstrate 

the existence of gravitational waves, the studies of black hole mergers will 

also explore the nature of space-time under conditions of extreme gravity, 

where Einstein’s theory could never be verified and where fundamental 

questions of physics remain open. It is also possible that in the future


Figure XIV, 4. LISA. The three spacecraft of this ESA–NASA project detect low 

frequency gravitational waves by measuring their relative distances by laser interferometry. 

Separated by 5 million km, they trail the earth in its orbit by 20°. The plane 

defined by the three has an inclination of 60° with respect to the ecliptic, so that the 

triangular formation is preserved by the three orbits. 

gravitational waves from the earliest phases of the Big Bang at the origin of 

the Universe will be observed. If so, they would give evidence about conditions 

closer to that singular event than any other observations. However, they 

may also create a background that makes the detection of other sources with 

LISA more difficult. 

The present prospects of VIRGO and LIGO are still limited. Perhaps 

some supernova related events will be seen. Alternatively, some black hole 

or neutron star coalescences will be observed. Our inability to predict the 

annual number of such events leaves a large range of possibilities. 

Current estimates suggest that LISA should be able to detect several 

close binaries whose properties are known from optical studies. However, 

their interest in testing General Relativity is limited since the gravitational 

fields involved are rather weak. They might be particularly useful in the experimental 

evaluation of the performance of LISA. Mergers of black holes 

would be more interesting. It has been frequently noted that if a binary of 

two million solar mass BH coalesces, LISA should detect the event anywhere 

in the Universe with a very high signal-to-noise ratio. Unfortunately, we do 

not know how frequent such events are; they may well occur much less than 

once a year. A more plausible source of gravitational waves might be the infall 

of BH with masses of some 10 solar masses into the massive BH at the centers 

of galaxies. Here the stellar density is high. So the frequency could be much 

higher, while such events could still be detected out to a redshift z = 1. Also 

infalling neutron stars or even white dwarfs might be detectable. Thus, there 

are many possibilities, though here also we are incapable to reliably predict 

to the frequency of occurrence. As a result, we also do not know what


problems may result from source confusion. For example, if close white 

dwarf binaries are as common as some people think, a rather strong background 

of gravitational waves could result, which might make individual 

source detections more difficult. In any case, with so much uncertainty, all 

that can be done is to launch LISA and to see what there is to be discovered. 

Other more pure physics experiments also benefit from the weightlessness 

in space and from the absence of disturbances. At the heart of the 

General Theory of Relativity is the “principle of equivalence” which asserts 

that mass determined from gravity is the same as mass determined from 

inertia, independent of the nature of the matter. This has been verified on 

the ground to one part in 10 12 . The French “MICROSCOPE” mission, with 

ESA participation, to be launched in 2007 should improve this to one part 

in 10 15 , a factor of 1000 improvement. A large NASA mission “Gravity Probe 

B” launched in 2004 will check on specific predictions of Einsteinian theory 

around the rotating earth. 

One may wonder if it is justified to invest so much effort and money 

in fields like gravitational waves and physics experiments which have rather 

uncertain returns. However, the potential rewards are very large. The nature 

of gravity is fundamental to an understanding of physics and the Universe. 

Gravitational waves provide the only way to experimentally study strong 

gravitational fields. In combination with the subtle physics experiments they 

provide the only means to ascertain the adequacy of Einsteinian theory.

XV. 

Looking for Planets and Life in the Universe 

It is in the highest degree unlikely that this earth and 

sky is the only one to have been created … You are 

bound therefore to acknowledge that in other regions 

there are other earths and various tribes of men and 

breeds of beasts. 

Lucretius 1) 

One of the great questions about the Universe – and not only for 

scientists – is whether earth-like planets orbit other stars and, if so, whether 

there is life on such planets. In antiquity Lucretius and at the dawn of the 

present era Giordano Bruno answered the question positively on the basis 

of general plausibility. Now, however, the issue is moving from the realm of 

speculation into the domain of scientific investigation and observation. 

Three methods for detecting exoplanets are available: measuring the 

reflex motion of the star around which the planet orbits, measuring the loss 

of light when the planet transits in front of the star, and direct imaging of 

the planet. The first two methods have produced results, though no earthlike 

planets have yet been detected. Direct imaging is, of course, the ultimate 

goal, but it is also the most difficult. 

Stellar Reflex Motion 

When we say that a planet orbits the sun or a star, the statement is 

not entirely correct. Actually both orbit the common center of gravity. In the 

case of Jupiter and the sun the ratio of the masses is 1:1047 and so the sun 

is 1047 times closer to the center of gravity, and therefore its orbital speed 

is also 1047 times smaller. Jupiter’s average speed is 13 km/sec and so that 

of the Sun in its orbit is 12.5 m/sec or 45 km/hour. Of course in our solar 

system there are other planets which also contribute to the reflex motion of


the Sun, but since the mass of Jupiter dominates over that of the others the 

result is not changed very much. 

The orbital motion of a star (Figure XV, 1) due to an exo-Jupiter 

would be detectable by the Doppler effect – the shift in wavelength of spectral 

lines when a star has a velocity component in the radial direction – along 

the line of sight. Most searches for planets were made initially on the 

assumption that other planetary systems would be like our own. Since Jupiter 

has an orbital period of around twelve years, no very frequent observations 

would be needed. Fortunately, Michel Mayor and Didier Queloz looked more 

frequently with their spectrographic device that allowed a precision of some 

10 m/sec to be attained. In 1995 they detected 2) the first exoplanet around 

the star 51 Pegasi, with a period of only four days. According to Kepler’s third 

law the planet, with a mass of the same order as that of Jupiter, is only some 

0.05 Sun-Earth distances (Astronomical Units or AU) away from the star. 

Since the search for planets does not require observations of faint stars, the 

1.9-m telescope at the Observatoire de Haute Provence was sufficient for the 

purpose. In the meantime, more than a hundred such Jupiters have been 

discovered, some with even 2-3 times shorter periods. Such planets would 

be even closer to the star and therefore very hot, more than 1000 °C. At such 

high temperatures a planet like Jupiter would begin to shed gas from its 

atmosphere. In fact, in one such system absorption by the escaping gas in 

front of the star has been detected 3) . 

It is now generally assumed that the Jupiter like planets have formed 

further out. They then would have spiralled inwards owing to the drag of 

material that was left around the newly formed star after the main period of 

planet formation had ended. What caused the planets to come so close to 

the star without falling into it, is still not very clear. In any case, these discoveries 

indicate that planets around other stars are not at all rare, but that 

our solar system with the major planets far out is far from typical. 

• 

> O 

Figure XV, 1. A star and a planet revolving 

around the common center of gravity. In the 

drawing the relative radius of the planetary orbit 

is much smaller than in reality. When the star and 

the planet are as indicated by filled circles and 

when the observer O is more or less in the orbital 

plane, the planet shadows part of the star and its 

brightness is diminished. When the star and planet 

are in the position of the open circles a quarter 

period later, the approach velocity of the star is largest and the stellar spectrum is 

shifted bluewards. At the same time O sees the stellar position shifted maximally. Half 

a period later the position shift is in the opposite direction and the recession velocity 

shifts the spectrum redwards.

Looking for Planets and Life in the Universe 245 

A new instrument HARPS (High Accuracy Radial velocity Planet 

Search), constructed by the Observatoire de Genève in cooperation with 

ESO, has been installed at the 3.6-m telescope at La Silla 4) . With its 1 m/sec 

accuracy it should be able to detect planets with 20 earth masses at 1 AU 

from a star like the Sun. However, earth-like planets could not be detected 

with this instrument. The mass of the earth is 314 times smaller than that 

of Jupiter or 329 000 times less than that of the Sun. With the earth’s orbital 

speed 30 km/sec, the reflex speed of the Sun is only 0.09 m/sec. Even if we 

were able to measure such a small speed, turbulent motions in the stellar 

atmosphere would tend to obscure the signal. A planet with a mass of only 

14 earth masses was very recently detected with HARPS though at less than 

1 AU from the star (Figure XV, 2). It should be noted that all quoted masses 

are minimum values because of projection effects, although in most cases they 

should be rather close to the real value. 

The motion of the star will also cause a displacement of its image on 

the sky. If our solar system were observed from a distance of 30 light years, 

the amplitude of the displacement of the Sun due to Jupiter would be 

0.5 milliarcsec and that due to the earth some 0.3 microarcsec. Since the 

angular displacement would be inversely proportional to the distance of the 

star, only relatively nearby systems could produce detectable motions. With 

the VLT Interferometer (chapter VII) a precision of some 10 microarcsec in 

a stellar position should be attainable. Since the displacement is also proportional 

to the star-planet distance, the VLTI has excellent prospects of inferring 

major planets in planetary systems like our own. Also the ESA GAIA mission 

(Chapter VIII) should be able to discover numerous Jupiters in the general 

neighborhood of the Sun. Earth-like planets would be out of its reach. NASA 

is developing SIM – the Space Interferometry Mission 5) , which should reach 

Figure XV, 2. The radial velocity curve of the star µ Arae indicates the presence of 

a planet in a circular orbit with a minimum mass of 14 earth masses. Based on observations 

with HARPS at the 3.6-m telescope at La Silla, it constitutes one of the 

smallest planetary masses detected to-date. 2)


microarcsec precision and so be able to infer earth-like planets around stars 

very close to the Sun. There are only a few stars near enough and so success 

depends on earth-like planets being sufficiently frequent. 

Occultations 

When a planet passes in front of a star, it occults part of its light. The 

radius of Jupiter is about ten times smaller than that of the Sun, and so the 

fraction of the light intercepted is about 1%, which is rather easy to detect. 

However, the occultation is seen by us only when the line of sight to the star 

is more or less in the orbital plane of the planet. The probability of this being 

the case is rather small, of the order of the ratio of the radius of the star to 

the star-planet distance, and so only a few instances are known. In three of 

these the periodic variation in the speed of the star was first found from the 

radial velocity variations. This allowed the orbit to be determined and if the 

orbital plane had the right inclination the moment of occultation to be 

predicted. The prediction exactly fitted the observation, confirming that the 

velocity variations are really due to a planet and not to some ill understood 

effect of motions in the atmosphere of the star. Recently radial velocity variations 

were detected with the VLT in a faint star 6) where an occultation had 

been suspected previously. In fact, the occultation coincided precisely with the 

moment when the radial velocity showed the planet to be in front of the star. 

The earth is 11 times smaller than Jupiter, and so an earth-like planet 

would take away only of the order of 0.01% of the star light. This is too small 

to be detected from the ground because of small fluctuations in the atmospheric 

transmission. However, in space this is no problem. A mission by the 

French Space Agency (CNES), with a major contribution from ESA, named 

COROT 7) , should be able to carry out very accurate stellar photometry. 

Launch is foreseen for 2006. Part of its mission will be to measure stellar 

oscillations (asteroseismology) in selected stars to gain information on their 

internal structure. In addition, it will observe 12 000 stars during 150 days 

in each of five fields of 4 square degrees, for a total of 60 000 stars, to look 

for occultations by planets. With its 27-cm telescope it should be able to detect 

earth-like planets around stars somewhat smaller than the Sun. However, its 

150 day observing periods are too short to detect such planets at 1 AU from 

such a star, since at least three idential occultations are needed to be sure 

that planetary transits are observed rather than some erratic stellar variability. 

As a result, the orbital periods will have to be less than 75 days, and 

such planets will be close to the star and therefore quite hot. Since the 

required orientation of the orbital plane of the planets occurs so seldom, the 

number of detections will remain rather small. 

A much more ambitious mission of the same type as COROT has been 

proposed for the ESA program. “Eddington” 8) would be composed of three 

parallel 70-cm telescopes with a field of view of 7 square degrees. During its


first two years it would obtain asteroseismological data for some 50 000 stars 

in a number of fields and subsequently for more than three years continuously 

observe a rich field of stars. With the three telescopes stellar colors may be 

obtained. With the three year duration of the planet finding phase, planets like 

the earth in the “habitable zone” may be detected. Unfortunately, Eddington 

has been taken out of the ESA program because of financial problems. 

The habitable zone in the solar system is the domain where liquid water 

may occur. Inside the orbit of the earth temperatures would become higher 

and a planet may lose its water into space, as has happened on Venus. 

Further out water is frozen, as occurred on Mars, except perhaps during early 

days in the life of the planet. Thus, there is a rather narrow zone that could 

be hospitable to life as we know it. Of course, there are also other factors 

affecting the habitability of a planet, like its mass. 

Also elsewhere space missions have been developed for asteroseismology 

and the detection of occultations by planets. The first was MOST, a 

Canadian microsatellite launched in 2003, with a 15-cm telescope essentially 

restricted to asteroseismology 9) . The next one will be Kepler 10) , a NASA 

mission scheduled for launch in 2007. Kepler will have a 95-cm telescope, a 

field of view of 100 square degrees and a camera with of the order of 

100 million pixels. It will observe some 100 000 stars during a four year 

mission. This is said to potentially yield a harvest of more than a hundred 

earth-like planets in or near the habitable zone. 

In Table XV, 1 are indicated the relative merits of the radial velocity, 

astrometric and occultation methods for finding planets. It appears that the 

Table XV, 1. The detectability of planets by different methods around a Sun-like star. 

The columns from left to right columns give the orbital radius R in AU, orbital period P 

in years, the reflex velocity of the Sun V sun in m/sec, the amplitude of the angular 

displacement θ in microarcseconds if at 30 light years distance, and the relative dip 

∆I/I in % of light intensity of the Sun due to the Earth, Jupiter and three imaginary 

planets placed at various distances. The last column gives the chance in % that the 

orbital planes are in the right orientation for an occultation to occur. Realistic observational 

limits during the coming decade are likely to be 1 m/sec, 1 µas and for the 

photometry well below 0.01 but depending on the stellar brightness. 

R P V sun θ ∆I/I Chance 

(AU) (yr) (m/s) (µas) (%) (%) 

Earth 1.0 1.00 0.09 0.30 0.009 0.50 

Jupiter 5.2 12.0 12.50 540.00 1.100 0.09 

“earth” 0.1 0.03 0.30 0.03 0.009 5.00 

“jupiter” 0.1 0.03 90.00 10.00 1.100 5.00 

“earth” 5.2 12.0 0.04 1.70 0.009 0.09


radial velocity searches tend to detect massive planets close to the parent star, 

that the astrometric methods favor massive planets far from the star, and 

that the photometric measures are most likely to discover larger planets 

close to the star. Realistic observational limits during the coming decade 

should be 1 m/sec and 1 µas. The occultation data pose no insurmountable 

problem of precision, but, of course, the probabilities of a favorable inclination 

of the orbital plane are low. 

Imaging 

Of course, it would be far preferable to observe the planet directly. 

Unfortunately, this is difficult owing to the proximity of the faint planet to 

a star of much greater brightness. In Figure XV, 3 are indicated the 

brightness of the Sun, Jupiter and the earth as seen from a distance of 

15 light years. In visible light the Sun would be 1000 million times brighter 

than the earth. In the infrared the situation improves, but even at 15 µm 

the factor remains some 2,000,000. And the angular distance to the 

luminous source would be only 0.22 arcsec for the earth or 1”14 for Jupiter. 

In principle, the angular resolution of HST would be sufficient, at least for 

the latter. With a fully effective adaptive optics system also OWL would be 

Figure XV, 3. The brightness of the Sun, Jupiter and Earth at different wavelengths 

when placed at a distance of 15 light years. Since at visible wavelengths the Sun is 

10 9 times brighter than the earth, it would be difficult to detect the latter. In the 

infrared at 10 µm the situation is somewhat more favorable.


able to see such an earth-like planet and even would have the sensitivity to 

take a visual-near IR spectrum. But light from the star scattered in the optics 

or in the atmosphere might be a problem. Moreover, the most interesting 

spectral features are probably in the mid-IR. Interferometry may provide 

the answer to such problems. In a typical interferometer the light is made 

to interfere positively so that the object is seen with the best angular resolution. 

However, in a “nulling interferometer” the optics are arranged differently 

so that at the center the interference is destructive and, as a result, 

there is a black spot. In this way the stellar light may be very much reduced. 

ESO and ESA are collaborating to develop such a nulling interferometer at 

Paranal to try out the technique and to attempt to detect exo-Jupiters 

directly. In the second decade of this century “Darwin” (Figure XV, 4) is 

planned by ESA. It would be an interferometer of maybe six 1.5-m telescopes 

flying in formation and operating in the IR 11) . If an earth-like planet 

was detected, its spectrum would give information about the composition 

Figure XV, 4. Artist’s impression of ESA’s Darwin mission. Six 1.5-m telescopes on 

independent spacecraft send light beams to a central laboratory where they are 

combined to form a “nulling interferometer” which suppresses the light from the star. 

The spacecraft fly in formation with their relative positions controlled to a fraction 

of a wavelength by ion propulsion units.


of its atmosphere. In particular the molecules CH 4 (methane), CO 2, H 2O and 

O 3 (ozone) could be looked for (Figure XV, 5). Ozone formation requires 

oxygen, and it is believed that abundant oxygen implies the presence of at 

least bacterial life. The earth’s oxygen would rapidly disappear by oxydative 

processes if oxygen production stopped. Methane is more ambiguous, since 

abiogenic processes may also produce it. 

The zodiacal light – scattered or emitted by dust particles in our solar 

system is likely to be a limiting factor in the detection and spectroscopic 

analysis of planets. It creates a diffuse glow which makes it difficult to see 

the planets. Calculations show that this would limit the detection of ozone 

to earth-like planets nearer than about 10 light years. The solution might be 

to send the telescopes of Darwin to an orbit much further away from the Sun. 

Current models of the zodiacal dust distribution suggest that Darwin at 

about the same distance as Jupiter would be able to detect ozone up to 

60 light years away, which would yield more than a thousand stars where 

planet detection would be possible. Of course, such a project would also 

become much more complex and costly. An additional problem could be the 

zodiacal light in the exoplanetary system itself. The current interferometric 

studies from the ground may give an indication of how serious this is. Also 

some spectroscopic information about the planetary surface may be obtained. 

If such a planet has continents and oceans with their different reflectivities, 

photometric variations would result from rotation. NASA is planning a 

mission similar to Darwin, the “Terrestrial Planet Finder”, and current plans 

Figure XV, 5. The spectra of Venus, Earth and Mars. In contrast to the other two, 

Earth shows strong absorption due to water (H 2O) and ozone (O 3).


are to explore the possibility of combining the two missions. For ESA it could 

then be a “flexi mission”, a mission with a cap of around 200 M€ , although 

this seems an optimistic figure. 

Evidently Darwin is only a first step in a long program. If a planet 

with oxygen and water is found, we would wish to know if there are continents 

with vegetation, if there are oceans, if there are seasonal changes and 

many other things. That will take more than Darwin can provide. Larger 

telescopes and larger separations between them are required to have the 

sensitivity and the angular resolution to answer such questions. If any space 

science project could capture the imagination of the citizens in Europe, it 

would be this.

XVI. 

Publications 

Since verbal science has no final end 

Since life is short, and obstacles impend 

Let central facts be picked and firmly fixed 

The Panchatantra 1) 

Articles in scientific journals constitute the most direct product of the 

astronomical research activity. Unless the scientific community is aware of 

what has been done, it is not possible to take the next step in the construction 

of our understanding of the physical world. Future research is organized on 

the basis of what is already known. Once that research has been completed, 

it will be reported in the journals allowing new programs to be developed, 

and so on. Of course, all of this is too schematic: many tracks are followed 

in parallel and many new investigations begin before the data of the previous 

ones have been published. But to allow progress it is necessary to have a repository 

of all previously obtained knowledge. If we did not, we would repeat 

what has been done before rather than use it as a stepping stone for further 

progress. But certain results are more reliable than others. So it is necessary 

to not only publish the results, but complete articles that also describe how 

they are obtained. As a consequence, the more than ten thousand practitioners 

of the astronomical sciences publish annually some 75,000 pages of 

printed text in the international journals. 

Of course, no scientist can read all of these 75,000 pages. So their 

contents are summarized in reviews or books and discussed in conference 

proceedings, in the latter case in part before they are published in journals. 

But if one really needs to know in detail how a particular result was obtained, 

there is no alternative but to read it in one of the journals. Modern informatics 

have helped much in this. With the data bases at the Centre de 

Données Astronomiques de Strasbourg and the NASA Astrophysical Data


System it has become easy to locate references to articles on a given subject 

or object. Since the original astronomical literature contains virtually all the 

results of the research activity, we shall not consider any further the secondary 

sources of information. 

If we wish to quantitatively study the astronomical literature and the 

contributions to it by different countries, it is necessary to define what constitutes 

astronomy or the astronomical sciences. Some would include the sun, 

but perhaps not planetary research. However, it hardly seems reasonable to 

exclude objects that in the past were certainly part of astronomy for the sole 

reason that space missions allow now a much more detailed study. Others 

would include the heliosphere and the interplanetary medium, but not the 

magnetosphere of the earth. However, the interaction between the solar 

wind and the magnetosphere takes place in a complex region which also 

contributes much to the understanding of the former. So we shall include in 

situ observations of the transition region and the upper magnetosphere by 

spacecraft, but leave aurorae, the ionosphere and adjacent lower magnetosphere, 

magnetic storms observed on the ground and the quasi-steady part 

of the earth’s magnetic field to the geophysicists. 

The boundary between physics and astronomy is equally fluid. Where 

does particle physics end and the study of the early Universe or of dark matter 

begin? We shall exclude all particle physics in the laboratory or with cosmicray 

beams in the astmosphere, but include the study of the origin, acceleration, 

composition and propagation of cosmic rays in the Galaxy. Observations of 

neutrinos from the Sun and beyond, as well as searches for dark matter also 

belong to astronomy. It would hardly be reasonable to include all of General 

Relativity, but the astrophysics of black holes and the detection of gravitational 

waves from cosmic sources certainly are part of astronomy. Space experiments 

in fundamental physics, as for example the test of the “principle of 

equivalence”, are more ambiguous in character. However, pragmatically we 

include it since the technology is the same as that for the detection of gravitational 

waves; in the ESA program it serves as a technology demonstrator 

for the latter. Of course, this discussion shows the impossibility to have neat 

boundaries in an interdisciplinary subject. In practice, the matter is less 

complex because authors select the journals in which they publish, and as a 

result almost all articles in one particular journal tend to be entirely within 

or without the subject. The main exceptions occur in some geophysical 

journals. 

