I N S I D E T H I S I S S U E

More documents

Recommendations

Info

committees in several countries to provide places for expertsfrom outside the lighting industry.1.Boyce, P.R., Eklund, N.H., Hamilton, B.J., & Bruno, L.D., Perceptionsof safety at night in different lighting conditions. Lighting.Res. Technol. 2000; 32: 79-91.2.Campaign to Protect Rural England. Night blight. London:Campaign to Protect Rural England, 2003, ISBN: 1 90278659.9. Web site:www.cpre.org.uk/resources/pub/pdfs/landscape/light-pollution/night-blight-report-32pp.pdf3.International Dark-Sky Association, Tucson, AZ: InternationalDark-Sky Association, 2005. Web site: www.darksky.org4.Schaefer, B.E., Telescopic limiting magnitudes. Publicationsof the Astronomical Society of the Pacific 1990; 102: 212-2 29.5.Clark, B.A.J., Outdoor lighting and crime, Part 2: coupledgrowth. Melbourne, Australia: Astronomical Society ofVictoria Inc. May 2003.6.Cinzano, P., Falchi, F., & Elvidge, C.D., The first world atlas ofthe artificial night-sky brightness. Monthly Notices of theRoyal Astronomical Society 2001; 328: 689-707.http://xxx.lanl.gov/abs/astro-ph/01080527.Longcore, T. & Rich, C., Ecological light pollution. FrontiersEcol. Environ. 2004; 2:191-198.8. Wiley, I.S. & Formby, B., Lights Out: Sleep, Sugar and Survival.New York, NY: Simon and Schuster Pocket Books, 2000.9. Pauley, S.M., Lighting for the human circadian clock: recentresearch indicates that lighting has become a public healthissue. Med. Hypotheses 2004; 63: 588-596.10. Dawson, D. & Reid, I.L., Fatigue, alcohol, and performanceimpairment. Nature 1997; 338: 235.11. Williamson, A.M. & Feyer, A-M., Cognitive, motor impairmentsimilar for sleep deprivation and alcohol intoxication.Occup. Enviro. Med. 2000; 57: 649-655.12. Struts, J.C., Wilkins, J.W., & Vaughn, B.V., Why do people havedrowsy driving crashes? Input from drivers who just did.Washington, DC: AAA Foundation for Traffic Safety,November 1999. www.aaafoundation.org/pdf/sleep.pdf13. Clark, B.A.J., Outdoor lighting and crime, Part 1: little or nobenefit. Melbourne, Australia: Astronomical Society ofVictoria Inc. November 2002.14.Morrow, E.N. & Hutton, S.A., The Chicago Alley LightingProject: Final Evaluation Report. Chicago, Illinois: IllinoisCriminal Justice Information Authority, Research andAnalysis Unit, April 2000.www.icjia.state.il.us/public/pdf/ResearchReports/Chicago%20Alley%20Lighting%20Project.pdf18th INTERNATIONAL CONFERENCE ONGENERAL RELATIVITY AND GRAVITATIONANDTHE 7th EDOARDO AMALDI CONFERENCE ON GRAVITATIONAL WAVESJULY 8 to 14, 2007Sydney Convention & Exhibition Centre, Darling HarbourSYDNEY, AUSTRALIAJoining forces in Sydney in 2007 these conferences will bring together the world’s leading scientists working in the fields of GeneralRelativity and Gravitation.The program for GRG18 will incorporate all areas of General Relativity and Gravitation including Classical General Relativity; RelativisticAstrophysics and Cosmology, Experimental Work on Gravity, and Quantum Issues in Gravitation. The Amaldi 7 program will cover allaspects of Gravitational Wave Physics and Detection.Sydney is situated on one of the world’s most beautiful and famous harbours. Renowned for its iconic landmarks, the Sydney OperaHouse and Harbour Bridge, Sydney boasts many attractions including stunning beaches, fantastic shops, and restaurants.The conference will be held at Darling Harbour located within walking distance of the heart of the city. It is one of Sydney’s mostexciting tourist precincts, offering waterfront restaurants and cafes, beautiful gardens, and a range of exciting attractions.To find out more about GRG18 or Amaldi7, please register your interest now at www.grg18.com or www.Amaldi7.com214JRASC October / octobre 2006
Second LightSmall Kuiper Belt Bodies Seen by X-ray Occultationby Leslie J. Sage (l.sage@naturedc.com)The Kuiper (pronounced “kwiper”) Belt is a collection ofrocky-icy bodies beyond the orbit of Neptune. Pluto andits moon Charon are part of the Kuiper Belt, and thereare several other bodies whose sizes are comparable to, or evenlarger than, Pluto. About a thousand such bodies are known,but there must be many more that are too small to see directly,because in any population of bodies that collide with each otherthe number in each size range rises approximately as the inversecube of the diameter. For example, 100-km bodies are about athousand times more numerous than 1000-km bodies. Extrapolatingthat to 100-m-sized bodies predicts about 10 14 of them. But theonly practical way to “see” such small bodies is through stellaroccultations. Several projects are underway using opticaltelescopes, but a very interesting approach by Hsiang-KuangChang of the National Tsing Hua University in Taiwan uses X-ray occultation and recently reported 58 events (see the August10, 2006 issue of Nature).Chang used data from the orbiting Rossi X-ray TimingExplorer, with Scorpius X-1 as the background source. It is thebrightest X-ray source outside the Solar System and convenientlylies just six degrees away from the ecliptic. Even so, there werenumerous technical difficulties that Chang