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Ambitious sky survey gets under way.

It took five scientists to unfurl the 30-foot-long segment of the first high-resolution picture taken by the Sloan Digital Sky Survey.

"On behalf of the American Astronomical Society, `Wow!'" exclaimed the society's president-elect, Robert D. Gerhz of the University of Minnesota in Minneapolis. Researchers displayed the heavenly panorama at a meeting of the society in San Diego this week.

As impressive as that trove of stars and galaxies is, it represents a mere I percent of the survey's first detailed image, a 7.5-minute exposure taken on May 27 at Apache Point Observatory near White Sands, N.M. That image, in turn, pales in comparison with what's yet to come.

Astronomers expect that when the $77 million Sloan survey is completed, 5 to 7 years from now, it will have generated the first three-dimensional map of the northern celestial hemisphere. The map will include images of 100 million heavenly objects recorded in five colors, along with spectra of the brightest 1 million galaxies and 100,000 quasars. The spectra will yield the redshift, a measure of distance.

Sloan can gauge the distance of galaxies that lie within 2 billion light-years of Earth and of quasars as far away as the edge of the observable universe. Such information will indicate where in the cosmos galaxies and quasars are clustered and where they are relatively scarce.

Researchers conceived the ambitious project a decade ago "to understand how structure in the universe formed from the formless quark soup that existed during the [cosmos'] earliest moments," says team member Michael S. Turner of the University of Chicago and the Fermi National Accelerator Laboratory in Batavia, Ill.

The survey relies on a 2.5-meter telescope and a camera with a foot-long expanse of solid-state light detectors that contain more pixels than the human eye. Rather than scan the sky by slewing to and fro--a time-consuming process--the telescope remains stationary and, as Earth rotates, the sky drifts by.

The flood of data from the survey will constitute "a permanent digital encyclopedia of the sky," says Bruce H. Margon of the University of Washington in Seattle. He asserts that astronomers will soon be able to solve many problems by going to that archive rather than to a telescope.

In a year or two, says Turner, the Sloan survey is likely to have gathered enough data to test cosmological models rigorously. For example, it might provide evidence indicating whether the universe will expand forever or eventually collapse in on itself.

A complementary, but smaller, survey, begun last fall, has measured the distances to some 10,400 galaxies in the southern celestial hemisphere. That survey uses an Australian telescope and plans to take spectra of 250,000 galaxies by 2000.
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Title Annotation:Sloan Digital Sky Survey
Author:Cowen, Ron
Publication:Science News
Article Type:Brief Article
Date:Jun 13, 1998
Words:451
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