The Astronomical Journals 

Four non profit journals dominate the field: “Astronomy & Astrophysics” 

(A&A), published by ESO on behalf of a (continental) European 

board under contract with a semi-commercial publisher, the “Monthly Notices

Publications 255 

of the Royal Astronomical Society” (MNRAS) of the UK, the “Astrophysical 

Journal” with its supplements (ApJ) and the “Astronomical Journal” (AJ) of 

the American Astronomical Society. These four account for some 84% of the 

publication volume in the astronomical sciences in the EU and US. In 

addition, there are to be considered the “Journal of Geophysical Research” 

(JGR) and the “Geophysical Research Letters” (GRL), both published by the 

American Geophysical Society. These contain sections on the planetary 

systems, the heliosphere and the earth’s magnetosphere in addition to more 

strictly earth-science related topics. The much smaller “Publications of the 

Astronomical Society of the Pacific” contain original articles in astronomy, 

but also some reviews and other matters. The American journals are partly 

financed by “page charges”, paid by the institutions to which the authors 

belong, and partly by the income derived from the subscribers. In principle, 

the page charges cover the costs of refereeing, editing and layout. The 

“Monthly Notices” derives all its income from subscriptions, “Astronomy 

and Astrophysics” most of it from subscriptions except that the governments 

of the participating countries subsidize the editorial offices, and a small 

amount of page charge income is derived from authors in other countries. 

Not surprisingly, the cost of a subscription to the European journals is higher 

(at least for libraries) than that of the American ones, as it covers a larger 

fraction of the total cost. 

A&A was created in 1969 by the merger of several national journals in 

Europe. Around the middle of this century the impact of the national journals 

had become much more limited in part because some were published in 

German or French. Initially, some authors continued to publish in A&A in 

these languages, which remained permitted under the conditions of the 

merger. However, authors wanted to be read and by now the journal is, in 

practice, entirely in English. Whether one likes it or not, English has taken 

over the role of Latin as a universal means of scientific communication. 

Fears that this will affect the survival of the other languages seem highly exaggerated. 

The scientific community is only a small subset of society and the 

dangers to other languages from popular “culture”, television, etc. are infinitely 

greater than those from scientific papers written in English. The scientific 

enterprise is by definition international and needs a common language. 

In middle Europe, the Czech journal has recently also been merged 

into A&A, while the Polish “Acta Astronomica” still survives. A new journal 

“Baltic Astronomy” was created some years ago. It remains to be seen 

whether this was a good idea. After all, the Estonians who publish mainly 

in the international journals are well known, perhaps more so than their 

brethren to the south. The Russians continue to publish several journals in 

Russian, but English editions of these are also available. They also make more 

and more use of the international journals. Japan and China have national 

journals, in English and Chinese respectively, but are increasingly publishing 

in the international ones; the Indian journal “Astrophysics and Astronomy”


has undergone a steady shrinkage. It is clear that scientists everywhere want 

their best results published where they will have the greatest impact. But 

deprived of the best papers, the national journals fight a losing battle for an 

audience. 

An increasing number of frequently more specialized journals produced 

by commercial publishers completes the picture. These include from Kluwer 

(now Springer) “Solar Physics”, “Experimental Astronomy”, “Celestial Mechanics”, 

“Earth, Moon and Planets” and “Astrophysics and Space Science”, the last 

three containing also conference proceedings. From Elsevier there are “Icarus” 

(planets), “Astroparticle Physics”, “Planetary and Space Science” (including 

some conference proceedings), and “New Astronomy”. Wiley-VCH has 

recently revived the venerable “Astronomische Nachrichten” in part also with 

conference proceedings. In the following we shall only consider the original 

papers. 

Finally, there are “Nature” and “Science” which are high profile weeklies 

covering all the sciences. Also astronomical papers appear occasionally in 

physics journals. Because quantitatively the number is relatively small, and 

since the boundary between physics and astronomy is fluid, we shall not 

consider these further. In compensation, in the astronomical literature there 

also appear articles reporting results in atomic physics and other areas which, 

it could be argued, do not belong to astronomy as such. 

All of the international research journals have a strict refereeing 

system: every paper is evaluated by one or more anonymous expert referees 

as to its suitability for publication. Because of the time this process and the 

subsequent editing take, many scientists used to send out preprints of their 

papers. These have now been largely superseded by the “Astro-ph”, a web 

site which allows papers to be posted electronically. There is no refereeing, 

though really cranky papers are kept out. While this system is very fast, it 

may create problems in fast moving fields with issues of priority. It is all too 

easy to quickly send out a first version of a paper to a journal and to Astro-ph 

and subsequently refine or correct it if needed. 

The different journals have different page contents which also have 

varied over time. In the further discussion we shall normalize to pages with 

a content of 7000 characters per page, including also the empty spaces 

between words or at the end of a paragraph. While this puts the different 

journals on the same basis as far as printed text is concerned, there may 

remain some differences in page content associated with the layout of figures, 

photographs and tables. During recent years the situation has become more 

complex, because some of this material is presented only electronically or 

deposited in centralized archives. How much of this would have been 

published in print in the past is difficult to evaluate, since there now is less 

economic pressure to present it in compact form. 

In Table XVI, 1 we have listed the journals which in 2002 contained 

more than 1000 normalized pages of original research in astronomy. It is

curious to see that even though most papers are submitted electronically, there 

remains a relatively strong tendency for the European and US communities 

to send their papers to journals edited locally. While this is understandable 

for the Europeans, who frequently have difficulties in paying the page charges, 

the phenomenon is actually strongest in the US. Taking into account that 

“Icarus” is published by Academic Press, now part of Elsevier, but still US 

based, we see that only 10% of US pages are published outside the country 

versus 22% of European papers published in the US. 

Productivity of the European Countries 


Table XVI, 1. The international journals containing more than 1000 normalized pages 

(7000 ch/p) reporting original research in the astronomical sciences during 2002. 

Subsequent columns give the name, the number of pages for the countries of the EU, 

the US and the whole world. The last two lines give the sum of the eight smaller 

journals and the totals. All figures have been rounded to the nearest multiple ten. 

EU US Total 

Astronomy & Astrophysics 13380 610 17450 

Monthly Notices RAS 8060 1430 12310 

Astrophysical Journal 3960 17670 26430 

Astronomical Journal 720 5090 7130 

Pub. Astron. Soc. Pacific 100 840 1120 

Solar Physics 410 450 1400 

Icarus 780 1880 3110 

J. Geoph. Res., Geo. Res. Let. 870 1940 3370 

8 smaller 1590 490 3430 

Total 29870 30400 75750 

To investigate the astronomical productivity of the different countries, 

we could count the number of pages published by researchers based in those 

countries. Since close to half of the papers published by Europeans involve 

authors from different countries, the simplest procedure is to allocate the 

papers to the country of the first author. It is not always clear that this is 

correct. When authors have made equal contributions, they are frequently 

listed alphabetically. However, statistically this should average out, unless the 

alphabetical distribution of names is different in different countries. Actually, 

such an effect exists. For example, Italian names tend to begin more 

frequently with a letter in the first half of the alphabet. However, the final 

effect on our statistics should not be more than a few percent. 

Based on counts of all the pages published during 2002 in the journals 

of Table XVI, 1, the results collected in Table XVI, 2 have been obtained.


Of course, these numbers do not contain much information and they have 

to be considered with reference to other quantities. Here we shall refer 

them to the number of inhabitants or to the GDP of the various countries 

(Figure XVI, 1). The great productivity in astronomy of the UK and the 

Netherlands is in evidence, while also Finland and Sweden do well – though 

here the statistical basis of the result is more limited. Austria has low productivity; 

the same is true for Greece and Spain, though here it seems more associated 

with a low per capita GDP. The low values of Eire, Norway and 

Portugal, though of poor statistical accuracy, are also noteworthy. In the case 

of Norway it may be partly related to a concentration of their efforts on 

auroral and ionospheric research, while Portugal appears to be in the early 

stages of a rapid increase following its adhesion to ESO and ESA, and the 

appointment of a number of young researchers. 

In Table XVI, 2 the numbers of pages in the international journals for 

the countries of middle Europe are indicated, where it has to be taken into 

account that the Polish “Acta Astronomica” and the largely Lithuanian “Baltic 

Astronomy” are not included. The former would add 207 pages to the number 

for Poland, the latter 106 for Lithuania. However, these journals include much 

material that would be published only electronically in the typical international 

journals. Though the statistics are rather limited, it is encouraging that 

Czech (24 p./M inhabitants), Estonia (81 p./M inh), Hungary (18 p./M inh) 

Table XVI, 2. Normalized pages (7000 ch/p) published during 2002 in all the astronomical 

sciences as defined in the text in the journals listed in Table XVI, 1. Data 

are given for the EU (2002) countries (including here also Iceland, Norway and Switzerland) 

and for the countries of middle Europe that have become members of the 

European Union or may do so in the near future. Page numbers marked with an 

asterisk are for countries with important local journals (see text). For Eastern Europe 

and Japan see note 2. 

Pages Pages Pages 

F 4027 Ic 21 Bul 68* 

D 5363 Ei 110 Cro 51* 

I 4636 NL 1836 Cz 247* 

UK 8028 N 120 Est 114* 

A 279 P 176 Hun 178* 

B 612 ESP 1848 Lith 16* 

DK 331 S 848 PL 655* 

SF 543 CH 628 Ser 52* 

GR 448 Slvk 71* 

Slvn 8 

EU 29863 US 30408

1 

0,8 

0,6 

0,4 

0,2 

0 

-0,2 

-0,4 

-0,6 

-0,8 


F D I UK A B DK SF GR NL ESP S CH 

Figure XVI, 1. Astronomy pages per inhabitant ■ and per unit GDP ❑. Plotted are 

the fractional differences with respect to the EU average of 77 standardized (7000 ch/p) 

pages per Minh and of 4.4 pages per G€ of GDP. The corresponding values for Eire 

–0.61/–0.55, Norway –0.62/–0.70 and Portugal –0.77/–0.66 have not been plotted, 

since their statistical significance is low. On the same scale the US would be at 

0.43/–0.23, the latter figure fluctuating with the exchange rate, as it is also the case, 

but to a lesser degree, for the EU countries outside the euro zone. 

and Poland (17 p./M inh) already exceed the 14 p./M inh of the EU some 

26 years earlier. This and the evidence of growth augur well for the future. 

The situation in these countries will be further discussed in the next chapter. 

Next we turn to the evolution of publication rates with time. Our 

earlier studies of data for 1976, 1987, 1992 and 1997 were based on more 

limited samplings of typically 4–6 months worth of the first seven journals 

in Table XVI, 1 supplemented by “Planetary and Space Science”. In 2002 

these journals accounted for 92–93% of the EU and US production, and so 

their evolution should be representative of the total. In Figure XVI, 2 the 

resulting growth rates over the 12.5 year period from the average of 1987 and 

1992 to 2002 are presented, while for the larger countries, the EU and the 

US the detailed evolution is shown in Figure XVI, 3. The figures illustrate 

the enormous increase in astronomical publications over the last 26 years, 

a factor of 2.7 for the US and 5.6 for the EU. In 1976 the EU published half 

as much as the US; by 1997 equality was reached.


2,5 

2 

1,5 

1 

0,5 

F D I UK A B DK SF GR NL ESP S CH EU US 

Figure XVI, 2. Growth in pages determined from 2 p (2002)/[p (1987) + p (1992)]. 

Pages are from the first seven journals in Table XVI, 1, and also include Planetary and 

Space Science. The open bars are of lower statistical significance. Eire, Norway and 

Portugal have all increased, but the numbers of pages are too small for a meaningful 

result. 

From data assembled by the US National Science Foundation 3) it is 

seen that the total number of papers in all sciences in peer reviewed journals 

increased by 3.7%/y for W. Europe and by 0.9%/y for the US during the 

period 1988 to 2001. The corresponding growth rates in astronomy from 

Figure XVI, 3 are 5.0%/y and 2.6%/y for the EU and the US respectively. So 

in both regions astronomy publications were increasing at a faster rate than 

publications in all sciences. The overall publication volume in the EU in 2001 

exceeded that in the US by 14%, while in astronomy equality between the 

two has prevailed since the mid-nineties. 

The increased access to state-of-the-art instrumentation played a major 

role in the European advances. In 1992 Germany launched the ROSAT X-ray 

satellite. Five years later some 300 ROSAT related papers, corresponding to 

2000 pages, were published during the year. Even though not all of these had 

first authors in Germany, this easily explains the peak in 1997. The same 

appears to have happened in Italy, where the launch of Beppo SAX in 1996 led 

to an accelerated publishing activity some five years later. The UK has a particularly 

vibrant, competitive astronomical community, well integrated with their 

US counterparts and, as a result, have had access to a wide variety of instrumentation. 

One only has to look at the effective use they have made of the

Number of pages published annually 

8000 

6000 

4000 

2000 


0 

1977 1982 1987 1992 1997 2002 

Year 

Figure XVI, 3. Evolution of the number of pages published annually in the journals 

of the first seven lines of Table XVI, 1 + Planetary and Space Science in some countries, 

the EU (2002) and the US. The data points are for 1976, 1987, 1992, 1997 and 

2002. The lines are linear interpolations. 

X-ray satellites Newton-XMM and Chandra launched by ESA respectively 

NASA in 1999. France did well in the beginning, but has slowed a bit. 

Employment practices have prevented the effective use of postdocs, while the 

early hiring waves have had the consequence that by 2002 nearly 40% of the 

permanent researchers were within 10 years of retirement. 

Of all EU countries, Spain has had the fastest growth. Once the 

government began to fund research more amply, a substantial inflow of 

young, active researchers and increased availability of instrumentation led 

to enhanced publishing activity. Nevertheless, in comparison with the other 

large countries it remains low, undoubtedly due to its lower per capita GDP 

and R&D spending. In 1998 its R&D was still below that of the Netherlands, 

F 

D 

I 

UK 

NL 

ESP 

EU/3 

US/3


although its population was 2.5 times larger. The Dutch started out very high 

in the European astronomy publication picture, owing to their early prominence 

in radio astronomical instrumentation, and as a result have not 

increased all that much thereafter, though Figure XVI, 1 shows that they still 

are close to the top in publications per capita. The situation in most other 

countries is apparent from Figures XVI, 1 and 2, though the statistical fluctuations 

from year to year are relatively large. 

We next turn to the subjects of the articles. From the 2002 data it 

appears that 14% of the astronomical publications in the EU dealt with the 

solar system (including the Sun), while in the US the corresponding figure 

was 21%, not surprising because of the large NASA program of in situ 

missions. The details for the EU countries are exhibited in Figure XVI, 4; of 

course, for the smaller countries the year to year variations are far from negligible. 

In 1997 a more detailed analysis of the numbers of pages in different 

astronomical research areas had been made on the basis of samplings of the 

pages in the first seven journals of Table XVI, 1, augmented by Planetary and 

Space Science. In most journals only four months worth of data were 

sampled. Since the geophysical journals were not included, no reliable data 

on solar system research could be obtained. In Figure XVI, 5 the relative 

percentages of five research areas are shown for the EU and the US, and for 

the four largest EU countries separately. In these figures the similarity of the 

0,7 

0,6 

0,5 

0,4 

0,3 

0,2 

0,1 

0 

F D I UK A B DK SF GR NL N ESP S CH EU 

Figure XVI, 4. The fraction of pages devoted to the Solar System in the journals 

listed in Table XVI, 1 in 2002. Open bars correspond to inadequate statistics. 

US

0,45 

0,4 

0,35 

0,3 

0,25 

0,2 

0,15 

0,1 

0,05 

0 


Galaxies & Cosmology Milky Way Galaxy Intersellar Matter Stars Sun 

Figure XVI, 5. Relative fractions of pages for five astronomical research areas in 

1997. In each area the columns from left to right are the US, the EU, France, Germany, 

Italy and the UK. 

distributions of research interests is almost more striking than the differences. 

The statistics for the other countries are too limited for accurate results, but 

Spain and Sweden appeared to concentrate their activities in the area of 

galaxies and cosmology, while Austria, Belgium and Switzerland were particularly 

concerned with stars and the Sun, and the Dutch with neutron stars 

and related high energy phenomena. However, the limited sampling may lead 

to large year to year variations. 

The 1997 data also showed that theoretical research accounted for 

33% of the activity in the EU versus 25% in the US. Some 45% of EU publications 

involved international cooperation, versus 24% in the US. Of course, 

the lower value for the US reflects the size of the country. More than half of 

the cooperations of the EU countries involved at least two within the EU. So 

in many ways the “European Research Area” already exists in astronomy. 

While it is straightforward to determine the quantity of published 

material, it is far more difficult to make a judgment as to its quality. This 

has led to a simple minded “citation index” assuming that role. Increasingly 

it is being used by university administrators and research councils in decisions 

about appointments, promotions and funding. 

The “Institute for Scientific Information” in Philadelphia counts the 

number of times a paper is cited in other papers in a large number of


journals. From this a citation index or an impact factor is constructed. 

The connection to quality then follows from the assumption that a larger 

number of citations indicates a higher quality. Trivial counterexamples may 

be given: an erroneous paper on a timely subject may have many citations 

simply to point out that it is wrong! But a more fundamental objection is 

that there is a strong sociological factor in citations. 

If one of my friends has written a paper, it gives both of us pleasure 

if I cite that paper. I shall be equally inclined to cite the friend’s students, 

since it is good for their career. The extremes that are possible in this respect 

are the “citation clubs” in the US, whose members agree to cite each other 

to improve their prospects or standing. In the US there is a tendency to 

believe that what is done in the Anglosaxon countries in general, and more 

specifically in the US, is particularly worthy of confidence and, therefore, of 

citation. Not surprisingly the US journals do well in their “impact factors”. 

Frequently it is not at all evident that the cited article has been read 

or made use of. In recent studies it was found that typographical errors in 

cited references propagate rapidly through the literature, presumably because 

people copy the citation 4) . All of this does not mean that the citation indices 

are totally without value. First of all, even though the number of citations is 

not very informative, their absence is. In addition, within well defined 

communities they may have some value. For example, if two scientists in an 

institute compete for a position in the same subject area and if they have 

written in the same journals, the relative numbers of citations may contain 

some information. As a basis for a judgment of the relative quality of the 

totality of the papers published on the two sides of the Atlantic, the canonical 

impact factors are totally irrelevant. 

In addition, there have been more trivial, but serious errors in the 

citation indices. The journal Astronomy and Astrophysics was normally 

referred to as Astron. Astrophys. However, gradually the abbreviation A&A 

has been taken over, which was not recognized by the ISI software. As a 

result, the “impact factor” of the journal for 2000 was listed as 2.36, but 

following complaints corrected to 4.35 5) . Similar problems occurred in other 

years. Some university administrations in Europe count publications of candidates 

for professorships multiplying the numbers for low impact journals by 

0.5. So young European scientists who published in the European journal 

A&A, to which various governments make a contribution, were set back 

compared to their colleagues who published in non European journals for 

which payment was required. In several cases irreparable harm was done to 

careers. All of this shows again the dangers of both the belief that quality 

can be quantified in simple ways and in leaving it to commercial enterprises 

to determine scientific quality.

XVII. 

European Astronomy: 

Researchers and Funding 

Fundamental science cannot be driven by institutional, 

industrial, governmental or military pressure. This is the 

reason why I decided as far as possible not to accept 

money from Government. 

C.V. Raman 1) 

Europe spends less on R&D as a proportion of its GDP (1.9%) than either 

the US (2.8%) or Japan (3.0%). In parallel with this there are also fewer 

researchers per capita, 2.2% in the EU versus 3.5% and 4.4% in the US and 

Japan respectively. These figures of course are totals of all types of research 

performed by very different actors: pure or applied research and government 

or private industry. As noted by R. May 2) , if only science base (universities, 

government funded laboratories, etc.) spending is compared, the situation is 

more favorable with EU, US, Japan spending 0.65%, 0.63% and 0.85% of GDP 

respectively, the difference with the other figures being accounted for by larger 

Development spending. It is also true, however, that in large pure science 

projects industrial development plays an important role. The development of 

mirror materials has much benefitted the VLT, detector development has been 

essential to photon detection on the ground and in space; in fact, much of industrial 

development for the military has benefitted the construction of satellites 

for space research. So the overall R&D deficit in Europe still has a negative 

effect also on “pure” research. EU governments talk much about the “knowledge 

economy” and about the need to improve education at all levels, but when 

it comes to budget time this is all too easily forgotten. Especially during the 

last decade a generalized pessimism seems to have set in that has had a paralyzing 

effect on research and education. This has been particularly visible in 

the budgets for space research. Both ESA and national space science budgets 

have tended to decline during the last decade in real value, amounting now in


total to less than 20% of those on the other side of the Atlantic. In ground based 

astronomy the situation is more favorable, but much effort will be needed to 

maintain the rough equality that has been achieved. 

How much does Europe spend on the astronomical sciences and how 

many astronomers are there? Since essentially all funding comes from governments, 

one could have thought that such questions would be easy to answer. 

Nothing is farther from the truth. Some countries have only a very nebulous 

idea on their astronomical personnel or spending. This is partly due to the 

fact that at universities funding may not have very clear destinations as far 

as disciplines go. Moreover, in some countries universities are dealt with at 

the provincial rather than the national level. Another factor is that funding 

for organizations like ESA and ESO passes through different ministries in 

different countries: education, foreign affairs and even economics ministries. 

Finally there is pure sloppiness: as an example, one country reported to ESA 

a figure of 500 space scientists working there in 1994 and 300 in 1996. One 

wonders what disaster befell the 200 missing ones! Even more mysterious 

is the increase from 400 to 1107 over a two year period in another country. 

So, even official figures may have to be carefully analyzed or corrected. 

