New observatory rises on South African mountaintop (Forwarded)

University Communications
University of Wisconsin-Madison

Contact:
Terry Devitt, 608-262-8282,
Matthew Bershady, 608-265-3392,
Kenneth Nordsieck, 608-262-1163,

07/24/03

New observatory rises on South African mountaintop
By Terry Devitt

A new observatory that promises to give Wisconsin astronomers unique access to
the southern sky is now a prominent feature on a remote South African plateau.

The observatory that will house the largest optical telescope in the Southern
Hemisphere, known as the Southern African Large Telescope (SALT), is now nearly
complete, according to astronomers at UW-Madison. Although the telescope itself
is still 18 months from completion, the mirror segments that will make up the
11-by-10-meter hexagonal primary mirror are starting to come together, says
Matthew Bershady a UW-Madison professor of astronomy who is helping to oversee
planning and construction of the new observatory.

"We are at a point where we have a structure that is nearly completed," says
Bershady of the observatory situated 220 miles from Cape Town on a mountain
plateau at the southern end of the Kalahari Desert. "Now, we are starting to
populate the (telescope) truss with glass."

The $18 million SALT Observatory is being built by a consortium of government
and academic institutions from six countries. In addition to UW-Madison, Rutgers
and Carnegie Mellon universities, Germany's University of Gottingen, the
University of Canterbury in New Zealand, the United Kingdom Consortium, and the
governments of Poland and South Africa are partners in the SALT consortium.

UW-Madison's contribution is a $3 million imaging spectrograph that is being
built under the direction of astronomy Professor Kenneth H. Nordsieck. A
spectrograph is a device that breaks light down into its constituent
wavelengths, each of which has a different story to tell about the star or
galaxy from which the light is gathered.

"We're past the design stage now," says Nordsieck of the 500-kilogram instrument
that will be at the heart of the new observatory. "We're cutting metal and
polishing glass."

The Wisconsin spectrograph will be the telescope's primary scientific
instrument. Positioned high above the huge segmented mirror at the prime focus
of the telescope, the device will be capable of capturing spectra at a rate of
10 times a second.

To explain the importance of spectroscopy to astronomy, one spectrum -- in the
words of one astronomer -- is worth a thousand pictures.

The device, says Nordsieck, will sample light in the near ultraviolet part of
the electromagnetic spectrum: "This is light that our eyes can't see, but it
still gets through the atmosphere. It's the same kind of light that causes sunburn."

In addition, the spectrograph will be capable of doing polarimetry, measuring
how light waves are scattered as they bounce off objects in space and are pushed
and pulled by the immense magnetic fields of interstellar space. Polarimetry,
Nordsieck says, helps reveal geometric information, giving astronomers insight
into how starlight interacts with the objects it encounters.

"We will also have one of the first large Fabry-Perot devices," he adds. "It is
basically a tunable filter" capable of imaging a large part of the sky.

Fittingly, among the system of lenses to be included in the spectrograph will be
a set made of sodium chloride -- or salt.

Together, the large, segmented primary mirror and the novel scientific
instrumentation will position SALT to break plenty of new ground in the southern
skies.

"One of the big things this telescope will be tuned for are the Magellanic
Clouds," says Bershady. "They are important because they are the galaxies
nearest to our own, and they offer the best opportunity to study stars and
galaxies outside of the Milky Way. It's always a good thing to look outside of
your own immediate environment to find out how unique you are, if at all."

The SALT construction schedule is right on time, Bershady adds. "That we haven't
slipped at all is amazing," he says. "Our hope is to stay on track for first
light in late 2004."

Note to photo editors: High-resolution photos of the South African Large
Telescope are available at
http://www.news.wisc.edu/newsphotos/salt.html