had to overcome,including the lack of photons and deciding whether the observeddips arose from something at the source or an instrumentaleffect. He took all of the observations of Sco X-1 by RXTE overthe period from 1996 to 2002, with a total exposure time of322,000 seconds, and found that there was an excess of “dips”in the X-ray flux, with most events lasting two to three milliseconds(the longest is seven milliseconds). The occurrence times of thedips in X-rays are random. While Sco X-1 is known to flare onmillisecond timescales, dips were hitherto unknown. WhenChang looked at the Crab Nebula he saw no dips. Because theCrab is an extended source, there should be no small fluctuations:their absence implies that the dips for Sco X-1 are not aninstrumental effect. This leaves occultation by Solar Systemobjects as the most plausible explanation.One problem with this result is that Chang’s estimate ofthe number of bodies in the 10 to 100-metre-size range is ~10 15 ,far more than the ~10 12 suggested by computer models of thecollisional evolution of the Kuiper Belt. This could be due to alower average collision rate between the bodies than assumedby the models, or (Chang suggests) it might indicate the presenceof another component of smaller KBOs at distances greaterthan the generally assumed 50-AU cut-off for the Kuiper Belt.Two other groups are looking for Kuiper Belt occultationsin the optical range. One, led by Françoise Roques of theObservatoire de Paris, has a paper in press with the AstronomicalJournal reporting the detection of three objects with sizes rangingfrom 220 to 600 m. They used a clever technique at the WilliamHerschel telescope on La Palma, in the Canary Islands. Thesmallest of the three appears to be in an orbit between Saturnand Uranus, while the other two are much further away fromthe Sun than usual for the Kuiper Belt (140 and 210 AU). Theycomment that finding these two objects suggests a large populationof small bodies in the “outer solar disk,” and first suggested thisat the annual meeting of the Division of Planetary Sciences (ofthe American Astronomical Society) in Louisville two years ago.The third group is the Taiwanese American OccultationSurvey (TAOS), which uses four telescopes to weed out “falsepositives” arising from variations in the star’s brightness. Thefour telescopes are installed in the mountains of a national parkin central Taiwan.They have not yet reported any detections of unexpectedoccultations, but they have seen occultations coming fromknown asteroids. The project is a multi-year automated surveyof ~3000 stars.It is worth emphasizing again that occultations are theonly way to find objects this small in the Kuiper Belt. Even thelargest telescopes struggle to find KBOs much larger (in the1000-km-size range), though the hope is that, after finding somethrough occultations, follow-up observations with a 10-m-classtelescope will be able to locate the ones that are larger thanabout 25 km. The field of view of the Keck telescopes is just 37arcseconds, however, so the follow-up observations must bedone quickly. No telescope currently under consideration couldever detect objects as small as those found by Chang and Roques.With all the work being done on high-redshift galaxiesand investigations of the Big Bang, it is a little disconcerting torealize that we have not yet completed the inventory of our ownSolar System!Leslie J. Sage is Senior Editor, Physical Science (Astronomy), for NatureMagazine and a Research Associate in the Astronomy Departmentat the University of Maryland. He grew up in Burlington, Ontario,where even the bright lights of Toronto did not dim his enthusiasmfor astronomy. Currently he studies molecular gas and star formationin galaxies, particularly interacting ones, but is not above looking ata humble planetary object.October / octobre 2006 JRASC215
Page 4 and 5: Editorialby Jay Anderson ( jander@c
Page 7: effect of the expanding Universe th
Page 10 and 11: starts to decay. Green trains are n
Page 12 and 13: ReferencesAbe, S., Ebizuka, N., Mur
Page 14 and 15: Theoryall perfectly circular orbits
Page 16 and 17: The value of r cp (the B coefficien
Page 18 and 19: Astronomy and Astrologyby Roy Swans
Page 20 and 21: Table 1. The Sun in the Zodiac acco
Page 22 and 23: Creating a High-Dynamic-RangeSolar
Page 24 and 25: to Gray. For Source 2, set Layer to
Page 26 and 27: Is Artificial Light at Night Too Mu
Page 30 and 31: Deep-Sky Contemplationsby Warren Fi
Page 32 and 33: Through My EyepieceCity Mouse and C
Page 34 and 35: The Sun is a fascinating study. Whe
Page 36 and 37: other words, astrophotography, astr
Page 38 and 39: A Moment With…Dr. David Guentherb
Page 40 and 41: Carpe Umbramby Guy Nason, Toronto C
Page 42 and 43: Pen & PixelFigure 1 — NGC 4565 in
Page 44 and 45: now search for successive fractions
Page 46 and 47: Net Astronomyby Paul J. Langan (Pau
Page 48 and 49: numbered equations and still find a
Page 50 and 51: Astrocrypticby Curt Nason, Moncton
Page 52: Publications and Products ofThe Roy

I N S I D E T H I S I S S U E

Create successful ePaper yourself

Delete template?

Save as template?