In this chapter we shall analyze the staffing and funding for astronomy 

in various countries. As in the previous chapter I define “astronomy” as 

including all studies of objects outside the magnetopause of the earth. It 

should be remembered that others frequently use more restrictive definitions. 

However, I have difficulty in seeing that exoplanets and stellar winds belong 

to the subject, while the planets in the solar system and the solar wind do 

not. Moreover, there is a substantial overlap in funding and personnel, especially 

in ESA and in the national space programs. 

In addition, there is the question: what is a researcher? Are PhD 

students working on their thesis to be counted as researchers? We shall do 

so. Are astronomers building instruments scientists, but engineers doing the 

same not? We include the former who also frequently use the instruments 

later on, but not the “pure” engineers, i.e. specialists in mechanical, optical 

or electronic engineering, though the distinction between the two is not 

always evident. Of course, engineers and technicians working on astronomical 

projects are included in the funding figures. Because of outsourcing, the 

numbers of technical and administrative personnel have become less significant, 

but the overall cost figure is. In some countries the retirement age is 

low, but many researchers remain active, though not included in the statistics; 

in others scientists may be counted to a high age. Some scientists work 

nominally part time, though in reality they do more. Others have moved 

permanently or temporarily into administrative positions. In the US some 

scientists have created small enterprises which perform research sponsored 

by the government. Some scientists work in industry, while remaining active 

researchers. Hence, it is clear that statistics of astronomical personnel will 

always remain of limited accuracy.

Relatively detailed information is available for the four major countries 

in European astronomy. France every so often has a “colloque de prospective” 

and Germany a “Denkschrift”, the most recent ones both in 2003. 

In Italy rather detailed data are available as a result of governmental plans 

for restructuring, and in the UK the Particle Physics and Astronomy Research 

Council regularly provides information on its spending plans. The central 

funding sources are easier to analyze than the regional or provincial ones, 

which in some countries assume increasing importance. European Union 

funding may suffer from fluctuations. A relatively large contribution may also 

be made by many universities in which there is astronomical personnel 

without there being a formal astronomy department or institute. It is not 

always easy to discover such cases. 

In the smaller countries the situation is even more varied. The 

Netherlands have regular planning exercises with good documentary material, 

while Spain also recently made an excellent analysis. Easily accessible and 

complete data are lacking in several countries. So the estimates have more 

uncertainty. Upon request several persons have tried to collect the necessary 

data in their country; these form the basis of the corresponding data in this 

chapter; nevertheless, they had to be modified in some cases to correct for 

different definitions of “astronomy”. There also is a recent joint brochure of 

the European Science Foundation and the European Astronomical Society 

entitled “European Survey of National Priorities in Astronomy”. Though its 

intent is laudable, it is unfortunately very short on specifics and quantitative 

information. 

Staffing 

European Astronomy: Researchers and Funding 267 

Few countries in Europe have done much rational planning in hiring 

astronomers. In some years governmental policies were favorable and relatively 

numerous researchers could be engaged, while at other times the 

opposite happened. This has had several negative consequences. If in some 

years many recent PhD’s are hired, the average quality will be lowered. But 

in the years of scarcity they cannot wait without employment and so even 

very good PhD’s will leave the field, frequently forever. Thus, if one wishes 

to retain the best students, a relatively stable inflow would be preferable. 

However, from the point of view of a director of an institute, it is impossible 

not to use the opportunity of hiring some new staff: if the favorable years 

are not fully utilized, one is likely to get even fewer positions in the bad years. 

Favorable and unfavorable periods tend to have durations of several 

years or even decades. In countries where life time employment laws prevail, 

this has the consequence that the age distribution of researchers may have 

important hills and valleys. While many researchers remain active to a high 

age, it is, nevertheless, true that flexibility decreases with age and that for


the scientific liveliness of an institute an important fraction of young researchers 

bringing in new ideas is essential. 

Two different philosophies occur. In countries like France the inflow 

into PhD programs has been set at such a level that an important fraction 

of the PhDs can find employment in the astronomical area, while post 

doctoral jobs of limited duration are only accepted under very specific conditions. 

The situation in Italy has been rather similar but is beginning to 

change. In other countries, like the UK, the inflow into PhD programs is much 

larger, many PhDs obtain positions as “post docs” for a few years at a time, 

and only a small number can obtain permanent employment in the field. 

The latter system has definite advantages. A continuous rejuvenation 

takes place, competition for the permanent jobs stimulates activity, and the 

selection process is much less open to error, since a judgment on the suitability 

of candidates for a permanent position is based on a substantial number 

of years of research production rather than just on the PhD. A negative aspect 

may be that it may lead to risk aversion. For a post doc to engage in a long 

term project that may not lead to results is dangerous. From a social point 

of view the situation is more ambiguous. Having an army of post docs, many 

beyond forty years of age, looking every few years for new positions in 

different universities, creates problems in particular for researchers with 

families. However, if there are enough possibilities to find employment 

outside the astronomical field, it is a question of personal choice. For example, 

in the Netherlands more than two thirds of the PhDs in astronomy find jobs 

in informatics, governmental planning agencies and even in banks and insurance 

companies. Also quite a few are leaving the country to find positions 

elsewhere. However, if most PhDs cannot remain in the field, there should 

be a certain obligation for the universities to ensure that the education is sufficiently 

broad so that the transition to the outside world is facilitated. In 

practice, this is rarely considered. Furthermore, prospective PhD students 

should be informed very clearly about the prospective employment situation. 

In all of this there is, of course, also an economic aspect. In most countries 

PhD students work for little money, and so they represent a low cost 

work force which makes a major contribution to the analysis of the data 

stream that comes from ever more prolific instruments. To a lesser extent 

the same is also true for the post docs. It is no accident that the UK is at the 

top of the publication rate per unit GDP. Also in Germany the number of 

PhD students and post docs has increased rapidly. Here, however, the educational 

system has tended to cause the average age for the award of the PhD 

to be relatively high. At the same time, the employment laws make it difficult 

to continue giving non permanent jobs to people in their forties. 

More and more EU countries recruit PhD students and post docs without 

regard to nationality. This has many positive aspects. The pool of young talent is 

increased, and it could be anticipated that the more mobile researchers tend to 

be also the more imaginative. Here also the EU commission makes a contribution


in funding various internationalization programs. And, of course, this also fosters 

European integration and the creation of a “European Research Area”, so 

eloquently fostered by the EU commissioner Ph. Busquin. 

In Table XVII, 1 we have assembled the available information on 

researchers in Europe. Subsequent columns give our estimates for the number 

of researchers with PhD and of PhD students, the percentage this represents 

of all researchers in the countries and the number of pages published (from 

Table XVII, 1. Astronomical researchers in various countries. The columns from left 

to right give our estimates of the number of post PhD scientists and of graduate PhD 

students, the percentage of both of these of all researchers (R&D), the pages published 

per researcher, and the number of astronomers per million inhabitants. Thereafter 

follow the numbers of IAU members in 2004 and their average annual growth rate 

over the period 1992–2004. While the IAU numbers are subject to certain selection 

effects (seniority, underrepresentation planetologists) they are exact in contrast to the 

numbers of scientists which are subject to uncertainties. EU refers to the pre-2004 

membership plus Norway and Switzerland. Values for Sci + PhD st for Belgium and 

Norway have been obtained by multiplying IAU with 1.9, the average EU ratio. 

% ast/M IAU/M + %/ 

Country Sci PhD st all res. p/ast inh IAU inh yr 

F 800 200 0.65 4.0 17 633* 11 1.0 

D 850 500 0.58 4.0 16 492* 6 1.1 

I 950 100 1.39 4.4 18 443* 8 1.4 

UK 800 500 0.91 6.2 22 582* 10 1.6 

A 50 50 0.78 2.8 12 34* 4 1.3 

B (191) (0.83) (3.2) (19) 101* 10 1.9 

Dk 45 13 0.35 5.7 11 59* 11 1.4 

SF 75 46 0.72 4.5 23 54* 10 5.3 

Gr 130 30 2.0 2.8 15 105* 10 1.4 

Ic 4 1 0.44 4.2 18 4* 14 2.4 

Ei 32 28 0.72 1.8 16 35* 9 2.5 

NL 125 80 0.65 9.0 13 153* 10 0.9 

N (42) (0.26) (2.9) (9) 22* 5 0.8 

P 65 0.56 2.7 7 35* 4 6.7 

ESP 315 133 0.86 4.1 11 245* 6 3.6 

S 100 70 0.50 5.0 19 108* 12 2.1 

CH 100 55 0.72 5.2 14 89* 12 4.1 

EU 4200 1900 0.71 4.9 16 3219* 8 1.6 

US 4500 (900) 0.56 5.6 20 2457* 8 1.4 

* 25 estimated ESA personnel deducted.


Table XIV, 2) per astronomical researcher. In the table we have not made a 

distinction between tenured (permanent) scientists and others. For the long 

term health of the subject a reasonable balance between the two is necessary. 

In quite a few places the average age of the tenured scientists is excessively 

high with the risk that only part of these positions will be retained by the 

universities. Situations differ considerably as a function of national policies 

in the matter. But some illustrative examples show the problem: in the two 

main Danish universities 15 out of 20 tenured scientists are above 55 years 

of age, at the university of Lund all but one. 

Most professional astronomers are members of the International Astronomical 

Union (IAU). Such membership is free of charge, the IAU being 

financed by contributions from national academies and equivalent bodies. 

Usually, researchers become members shortly after their PhD. The numbers 

of IAU members as a measure of the astronomical research population, given 

in the fifth column of Table XVII, 1, have the advantage of being very precise 

and to refer to people who consider themselves “astronomers”. However, 

planetary and magnetospheric scientists tend to be underrepresented, while 

retired members without research activity may retain membership. New 

members are elected every three years. In the right hand column is the mean 

annual growth rate of the number of IAU members for the period 1992–2004. 

It should be noted that the growth is showing signs of leveling off. Annual 

growth during the six year period 1986–1992 was still 3.6%/yr; in France the 

number was even 10 less in 2004 than in 2001, the first decline in Europe. 

Inspecting Table XVII, 1, we see the similarity in the numbers of astronomers 

per million inhabitants in France, Germany and Italy, with the UK 

being particularly research and astronomer friendly. Italy has a high fraction 

of astronomy researchers, but its total researcher population is low. Among 

the smaller countries, Norway, Portugal and Spain are low in the number of 

astronomers, as they were in publication rates, though the latter two appear 

to be improving rapidly. 

Funding 

While it is not easy to determine the number of researchers with 

precision, it is still harder to determine the number of euros spent by different 

countries on astronomical activities. One component, however, is known 

precisely: the contributions to ESA and ESO, which in 2003 amounted to 

361 and 100 M€, respectively corresponding on average to 0.048 and 0.015% 

of GDP, respectively, for their member countries. Alternatively stated, the two 

account for some 36% of all EU funding for astronomy. If we add to this an 

estimate of the funds spent by the countries on payloads for ESA and instruments 

built for the VLT, the total ESA/ESO related annual expenditure 

becomes of the order of 540 M€ per year. This means that some 42% of the


total astronomy spending has been “europeanized”, i.e. its content is largely 

decided by Europe-wide decisions, even though, of course, a national 

consensus is also needed. Again, the “European Research Area” is seen to 

exist already in the astronomical sciences. This calculation is based on the 

fact that during the nineties the sum spent on payloads for ESA amounted 

to 24% of the annual contributions according to information provided by the 

member countries. Undoubtedly, this has diminished in the meantime. We 

have adopted an uncertain 20% for 2003. For the VLT instruments we 

estimate member country contributions at some 5 M€ /year. 

To ascertain the national spending in astronomy, a more detailed 

analysis of sometimes rather fragmentary data is needed. The results are to 

be found in Table XVII, 2, where the cost per astronomical researcher (from 

Table XVII, 2. Estimated European funding for astronomical research in 2003. The 

columns from left to right give the contributions to ESA/ESO and the estimated total 

spending in M€ , the part of GDP spent on astronomy in %, the costs per astronomical 

researcher and per page published both in k€. Figures in parentheses are particularly 

uncertain estimates. 

ESA/ESO Total % GDP per ast per page 

M€ M€ (k€) (k€) 

F 77.1 240 0.15 240 60 

D 107.9 285 0.13 211 53 

I 63.7 225 0.17 214 49 

UK 83.9 210 0.13 162 26 

A 8.3* 19 0.08 190 68 

B 13.9 (33) (0.12) (173) (54) 

Dk 9.1 17 0.09 293 51 

SF 5.1** 16 0.11 132 29 

Gr 0 8 0.05 50 18 

Ic 0 0.3 0.03 60 14 

Ei 3.5* 8 0.06 133 73 

NL 22.4 55 0.12 268 30 

N 6.3* (11) (0.06) (262) (83) 

P 5.4 (9) (0.07) (138) (51) 

ESP 25.3* 70 0.09 156 38 

S 12.7 29 0.11 172 34 

CH 16.9 43 0.15 277 68 

EU 461 1280 0.13 210 43 

* Only ESA. ** From mid-2004 + 1.9 ESO.


Table XVII, 1) and per page of research results (from Table XV, 2) is also 

given. The figures have been based on information provided by scientists in 

the various countries or on more official documents, except where given in 

parentheses when they are my very crude estimates. In most cases, with 

regard to both the definition of “astronomy” and the items included, I have 

made adjustments to bring them as much as possible on a common basis. 

Thus, the values tend to be somewhat higher than those given by countries 

with more parochial definitions of astronomy where the subject (except for 

the Sun) begins only beyond the orbit of Pluto. 

Middle and Eastern Europe 

Ten countries have joined the European Union in 2004. Several others 

are expected to do so later in this decade. Economic circumstances are harsh, 

currencies have fluctuated and many researchers spend a significant part of 

their time abroad to gain access to advanced equipment or to improve their 

finances. None of these countries are members of ESO or ESA. For several 

countries realistic statistics are not easy to come by. So here we shall restrict 

ourselves to two easily available data, the number of IAU members and the 

publication data from Table XVI, 2 assembled in Table XVII, 3. Data are given 

for the four countries with more than 100 pages in 2002. The other countries 

have too large statistical fluctuations and their data has been added together. 

From the Table it is clear that the numbers of astronomers are still on 

the low side and that the same is the case for the productivity. However, the 

Table XVII, 3. IAU members (2004), annual growth rate over last 6 years, IAU per 

million inhabitants, pages (Table XVI, 2) per IAU and the fraction of all researchers 

who are IAU members, for four countries, for all other Middle European countries 

with astronomical activities, compared to data for W. Europe. 

IAU/M 

IAU %/yr inh p/IAU IAU/all res. 

Czechia 74 0.7 7.2 3.3 0.00 59 

Estonia 23 0.7 15 5.0 

Hungary 45 1.6 4.5 4.0 0.00 40 

Poland 128 1.5 3.3 5.1* 0.00 24 

Other M. Eu 192 1.5 3.9 1.8 

All M. Eu 462 1.3 4.0 3.2 

W. Europe 3219 1.5 8.3 9.3 0.00 37 

* Poland publishes a national journal “Acta Astronomica”; so productivity may 

be slightly underestimated.


fraction of all researchers that are astronomers is on average the same as in 

the West. So it reflects an overall weakness in the research activity, related 

to the still low GDP/capita. In 2003 GDP/capita in the most favorable case, 

Czech, amounted to 7400 €, compared to the W. European average of 25,000 €. 

Since in the period 1995–2003 the ratio of the GDP of Cz + Hun + PL to that 

of W. Europe increased by 5% per year, it may be expected that also the 

research activity will slowly improve. At this rate in 25 years equality would 

be reached. While this may seem very far into the future, the planning 

horizon for the large future projects in astronomy we are considering also 

extends into the third decade of the present century. So it would be reasonable 

to include the Middle European countries in our planning exercises 

now. 

Russia with 377 and the Ukraine with 162 IAU members are still 

rather low with 2.6 respectively 3.2 IAU/M inh. The 6 yr annual growth rate 

in IAU is 1.5 respectively 5.3%/yr. Productivity seems low with 3.4 respectively 

2.3 pages/IAU. However, here it has to be taken into account that at 

least one high quality regional journal serves these countries. So the true 

productivity is well above these figures. With a large population of well 

educated physical scientists remaining, a rapid growth could be expected, 

once the economy improves, provided the governments retain their interest 

in pure science. 

Why pay for astronomical research? 

Why should governments support astronomical studies? When in 1768 

the Royal Society wrote a memorandum to King George III requesting funding 

for the Cook expedition to observe the transit of Venus in front of the Sun 

and thereby to infer the Sun-Earth distance, they listed three grounds for such 

support 3) : it would avance knowledge, it would contribute to the solution of 

an important practical problem, and it would enhance national prestige. 

The first item has moved many a king, government or philantropist, 

frequently in conjuction with the third one. One only has to look at the 

evidence from Tycho’s observatory on Hven (Dk) or at the well preserved 

remains of the observatory of Jai Singh at Jaipur (India) to realize that 

sometimes a non negligible part of GNP was devoted to an enterprise whose 

sole purpose was to advance knowledge. Today many remain convinced that 

increasing our understanding of the Universe is a worthy aim. Also national 

prestige has played a large role: the “race” to the moon and the visits to other 

planets were very much motivated by this. 

The solution of an important practical problem in Cook’s time was the 

determination of the position at sea. The Global Positioning Systems have 

now solved this problem, but in their development there is an important 

astronomical heritage. A few more current examples may also be mentioned.


The study of the Sun has certainly a direct societal importance. Solar 

flares which cause storms in the solar wind have an impact on radio communications, 

on satellite performance, and even on electricity grids. A better 

predictability of such events would be useful. Also, solar variability and 

perhaps the solar wind have an effect on terrestrial climate. Their detailed 

study is necessary to ascertain the precise role of human activities in global 

warming. 

Asteroids or comets are sometimes in orbits where they may hit the 

earth. The great extinction at the end of the Cretaceous (extinction of dinosaurs 

and many others) was caused by such an event. In 1909 the very much 

smaller Tunguska object destroyed a 40 km diameter forest area in Siberia. 

Had it struck a few hours later, it could have destroyed an urban area in 

Europe. Discovery of dangerous objects and consideration of remedial 

measures, therefore, have some importance. Some scientists believe that 

valuable minerals may be mined in asteroids or perhaps the moon. While at 

the present cost of space transport this seems far fetched, it could be a 

motive for further study. 

Mars is the planet most like earth, but is currently hostile to life 

because of its tenuous atmosphere and low temperatures. It has been 

suggested that the introduction of highly effective greenhouse gases could 

raise the temperature and evaporate frozen CO 2 and water; this could possibly 

make the planet suitable for plant life and later even for humans. Some people 

have proposed to colonize Mars so that if disaster befalls earth, humanity 

could continue. Again, by stretching probabilities a bit, the study of Mars 

could be considered “useful”. 

Such practical or semipractical reasons to support astronomy could be 

and have been advanced. However, the principal reasons are others. We wish 

to know the nature of the Universe we live in, its origin and its future. We 

wish to know where we came from, if there are planets like ours, if there is 

life elsewhere and, if so, its similarities or dissimilarities with life here. And 

the general progress of science requires progress in all of its domains. Much 

of progress in physics, for example, has come about by interaction with 

astronomy, and the tie between the two has become stronger in recent times. 

Finally, societies that make advances in science make progress in technology 

and vice versa. This is not only because technological progress depends on 

an understanding of physics, but also because the mind set that is propitious 

to progress in science is the same as the one that leads to advances in technology 

and the construction of a rational society. 

The same point has been made in purely financial terms in a study 

carried out by the Bureau d’Economie Théorique et Appliquée (Strasbourg) 4) 

in which the indirect economic effects of ESA’s programs were evaluated. It 

was found that direct ESA payments of 3901 MAU to industrial firms had 

generated indirect benefits to these firms of 12677 MAU, or a return coefficient 

of 3.25, confirming an earlier study which had yielded a coefficient


of 2.9. The most important contributions to these spin-offs were made by 

“technological effects” (sale of products designed for ESA and diversification 

thereof) and “work related effects” – the increased capabilities of design and 

production teams. While these figures refer to ESA’s overall program, the fact 

that the science program contributes particularly effectively to innovation 

within ESA makes these figures important in the science context. 

While one may be convinced that funding for the sciences, including 

astronomy, is justified, this does not tell one yet at what level this should be. 

Four factors have to be considered: past commitments and levels of support, 

equilibrium with adjoining sciences, interest to an educated public, and international 

competition. 

The first point is obvious. If an institute exists or a project has been 

started, it is difficult to suddenly terminate it. Apart from contractual aspects 

with regard to personnel or to industry and other suppliers, it would be 

wasteful. If, for example, ESO funding would have ceased just before 

completion of the first telescope of the VLT, a large sum of money would 

have been spent, but nothing useful would have been achieved. A certain 

continuity is necessary. Also too sudden increases in funding have dangers: 

neither the intellectual nor the administrative infrastructure may exist to 

effectively utilize the funds. In some European countries available positions 

for young scientists have fluctuated wildly with several years of drought 

being followed by sudden abundance. During the years of drought brilliant 

students have come from the universities; no positions in the chosen field 

being available, they have taken other jobs to make a living. During the years 

of abundance there may not be enough top level students delivered by the 

universities and positions will be given to those with inadequate abilities for 

a scientific career. Both factors will lead to a lowering of the average level. 

However, while continuity is thus important, this does not mean that every 

scientific discipline should have a fixed fraction of the total funding. The 

promise of the field for innovation and fundamentally new results should very 

much influence its support. As an example, it is not at all surprising that the 

share of the biological sciences has increased in several countries, both in 

view of their intellectual promise and their potential utility for human welfare. 

For several decades science funding in Europe has gone up, and to privilege 

some areas could be done without taking much away from others. At present, 

overall funding has been stable or even diminishing in some countries, and 

frequently painful decisions are necessary. An example of an organization that 

has done this well is the Max-Planck-Gesellschaft in Germany which is 

responsible for the funding of more than fifty scientific institutes. To make 

room for new institutes in new fields of science, several existing institutes 

have been terminated. The alternative would have been an underfunding of 

all areas of science. 

