Sloan Digital Sky Survey

June 8, 1998


San Diego -- Scientists of the Sloan Digital Sky Survey, the most ambitious sky-mapping project ever undertaken, announced today (June 8) that the project's unique telescope, located at Apache Point Observatory in southern New Mexico, has achieved first light. In a presentation at the San Diego meeting of the American Astronomical Society, Constance Rockosi, a University of Chicago graduate student and member of the Sky Survey collaboration, discussed the team's achievement.

"With first light, we have demonstrated that we have the tools in place to make a deep, high-resolution, multicolor, digital map of the sky," Rockosi said. "It is an exciting and important milestone in our project to chart the large-scale structure of the universe."

Years of work by project collaborators, along with recent round-the-clock efforts by a team of scientists and engineers on the mountaintop, culminated in first light on the night of May 9 and the first high-quality images of a large swath of sky in the constellations Serpens and Ophiuchus on the night of May 27.

"When I saw the starry images appear on the monitor, it was suddenly worth the 18 trips I have taken across the Pacific," said astronomer Mamoru Doi, of the University of Tokyo, whose work on the project includes contributions to the system that renders the starry images in brilliant color. Chicago's Rockosi echoed his excitement at seeing the first images scrolling across a bank of computer monitors.

"It was incredible to see such a large piece of the sky presented in such depth and fine detail -- really a beautiful sight," she said.

Several elements of forefront astronomical technology came together in the new telescope to yield the first celestial images. Chicago's Rockosi is part of a team, headed by Princeton University astronomer Jim Gunn, the Survey's project scientist, that designed, built and installed the telescope's digital camera, the most complex imaging instrument ever developed for astronomy. It uses a large array of silicon charge-coupled devices to create five-color digital images of the sky.

"The camera has come together in concept and in metal, glass, and silicon over the past many years," Gunn said, "and has, of course, been thoroughly tested in the laboratory. So we did not really doubt that it would work on the sky. But the thrill of seeing real images and knowing that the Survey was truly going to work after so many years of the sweat and tears of so many people was quite incredible."

The telescope will also incorporate two spectrographs, built by scientists at The Johns Hopkins University. The spectrographs provide information about the chemical composition of the astronomical sources and information about their distances, to pinpoint their positions in three-dimensional space.

"The spectrographs are our 3-D glasses," said Johns Hopkins astrophysicist Alan Uomoto, who led the spectrograph team. "They make the Sky Survey far more than just cosmic cartography. The information provided by the spectrographs is vital if we hope to understand the origin and evolution of the universe and its constituents."

The new telescope has an unusually wide field of view, enabling it to map large areas of sky in a practical length of time. It features very accurate tracking, necessary for precision measurements of star positions.

"The telescope, though small, was particularly challenging, because it has to produce good images across a wide field," said Walter Siegmund, of the University of Washington, the Survey's project engineer.

After several months of commissioning, Survey operations will begin. The collaboration's astronomers will use the images and spectra to construct the most comprehensive three-dimensional model of the cosmos ever attempted. Five years of data-taking by the Survey will produce a catalog of the positions and brightnesses of more than 100 million stars, galaxies and quasars, according to University of Washington astrophysicist Bruce Margon, the Sky Survey's scientific director.

"The Sloan Digital Sky Survey will be significantly more sensitive than our current comprehensive guide to the heavens, the forty-year-old Palomar Sky Survey," Margon said. "The Palomar survey used photographic plates to produce two-color, two-dimensional images. Our survey will use digital technology and spectroscopy to produce five-color images in three dimensions. It will map one quarter of the sky and give us a three-dimensional picture of the universe through a volume a hundred times greater than anyone has explored before."

Scientists will use the new map to explore critical questions about the nature and evolution of the universe.

"The Sky Survey will greatly advance our knowledge of the universe -- past, present and future," said University of Chicago/Fermilab astrophysicist Michael Turner, the project's scientific spokesman. "We are struggling to understand how the wondrous panoply of structure we see in the universe today -- galaxies, clusters of galaxies, voids and great walls of galaxies -- arose. Our best explanations involve what happened in the first instants after the Big Bang and relate to the unification of the fundamental forces of nature. So the Sky Survey may give us not only a clearer picture of outer space but also of the inner space at the heart of matter."

Ultimately, the Sky Survey will make its historic celestial catalog available to astronomers around the world, for a wide range of future studies. The catalog's unprecedented volume of data creates challenges for the scientists who will use it.

"The techniques that astronomers use today do not scale to this survey, whose information content will rival the Library of Congress," said Johns Hopkins astronomer Alex Szalay, who is designing data-analysis systems for the project. "The Sky Survey requires a novel computing and analysis environment. In fact, the Sky Survey approach is creating new standards in data analysis for astronomy that may well apply to other fields, such as the study of the human genome, that require extraordinarily large data sets."

Data from the mountaintop will be transferred daily to computer systems at Fermi National Accelerator Laboratory near Chicago. Software systems called data pipelines will translate the raw data into images of the sky.

"Creating the data-processing software has been a major effort of the project," said astronomer Jeff Pier, of the U.S. Naval Observatory. "Scientists across the collaboration developed the pipelines, which are then integrated at Fermilab."

Eventually, the Sky Survey's data will be available to the public over the Internet. Professional and amateur astronomers, teachers and budding school-age astronomers anywhere in the world will be able to dial up an image of a selected piece of the sky in five colors. When the Next Generation Internet arrives, they will be able to conduct complex searches of the Sky Survey archives.

The Sky Survey collaboration includes scientists from the University of Chicago, Fermilab, the Institute for Advanced Study, the Japan Participation Group, The Johns Hopkins University, Princeton University, the United States Naval Observatory and the University of Washington. Apache Point Observatory, site of the Sloan Digital Sky Survey, is owned by the Astrophysical Research Consortium, a nonprofit corporation consisting of seven research institutions, and is operated by New Mexico State University. Funding to date for the project has been provided by the Alfred P. Sloan Foundation, Sky Survey member institutions, the National Science Foundation and the U.S. Department of Energy. In addition to its support for the Sloan Digital Sky Survey, NSF provides more than $110 million annually for ground-based astronomy and astrophysics. Support from DOE, a longtime stronghold of high-energy physics research, reflects the increasing convergence of particle physics and cosmology.


Images supporting this release are available at http:/

Additional images from the AAS meeting are available at

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