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Mapping The Heavens

The most ambitious mapping of the heavens ever undertaken is about to start from a remote observatory in New Mexico, using the most complex camera ever built.

The $77 million project, called the Sloan Digital Sky Survey, will probe 40 times farther into the universe than any earlier survey, taking pictures in three dimensions and in five colors, astronomers announced here Monday.

When the survey is complete, it will provide an atlas of the skies 100 times clearer than the star charts relied upon for decades and will have pinpointed the location of more than 100 million galaxies.

Yet, the survey will produce images that anyone will be able to view on a computer. One day, say the astronomers, schoolchildren will be able to display on their computers the same images experts use to study the heavens.

"This is not just a telescope," said Jim Crocker of Johns Hopkins University, one of nine organizations participating in the project. "This is a science factory."

Members of the project team unfurled a 35-foot-long photo swatch of the heavens taken during the project's "first light," the initial pictures taken by a new telescope. The photo contained thousands upon thousands of stellar objects in different colors.

"What you see is 1 percent of one second of data from this instrument," said Bruce Margon of the University of Washington, the science director of the project. He said that by the time the survey is finished, it will have collected 10 terabytes (10 followed by 13 zeros) of data. The amount of data will equal what is now stored in the Library of Congress.

The goal is to completely map, in three dimensions, more than half of the heavens, cataloging 100 million of the brightest galaxies and 100,000 quasars. From its location at Apache Point, N.M., north of White Sands, the telescope cannot see some of the sky over the Southern Hemisphere.

For the galaxy catalog, the telescope will be able to detect objects out to 2 billion light-years. For quasars, the most energetic objects in the universe, the telescope will see out to 10 billion light-years. A light-year is the distance travels in one year, or about 6 trillion miles.

"For quasars, we get to the very end (of the universe), as deep as the Hubble" Space Telescope, said Neta Bahcall, a Princeton astronomer and a member of the survey team.

The 2.5-meter telescope is teamed with a digital camera that Mike Turner of Fermilab, one of the sponsoring institutions, called "the most complicated camera ever built."

The camera includes 54 light amplifiers and is able to gather more pixels of light than the human eye. In contrast to digital cameras that capture images on tiny chips of silicon, the camera includes a full square foot of silicone.

Images, in digital form, flow from the camera into a computer system at the rate of 8.5 million bytes a second, said Constance Rockosi, a Univesity of Chicago graduate student credited with much of the key assembly work on the camera.

The system includes two spectrographs, instruments that break down the wavelengths of light, that will be able to tell the composition of objects, their speed of motion and their distance from Earth.

Spectrographs have been used for decades by astronomers, but not like this, said Crocker.

"In the first two weeks, we will collect more spectra than all of the other surveys in history," he said.

Margon said the current sky survey by astronomers is a 40-year-old collection of black-and-white photo plates taken at the Palomar Observatory with a conventional astronomy camera.

The new survey will go out at least 40 times farther and will be in five colors. "This will be a permanent digital encyclopedia of the sky," he said.

Eventually, the work will be contained on 200 CD ROM computer disks and be available on the Internet. People will be able to slip in a disk or connect to the Web site "www.sdss.org" and see high definition views of the heavens.

"For generations to come, many groups will be able to study galaxies and clusters of galaxies," said Bahcall. "With this data, we'll be able to take a journey through the universe."

The first light image of the survey was unveiled at the national meeting of the American Astronomical Society.

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