An appropriate equilibrium with other adjoining branches of science 

is an important factor. Information about particle physics may be obtained


from studies with accelerators on earth or from astrophysical studies. As a 

consequence, it would not be appropriate to put all funding in one or the 

other. Since many physicists will have an interest in both and may make 

proposals for funding in both, an equilibrium between the two may arise from 

the scientists themselves. 

Since the financial support for science comes through the political 

process, an appropriate role for the educated public cannot be denied. As 

many of the issues cannot be judged by non scientists, this role cannot be 

dominant, but it cannot be negligible either. For various reasons the public 

is motivated to support studies of the origin of the Universe, exoplanets, Mars, 

the origin of life, as well as of various diseases, ecology and global warming, 

to name just a few. In the US, where private philantropy has a long tradition, 

donations to such fields have made an important contribution. In Europe, 

where this is not so much the case, the governments have to take such 

factors into account. A corollary is that the scientists have a great necessity 

to explain what they are doing to a broader public than just to their 

colleagues. 

Finally, international competition plays an important role. There is no 

point in basic science in doing things that have been done elsewhere ten years 

earlier. So in the basic science areas that a country wishes to pursue, the 

funding has to be comparable to that in other countries. Of course, the 

different cost and salary levels have to be taken into account. Countries with 

limited financial possibilities have to be selective in what they are doing. For 

Europe the reference has been mainly the US. With 40–50% more population 

it has a smaller R&D work force overall (15% less) than the US, but spends 

about the same fraction of GNP on government sponsored R&D, however 

much less in total R&D. In astronomy the European spending is about half 

that in the US, mainly because of the much lower spending on space research. 

However, the number of astronomers per inhabitant is about 10% larger. As 

a consequence, the overall funding per astronomer is substantially lower in 

Europe.

XVIII. 

The Future 

Then was not non-existent nor existent… Who verily 

knows and who can declare it, whence it was born and 

whence comes this creation? 

Rig Veda 1) 

During the last decade European astronomy has seen remarkable 

progress. In the radio domain MERLIN, EVN and IRAM, in the IR ISO, in 

the optical the VLT, in X-rays ROSAT, BeppoSAX and XMM-Newton, in soft 

γ-rays INTEGRAL, and in the hardest γ-rays HESS and MAGIC have allowed 

the coverage of nearly the complete electromagnetic spectrum. They have 

created opportunities for research equal to and not infrequently superior to 

the best available elsewhere in the world. In the solar system Cluster, 

Huygens, Rosetta and Mars Express represent unique facilities. The half 

shares in the equally unique Ulysses and SOHO and the 15% share in HST 

have been important assets to European scientists. 

The near future looks equally bright. ALMA will explore the submm 

Universe with unprecedented angular resolution and sensitivity. Herschel will 

study the adjacent wavelength region in the far IR which until now has been 

largely unexplored, and Planck will observe the Cosmic Microwave Background 

left over from the Big Bang over the whole sky with unmatched 

angular resolution. The VLT will be supplemented by two large telescopes in 

the northern hemisphere, the Spanish 10-m GRANTECAN on La Palma and 

the Germany/Italy half share of the LBT in Arizona. GAIA will observe 

distances and motions of a thousand million stars, 1% of all that exist in our 

Galaxy. Solar Orbiter will size up the Sun from close by. Venus Express will 

orbit the planet that has not seen a spacecraft for a decade, and B.Colombo 

Mercury. VIRGO, GEO-600 and LISA will be looking for gravitational waves. 

For all these facilities and for many others sophisticated auxiliary instruments 

have been or will be constructed.


Spectacular discoveries have been made in Europe during the last 

decade. If I had to choose three, it would be the first ever exoplanet around 

a solar-type star, the resolution of the more than thirty year old mystery of 

gamma-ray bursts, and the definitive evidence for a black hole, and the 

precise measurement of its mass, in the center of our Galaxy. Others might 

select other items, since there is a long list of discoveries. 

It might be concluded that all is well and that European astronomy can 

continue to coast at its present level. This would mean to misunderstand the 

dynamics of science. What today is at the forefront of science, will be history 

tomorrow. The scientific results obtained with the current equipment will lead 

to the formulation of new problems which can only be solved by new, more 

powerful instruments. Moreover, the competition never sleeps. If Europe would 

stand still, its recently acquired high status would soon vanish. What at the 

moment is an instrument that is the envy of the world, may be ready for the 

museum when we or others will have built still more powerful instruments. If 

no up to date equipment can be constructed, the best scientists and engineers, 

who give the field its dynamics, will move elsewhere or to other fields of science. 

The major instruments with which today’s discoveries are being made have 

been conceived up to 2–3 decades ago and developed and funded during the 

decade preceding their completion. So now is the time to begin to think of the 

instruments for the 2015–2030 period. Of course, new scientific and technological 

developments will occur in the meantime. So we should not set plans for 

future instruments and missions in stone. If circumstances change drastically, 

we should be willing to scrap the plans we have made when these are no longer 

relevant. Nevertheless, long term planning is necessary to determine in which 

directions we should orientate our current efforts in both science and technology. 

So let us see what could be the projects in different areas that are just 

over the present European horizon. I would select the following four as particularly 

unique, timely, realistic and important: SKA, the Square Kilometer Array, 

in radio astronomy (Chapter IX); OWL, the 100-m Overwhelmingly Large 

Telescope, in the optical (Chapter VIII); XEUS, the large X-ray facility 

(Chapter XI); and Aurora, the Mars exploration program (Chapter XII). Two other 

projects would have equal importance but less evident realizability in the time 

frame considered: Darwin, the IR space interferometer in space (Chapter XV) 

with a broad range of aims, but in particular the discovery and study of earthlike 

planets, and Solar probe to in situ study the region where the solar wind has 

its origin. Since the money streams for ground and space based projects are still 

largely separate, we shall consider the two separately. But before this, we should 

see what are the principal science themes that we wish to study. 

Science themes 

Notwithstanding the successes that have been achieved, the list of 

unsolved problems remains long. I see eight science themes to be at the center

The Future 279 

of current interest. Some of these may perhaps be solved during the coming 

two decades. The first five themes are of a fundamental nature in the sense 

that we are ignorant or uncertain about the basic physics involved. The last 

three are of great complexity – a bit akin to the study of the climate of 

the earth. Even if the basic physics were fully understood, the number of 

processes that need be studied is so large that progress is slow. In 

Table XVIII, 1 are summarized the themes and the instruments which may 

contribute to their elucidation. A brief description follows: 

1. Dark Energy. Observations of the brightness of supernovae seem 

to indicate that the expansion of the Universe is accelerating with cosmic 

time, contrary to expectation. It had been assumed that gravity would lead 

to a deceleration. It is then said that this is due to some kind of repulsive 

“dark energy”. So far, the evidence depends on supernovae of type Ia with a 

redshift less than z = 2. To further investigate this it is necessary to observe 

supernovae (also of other types) at large redshifts. These would be so faint 

that telescopes like OWL are needed. 

2. Dark Matter. In galaxies and clusters of galaxies there is much 

matter that generates gravity, but is otherwise unobservable. Its nature is 

unknown. At first it was thought that it could consist of low mass stars or 

gas at temperatures where little radiation is emitted. Observations with 

current optical and X-ray facilities indicate that this is not the case. More 

likely it is composed of neutralinos, axions or other particles beyond the 

“standard model” of particle physics. If so, the next accelerator at CERN, the 

LHC, may contribute evidence. Direct detection of dark matter has been 

attempted with particle detectors, but so far without result. It is also possible 

that dark matter particles and antiparticles annihilate. The resulting γ-rays 

might be detectable with instruments like HESS and MAGIC. 

3. The Earliest Universe. Various lines of evidence suggest that 

there has been an early period of inflation, a very rapid expansion of the 

Table XVIII, 1. Principal Themes of Astronomical Research. 

European Instruments 

Theme most directly involved 

Dark Matter HESS / MAGIC, particle detectors, LHC 

Dark Energy OWL 

Earliest Universe Planck, Virgo? 

Black Holes Virgo / LISA, XEUS, SKA… 

Extreme Energy Cosmic-rays Auger, EUSO, neutrino detectors 

Galaxy / Star Formation JWST, Herschel, OWL, ALMA, SKA… 

Sun Solar Orbiter, Solar Probe 

Life in Universe Darwin, SKA


Universe. The cause is unknown. Quantum fluctuations from still earlier 

epochs would have been the seeds from which much later galaxies and other 

structures in the Universe have formed. The imprint of such fluctuations has 

been detected by observations of the Cosmic Microwave Background. Planck 

and possibly observations of gravitational waves will give information on the 

very early epochs. 

4. Black Holes and their immediate environment have been studied 

at radio, optical and X- and γ-ray wavelengths. The VLT has obtained particularly 

compelling data on the black hole at the center of our Galaxy. Much 

remains to be done with more powerful X-ray and radio instruments like 

XEUS, SKA and (space) VLBI. The most conclusive information might result 

from gravitational wave detectors like Virgo and LISA. 

5. Extreme Energy Cosmic-rays. While we know that they exist, 

little is known about their characteristics. But their high energies show that 

they contain a message about extreme situations in the Universe, though 

because of their rarity we are still unable to decipher the message. Auger, 

EUSO and various neutrino detectors should contribute to our understanding 

of these remarkable events. 

6. Galaxy and Star Formation. Much has been learned from observations 

with the VLT, ISO and IRAM and other radio telescopes. But sensitivity 

and angular resolution are inadequate to study the early stages of 

galaxy formation on more than the grossest features of star and planet 

formation. Also only a beginning has been made with the analysis of the 

evolution of the elemental composition and the chemistry of matter in 

galaxies and star forming regions. JWST, Herschel, OWL, ALMA, GAIA and 

SKA will open up this field which in the near future should benefit much from 

the VLTI. 

7. The Sun remains an object of much interest because of its effect 

on the earth’s climate and environment. Only a start has been made with the 

study of the heating of the corona and the solar wind. The complexity of the 

processes involved in solar activity makes continuing observation at high 

spatial, spectral and time resolution a necessity. Following SOHO, Solar 

Orbiter and also ground based solar observations should contribute significantly 

to the field. 

8. Life in the Universe. The discovery of exoplanets indicates that 

abodes for life may be widespread beyond the earth and possibly Mars. 

Evidently, the search for biological markers in the Universe is becoming a 

major activity. The Aurora program, project Darwin and SKA could make 

major contributions. 

These eight topics may be considered central themes in the exploration 

of the Universe. However, the large instruments that are most likely to 

address these themes will also make many other discoveries that will further 

complete our picture of the Universe – or perhaps change it radically. We 

now turn to some aspects of the instrumental projects beyond 2005.

Ground based projects 


OWL is currently being studied at ESO as a 100-m optical, near IR 

telescope. According to present plans, first science operations with part of 

the primary mirror could begin in 2017 with full completion in 2021. The 

capital cost is estimated at 940 M€. A smaller 60-m version would cost 

perhaps half as much. Some industrial studies are at the basis of these estimates. 

More modest versions (20–40 m) have been studied in Sweden in 

cooperation with other countries. In the US plans are being made for a 30-m 

telescope at a capital cost of 400 MUS$. If we exclude the cost of interferometry, 

Paranal development and instrumentation, the cost of the VLT would 

have been around 260 M€ (2004 value). Thus, the extraordinary claim is that 

improved technology allows a 30-m to be built at the same cost as the 16-m 

equivalent VLT and the 100-m version of OWL for less than four times that! 

Even if these estimates were correct, the question is from where the 

financing is to come. Till 2011 ESO will invest some 30 M€/yr in ALMA. At 

the same rate some 300 M€ would be available by 2021. New member countries 

might add to the ESO budget some 10 M€/yr in investment money. In 

addition, European countries have invested some 200 M€ in telescope projects 

like LBT, GRANTECAN, VST, VISTA and others. So if funds of the same order 

of magnitude would be directed towards OWL, the total available on a decadal 

basis could be some 600 M€. The requirement for “new” funding would be 

brought down to 30–40 M€/yr for ten years. While in the present pessimistic 

economic mood any new money would be hard to come by, such a sum does 

not seem unattainable especially if the European Union would begin to 

distribute significant research funding as is under consideration. 

The main danger to OWL may be a lack of commitment in Europe. Here 

and there one hears that one should buy into a US project to obtain access to 

a large telescope more quickly. Obviously, if one or two countries would follow 

such a route, there might not be enough money left to participate in the 

European project. It is worth remembering that whatever harm may have been 

done to European astronomy by having to wait some eight years for the full VLT 

after the completion of the first Californian Keck telescope, has been more than 

compensated by the possession now of the world’s top telescope, with an enviable 

set of instruments. Certainly after this Europeans should not be content to 

become again the poor relation with limited access to someone else’s big 

telescope. Better to wait a while longer and then to leapfrog to the forefront. 

SKA is a very different story. With a large number of partners, who 

have a long tradition of cooperation, it is an ideal project for a worldwide 

collaboration. SKA is currently envisaged as an array of radio telescopes with 

a total collecting area of 1 km 2 , scattered over an area of perhaps 3000 km 

in diameter. The total cost has been capped at a thousand MUS$. By its very 

nature an array is particularly suitable as a cooperative project. Issues of 

industrial return are more easily solved, since there is no need to build all


elements in the same industry. In a monolithic telescope it is more difficult 

to divide the roles, and if a partner cannot meet its commitments a catastrophic 

situation may arise. In an array one would redistribute the roles or 

make the project somewhat smaller. 

Radio astronomy in Europe has generally been financed on a rather fragmented 

basis. The only major international project has been IRAM with a 

French-German investment of some 60 M€. Actually it started out as a simple 

superposition of two national projects which were combined, since on a national 

basis money was available but no staff positions. Since the staff were then on 

the IRAM payroll, it did not count for the national personnel limits. Of much 

smaller financial size is the EVN center which coordinates the observations of 

the national telescopes of the European VLBI network. Current investments in 

European radio astronomy include a 64-m radio telescope in Italy, LOFAR in 

the Netherlands and a 40-m telescope in Spain, at a combined cost of more than 

200 M€. In addition, several other countries have made significant investment 

in the radio domain. Hence, a total European investment in SKA of some 

250–300 M€ over a 10–15 year period would not need to be prohibitive. 

However, the projects mentioned were all on the national territory. With SKA 

undoubtedly outside Europe, the funding might be more difficult to obtain. And, 

of course, with SKA and OWL occuring over the same time period does not help. 

Space Projects 

XEUS has been proposed by a broad coalition of European high energy 

astrophysicists as their next project. A strong X-ray community in Europe has 

been built up in the past around the four projects in this area: EXOSAT, ROSAT, 

BeppoSAX and XMM-Newton. In addition, European scientists have been active 

participants in Japanese, Russian and US projects by contributing instruments. 

But XMM-Newton is expected to end its useful life not long after 2010, and it 

becomes important to consider its successor. XEUS should have an effective area 

of some 10 m 2 and a sensitivity two orders of magnitude better than XMM. In 

addition, it should allow observations of hard X-rays up to around 50 keV and 

a much better spectral resolution. Cost would probably be in the 500–1000 M€ 

range. In the US there are plans for Constellation-X, an X-ray facility of four 

telescopes on four separate spacecraft, at a projected cost of 800 MUS$. Also 

in Japan an X-ray facility with emphasis on hard X-ray optics is under consideration. 

Perhaps a joint European-Japanese project would be an attractive 

option. For the moment, there would be no room in the ESA budget for XEUS 

before the later half of the second decade, but, of course, economic circumstances 

and ESA’s fortunes are hard to predict so long in advance. In any case too long 

a wait would be most damaging to what may well be the strongest space science 

community in Europe which has been built up with much effort and money. 

Aurora is the Mars exploration program that has been started within 

ESA as an optional program; every country decides how much it will

contribute and receives a proportional amount of industrial return. Current 

funding is modest (2005–2006: 31 M€), with Italy and the UK contributing 

the most. The stated aim of Aurora is manned exploration by 2033. Obviously, 

precursor missions are needed. The present planning includes a rover on 

Mars by the end of the decade and a sample return mission later. Two years 

after the start of Aurora, the US announced a major initiative for exploration 

of the moon and Mars. Undoubtedly, as with the Space Station, there will 

be pressure on Europe to participate as a junior partner; as in that case, it 

is not clear that this would serve European interests. 

Possible Space Projects 

Darwin is an ambitious project to detect earth-like planets and to 

analyze their spectra for evidence of life. It would be a large IR interferometer 

with perhaps six telescopes on independent spacecraft and two more 

spacecraft for a variety of necessary functions. In the US a similar project, 

the Terrestrial Planet Finder, is being studied. TPF is presented as a project 

for the next decade at a cost of 1700 MUS$. Discussions have taken place 

between ESA and NASA about a joint mission. However, even half of Darwin 

would be a major budgetary problem for ESA; if participation were much less 

than half, would it really be in Europe’s interest to participate? 

Solar Probe was one of the “green dreams” of Horizon 2000, 20 years 

ago, and reappeared with the same status in Horizon 2000 Plus. It would 

involve a spacecraft in a Ulysses-like orbit, but approaching the Sun within 

four solar radii to study the origin of the solar wind. Obviously, thermal 

problems are very severe at that distance. Also the probe would move so fast 

that it would pass through the critical region in less than a day. NASA considered 

such a project with two passes separated by five years but because of 

budgetary problems as yet nothing definite has happened. Evidently, these 

problems would be still more prohibitive in the ESA context. 

Of course, many other proposals have been made. How about travelling 

to Jupiter’s moon Europa to see whether there is an ocean under the frozen 

surface? Or even further afield, what about Neptune or a super Cluster-type 

mission or a super LISA? In judging such proposals one has to be aware that 

there is a fundamental difference between what is reasonable in the context 

of an ESA budget and that of a NASA budget. If one is rich, one can afford 

occasionally missions addressing issues of rather specialized interest. If not, 

one better concentrate on missions of interest to a broad community and at 

the center of current scientific activity. 

International Collaborations 


International cooperation could play an important role in future large 

and small European projects. Until now, NASA has taken a prime place


among ESA’s collaborations – in some cases like Huygens, HST and SOHO 

with very positive outcomes. A stronger diversification of partners would be 

very much in the European interest. It would better ensure the autonomy of 

the European program. 

Relations with Russia have developed in a very positive way. INTEGRAL 

is the prime example which followed the earlier French SIGMA collaboration 

in gamma-rays. Cluster II and Mars Express have been placed into orbit with 

Russian launchers, and a more general cooperation in the launcher area has 

been established. Also in Mars-96 an extensive participation of European 

scientists went very well, though unfortunately the mission failed at launch. 

It would seem particularly attractive to continue that collaboration in the 

framework of Aurora. 

Also Japan offers many possibilities for cooperation. It is a partner in 

the ESA Mercury mission and it made an effective contribution to ISO. In 

X-ray astronomy, both solar and beyond, Japan has established an enviable 

record. It could be a very suitable partner in XEUS. The UK has participated 

very successfully in several Japanese X-ray missions. ESA is participating in 

the X-ray mission ASTRO E2 by providing a ground station and is also 

gaining some access to ASTRO F in the IR. The possible future SPICA mission 

in the IR is also of much interest. 

China is making rapid progress in the space field as in other areas of 

science. China and ESA are already collaborating in the magnetospheric 

mission “Double Star”. Future collaboration could be particularly fruitful in 

the solar area where China has been considering a space telescope. Also India 

is developing a substantial X-ray/uv satellite for launch in 2007, while a lunar 

orbiter is planned for 2008. Discussions are taking place about a possible 

European instrumental contribution to the latter. The beginnings of an 

interest in space activities are also in evidence in Latin America. So it is clear 

that there are many possibilities for cooperative missions worldwide. Europe 

has much to offer in this respect. In space technology it has reached maturity 

and politically it imposes few constraints on its collaborations. The advantage 

has been illustrated by the case of “Double Star”. Because of US export regulations 

with their extraterritorial reach, some existing instruments had to be 

rebuilt in order to eliminate parts of US origin. With so much trouble created 

by the US side, Europe began to look like a more attractive partner. So, why 

not profit from that? 

A final point concerns the Space Station. At the time that European participation 

was decided, it was the usual scenario. The Germans wanted to join a 

US project, the French to advance the European launcher capacity. In practice, 

the German participation in Ariane was traded for a French participation in the 

Space Station. The apparent motive on the US side was even more interesting 2) : 

“part of Begg’s [the NASA Administrator] rationale for inviting European cooperation 

had been to forestall competition with NASA’s capability”. Many voices 

were raised at the time contesting the utility of the Space Station for research 3) .

There were also warnings that the funding for the Space Station would squeeze 

funding for space research. In fact, Germany stated that it could not participate 

in Aurora because of the heavy expenses it still incurs for the Space Station 4) ! 

Fortunatly this decision has been reserved in 2005. 

Because of the large amount of money going into the Space Station, 

scientists have tried to think how to put it to some use at least. Examples 

are the ROSITA, Lobster-ISS (Chapter XI) and EUSO (Chapter XIV). So what 

does one hear now from the other side of the Atlantic? That the US Administration 

is eager to finish and close down by the next decade the Space 

Station and the shuttle. The new head of NASA could not have been more 

explicit: “It is beyond reason to believe that [the ISS] can help to fulfill any 

objectives, or set of objectives, for space exploration that would be worth the 

$ 60 billion remaining to be invested in the program” 5) . While one may agree 

with the statement, why did Europe let itself be dragged along at a cost of 

thousands of millions of euros in a profitless enterprise? The high cost and 

modest returns of Spacelab in the preceding decade should also have been a 

warning 6) . Hence, the conclusion is clear. International cooperation is a 

valuable asset, but Europe has to have clear aims and ensure that such 

cooperation fosters European interests. Moreover, partners should have 

unambiguous agreements and feel bound to their execution. As Bonnet and 

Manno 7) wrote “For European scientists, the best partners are those for 

whom international cooperation represents a moral commitment, a way of 

behaving, and an irreplaceable asset.” 

Organizational Issues 


Who will determine the future choices of large projets in Europe? 

