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Stanford astronomers get their own telescope

STANFORD -- Stanford's astronomy program, one of the most active small programs in the country, is finally getting its own large telescope.

After years of borrowing time from other institutions' telescopes or analyzing data collected by others, Stanford is becoming a minority partner in what will be the world's largest optical telescope, planned for the wastelands southeast of El Paso, Texas. The University of Texas and Pennsylvania State University are the majority partners. Two German universities, Munich and Gottingen, also are minority partners.

Stanford is contributing $1.3 million, about one-tenth of the cost, through university and private funds, according to Vahe Petrosian, director of the astronomy program. Almost all - but not all of it - has been raised, he said. That share will buy the kind of time the program needs to study such things as quasars, the geometry of the universe, black holes and neutron stars.

"This is something everyone's wanted to do," Petrosian said. "Someday we hope to have enough money to have a sister telescope in the Southern Hemisphere."

Stanford's program has more than 25 graduate students and more than 100 undergraduates taking various courses, a larger number than some bigger, more-established programs, Petrosian said.

Most of the dozen faculty members are associated with the physics department, some in applied physics or electrical engineering. The program, which has not had substantial access to any large telescope, has been largely theoretically based, with the astrophysicists in the program using data gathered by others.

The telescope, currently named the Spectroscopic Survey Telescope (SST), should see "first light" in 1996 and begin doing science the next year. By that time, it probably will be renamed for two major donors to Texas and Penn State.

The device will be located 300 kilometers (about 185 miles) from El Paso, near Big Bend National Park, on a mountain approximately 2,012 meters (6,600 feet) high. The area is the darkest site in the continental United States, said Roger W. Romani, assistant professor of physics, far from any city or other light source.

The Texas telescope will collect visible light, which is the radiation between near infrared and the near ultraviolet.

Romani said the SST's primary mirror will be slightly larger than the 10-meter Keck telescope on Mauna Kea on the Island of Hawaii, which recently began its exploration. Because it uses an entirely different technology, SST will cost about one-eighth of the Keck's $100 million price. All the SST money is from the participating universities or private funds, with no federal funding involved.

"It's a way of doing big science for a small fraction of the normal cost," Romani said.

SST will use a system devised for the radio telescope at Arecibo, Puerto Rico. It has a stationary spherical mirror and a movable computer-controlled tracker comprising two smaller mirrors that correct for distortions (spherical aberrations) in the image.

"The light comes down, hits the big mirror, bounces back up and hits a double mirror that forms the final image," Romani said. The small double mirror tracks the sky, not the large main mirror.

"This is the first time this has ever been attempted with an optical telescope," Romani said.

The primary mirror has 91 identical hexagon mirror elements, measuring a total of one meter across. Because all the elements are identical, there is an economy of scale. Keck's mirror is a parabolic surface, so the 36 hexagons there are not identical and more expensive.

More conventional telescopes, such as the one at Mauna Kea, mechanically track celestial objects as they arch across the sky; SST sits still as the objects transit above. The tracker moves to follow the object and reduce distortion. It can watch 70 percent of the sky.

Petrosian said SST has several disadvantages because of its design. It cannot track a star or galaxy all night, from horizon to horizon. Observation time is only an hour or so, depending on the object. It is not as good for taking photographs as the Keck device, although it can be used that way.

However, these compromises will not affect spectroscopy, which is the primary use of large telescopes, Romani said.

He said that the future of observational astronomy may lie with SST-like devices. As astronomers look at fainter, more distant objects, they need to collect every possible photon that arrives from the object, and that will mean larger and larger devices.

It also will be one of the best telescopes in the world for spotting extrasolar planetary systems.

"It's no longer a question of improving the efficiency of the system," he said. "You've got to make it bigger. That's something that's liable to cost a lot."

This technology, which came from Penn State, is a more cost- effective way of make a bigger telescope.

Mobile telescopes such as Keck also have a size limit because of their complexity.

"The SST just sits there," Romani said. "You set it and forget it."

Petrosian and Romani credited Provost Gerald Lieberman with getting the funding for the project. The university has a matching grant currently in place.



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