Sol Lucet Omnibus - ESO

Heidi Korhonen
Born in Hamina, Finland
Biography
Heidi was born in south-east Finland and during her childhood lived in many different places
in Finland, from the southern coast to all the way north of the Arctic Circle. She was always very
interested in astronomy, but was never the kind of amateur who would spend her nights staring
at the stars. Still, when the time came to decide what to do after high school, she didn’t hesitate
to start studying astronomy. She had no idea what professional astronomers actually did, so it
was a real jump into the unknown; a jump that she hasn’t regretted! Heidi completed her Master’s
degree at the University of Oulu in Finland. Afterwards, in 1998, she moved to sunny La Palma
in the Canary Islands. She worked there for 18 months at the Nordic Optical Telescope, where
she met her husband, a fellow astronomer. After moving back to Oulu with him, their daughter
was born in 2001 and Heidi received her PhD soon after. Next, Heidi got a position in Germany
with the Astrophysical Institute Potsdam. Her second child, this time a boy, was born in Potsdam
in 2003. In the summer of 2007 Heidi and her family decided it was time to move, so they
relocated to southern Germany, to the Munich area. Heidi spends ten months of the year working
at ESO Headquarters near Munich, and the other two at ESO’s observatory in Cerro Paranal, Chile.
European Southern Observatory (ESO)
ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most
productive astronomical observatory. It operates three sites in Chile — La Silla, Paranal and
Chajnantor — on behalf of its fourteen member states. It is building ALMA, the Atacama Large
Millimeter/submillimeter Array, together with international partners, and designing the European
Extremely Large Telescope.
www.eso.org
Sunspots and Starspots
Magnetic Islands Larger than our Planet
The Sun may appear as a perfect
sphere in the sky, but it actually
has blemishes called sunspots.
Their nature was a mystery until
modern science was able to explain
their nature and workings. Now,
astronomers have a new task: to
determine whether other stars
exhibit the same phenomena!
As Heidi Korhonen explains, this
research gives interesting answers
but also raises fresh questions.
A detailed image of the largest sunspot is seen on the
picture of the full solar disc overleaf. This observation has
been obtained with the Dutch Open Telescope on La Palma,
Spain, on 2 November 2003. The complexity of this huge
sunspot group is breathtaking.
If you glance at the Sun through fog, clouds or darkened glass you will
usually see a perfectly white disc (never look at the Sun directly because
of the damage it will do to your eyes!) Sometimes you might see dark
patches on this smooth surface. Usually these sunspots are so small that
you would see them only with the aid of a telescope, but occasionally
large spots occur, many times larger than the Earth and these are visible to
the naked eye.
Dark or light?
Even though sunspots appear dark they still radiate light, and actually
they are brighter than the full Moon. They just appear dark when
compared to the rest of the Sun. What is causing this apparent darkness?
When scientists first started regular observations of sunspots, after the
development of the telescope in the early 17th century, their origin was
already hotly debated. Some thought that they were clouds in the solar
atmosphere, others that they were small bodies orbiting the Sun. Quite
soon scientists agreed that they were actually something that was in
the Sun itself, but it took a couple of hundred years before people really
started to understand what sunspots are.
Mysterious magnetism
In 1908 the magnetic origin of sunspots was discovered by an American
astronomer, George Ellery Hale. In the presence of a magnetic field,
spectral lines are split into several components. Hale used this so-called
Zeeman effect to show that sunspots harbour very strong magnetic fields.
The Earth’s magnetic field at the equator is approximately 0.3 Gauss;
the field in sunspots can be as high as 3000 Gauss. In the normal solar
atmosphere material is transported from the hot interior, causing an
outward flow of heat and energy. In sunspots, the magnetic field acts as
a valve hindering the normal heat transport. Some heat transport still
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