A number of organizations could have a larger or smaller role: The International 

Astronomical Union, the Organization for Economic Cooperation and 

Development, the European Science Foundation, the European Astronomical 

Society, EU networks, ESA, ESO and a variety of national governmental 

bodies. Of course, the financial envelope within which the projects are realized 

is ultimately set by the national governments – individually and collectively. 

The IAU constitutes a global forum for the discussion of issues and 

possible cooperations. For example, the agreement of scientists in a number 

of countries to work together towards the financing and construction of SKA 

was concluded at the last triennial meeting of the IAU. But the IAU is barely 

able to scrape together a minimal budget for its administrative services, and 

it has neither the mission nor the structures needed to set priorities. 

The OECD through its Megascience Forum from time to time has held 

meetings with the aim to discuss possibilities of cooperation in or coordination 

of large science projects. While the aim is laudable, the impact has 

been limited. The major science agencies already have their channels through


which they interact; an example is the Inter Agency Consultative Group of 

the four principal space agencies. Of course, in practice the direct contacts 

between these agencies may be even more important. As a consequence, they 

felt that there was little to be gained from the OECD initiatives. In fact, both 

ESA and NASA declined to participate in the 2003 Megascience Forum held 

in München. There are, however, some areas where the OECD may have a 

unique role to play. For example, major investments have been made by the 

OECD countries in radio astronomical facilities. With SKA on the horizon, 

these will be further increased. However, radio interference from telecommunications 

and other sources might very much reduce the value of these 

investments. It is entirely within the purview of the OECD to intervene with 

governments to see what can be done. In fact, it has already begun to do so. 

The ESF is an association of European research councils which has been 

effective in coordinating activities in areas of science where strong European 

organizations are lacking. Its role in organizing a cooperation to obtain a geological 

cross section of the continent or in ocean floor drilling projects has won 

high praise. However, there is little it can add to what ESA and ESO are doing. 

In the US every decade a report is made, under the auspices of the 

National Academy of Sciences, in which priorities are set for the next decade. 

Several European scientists have thought that such a report should also be 

framed in Europe, and that the ESF might be the organization to do this. 

However, some care is needed in simply taking over the procedure. In the 

very large projects, ESA and ESO between them cover some 90% of the 

subjects in the astronomical sciences in Europe. They have extensive and well 

functioning advisory structures, and their planning horizon extends for 

10–20 years. Some of the countries have also their national plans which 

extend over a decade or more. Could an ESF planning exercise for the coming 

ten years be more than a superposition of the existing plans? Certainly it 

would be difficult for the ESF or another such body to contest the priorities 

of the national plans or those of ESA and ESO. A recent glossy brochure 

produced by ESF and EAS conjointly is hardly encouraging. 

The European Astronomical Society was founded in 1990 during a 

regional meeting of the IAU in Davos. From the beginning it was organized 

as a panEuropean entity, including West, Middle and Eastern European 

scientists. At the time there was some controversy as to whether it was to be 

a society of national societies or a society of members. In the former case, 

the governing council would have been composed of representatives of the 

national societies of which the Royal Astronomical Society in the UK and the 

Astronomische Gesellschaft in Germany are particularly strong. While initially 

these societies contested the need for a society of members – with the 

members fully controlling the society – during the subsequent decade positive 

relations have been developed. In particular the annual meeting of the EAS 

is organized conjointly with a national society, as a JENAM (Joint European 

National Astronomy Meeting), a format which has generally been rather


successful. Nevertheless, it still has not quite found its role on the European 

scene. The comparison with the American Astronomical Society is quite 

striking. With an annual budget of some 8,000,000 $, it publishes two major 

journals, has an office with influence in Washington, engages in extensive 

educational activities and organizes meetings that few young PhDs looking 

for a job will fail to attend. The main problem is that the EAS came late in 

the day when other arrangements for publications had been made and 

national societies had their spheres of influence and patronage. 

ESA and ESO have been very successful in combining the scientific 

quality, technical feasibility and financial viability of their projects within the 

limits set by governmental financial limits. They have largely avoided having 

committees that discuss all the great science one could think of, without 

considering the technical and financial aspects. With the ST/ECF they have 

created a structure that contributes to the effective interaction between the 

two, although perhaps more could be done in this respect. Both have an organizational 

setup with a top layer of governmental representatives (including 

scientists), and below this an ample scientific advisory structure which also 

ensures a sufficient level of communication with the scientific community at 

large. Whatever other initiatives may be taken, it is important that the system 

be preserved which has served European astronomers so well. As the 

Americans would say: “If it ain’t broke, don’t fix it”. 

It is sometimes said that ESA and ESO serve only part of the astronomical 

sciences. This book shows that this is only very partly true. The 

effective roles of ESO in ALMA and of ESA in the area of fundamental 

physics in space show that most subjects are covered. For the few that are 

not, effective solutions have been found. RadioNet with some modest support 

of the European Commission is a case in point. 

In fact, there are now several EU related and partly EC funded networks. 

RadioNet will conduct joint activities on interferometric software, phased 

arrays and mm-wave technology. In addition, it organizes the transnational 

access program for European radio facilities and provides some funds for trips 

to such facilities. RadioNet currently receives 2.5 M€ annually from the EU. 

OPTICON is another EC funded network. It deals in particular with 

ELTs, the extremely large telescopes. OPTICON started out at a time when 

the UK was not a member of ESO. Now that the UK has joined and that it 

also seems likely that Spain will do so in the coming years, one should 

wonder if there really is an advantage in having such a structure outside ESO, 

which could easily lead to more division. In addition, OPTICON organizes 

its transnational access program for medium sized optical telescopes and a 

number of Joint Research Activities, including uv astronomy, interferometry 

and astronomical technology. Current EC funding appears to be of the order 

of 4 M€ per year. A new network ILIAS, involving some 70 laboratories, 

focusses on astroparticle physics and gravitational waves.

XIX. 

Epilogue 

…entre européens depuis l’Atlantique jusqu’à l’Oural. 

Charles de Gaulle 1) 

In this book I have tried to show that European astronomy is in 

excellent shape and that it has the full potential to remain so during the 

coming decade. With a slightly increased financial envelope for ground based 

facilities and a more substantial increase for space research this should also 

continue thereafter, provided careful choices are made between the desirable 

and the feasible. A largely autonomous European program appears to be 

possible, but suitably selected international cooperation can very much enrich 

it. Of course, individual scientists will continue to collaborate worldwide, as 

they have done in the past. I have described only superficially what others 

are doing to provide the backdrop for European developments. Others have 

amply described the world from their point of view. 

One last point should still be made. The European Union has recently 

acquired ten new member states, and some others are likely to join by the 

end of the decade. As a corollary it follows that we have to see how to integrate 

these countries in the European scientific organizations, both for their 

benefit and for ours. Sometimes one hears that these countries will dilute 

the observing time or the mission opportunities without contributing much 

to enlarging the financial envelope for European astronomy. Interestingly, 

one is also told that the data flow of the new instruments is so high that there 

are not enough scientists to deal with it. Since several of the countries in 

question have well educated scientists, one problem may solve the other. 

Furthermore, while several W. European economies are stagnating, in middle 

Europe quite a few have high rates of growth. So even if one did not have a 

sense of collegiality for one’s fellow European scientists, one should welcome 

these countries because in the future their contributions will become more 

significant.


With increasing membership, adjustments will have to be made to the 

way in which scientific organizations function. It is impossible to give the 

same powers of decision to countries who pay 0.1% of the budget as to those 

with 10%. Since already some steps have been taken in the direction of 

increased voting weight for the larger countries in the W. European scientific 

organizations, this should not lead to too much trouble. After all, the 

European Union is facing the same problem in a more acute way and is considering 

solutions. 

Ultimately, it would be natural to also include Eastern Europe in the 

overall European framework. Russia and the Ukraine have many excellent 

physicists and astronomers and much experience in space matters. Their 

space industry continues to function well. In fact, some discussions are 

taking place between Russia and ESA about a closer association. Obviously, 

there are many problems to be resolved. But is it too much to dream of the 

day when pan-European scientific organizations foster research on the 

continent, create a scientific center for peaceful research second to none and 

collaborate on a basis of equality with others who have the same aim?

Introduction 

1) ESO, Garching, 1991. 

2) Harvard University Press, 1994. 

3) Kluwer Academic Publishers, 2001. 

Chapter I 

Notes 

1) Pliny the Elder, Natural History, Book II, 55. 

2) A few foundations in Europe are the exception: For example, the Volkswagen- 

Stiftung has made some important contributions to the cost of radio telescopes, 

while also the Carlsberg Foundation in Denmark and the Wallenberg Foundation 

in Sweden made contributions. While important, the total of these and other such 

contributions represents a very small part of astronomical investments in Europe. 

3) G.E. Hale, The Possibilities of Large Telescopes, Harper’s Magazine 15, 639, 1928. 

Chapter II 

1) C. Darwin, The Voyage of the Beagle. 

2) F. Hoyle, Home is where the wind blows, Univ. Science Books, Mill Valley, California, 

1994. 

3) H. Siedentopf (ESO Bulletin 1, 11, 1966) found on 3 sites in South Africa 1285–1750 

clear hours, to be compared with in Chile 2300 at Tololo and 2760 near Copiapo. 

4) Derived from data in A. Blaauw, ESO’s Early History, ESO, 1991. 

5) A. Blaauw, l.c., p. 157 states without further comment that it was used only in radio 

telescopes and in the design of the 6-m of the USSR, while C. Fehrenbach (Des 

hommes, des télescopes, des étoiles, éd. du CNRS, 1990, p. 435) writes that such 

a design presents many difficulties and is only interesting for telescopes larger than 

5 m. Another reason that more revolutionary designs were not considered may be 

related to the fact that decisions were in the hands of the “Instrumentation 

Committee” (IC), composed of senior astronomers well versed in optics, but less 

conversant with developments in mechanical engineering and control concepts. A 

similar conservatism may be noted in the rejection by the IC of Strewinski’s more 

daring design of the Schmidt telescope (Blaauw, l.c., p. 192).


6) A. Blaauw, l.c., p. 166. 

7) A. Blaauw, l.c., p. 240. 

8) Just as an example, at the last moment in 1974, the cooks had been moved up a 

notch because an incompetent cook could poison people, and the night assistants 

because an incompetent one might destroy a telescope. After having had three 

“Heads of Personnel” at ESO, I left the post vacant, since that took the smallest 

amount of my own time. Evidently after the VLT project led to a major expansion, 

this was no longer possible. 

9) The building was designed by the architects Fehling and Gogel who made a remarkably 

imaginative design. While staying within the unit costs of German university 

type buildings, they managed to have a huge entrance hall that gave the building 

its identity. During the construction the building company went bankrupt, but 

through the rapid intervention of the German government delays were minimized. 

In September 1980 the Geneva establishment of ESO was transferred to the new 

headquarters, which were inaugurated by the President of Germany on 5 May 

1981. The proceedings of the accompanying symposium “Evolution in the Universe” 

were published by ESO in 1982, edited by P.O. Lindblad and L. Woltjer. 

Chapter III 

1) Ovidius, Ars Amatoria, 26. 

2) R.J. Weyman, N.P. Carlton, The Multiple Mirror Telescope Project, Sky and 

Telescope 44, 159, 1972. 

3) A. Labeyrie, Stellar Interferometry Methods, Annual Reviews of Astronomy and 

Astrophysics 16, 77, 1978. 

4) M.J. Disney, Optical Arrays, Monthly Notices Royal Astronomical Society 160, 213, 

1972. 

5) L. Woltjer, The Case for Large Optical Telescopes, in ESO Conference “Optical Telescopes 

of the Future”, ed. F. Pacini, W. Richter, R.N. Wilson, p. 5, 1978. 

6) R.N. Wilson, The Messenger (ESO), 29, 24, 1982. 

7) R.N. Wilson, Reflecting Telescope Optics II, chapter 3.5, Springer Verlag Berlin, 

1999; The History and Development of the ESO Active Optics System, The 

Messenger (ESO), 113, 2, 2003. 

Chapter IV 

1) A till then unknown common spirit which could almost be considered political, has 

developed an organisation which aims to reach a scientifically entirely new level. 

O. Heckmann, Sterne, Kosmos, Weltmodelle, R. Piper & Co. Verlag, München 1976. 

2) Proceedings of the Workshop on ESO’s Very Large Telescope, ed. J.P. Swings and 

K. Kjär, ESO 1983. 

3) P. Léna, Aperture Synthesis in the Infrared: Prospects for a VLT, ibidem p. 129. 

4) F. Roddier, Future Possibilities of Ground-based Interferometry in the Visible, 

ibidem p. 135. 

5) R.N. Wilson, Reflecting Optical Telescopes II, ch. 3.3.5, Springer-Verlag, 1999. 

6) D.E. Enard, ESO 16 Metre Very Large Telescope: The Linear Array Concept, in IAU 

Colloquium 79, Very Large Telescopes, their Instrumentation and Programs, ed. M.-H. 

Ulrich, K. Kjär, ESO 1984, p. 767.

Chapter V; Most notes refer to documents of ESO Council and Finance 

Committee. Many other facts can be found in the ESO Annual Reports 

1) J. Conrad, Heart of Darkness. 

2) Cou-403, 1988. 

3) Cou-457, 1991. 

4) FC-833, 1989. 

5) Cou-448, 1991. 

6) Cou-443, 1990. 

7) Cou-413, 1988. 

8) Cou-433, 1990. 

9) Cou-434, 1990. 

10) Cou-528, 1994. 

11) Cou-578, 1995. 

12) Cou-453, 1991. 

13) Cou-403, 1988. 

14) Cou-429, 1989; see also Cou-458, 1992. 

15) For a general description of Chilean astronomy, see L. Bronfman, ESO Messenger, 

107, 14-18, 2002. 

16) O. Heckmann, Sterne, Kosmos, Weltmodelle, pp. 300-301, Deutscher Taschenbuch 

Verlag, München, 1980. 

17) Cou-521, 1994. 

18) Cou-613, 1996. 

19) Cou-570, 1994. 

Chapter VI 

1) I. Newton, Optiks. 

2) C. Piazzi Smyth. The Friday evening discourses in Physical Sciences at the Royal 

Institution 1851–1939, Astronomy volume 1, 16; edited by B. Lovell, Elsevier publ. 

1970. 

3) Surveys had been made in the Peleponesos and in Spain. Much importance was 

attached by the Director, Prof. W. Elsässer, to a European continental site, to avoid 

possibly increasing air fares. Ironically touristic developments have had the consequence 

that air fares to the Canaries are particularly low. Also the French had 

studied a site closer to the Spanish coast, some 50 km SW of Calar Alto, and found 

it to be unsatisfactory, though better than sites in France (R. Cayrel in ESO 

Conference Proc. 18, 45, 1983). 

4) C.G. Abbot, Annals Smithsonian Institution 6, 6, 1942. In Smithsonian Miscellaneous 

Collections 101, No 12, Abbot presents data for a number of sites, including 

Mt. Brukkaros in Namibia, which show that even in the most favorable month 6 mm 

of H 2O was present at 1600 m altitude. In the northern hemisphere a 2600 m high 

summit near the St. Katherine monastery in the Sinai was found to be the best site; 

it was operated from 1934–37 when fear of war led to its abandonment. The annual 

mean precipitable water vapor was 2.5 mm, corresponding to a median value as 

low as Paranal. It might be interesting to investigate the area more closely. 

5) A. von Humboldt; see L.A. McIntyre “Die Amerikanische Reise”, p. 258, GEO 

Verlag 1982. 

Notes 293


6) P.C. Keenan, S. Pinto, H. Alvarez. The Chilean National Observatory (1852-1965), 

Universidad de Chile 1985. 

7) Information Bulletin for the Southern Hemisphere, 12, 29, 1968; H.W. Duerbeck 

et al., ESO Messenger 95, 34, 1999 

8) J. Stock, Science 148, 1054, 1965. 

9) H. Siedentopf (ESO Bulletin, 1, 11, 1966) found sites in S. Africa with 1285–1750 clear 

night hours to be compared with for Tololo and Copiapo 2300 respectively 2760 

hours. Image quality at Tololo was “distinctly better” than for the S. African sites. 

10) A. Blaauw, ESO’s Early History, ESO, 1992, p. 44, even though later the opposite 

was stated, pp. 47/48. While after the coup d’état in 1973 political relations 

between Chile and Europe became rather cool, it would have been politically more 

difficult to operate an observatory in S. Africa. 

11) Ibidem, pp. 56-62. 

12) Major coups occurred in 1891, 1924, 1931/32 and 1973; see S. Villalobos et al., 

Historia de Chile, Editorial Universitaria, Santiago 1974. 

13) J. Stock. Astronomical Observing Conditions in Northern Chile, ESO Bulletin 5, 

38-40, 1968. 

14) Information Bulletin for the Southern Hemisphere 18, 19, 1971. 

15) Ibidem, 10, 20, 1967. 

16) According to J.W. Warner (Pub. Ast. Soc. Pacific 89, 724, 1977) 6% of time at 

Chacaltaya had less than 1 mm H2O against 16% at Mauna Kea, the latter being 

1200 m lower. Less than 3 mm occurred 50% of time against 83% at Mauna Kea. 

At Chacaltaya median cloud cover was about 50%. According to the data for the 

station of the Smithsonian Institution near Arequipa, Peru, presented by G.P. Kuiper 

(Lunar and Planetary Laboratory Communication 156, Univ. of Arizona), the 

average of the median monthly cloudiness there during day time is 44%. So there 

seems to be no advantage to go northward beyond the Chilean border. 

17) I have given a description of the expedition in ESO Messenger 64, 5, 1991, following 

a first account in Site Testing for the VLT in Northern Chile, ESO Conference Proc. 

18, 147, 1983. 

18) A. Ardeberg, in Very Large Telescopes, their Instrumentation and Programs (IAU 

Coll. 79), ed. M.-H. Ulrich & K. Kjär, ESO, p. 417, 1984. 

19) In the Paranal area Sarazin also made seeing measurements at Co Armazoni 

(3060 m), some 20 km east of Paranal, and Co La Montura, a few km to the north. 

The former was found to be very similar to Paranal, the latter slightly worse (VLT 

Report 62, VLT Site Selection Working Group, ed. M. Sarazin, 1990). 

20) R. Kurz, S. Guilloteau, P. Shaver, The Atacama Large Millimetre Array, ESO 

Messenger, 107, 7, 2002. 

21) M. Sarazin at ESO web site on astronomical climate. 

22) F.P. Chavez et al., From Anchovies to Sardines and Back: Multidecadal Change in 

the Pacific Ocean, Science 299, 217, 2003. 

23) E.K. Duursma, Rainfall, Riverflow and Temperature profile trends; Consequences 

for Water Resources, Heineken NV, Amsterdam 2002, p. 24. 

24) M. Grenon, ESO internal report. 

25) L. Núñez, M. Grosjean, I. Cartajena, Human Occupations and Climate Change in 

the Puna de Atacama, Chile, Science, 298, 821, 2002. 

26) M. Sarazin, F. Roddier, The ESO differential image motion monitor, Astronomy 

& Astrophysics 227, 294, 1990.

27) E. Carrasco, R. Avila, A. Carramiñana, Pub. Ast. Soc. Pacific 117, 104, 2005. 

28) For this, the Asian sites and the South Pole, see Astronomical Society of the 

Pacific Conference Series 266, 2002. 

29) C. Muñoz-Tuñón et al., New Astronomy Rev. 42, 409, 1998, give a (~ 1 year) mean 

value of the seeing of 0”75 for these subsites, to be compared with 0”80 as the 

long term mean for Paranal. 

30) M.R. Kidger, New Astronomy Rev. 42, 537, 1998. 

31) A. Jabiri et al., Astronomy & Astrophysics Suppl. 147, 271, 2000, give a 14 year 

average 1984–1998 of photometric nights for La Palma. 

32) J.S. Lawrence et al., Nature 431, 278, 2004. 

33) D. Hofstadt, personal communication 2004. 

34) S. Barrientos, Regionalización Sísmica de Chile; thesis Universidad de Chile, 1980. 

Chapter VII 

1) Thomas Mann, Doktor Faustus, Fischer Verlag 1967, p. 361. The data of the cosmic 

creation are nothing but an anaesthetizing bombardment of our intelligence with 

numbers, endowed with a comet tail of two dozen zeros which pretend to have still 

something to do with measure or reason. 

2) R. Arsenault et al., ESO Messenger 115, 11, 2004. 

3) R. Arsenault et al., ESO Messenger 112, 7, 2003. 

4) T. Ott et al., ESO Messenger 111, 1, 2003; R. Genzel et al., Nature 425, 934, 2003. 

5) A. Glindemann et al., ESO Messenger 98, 2, 1999. 

6) Ch. Leinert et al., ESO Messenger 112, 13, 2003. 

7 ) A. Richichi & R.G. Petrov, ESO Messenger 116, 2, 2004. 

8) W. Jaffe et al., Nature 429, 47, 2004. 

9) K. Kuijken et al., ESO Messenger 110, 15, 2002. 

10) J.P. Emerson et al., ESO Messenger 117, 27, 2004. 

Chapter VIII 

1) Galileo Galilei, Sidereus Nuncius. 

2 ) e.g. R.W. Smith, The Space Telescope, Cambridge U. Press, 1989. 

3) Scientific Research with the Space Telescope, IAU Coll. 54, pp. 10-13, 1979. 

4) NGST Science and Technology Exposition, Astronomical Society of the Pacific 

Conf. Proc. 207, 2000. 

5) R. de Jong et al., Space Telescope Science Institute Newsletter 20, iss. 1, p. 11, 2003. 

6) R. Gilmozzi, P. Dierickx, OWL, ESO Messenger 100, 1, 2000. 

7) Extremely Large Telescopes, ESO Conf. Proc. 57, 2000. 

8) Astrophysical Journal Letters 538, L1ff, 2000. 

9) Ibidem 619, L1ff, 2005. 

10) GAIA, ESA BR-163, 2000. 

11) Science 308, 935, 2000. 

Chapter IX 

Notes 295 

1) John Milton, Paradise Lost, Book II, 951-953, 1667. 

2) For a general overview of radio astronomical topics, see K. Rohlfs, T.L. Wilson, 

Tools of Radio Astronomy, 4th ed. 2003, Springer Verlag; B. Burke, F. Graham- 

Smith, Introduction to Radio Astronomy.


3) Various articles in recent publications describe the radio arrays in some detail. See 

for example IAU Symposium 205, 2001 and Astronomical Society of the Pacific 

Conference Proceedings 306, 2004. 

4) D. Hughes et al., Nature 394, 241, 1998. 

5) From a longer list presented by L.-Å. Nyman at the R. Booth 65th birthday 

symposium, available on the Onsala Space Observatory website. 

6) APEX – the Atacama Pathfinder Experiment, L.-Å. Nyman, P. Schilke, R.S. Booth, 

ESO Messenger 109, 18, 2002. 

7) LSA: Large Southern Array, ed. D. Downes, 1995. 

8) Science with large millimetre arrays, ed. P. Shaver, ESO Astrophysics Symposia, 

Springer-Verlag, 1996. 

9) The Atacama Large Millimetre Array, R. Kurz, S. Guilloteau, P. Shaver, ESO 

Messenger 107, 7. 2002. Science with the Atacama Millimeter Array (ALMA), 

Astronomical Society of the Pacific Conference Proceedings 235, 2001. 

10) Y. Sekimoto, Astronomical Society of the Pacific Conference Proceedings 235, 

245, 2001. 

11) Science with the Square Kilometre Array, ed. C. Carilli, S. Rawlings, New Astronomy 

Reviews 48, 979-1563, 2004. For a brief more general account see Science, 296, 

830, 2002. 

12) LOFAR, H. Röttgering et al. in “Texas in Tuscany”, World Scientific, Singapore, 

2003. 

13) Science 307, 1194, 2005. 

Chapter X 

1) H. Curien, Uranie et Cassandre: La coopération européenne dans l’Espace, ESA 

Journal 2, 93, 1978. 

The risk of overdependence on the US should, however, not be neglected. One should 

ensure that the part of our scientific activity that depends on American decisions, 

taken on the basis of considerations that are not necessarily our own, does not become 

too preponderant… Dependence. Independence. Interdepence and overdependence. 

There would be a good subject for a dissertation and that not only in space. 

2) A more detailed comparison between the US and European space science budgets 

for 2004 is as follows. The FY 2004 budget contains five major headings: Solar 

System exploration, Mars exploration, Astronomical search for origins, Structure and 

evolution of the universe, and Sun-Earth connection. Under each of these (except 

Mars) are four subheadings: Development, Operations, Research and Technology, 

and advanced concepts. Development essentially covers the construction cost of satellites 

and instruments. The totals for these four are respectively 905, 399, 887 and 

1185 MUS$ plus shares of the 595 MUS$ Mars program. The research has only a 

minor counterpart in the ESA budget, since in Europe research is funded not only 

through national space agencies, but also through universities, research councils, 

etc. In the nineties the European space agencies reported national space spending 

averaging 58% of their contribution to ESA. In the major countries this should be 

by now an optimistic assumption. So to make a conservative comparison, we group 

the ESA budget items according to the NASA headings and multiple these by 1.58, 

while we count only half of the “research” in the NASA budget. Expressing everything 

in M€ with 1 € = 1.2 US$, we reach the following comparison:

NASA 

(-1/2 “research”) ESA × 1.58 

Solar System (incl. Mars) 1460 107 170 

Sun-Earth connection 560 20 30 

Astronomical … + universe 930 273 430 

2950 400 630 

where we have distributed the basic activities in the ESA budget pro rata. Of 

course, at ESA the distribution over the programs changes from year to year. 

We note that the total projected spending in 2004 exceeded the ESA contribution 

level by some 30 M€. So even with optimistic estimates the difference between the 

US and Europe in the space sciences is a factor of five. 

3) European Space Science Horizon 2000, ESA SP-1070, 1984. 

4) Horizon 2000 Plus, ESA SP-1180, 1995. 

5) US-European Collaboration in Space Science, pp. 68, 67, National Academy Press, 

Washington, 1998. 

6) Horizon 2000 Plus, p. 31. 

7) Ibidem, p. 35. 

8) Science 300, 719, 2003. 


Chapter XI 

Notes 297 

1) Thomas Hardy, Two on a Tower, Chapter 1, 1882. 

2) M.F. Kessler et al., The Infrared Space Observatory (ISO) mission, Astronomy and 

Astrophysics 315, L27ff, 1996. 

3) Several articles in Advances in Space Research (COSPAR) 34, no. 3, 2004. 

4) COBE, dark matter and large-scale structure in the Universe, K.M. Górski, 

A.J. Banday, Chapter 18 of “The Century of Space Science”, ed. J.A.M. Bleeker, 

J. Geiss, M.C.E. Huber, Kluwer Academic Publishers, 2001. 

5) W. Hermsen, COS B, Advances in Space Research 10, 69, 1990. 

6) B.G. Taylor et al., The EXOSAT mission, Space Science Reviews 30, 479, 1981. 

7 ) The ROSAT mission, J. Trümper, Advances in Space Research 2, 241, 1982. 

ROSAT: A New Look at the X-ray Sky, J. Trümper, The Quarterly Journal of the 

Royal Astronomical Society 33, 165, 1992. 

8) The SAX mission for X-ray astronomy, R.C. Butler and L. Scarsi, Observatories in 

Earth Orbit and Beyond, ed. Y. Kondo, Kluwer Academic Publishers, p. 141, 1990. 

9) XMM-Newton observatory, F. Jansen et al., Astronomy and Astrophysics 365, L1ff, 

2001. 

10) For other X-ray missions see numerous articles in X-ray Astronomy 2000, Astronomical 

Society of the Pacific Conference Proceedings 234, 2001. 

11) XEUS, Proposal to ESA, 2004. 

12) SIGMA: the hard X-ray and soft gamma-ray telescope on board the GRANAT space 

observatory, J. Paul et al., Advances in Space Research 10, 223, 1990. 

13) V. Schönfelder, New Astronomy Reviews 48, 193, 2004. 

14) The INTEGRAL mission, C. Winkler et al., Astronomy and Astrophysics 411, L1ff, 

2003. 

15) ESO Messenger 113, 45-48, 2003.


16) ESO Messenger 113, 40-44, 2003. 

17) AGILE, M. Tavani, American Institute of Physics, Conference Proceedings 587, 729, 

2001. 

18) The Cerenkov telescopes are desribed in several articles, New Astronomy Reviews 

48, 323-366, 2004. 

Additional notes to Table XI, 2: 

19) Pub. Astron. Soc. Japan 46, L37, 1994. 

20) Astron. Soc. Pacific Conf. Series 234, 4, 2001. 


22) Ann. Rev. Astron. Astrophys. 30, 391, 1992. 

23) Ref. 8, p. 63. 

24) Ref. 12, p. 297. 

25) New Astronomy Reviews 48, 431, 2004. 

26) Ref. 17, p. 722. 

The ESA missions are also detailed in the biannual reports of ESA to COSPAR. 

Chapter XII 

1) Plato, Timaeus, 22. 

2) H.U. Keller, L. Jorda, Chapter 52 of “The Century of Space Science”, ed. J.A.M. 

Bleeker, J. Geiss, M.C.E. Huber, Kluwer Academic Publishers, 2001. 

3) Nature 383, 469, 1996. 

4) Rosetta: ESA’s Comet Chaser, C. Berner et al., ESA Bulletin 112, 10, 2002. 

5) The Death of a Comet and the Birth of Our Solar System, H. Boenhardt, Science 

292, 1307, 2001. 

6) High Ambitions for an Outstanding Planetary Mission: Cassini-Huygens, J.-P. Lebreton 

et al., ESA Bulletin 120, 11, 2004. 

7) B. Levrard et al., Recent ice-rich deposits formed at high latitudes on Mars by sublimation 

of unstable equatorial ice during low obliquity, Nature 431, 1072, 2004. 

8) Chapter 57 of “The Century of Space Science”. 

9) ESA’s Mars Express Mission – Europe on its Way to Mars, R. Schmidt et al., ESA 

Bulletin 98, 56, 1999. 

10) G. Neukum et al., Recent and episodic volcanic and glacial activity on Mars revealed 

by the High Resolution Stereo Camera, Nature 432, 971, 2004. 

11) J.B. Murray et al., Nature 434, 352, 2005. 

12) Science 307, 1390, 2005. 

13) Science 307, 1576ff, 2005. 

14) A Solar-Powered Visit to the Moon, G. Racca et al., ESA Bulletin 113, 14, 2003. 

Chapter XIII 

1) A general review of solar physics is presented in “Dynamic Sun”, edited by B.N. 

Dwivedi, Cambridge University Press, 2004. Chapter 20 of that book by B. Fleck 

and C.U. Keller gives a complete overview of “Solar observing facilities”. In the first 

chapter of “The Dynamic Sun” edited by A. Hanslmeier et al., Kluwer Academic 

Publishers, 2001. B. Fleck presents “Highlights from SOHO and future Space

Missions”. An excellent review on “The Solar Atmosphere” by S.K. Solanki and 

R. Hammer may be found in “The Century of Space Science”, edited by J.A.M. 

Bleeker, J. Geiss and M.C.E. Huber Kluwer Academic Publishers, 2001, chapter 45. 

In the same volume several other chapters on the Sun are worth reading. 

Chapter XIV 

1) E. Freundlich, Die Grundlagen der Einsteinschen Gravitationstheorie, Verlag Julius 

Springer, p. 48, 1916. [The experimental foundation of Einstein’s theory of gravitation 

has not yet come very far. That the theory nevertheless can claim universal 

respect already today has its full justification in the unusual unity and consequentiality 

of its basis.] 

2) For a general description of cosmic-rays: Astrophysics of Cosmic Rays, by V.S. Berezinskii 

et al., North Holland Press, Amsterdam 1990; composition around the 

knee, Astroparticle Physics 14, 245, 2001 and 20, 641, 2004, and for space projects 

at the highest energies, Astroparticle Physics 20, 391, 2004. Excellent reviews of 

the whole subject of particle astrophysics and gravitational waves are given in 

“Cosmic Ray, Particle and Astroparticle Physics”, ed. A. Bonnetti, I. Guidi, B. Monteleoni, 

Atti dei Convegni Lincei 133, Roma, Ac. Naz. dei Lincei. While these reviews 

are nearly a decade old, they very well describe the projects that were being started 

and are only now approaching completion. This has the advantage that there are 

fewer technical details, while the motivation and physical background are extensively 

discussed. For recent updates see “Texas in Tuscany”, XXI Symposium on 

Relativistic Astrophysics, ed. R. Bandiera, R. Maiolino, F. Mannucci, World Scientific, 

Singapore 2003, and the book “Cosmic Ray Astrophysics” by R. Schlickeiser, 

Springer-Verlag, 2002. 

Chapter XV 

Notes 299 

1) Lucretius, De rerum natura, ch. 2, strophe 1056-1077. 

2) D. Queloz and M. Mayor, Nature 378, 355, 1995. 

3) A. Vidal Madjar et al., An extended upper atmosphere around the extrasolar planet 

HD 209458b, Nature 422, 143, 2003. 

4) M. Mayor et al., Setting new standards with HARPS, ESO Messenger 114, 20, 2003. 

5) A. Quirrenbach, The Space Interferometry Mission (SIM) and Terrestrial Planet 

Finder (TPF), 36th Liège Colloquium, 2001, p. 100. 

6) ESO Press Release May 2004. 

7) C. Moutou et al., The COROT Mission: Status, Astronomical Society of the Pacific 

Conf. Series 294, 423, 2003. 

8) ESA SP-1276, section 5.6, 2004. 

9) J.M. Matthews et al., No stellar p-mode oscillations in space-based photometry of 

Procyon, Nature 430, 51, 2004. 

10) W.J. Borucki et al., The Kepler Mission: Finding the Sizes, Orbits and Frequencies 

of Earth-size and Larger Extrasolar Planets, Astronomical Society of the Pacific 

Conf. Series 294, 427, 2003. 

11) M. Landgraf et al., Darwin, ESA Bulletin 105, 60, 2001.


Chapter XVI 

1) The Panchatantra (translated by A.W. Ryder). 

2) Publication rates for Eastern Europe and also for Japan are more difficult to 

evaluate because of the presence of some regional or national journals of good 

quality. However, their share in the journals of Table XVI, 1 is rapidly increasing. 

For 2002 the values were Armenia 53, Georgia 12, Russia 1284, Ukraine 379 and 

Japan 2786 pages, normalized as in Table XVI, 2. 

3) Science 304, 808, 2004. 

4) D. Adam, Nature 415, 728, 2002 describes various errors in citation studies. See 

also Nature 435, 1003, 2005. 

5) Letter from ISI to Aage Sandqvist, Chairman of the Board of A&A, 8 August 2003. 

Chapter XVII 

1) C.V. Raman, A Pictorial Biography, S. Ramaseshan, C. Ramachandra Rao, Indian 

Academy of Sciences, Bangalore 1988, p. 177. 

2) R. May, Science 302, 5-65, 2003. 

3) R. Hanbury Brown, Quarterly Journal Royal Astron. Soc. 29, 466, 1988. 

4) ESA BR-63, The indirect economic effects of the European Space Agency’s 

Programmes, April 1991. 

Chapter XVIII 

1) Rig Veda, Book X, 129 (translated by R.J.H. Griffith). 

2) Creating the International Space Station, D.M. Harland, J.E. Catchpole, Springer- 

Verlag 2002, p. 97. 

3) For a description of the negotiations on the Space Station see R.M. Bonnet, 

V. Manno, International Cooperation in Space, Harvard University Press, 1994, 

pp. 108-119. 

4) Nature 431, 888, 2004. 

5) M. Griffin, testimony to US House Science Committee in 2004, as reported in 

Science 307, 1709, 2005. 

6) For a description of Spacelab see R.M. Bonnet, V. Manno, pp. 78-80. 


Chapter XIX 

1) Charles de Gaulle, Mémoires d’Espoir, le Renouveau 1958–62, éd. Plon 1970 

between Europeans from the Atlantic to the Ural.

Acronyms and Concepts 

– A – 

A Austria 

AAO Anglo Australian Observatory 

AAT Anglo Australian Telescope 

ABRIXAS A BRoad band Imaging X-ray All-sky Survey (D, failed) 

ACE Advanced Composition Explorer (NASA) 

ACP Aerosol Collector and Pyrolyser (on Huygens) 

ACS Advanced Camera for Surveys (HST) 

AGASA Akeno Giant Air Shower Array 

AGILE Astro-rivelatore Gamma a Immagine Leggero (I) 

AGN Active Galactic Nuclei 

ALMA Atacama Large Millimeter Array 

alt-azimuth telescope with one horizontal and one vertical axis 

AMANDA Antarctic Muon And Neutrino Detector Array (US) 

AMBER Astronomical Multiple BEam Recombiner (at VLT) 

AMPTE Active Magnetospheric Particle Tracer Explorer 

AMS Alpha Magnetic Spectrometer 

ANTARES Astronomy with a Neutrino Telescope and Abyss environmental 

RESearch 

ANS Astronomical Netherlands Satellite 

antimatter negatively charged nuclei + positrons 

Antu unit telescope-1 of the ESO VLT 

ANU Australian National University 

AO Adaptive Optics; also Announcement of Opportunity 

Apache Point site in New Mexico 

APEX Atacama Pathfinder Experiment (ESO) 

µ Arae star with planet 14 earth masses 

ARC Astrophysical Research Consortium (US) 

ARCHEOPS balloon experiment for CMB 

Arecibo location 300 m fixed radio telescope 

Ariane European rocket (now Ariane 5) 

Ariel UK satellite series 

ARISE Advanced Radio Interferometry between Space and Earth (US) 

Asca Japanese hard X-ray satellite


ASPERA Analyser of Space Plasmas and EneRgetic Atoms (on Mars 

Express and Venus Express) 

ASTE Atacama Submillimeter Telescope Experiment (J) 

ASTRO-E Japanese X-ray satellite now named Suzaku 

ASTRO-F Japanese IR satellite 

Astron Russian γ-ray satellite 

ASTROSAT Indian X-ray and uv satellite 

AT Australia (radio) Telescope 

AU 1. Astronomical Unit (Sun-Earth distance); 

2. Accounting Unit of ESA (N euro) 

Auger Extreme energy cosmic ray detection system (named after 

Pierre Auger) 

Aurora 1. Magnetospheric particles hitting earth atmosphere; 

2. ESA Mars program 

AVO Astrophysical Virtual Observatory 

AXAF Advanced X-ray Astrophysics Facility, now NASA’s Chandra 

– B – 

B Belgium 

Beagle-2 Lander for Mars Express (failed) 

BepiColombo future ESA mission to Mercury (named after B. Colombo) 

BeppoSAX Italian X-ray satellite (named after Beppo Occhialini) 

Big Bang event at origin of the expanding universe 

BIMA Berkeley-Illinois-Maryland Array 

BISON BIrmingham Solar Oscillations Network 

black body ideal radiator producing a spectrum which depends only on 

the temperature 

BOOMERANG Balloon Observations of Millimetric Extragalactic Radiation 

ANd Geophysics 

bow shock separates undisturbed medium from that perturbed by object 

moving supersonically 

– C – 

12 C, 13 C isotopes of carbon (6 protons + 6 respectively 7 neutrons) 

Calama nearest town with airport for ALMA/APEX 

Calar Alto site of German-Spanish observatory 

CANGAROO Collaboration of Australia and Nippon for a GAmma-Ray 

Observatory in the outback 

Capodimonte observatory in Napoli 

Cargèse location of 1983 VLT conference on Corsica 

Cas A remnant of 1680 (?) supernova 

Cassegrain two mirror telescope 

Cassini mission to Saturn 

Castelgrande site in Southern Italy 

CAT Coudé Auxiliary Telescope (at La Silla) 

CCD Charge Coupled Device

CDS 1. Coronal Diagnostic Spectrometer (on SOHO); 

2. Centre de Données Stellaires (now: Astronomiques) 

CELESTE CErenkov Low Energy Sampling and Timing Experiment 

CELIAS Charge ELement and Analysis System (on SOHO) 

CELT California Extremely Large Telescope ; See TMT 

Centaurus A nearest radio galaxy 

cepheid a type of variable star 

Cerenkov radiation radiation from energetic electrons 

CERN Centre Européen de Recherche Nucléaire 

CFHT Canada-France-Hawaii Telescope 

CGRO Compton Gamma-Ray Observatory (NASA) 

CH Switzerland 

CH 4 

methane 

Acronyms and Concepts 303 

Chacaltaya site in Bolivia 

Chajnantor site in Chile 

Chandra NASA X-ray facility 

Churyumov-Gerasomivitch – target comet for Rosetta 

Circinus galaxy nearby active galaxy 

citation index normalized count of references 

Cluster ESA mission of four magnetospheric satellites 

CMB Cosmic Microwave Background 

CNES Centre National d’Expériences Spatiales (F) 

CNRS Centre National de Recherche Scientifique (F) 

CO carbon monoxyde 

Co Calan site in Chile 

Co Chaupiloma site in Chile 

Co Chico site in Chile 

Co Duran site near La Silla 

Co La Montura site near Paranal 

Co La Peineta site in Chile 

Co La Silla ESO site in Chile 

Co Las Campanas site in Chile 

Co Pachon site in Chile 

Co Paranal ESO site in Chile 

Co Peralta site in Chile 

Co S. Cristobal site in Santiago, Chile 

Co Tacora volcano in Chile 

Co Tololo site in Chile 

Co Vizcachas site near La Silla 

COBE COsmic Background Explorer (NASA) 

COME-ON early ESO adaptive optics system 

COMPTEL COMPton TELescope (D) on NASA’s Compton Observatory 

Concordia French-Italian base in Antarctica 

CONICA COudé Near Infrared Camera (at VLT, but now at Nasmyth 

focus) 

Constellation planned NASA four spacecraft X-ray mission 

CONTOUR COmet Nucleus TOUR (NASA, failed) 

Coonabarabran site in Australia


Copiapo town in Chile 

cornerstone large ESA mission 

COROT COnvection, Rotation and Transits 

COS-B early ESA γ-ray mission 

cosmic rays energetic particles from beyond earth environment 

Cosmic Vision ESA’s current science plan 

COSPAR COmmittee on SPAce Research 

COSTAR Corrective Optics Space Telescope Axial Replacement (on HST) 

COSTEP COmprehensive measurements of the SupraThermal and Energetic 

Particle populations (on SOHO) 

coudé fixed focus of telescope 

Crab Nebula remnant supernova 1054 

CRIRES CRyogenic InfraRed Echelle Spectrograph (at VLT) 

– D – 

D Germany 

dark matter invisible, gravitating matter 

Darwin ESA proposal for earth-like planet search 

Deep Impact NASA comet mission 

delay line compensates variable optical path length in interferometer 

diffraction limited with the intrinsic angular resolution of perfect optics 

DIMM Differential Image Motion Monitor 

DISCO Dual Irradiance and Solar Constant Observatory (ESA, not 

selected) 

DISR Descent Imager / Spectral Radiometer (on Huygens) 

DIVA Deutsches Interferometer für Vierkanalphotometrie und Astrometrie 

(cancelled) 

Dk Denmark 

DM Deutschmark, past German currency: 1€=1.96 DM 

Dome C site in Antarctica, location of “Concordia” 

Doppler effect change in wavelength due to motion of emitter 

Double Star China-ESA two magnetospheric satellites mission 

Dutch open telescope – solar telescope at La Palma 

DWE Doppler Wind Experiment (on Huygens) 

Dwingeloo location of EVN center (NL) 

– E – 

EAS 1. Extensive Air Shower due to cosmic-ray particle; 

2. European Astronomical Society 

EAS-TOP EAS array near Gran Sasso (I) 

EC European Commission 

échelle grating permits stacking of spectral segments on a square detector 

ECF European Coordinating Facility for HST (at ESO, Garching) 

Eddington proposed ESA mission for occultations by exoplanets and 

astroseismology 

Effelsberg site in Germany 

EFOSC ESO Faint Object Spectrograph Camera

EGRET Energetic Gamma-Ray Experiment Telescope, on NASA’s 

Compton observatory 

Ei Eire or Ireland 

Einstein NASA X-ray mission 

EIT Extreme Ultraviolet Imaging Telescope (on SOHO) 

ELDO European Launcher Development Organization 

El Leoncito site in Argentina 

El Niño part of climatological cycle in S. Pacific 

ELT Extremely Large Telescope 

e-MERLIN upgrade of MERLIN 

EPIC European Photon Imaging Camera (on XMM-Newton) 

Equivalence Principle – states equivalence inertial and gravitational mass 

ERNE Energetic and Relativistic Nuclei and Electron experiment (on 

SOHO) 

ESA European Space Agency 

ESF European Science Foundation 

ESO European Southern Observatory 

ESOC European Space Operations Centre 

ESP Spain 

ESRIN ESA establishment in Frascati (I) 

ESRO European Space Research Organisation 

ESTEC European Space research and TEchnology Centre 

EU European Union; here frequently used for earlier 15-country 

EU + Iceland, Norway, Switzerland 

EURO 50 proposed 50-m telescope 

EUSO proposed ESA Extreme Universe Space Observatory 

EUV Extreme UltraViolet 

eV electron volt, a unit of energy 

e-VLA upgrade of VLA 

EVN European VLBI Network 

EXIST Energetic X-ray Imaging Survey Telescope (US) 

exoplanet planet around star other than the Sun 

EXOSAT European X-ray Observatory SATellite 

– F – 


F France 

FAME Full-sky Astrometric Mapping Explorer (NASA, cancelled) 

FIRST Far InfraRed Space Telescope, now ESA’s Herschel 

FLAMES Fibre Large Array Multi-Element Spectrograph (at VLT) 

fleximission low cost ESA mission 

Fly’s Eye Cosmic-ray detector (Utah) 

FOC Faint Object Camera on HST 

FORS FOcal Reducer/low dispersion Spectrograph (at VLT) 

FOS Faint Object Spectrograph (on HST) 

FOV Field Of View 

FREGATE FREnch GAmma-ray TElescope (on NASA’s HETE) 

FUSE Far Ultraviolet Spectroscopic Explorer (NASA)


– G – 

GAIA Global Astrometric Interferometer for Astrophysics (ESA) 

Galactic Center the center of our Galaxy at 25000 light years distance 

Galaxy our Milky Way galaxy 

galaxy large assembly of stars and gas 

GALEX GALaxy evolution EXplorer (NASA) 

GALLEX GALLium EXperiment (neutrinos) 

Gamsberg site in Namibia 

GCMS Gas Chromatograph Mass Spectrometer (on Huygens) 

GDP Gross Domestic Product 

Gemini two international 8-m telescopes 

GENIE Ground based European Nulling Interferometer Experiment 

(at VLT) 

GEO-600 Gravitational wave detector (D, UK) 

GHRS Goddard High Resolution Spectrograph (on HST) 

Giacobini-Zinner a comet visited by NASA’s ISEE-3 

Ginga Japanese X-ray satellite 

Giotto ESA spacecraft to comet Halley 

GLAST Gamma-ray Large Area Space Telescope (NASA) 

GMT Giant Magellan Telescope (US) 

GMRT Giant Metrewave Radio Telescope (India) 

GOES-12 Geosynchronous Operational Environmental Satellite, No 12 

(NASA) 

GOLF Global Oscillations at Low Frequency (on SOHO) 

GONG Global Oscillation Network Group 

GPO Grand Prisme Objectif, a small La Silla telescope 

GR Greece 

GRAAL Gamma-Ray Astronomy at ALmeria 

GRANAT Russian γ-ray satellite 

Gran Sasso mountain in central Italy with underground laboratories 

GRANTECAN GRAN TElescopio de las CANarias (ESP) 

GRASP Gamma-Ray Astronomy with Spectroscopy and Positioning 

(ESA, not selected) 

gravitational waves waves in the fabric of space-time 

Gravity Probe B large NASA satellite to study General Relativity 

GRB Gamma-Ray Burst 

Grigg-Skjellerup second comet visited by Giotto 

GTM Gran Telescopio Millimetrico (Mexico/US) 

– H – 

H hydrogen with a nucleus containing one proton 

2 H deuterium, with a nucleus containing 1 proton + 1 neutron 

H 2 

molecular hydrogen; each molecule contains two H atoms 

habitable zone the domain in a planetary system where earth-like planets can 

retain liquid water on their surface 

Hakucho Japanese solar X-ray satellite

HALCA Japanese satellite with radio telescope 

Halley’s Comet comet with 76 year period which has appeared since antiquity 

Hanle site in Indian Himalayas 

HARPS High-Accuracy Radial velocity Planetary Searcher (at La Silla) 

Hartebeestpoort site in South Africa 

HASI Huygens Atmospheric Structure Instrument (on Huygens) 

Haverah Park site in the UK 

HAWK-I new near-IR wide field camera (at VLT) 

HCN hydrogen cyanide 

HDF Hubble Deep Field 

HEGRA High Energy Gamma-Ray Astronomy (D, at La Palma) 

Helios 1, 2 German probes of the solar wind 

HEMT High Electron Mobility Transistor 

Herschel future far IR ESA satellite (was FIRST) 

H. Hertz German radio telescope (in Arizona) 

HESS High Energy Stereoscopic System (D, in Namibia) 

HET Hobby Eberly Telescope (Texas) 

HETE High Energy Transient Explorer (NASA) 

HIFI Heterodyne Instrument for the Far-IR (on Herschel) 

Hintori Japanese solar X-ray satellite 

Hipparcos HIgh Precision PARallax COllecting Satellite (ESA) 

H 2O water 

Horizon 2000 ESA long term plan 

Horizon 2000-Plus follow up to Horizon 2000 

Horizons 2000 Horizon 2000 + Horizon 2000-Plus, now named Cosmic 

Vision 

HRI High Resolution X-ray Imager 

HRSC High-Resolution Stereoscopic Camera (on Mars Express) 

H 2S hydrogen sulphide 

HSP High Speed Photometer (on HST) 

HST Hubble Space Telescope 

Huygens ESA sonde to Titan 

Hz Hertz; unit of frequency equal to one cycle per second 

– I – 


I Italy 

IAU International Astronomical Union 

IBIS Imager on Board the INTEGRAL Satellite 

IC Instrumentation Committee (ESO) 

Ic Iceland 

ICECUBE Large neutrino detector in Antarctica 

IFU Integral Field Unit for spectroscopy 

IHAP Image Handling And Processing system (ESO) 

ILIAS Integrated Large Infrastructures for Astroparticle Science 

Impact factor based on citation rates of a journal 

INSU Institut National des Sciences de l’Univers (F) 

INTEGRAL INTErnational Gamma-Ray Astronomy Laboratory 

IR InfraRed


IRAM Institut de Radio Astronomie Millimétrique 

IRAS Infrared Astronomical Satellite 

IRTS InfraRed Telescope in Space (Japan) 

ISAAC Infrared Spectrometer And Array Camera (at VLT) 

ISAS Japanese space science agency 

ISDC INTEGRAL Science Data Centre 

ISEE International Sun Earth Explorers 

ISO ESA Infrared Space Observatory 

ISOCAM camera of ISO 

ISOPHOT photometer of ISO 

isoplanatic patch angular area over which adaptive optics corrections are constant 

ISS International Space Station 

IUE International Ultraviolet Explorer 

– J – 

J Japan 

Jansky unit of electromagnetic flux; 1 Jy = 10 -26 watt m -2 Hz -1 

JAXA Japanese Space Agency 

JCMT James Clark Maxwell Telescope (submm, UK, NL) 

JEM-X Joint European X-ray Monitor (on INTEGRAL) 

JENAM Joint European National Astronomy Meeting 

JIVE Joint Institute for VLBI in Europe 

Jodrell Bank site in UK 

JOSO Joint Organisation for Solar Observatories 

juste retour where every country gets contracts in proportion to its contributions 

JWST James Webb Space Telescope (was NGST) 

– K – 

Kamiokande Japanese neutrino detector 

KAMLAND KAMioka Liquid scintillator Anti-Neutrino Detector (Japan) 

KASCADE KArlsruhe Shower Core and Array DEtector (D) 

Keck 1, 2 telescopes on Hawaii (US) 

Kepler European Mars mission (not implemented). NASA exoplanet 

mission 

Kepler’s laws describe properties of planetary orbits 

Kitt Peak site in Arizona 

KMOS new near IR Multi-Object Spectrograph (ESO) 

KORONAS solar activity satellite (Russia) 

Kourou European launch site in French Guyana 

Kreuz comets class of comets with perihelia close to the Sun 

Kuyen unit telescope-2 of the ESO VLT 

– L – 

L1 first Lagrangian point sunwards from earth 

L2 second Lagrangian point in antisolar direction 

La Niña part of climate cycle in S. Pacific

La Palma island of the Canary Islands 

La Réunion island in S. Indian Ocean 

LASCO Large Angle and Spectroscopic COronograph (on SOHO) 

LBT Large Binocular Telescope 

LDEF Long Duration Exposure Facility (NASA) 

LEP Large Electron Positron collider at CERN 

LEST Large European (later Earth based) Solar Telescope (abandoned) 

LHC Large Hadron Collider at CERN 

LGS Laser Guide Star 

Lick observatory in California 

LIGO Laser Interferometer Gravitational wave Observatory (US) 

LINEAR a comet that disintegrated 

LISA Laser Interferometer Space Antenna 

LMC Large Magellanic Cloud 

LMT Large Millimeter Telescope (Mexico, US) 

Lobster-ISS proposed hard X-ray survey instrument on the Space Station 

(ESA) 

LOFAR LOw Frequency ARray (NL) 

Long March Chinese launcher 

LSA Large Southern Array (now ALMA) 

LWS Long Wavelength Spectrometer (on ISO) 

– M – 


MACAO Multi Application Curvature Adaptive Optics (at VLT) 

M1, 2, 3 the first three reflecting mirrors in a telescope 

MACRO particle detector under the Gran Sasso (I) 

MAG MAGnetometer (on Venus Express) 

Magellan 1, 2 6.5-m telescopes (US) 

MAGIC Major Atmospheric Gamma-ray Imaging Cerenkov telescope (D) 

magnetopause the surface separating the solar wind from the region dominated 

by the magnetic field of the earth 

magnetosphere the region controlled by the earth’s magnetic field 

magnitude logarithmic unit of brightness ; + 5 mag corresponds to a factor 

of 100 fainter 

Maidenak site in Uzbekistan 

MAMBO MAx-Planck Millimeter BOlometer 

MARS MArs Radio Science experiment (on Mars Express) 

Mars-96 Russian Mars mission (failed) 

Mars Express ESA Mars mission 

Mars Observer NASA Mars mission (failed) 

MARSIS Mars Advanced Radar for Subsurface and Ionospheric Sounding 

(on Mars Express) 

Mauna Kea mountain in Hawaii 

McDonald observatory in Texas 

MDI Michelson-Doppler Interferometer (SOHO) 

Medicina site near Bologna


Melipal unit telescope-3 of the ESO VLT 

MERLIN Multi-Element Radio-Linked INterferometer (UK) 

Messenger ESO journal 

MESUR Mars Environmental SURvey (NASA, not selected) 

Metsähovi site in Finland 

MICROSCOPE MICROSatellite à trainée Compensée pour l’Observation du 

Principe d’Equivalence 

MIDAS Munich Interactive Data Analysis System (ESO) 

MIDI MID-Infrared interferometric instrument (at VLT) 

Mileura site in W. Australia 

Mills spectrograph early instrument in Chile (US) 

MIRI Mid-InfraRed Instrument (for JWST) 

µm micrometer (0.001 mm) 

MMA MilliMeter Array (US) 

MMT Multi-Mirror Telescope (Arizona) 

MPE Max-Planck-Institut für Extraterrestrische Physik (Garching) 

MPG Max-Planck-Gesellschaft 

MPIA Max-Planck-Institut für Astronomie (Heidelberg) 

MPIfR Max-Planck-Institut für Radioastronomie (Bonn) 

MSX Midcourse Space Experiment (US) 

Mt Graham site in Arizona 

Mt Hopkins site in Arizona 

Mt Palomar site in California 

Mt Wilson site in California 

– N – 

N Norway 

NACO NAOS-CONICA (at VLT) 

Nancy site in France 

Nanshan site in China 

NAOS Nasmyth Adaptive Optics System (at VLT) 

NASA National Aeronautics and Space Administration (US) 

Nasmyth telescope three mirror telescope 

NESTOR European neutrino detector 

neutrino nearly weightless particle with weak interaction with matter 

NGST Next Generation Space Telescope (now JWST) 

NH 3 

ammonia 

NICMOS Near Infrared Camera and Multi-Object Spectrograph (on 

HST) 

NIRCam Near InfraRed Camera (for JWST) 

NIRSpec Near InfraRed Spectrograph (for JWST) 

NL Netherlands 

Nobeyama site in Japan 

Noto site in Sicily 

NTT New Technology Telescope (ESO) 

NTT hill hill adjacent to Paranal 

nulling interferometer – interferometer with destructive interference eliminating the 

central image

O2 O3 – O – 

Odin 

molecular oxygen 

ozone 

Swedish satellite for radio astronomy and aeronomy 

OECD Organisation for Economic Co-operation and Development 

OH molecule with prominent radio lines 

Olympus Mons volcano on Mars 

OM Optical Monitor (on XMM-Newton) 

OMC Optical Monitor Camera (on INTEGRAL) 

OMEGA Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité 

(on Mars Express) 

Omega CAM large area camera for VLT Survey Telescope 

ONERA Office National d’Etudes et de Recherches Aéronautiques et 

Spatiales (F) 

Onsala site in Sweden 

Oort Cloud cloud of comets enveloping the solar system 

OPTICON OPTical Infrared COordination Network 

Oukamaiden site in Morocco 

OWL OverWhelmingly Large telescope (ESO) 

– P – 

P Portugal 

PACS Photoconducting Array Camera and Spectrometer (on Herschel) 

PAH Polycyclic Aromatic Hydrocarbon 

Pampa S. Eulogio site in Chile 

Panamericana road from Alaska to Chile 

Parkes site in Australia 

51 Pegasi star with the first exoplanet detection 

Pelícano river at the foot of La Silla 

PFS Planetary Fourier Spectrometer (on Mars Express and Venus 

Express) 

PI Principal Investigator 

Pico Veleta site in Andalusia 

PL Poland 

Planck ESA mission to study the cosmic microwave background 

Plateau de Bure site in the French Alps 

postdoc person holding a, usually not permanent, postdoctoral appointment 

PPARC Particle Physics and Astronomy Research Council (UK) 

PRIMA Phase Referenced Imaging and Microarcsecond Astrometry 

(at VLT) 

prime focus telescope focus reached after one reflection 

pulsar a rotating magnetic neutron star emitting pulses of radiation 

– Q – 


quasar an Active Galactic Nucleus with much stronger emission than 

the surrounding galaxy 

QPO Quasi Periodic Oscillation (e.g. in X-ray binaries)


– R – 

R&D Research and Development 

REM Rapid Eye Mount (La Silla) 

resolution the smallest separation observable in angular (∆θ) or wavelength 

(∆λ) measure. Spectroscopic resolution is frequently 

expressed as λ/∆λ. 

RGS Reflection Grating Spectrometer (on XMM-Newton) 

RHESSI Ramaty High Energy Solar Spectroscopic Imager (NASA) 

Rio Frio site in Chile 

Röntgen Kvant Russian X-ray instrument on MIR space station 

Roque de Los Muchachos – site on La Palma in the Canary Islands 

ROSAT Röntgen Satellite (D) 

Rosetta ESA’s comet mission 

ROSITA RÖntgen Survey with Imaging Telescope Array (D, ESA) 

RTG Radio isotope Thermoelectric Generator 

RXTE Rossi X-ray Timing Explorer (NASA) 

– S – 

S Sweden 

SAFIR Single Aperture Far InfraRed telescope (NASA proposal) 

Sag A* radio center of our Galaxy 

SAGE Soviet-American Gallium Experiment 

SALT Southern African Large Telescope 

San Pedro de Atacama – village in Chile 

San Pedro Mártir site in Mexico 

SAO Smithsonian Astrophysical Observatory (US) 

SAS-2 Small Astronomical Satellite (γ-rays, NASA) 

SAX Satellite italiano per l’Astronomia a raggi X (now BeppoSAX) 

SCUBA Submm Common User Bolometer Array (on UKIRT) 

SDO Solar Dynamics Observatory (NASA) 

Seshan site in China 

SEST Swedish-ESO Submm Telescope (no longer operating) 

Seyfert galaxy a lower luminosity quasar 

SF Finland 

Si IX spectral line from 8 times ionized silicon 

Siding Springs site in Australia 

Sierra Negra site in Mexico 

SIGMA Système d’Imagerie Gamma à Masque Aléatoire 

SIM Space Interferometry Mission (NASA) 

SINFONI SINgle Faint Object Near-infrared Investigation (at VLT) 

SIRTF Space InfraRed Telescope Facility (now Spitzer, NASA) 

SKA Square Kilometer Array 

SMA SubMillimeter Array (Mauna Kea) 

SMART-1 Small Mission for Advanced Research in Technology-1 (ESA) 

SMC Small Magellanic Cloud 

SMM Solar Maximum Mission (NASA)

SN supernova 

SNO Sudbury Neutrino Observatory (Canada) 

SOAR SOuthern Astrophysical Research (telescope) 

SOC Scientific Operations Center 

SOFIA Stratospheric Observatory For Infrared Astronomy 

SOHO SOlar and Heliospheric Observatory 

Solar-B Japanese X-ray mission 

Solar Orbiter future solar satellite (ESA) 

Solar Probe proposed in situ probe of the solar corona 

solar wind outflow of gas from the solar corona 

Soyuz Russian rocket 

spectrograph instrument for analyzing light as a function of wavelength 

Spectrum uv Russian mission for ultraviolet observations 

SPI SPectrometer of INTEGRAL 

SPICA SPace Infrared telescope for Cosmology and Astrophysics (Japan, 

proposed) 

SPICAM/V SPectroscopic Investigation of the Characteristics of the Atmosphere 

of Mars (on Mars Express and Venus Express) 

SPIRE Spectral and Photometric Imaging REceiver (on Herschel) 

Spitzer NASA IR mission (was SIRTF) 

SS Space Station 

SSP Surface Science Package (on Huygens) 

STACEE Solar Tower Atmospheric Cherenkov Effect Experiment (US) 

Star Dust comet tail sample return mission (NASA) 

STEREO Solar TErrestrial RElations Observatory (NASA) 

St Katherine site on Sinai peninsula 

ST-ECF Space Telescope European Coordinating Facility (Garching) 

STIS Space Telescope Imaging Spectrograph 

STScI Space Telescope Science Institute (Baltimore) 

STSP Solar-Terrestrial Science Programme (ESA) 

Subaru Japanese telescope in Hawaii 

SUMER Solar Ultraviolet Measurement of Emitted Radiation (on SOHO) 

Suzaku New name for ASTRO-E 

SWAN Solar Wind ANisotropies (on SOHO) 

SWAS Submillimeter Wave Astronomy Satellite (NASA) 

Swedish Solar Telescope – located at La Palma 

SWIFT fast response satellite for observing γ-ray bursts (NASA) 

SWS Short Wavelength Spectrometer (on ISO) 

synchrotron radiation – radiation from relativistic electrons in a magnetic field 

– T – 


TAMA 300 Japanese gravitational wave detector 

TAROT Télescope à Action Rapide pour les Objets Transitoires (La Silla) 

TD-1 early ESRO satellite 

Teíde volcano on Teneriffe 

Teneriffe island among the Canary Islands 

Tenma Japanese X-ray satellite


THEMIS Télescope Héliographique pour l’Etude du Magnétisme et des 

Instabilités Stellaires (F, I) 

44 Ti radioactive titanium isotope 

Titan satellite of Saturn 

TMT Thirty Meter Telescope (US) 

TNG Telescopio Nazionale Galileo (I) on La Palma 

Torun town in Poland 

TPF Terrestrial Planet Finder (NASA project) 

TRACE Transition Region And Coronal Explorer (NASA) 

Tunguska location of meteoritic impact crater in Siberia 

– U – 

UDF Ultra Deep Field (taken with HST) 

UK United Kingdom 

UKIRT United Kingdom InfraRed Telescope (Mauna Kea) 

Ulysses mission to study the solar wind in situ 

US United States of America 

UT Unit Telescope (of the ESO VLT) 

uv ultraviolet 

UVCS UltraViolet Coronal Spectrometer (on SOHO) 

UVES Uv-Visual Echelle Spectrograph (at VLT) 

– V – 

Vallenar town in Chile 

Vega Russian spacecraft, flew by Giotto 

Venus Express ESA’s Venus mission 

VERA VEnus RAdio occultation instrument (on Venus Express) 

VERITAS Very Energetic Radiation Imaging Telescope Array System 

(US) 

VIMOS Visible Multi-Object Spectrograph (at VLT) 

VIRGO 1. Variability of IRradiance and Gravity Oscillations (on SOHO); 

2. French-Italian gravitational wave detector (near Pisa) 

Virgo Cluster aggregate of numerous galaxies some 50 million light years 

away 

VIRTIS Visible and InfraRed Thermal Imaging Spectrometer (on Venus 

Express) 

VISIR VLT Imager and Spectrometer for the mid-InfraRed 

VISTA Visible and Infrared Survey Telescope (at Paranal) 

VLA Very Large Array (New Mexico) 

VLBA Very Long Baseline Array (US) 

VLBI Very Long Baseline Interferometry 

VLT Very Large Telescope (ESO) 

VLTI Very Large Telescope Interferometer (ESO) 

VMC Venus Monitoring Camera (on Venus Express) 

VO Virtual Observatory 

Volcano Ranch site in New Mexico 

VSOP VLBI Space Observatory Program (Japan) 

VST VLT Survey Telescope

– W – 

Wetzel site in Germany 

WFPC Wide Field and Planetary Camera (on HST) 

WIMP Weakly Interacting Massive Particle 

WIND spacecraft to study the solar wind (NASA) 

Wirtanen comet previously targeted by Rosetta 

WMAP Wilkinson Microwave Anisotropy Probe (NASA) 

Wolf-Rayet type of massive, evolved binary star 

– X – 

XEUS X-ray Evolving Universe Spectroscopy mission (ESA) 

XMM-Newton X-ray Multimirror Mission (ESA) 

X-shooter new wide wavelength range spectrograph (at VLT) 

– Y – 

Yakutsk site in Siberia 

Yebes site in Spain 

Yepun unit telescope-4 of the ESO VLT 

Yohkoh Japanese solar X-ray satellite 

– Z – 


Zelentchuck site in the Caucasus 

Zerodur low expansion material for mirror blanks

A 

AAT, 40 

Abbot C.G., 91 

active optics, 53, 54 

ACS, 129 

Acuerdo, 77, 79, 93 

Adaptive Optics, 109, 110, 112 

Advanced Camera for Surveys, 126 

– Composition Explorer, 227, 235 

AGASA array, 232 

AGILE, 200 

Allègre C., 169 

ALMA, 49, 96, 99, 100, 106, 149, 151- 

154-158, 182, 183, 186, 280, 281 

alt-azimuth, 56 

aluminium mirror, 62, 63 

AMANDA, 236 

AMBER, 120 

AMOS, 75, 80 

AMPTE, 221 

AMS, 236 

Andersen Johannes, 31 

angular resolution, 22 

ANS, 17 

Ansaldo/EIE/SOIMI, 71 

ANS satellite, 176 

Antarctic, 110 

Antarctica, 105, 106, 224 

ANTARES, 236 

AO, 128-130, 135, 229 

APEX, 152, 153, 155, 156 

ARCHEOPS, 184 

architects Fehling and Gogel, 39 

Ardeberg Arne, 95 

Ariane 5, 162, 182, 184, 221 

Ariel, 17, 188, 234 

Index 

Armazoni, 97, 106 

array telescope, 45 

ASCA, 194 

Astronomical Journals, 254 

– researchers, 269 

– sites, 105 

Atacama, 90, 96, 102, 107, 154 

ASTE, 156 

ASTRO-E, 194 

– E2, 284 

– -F, 186, 187, 284 

Astrometry, 137 

ASTROSAT, 137, 194 

astrosital, 56 

Auer & Weber, 77 

Aurora, 169, 214, 278, 280, 282, 283 

Australia Telescope, 145 

B 

Baade Walter, 25 

Bachmann Gerhard, 97 

background, 128 

Bannier J.H., 30 

Barrientos S., 107 

Beagle-2, 212, 213 

Behr Alfred, 29 

Bepi Colombo, 164, 215, 216 

Beppo, 174 

– SAX, 18, 189, 190, 192, 196, 282 

beryllium, 66, 74, 82 

Big Bang, 183 

BISON, 224 

Blaauw Adriaan, 30 

black hole(s), 115, 116, 121, 241, 279, 280 

Bleeker Johan, 163 

Blue Book, 67, 70, 73, 80-82


Boller & Chivens spectrograph, 31, 32 

Bonnet Roger, 163 

BOOMERANG, 184 

Booth Roy, 150 

bowshock, 220 

Breysacher Jacques, 31 

C 

21-cm line, 140, 141 

Calar Alto, 26, 40, 41, 90 

Caméra Électronique, 32 

CANGAROO III, 202 

Cargèse, 60 

Cassegrain, 27, 50, 51, 66, 67, 72, 74, 81, 

112 

Cassini, 167, 208 

CAT, 30, 32, 33, 47 

CCD, 21, 22, 41, 44, 54, 58, 122 

CCDs, 32 

CELESTE, 201 

Centaurus A, 140, 150 

Centre de Données Astronomiques, 253 

Cerenkov radiation, 200 

CERN, 14, 25, 27, 38, 171, 172 

CFHT, 26, 41 

Chacaltaya, 95, 105 

Chajnantor, 96, 99, 100, 104-106, 110, 

152, 154, 155 

Chandra, 192, 194 

Chile, 26, 37, 77, 78, 79, 82, 90-93, 96, 

156 

CINI Foundation, 67 

Climatic variability, 99 

Cluster, 164, 220, 222, 284 

CMB, 183, 184 

CNES, 168, 169, 206, 246 

CO, 141, 151, 157 

COBE, 184, 187 

COME-ON, 111 

comet Churyumov-Gerasimenko, 206, 

207 

comet Halley, 204, 205 

– LINEAR, 207, 208 

– Schwassmann-Wachmann 3, 207 

– Wirtanen, 206, 207 

COMPTEL, 197 

Concordia, 106 

CONICA, 111 

CONSTELLATION–X, 196, 282 

Copiapo, 91, 95 

Cornell, 104, 106 

Corning, 61, 69 

corona, 221 

Coronal Mass Ejections, 219 

COROT, 165, 170, 246 

COS B, 161, 188, 197 

cosmic-rays, 139, 231-236 

Cosmic Vision, 165, 171 

COSTAR, 125 

coudé, 27, 29 

Crab Nebula, 201 

Croce del Nord, 143 

Curien H., 161 

Curtis H.D., 91 

D 

1.5-m Danish telescope, 37 

Dark Energy, 279 

– matter, 140, 238, 279 

Darwin, 121, 165, 167, 249, 250, 278, 

280, 283 

Deep Impact, 208 

de Gaulle Charles, 289 

Denisse Jean-François, 31 

de Jonge Peter, 36, 150 

delay lines, 119, 121 

detectability of planets, 247 

DIMM, 103, 104 

DISCO, 224 

Disney M., 45 

DIVA, 137 

Dome C, 106 

Doppler effect, 244 

Dornier, 73 

Double Star, 165, 170, 220, 222, 284 

E 

Earliest Universe, 279 

earthquakes, 107 

EAS, 286 

ECF, 287 

Eddington, 170, 246 

Eduardo Frei Ruiz-Tagle, 79

Effelsberg, 142 

EFOSC, 32 

Einstein, 188, 194, 231, 238 

ELDO, 161, 162 

ELTs, 134, 136 

Enard Daniel, 31 

Equator-S, 221 

ESA(’s), 16, 17, 21, 113, 119, 121, 123, 125, 

126, 131, 132, 138, 146, 159-235, 240, 

241, 245, 246, 265, 266, 270-272, 

274, 275, 282, 283, 285-287 

– Convention, 163 

ESF, 286 

ESO, 16-18, 21, 24-120, 125, 127, 134, 

145, 150, 152, 154, 161, 171, 172, 266, 

270-272, 275, 281, 285-287 

– Convention, 17, 26, 49, 77 

ESOC, 162 

ESRIN, 162 

ESRO, 17, 161, 162 

ESTEC, 162 

European Research Area, 263, 271 

EUSO, 170, 234, 285 

EVN, 142, 145-147, 282 

EXIST, 196 

Exoplanets, 170 

EXOSAT, 18, 174, 179, 189, 194, 282 

Extensive Air Shower, 232 

Extreme Energy Cosmic-rays, 279 

F 

FAME, 137 

FIRST, 181, 188 

FLAMES, 117, 118 

FOC, 123, 124 

focal ratio, 51 

Fogo, 90 

Frequency Agile Solar radio Telescope, 

230 

Freundlich, Erwin, 231 

Funding, 270, 271, 275 

FUSE, 137 

G 

GAIA, 138, 165, 167, 170, 245, 280 

Galactic Center, 115, 116 

Index 319 

Galaxy Evolution Explorer, 137 

Galileo, 67, 167 228 

GALLEX, 237 

gamma-ray, 188, 190, 196 

– – bursts, 190, 198 

Gamsberg, 26, 40, 90 

Garching, 59 

GDP, 258, 260, 265, 268, 270, 271 

Gemini, 26, 83-85 

– Project, 71 

General Relativity Theory, 231, 238 

Genesis, 227 

GENIE, 121 

GEO 600, 239 

GIAT, 72 

Giacconi Riccardo, 77 

Ginga, 194 

Ginzburg Vitali, 231 

Giordano Bruno, 243 

Giotto, 163, 204, 205 

GLAST, 169, 200 

GOES-12, 227 

Golay Marcel, 48 

GONG, 224 

GRAAL, 201 

Graham (Mt.), 83, 84, 90, 104, 105, 150 

GRANAT, 196 

GRANTECAN, 83-85, 281 

Gravitational wave(s), 231, 238, 240, 242 

Gravity Probe B, 242 

GREGOR, 229 

Grigg-Skjellerup, 205 

H 

habitable zone, 247 

Hakucho, 188 

HALCA, 142, 146, 147 

Hale G.E., 13, 16 

HARPS, 245 

HAWK-1, 117 

Heckmann O., 38, 93 

HEGRA, 201 

Helios, 220 

Herschel-Planck, 162, 164, 177, 181-184, 

186, 187, 280 

HESS, 201, 202, 238, 279 

Hess Victor, 231


HET, 83, 85 

Hinotori, 227 

Hipparcos, 18, 137, 138, 163, 174 

H 2O, 104, 105, 152 

Hofstadt Daniel, 31, 77, 94 

Horizon 2000, 163, 165, 167, 171, 205, 

214 

– -Plus, 164, 170 

HST, 55, 110, 123-130, 134, 137, 163, 206, 

248, 284 

– instruments, 124 

Hubble Deep Field, 129 

– Ultra Deep Field, 129, 131 

Humboldt, 90 

Huygens, 208, 209, 216, 284 

I 

IAU, 19, 269, 270, 272, 285 

ICECUBE, 236 

ILIAS, 287 

impact factor(s), 263, 264 

inflatable dome, 73 

inflation, 81 

infrared, 33, 47, 74 

– space missions, 187 

Instrument(s), 209 

– at the VLT, 115 

– of ISO, 178 

INSU, 80, 148 

INTEGRAL, 18, 162, 197-199, 284 

Integral Science data Centre, 199 

– Field Unit, 117 

Interferometers, 143 

Interferometrically, 82 

interferometry, 65, 67, 73, 80, 81, 107, 

119, 120 

IR, 104, 106, 107, 110, 111, 114-119, 128- 

130, 136, 176, 179, 181, 185, 249 

IRAM, 148, 149, 153, 280, 282 

IRAS, 176, 186 

Iris, 224 

IRTS, 185, 187 

ISEE-2, 221 

ISO, 18, 132, 162, 163, 176-181, 185-188, 

280 

ISOCAM, 178, 185 

ISOPHOT, 178-180 

ISAAC, 114, 115 

ISAS, 165 

IUE, 17, 161, 162 

J 

Jansky Karl., 14, 139 

JAXA, 215 

JCMT, 90, 150 

JENAM, 286 

JIVE, 145 

Jodrell Bank, 142 

juste retour, 171 

JWST, 106, 132-134, 136, 137, 165, 170, 

186, 187, 280 


K 

KamLAND, 237 

KASCADE, 235 

Keck telescope(s), 82, 83, 90, 104, 281 

Kepler, 247 

KMOS, 118 

KORONAS-1, 228 

Kourou, 162 

Kuiper G.P., 91 

Krupp-MAN, 56 

L 

L2, 126, 181, 194 

Labeyrie A., 45 

La Palma, 26, 40, 41, 83, 84, 89, 105, 

106, 136, 201, 229 

La Peineta, 91 

La Réunion, 104, 105 

Large Magellanic Cloud, 192, 237 

Las Campanas, 50, 83, 93, 94 

La Silla, 27, 33-36, 40, 57, 58, 64, 73, 79, 

91, 93-95, 98, 100-102, 105-107, 122, 

150-152, 199, 245 

La Torre, 78 

LBT, 83, 84, 85, 281 

Léna Pierre, 60, 111 

LEST, 229 

LHC, 279 

LIGO, 239, 241

Linde, 75 

LISA, 164, 165, 170, 240-242, 280, 283 

– pathfinder, 240 

Lobster, 170 

– -ISS, 196, 285 

Lockman hole, 189, 193 

LOFAR, 158, 282 

Long Duration Exposure Facility, 234 

LSA, 153 

Lucretius, 243 

Lüst Reimar, 39 

M 

16-m equivalent telescope, 46 

16-m telescope, 79 

3.6-m, 27-31, 33, 37, 40, 47, 52 

3.6-m telescope, 80, 111 

8-m class telescopes, 83 

8-m mirror, 69, 71, 73 

8.2-m mirror(s), 72, 81 

8-m telescopes, 73, 74 

MACAO, 111 

MACRO detector, 235 

Magellan, 83 

MAGIC, 89, 201, 202, 279 

Magnetic fields, 139, 158 

magnetopause, 220 

Magnetosphere, 220 

Mars, 167-169, 211, 247, 272 

– -96, 169, 212, 284 

– express, 165, 170, 171, 209, 210, 212- 

214, 216, 284 

Mauna Kea, 16, 40, 41, 83, 90, 104-106, 

110 

MAXIMA, 184 

Mayor Michel, 244 

Mercury, 164, 168, 215, 216, 284 

MERLIN, 144-146 

Messenger, 216 

MICROSCOPE, 165, 170, 242 

Middelburg Frank, 38 

Middle European countries, 272 

MIDI, 113, 119 

MIRI, 133 

MMA, 154 

MMT, 52, 83 

Moon, 169 


MOST, 247 

MPG, 39, 40, 80, 148 

MPIA, 40 

MPIfR, 152, 153, 156 

Muller A.B., 91, 97 

multi-mirror telescope, 44, 45 

Multiple Object Spectrographs (MOS), 

117 

N 

Nancay, (F) radioheliograph, 230 

NAOS, 111 

NAOS-CONICA, 115, 116 

NASA, 18, 119, 125, 130-132, 137, 163- 

165, 167, 168, 170, 171, 176, 184, 185, 

192, 194, 196, 199, 200, 205, 206, 

208, 213, 216, 223, 226, 227, 234, 

240-242, 245, 250, 283, 285, 286 

– Astrophysical Data System, 253 

Nasmyth, 27, 29, 50, 66, 67, 72, 74, 81, 

112 

NESTOR, 236 

Neutrinos, 231, 236, 237 

Newton Isaac, 87, 88 

NEXT, 196 

NGST, 130, 132 

NICMOS, 126 

Nicollier Claude, 96 

NIRCam, 133 

NIRSpec, 133 

Normalized pages, 258 

NOT, 41 

NTT, 35, 41, 49, 50, 52, 55-58, 59, 64, 

69, 73, 77, 106, 117, 136 

– hill, 58, 98, 114, 122 

nulling interferometers, 249 

O 

Observatoire de Haute-Provence, 244 

Observatorio del Teide, 229 

Odin, 185, 187 

OECD, 285, 286 

Olympus Mons, 210, 213 

OMEGA, 213 

ONERA, 111 

Onsala, 156


Onsala Space Observatory, 154 

Oort, Jan, 25 

operation costs, 35 

OPTICON, 287 

oscillation modes, 223 

OWL, 19, 107, 129, 130, 132, 134-137, 

248, 278-282 

Ozone, 250 

P 

Pacini Franco, 48 

Palomar, 13, 16, 28 

Panamericana, 97 

Paranal, 37, 73, 75, 79, 82, 83, 95-105, 

107, 119, 122, 127 

Pauli Wolfgang, 231 

Pedro Martír, 104, 105 

Photometric nights, 103, 105 

PI countries on ESA missions, 173 

Pierre Auger Observatory, 232 

Planck, 165, 170, 182, 184, 187 

planetary missions, 209 

Pontecorvo Bruno, 237 

post docs, 268 

PRIMA, 121 

prime focus, 27 

Queloz Didier, 244 

Q 

R 

RADIOASTRON, 147 

RadioNet, 287 

Ramaty High Energy Solar Spectroscopic 

Imager, 227 

REOSC, 63, 70, 71, 73, 84 

Residencia, 75-77 

RME, 199 

Roddier François, 60 

ROSAT, 18, 174, 189, 190, 194, 260, 282 

Rosetta, 162, 164, 167, 206-208, 214 

ROSITA, 196, 285 

RTGs, 167 

Rutland F. 91 

RXTE, 194 

S 

SAFIR, 187 

Sag. A*, 117 

SAGE, 237 

Sagittarius A*, 115 

SALT, 83, 85 

Sanchez Francisco, 89 

San Pedro de Atacama, 94, 99, 152 

Sarazin Marc, 95, 99, 101, 103, 104 

Schenkirz D., 77 

Schmidt telescopes, 122 

Schott, 56, 61, 63, 69, 70 

Schuster Hans-Emil, 97 

SCUBA, 150 

segmented mirror, 45 

SEST, 150-152 

Setti Giancarlo, 48 

Sierra negra, 104, 105 

SIGMA, 196, 284 

SIM, 245 

SINFONI, 117 

SIRTF, 177, 185, 186 

SKA, 157-159, 278, 280-282, 285, 286 

SMART-1, 170, 171, 196, 215 

Smyth Piazzi, 87 

SOFIA, 185 

SOHO, 18, 164, 223, 225, 226, 229, 284 


Solar B, 227 

– irradiance, 223 

– Maximum Mission, 227 

– missions, 228 

– Orbiter, 165, 170, 223, 227 

– Probe, 227 

– wind, 219, 221, 223 

South Africa, 91 

Soyuz, 162, 170, 215, 222 

Spacelab, 285 

Space Station, 167, 169, 170, 194, 283, 

284, 285 

Spectrum uv, 137 

SPICA, 186, 187, 284 

Spitzer, 185, 187 

STACEE, 201 

Stardust, 207 

steel mirror, 62 

ST/ECF, 125 

Stephenson R., 88

STEREO, 227 

STIS, 126 

Stock J., 91, 93, 95 

Strewinski W., 27 

Strömgren Bengt, 31 

STScI, 123, 125 

Subaru, 83 

submm, 106 

– telescopes, 147 

Sudbury Neutrino Observatory, 237 

Sun grazing comets, 225 

SWAS, 187 

SWIFT, 199 

Swings Jean-Pierre, 59 

synthesis methods, 143 

T 

3.6-m telescope, 63, 64, 245 

6-m telescope, 29, 44 

8-m unit telescope, 66 

TAMA, 239 

Tarenghi Massimo, 56, 77 

TAROT, 199 

TD-1, 161 

Teíde Observatory, 88 

Teneriffe, 87, 88 

Terrestrial Planet Finder, 250, 283 

The 3.5–6 meter Astronomical Telescopes, 

42 

THEMIS, 88, 229 

Titan, 208 

Tololo, 91, 95, 107 

Transition Région And Coronal Explorer, 

227 

U 

UKIRT, 40, 90 

Ulysses, 18, 163, 223, 235 

Universidad católica, 79 

– de Chile, 79 

US export regulations, 284 

USSR, 93, 94 

UVES, 113, 117, 118 

Vattani U., 48, 49 

Venus, 167, 247 

V 


Venus express, 165, 170, 214, 216 

VERITAS, 201, 202 

VIMOS, 117, 118 

VIRGO, 239, 240, 241, 280 

Virtual Observatory, 122 

VISTA, 98, 114, 122, 281 

Vizcachas, 94 

VLA, 144, 156, 157 

VLBA, 145 

VLBI, 142, 145-147, 151, 157, 280 

VLT, 10, 12, 14, 17, 18, 26, 49, 50, 52, 55, 

56-65, 67, 71-73, 77, 80, 83, 85, 94, 

97, 99, 100, 103, 109, 111-114, 117- 

119, 128-130, 136, 139, 154, 171, 184, 

206, 208, 246, 265, 271, 280, 281 

– Advisory Committee, 61 

– Study Group, 59 

– Survey Telescope, 75, 114 

VLTI, 111, 112, 114, 119, 121, 280 

VST, 122, 281 

W 

Waldmeier M., 48, 49 

Walters K., 93 

Westerbork, 144 

Wilson Ray, 53, 56 

WIND, 221 

Whipple temlescope, 201 

WMAP, 184, 187 

X 

XEUS, 170, 194, 196, 200, 278, 280, 282, 

284 

XMM-Newton, 117, 162, 164, 174, 184, 

190-192, 194, 199, 282 

X-ray, 188 

X-shooter, 118 

50 year cycle, 101 

Yohkoh, 227 

Y 

Z 

Zeiss, 41, 57, 63 

Zerodur, 56, 57, 61-63, 66, 69, 70, 83 

Ziebell Manfred, 73

Photo credits 

p. 10 ESO 

I 1 ESO 

2 Jodrell Bank Observatory, University of Manchester 

3 ESO and C. Madsen 

II 2-4 ESO 

III 2 ESO 

4-7 ESO 

IV 1-4 ESO 

V 1 ESO/Schott 

2 ESO/REOSC 

3-6 ESO 

7 Instituto de Astrofísica de Canarias 

VI 1, 2 Instituto de Astrofísica de Canarias 

4 ESO/ESA 

5 U. Demierre 

6 ESO/University of Munich 

7-8 ESO 

VII 1-7 ESO 

VIII 2 NASA, ESA and S. Beckwith (STScI) and the HUDF Team 

4 NASA/Northrop Grumman Space Technology 

5 ESO 

IX 1 ESO 

2 Max-Planck-Institut für Radioastronomie 

3 Istituto de Radioastronomia CNR, Bologna 

4 National Radio Astronomical Observatory, US 

5 JIVE 

6 IRAM 

8 ESO 

9 ESO/National Observatory of Japan 

X 1 ESA 

XI 1 ESA 

3-4 ESA and the ISOCAM Consortium 

5 A. Moorwood 

6 ESA 

8-10 ESA 

11 ESA/G. Hasinger et al. 

12 ESA 

13 ESA/ISDC 

XII 1 ESA/Max-Planck-Institut für Aeronomie/U. Keller 

2 ESA 

3 ESO 

4-5 ESA/DLR/FU Berlin (G. Neukum) 

XIII 1-4 ESA 

XIV 2 ESA 

3 D. Enard/VIRGO Consortium 

4 ESA 

XV 2 ESO/M. Mayor et al. 

3-5 ESA

Achevé d’imprimer sur les presses de l’Imprimerie BARNÉOUD 

B.P. 44 - 53960 BONCHAMP-LÈS-LAVAL 

Dépôt légal : Novembre 2005 - N° d’imprimeur : 507011 

Imprimé en France

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