What has more than 88,000,000,000 pieces, is available to the public, and helps astronomers learn about such diverse topics as asteroids, the most distant quasars, and the structure of the Universe?

Just a month ago, the Sloan Digital Sky Survey (SDSS) made public a catalog of more than 88,000,000,000 objects, ranging from asteroids in our Solar System to some of the most distant quasars ever detected. Distances were measured for more than 350,000 of these, producing a three-dimensional map of part of the Universe. The SDSS public Web site is http://skyserver.sdss.org/

Over 200 astronomers from 13 different institutions are involved in deep mapping of one-quarter of the sky, using a dedicated 2.5 meter telescope at Apache Point Observatory in New Mexico. Ultimately, this group hopes to measure several hundred million objects, with distances to over a million of them.

One of the SDSS results of great interest to Goddard is the study of how galaxies are clustered in the Universe. While the Big Bang is thought to have been almost perfectly uniform and the microwave background radiation seen by the Cosmic Background Explorer (COBE) and the Wilkinson Microwave Anisotropy Probe (WMAP) has only tiny fluctuations, the distribution of stars and galaxies in the Universe is anything but uniform. By analyzing the scale on which galaxies are clumped, SDSS scientists can help test models for how the Universe has evolved. What they find is that the SDSS results match the COBE and WMAP results extremely well, offering confirmation that the Universe is filled with unobservable dark matter and mysterious "dark energy". Only about 5 percent of the Universe is the ordinary stuff we see around us and in the sky.

Other sources of information:

Home page of the Sloan Digital Sky Survey: http://www.sdss.org/sdss.html

Home page of the Wilkinson Microwave Anisotropy Probe: http://map.gsfc.nasa.gov/

About the SDSS 3D map of the Universe: http://www.sdss.org/news/releases/20031028.powerspectrum.html

This week's question is provided by Dr. Dave Thompson. Dr. Thompson is an astrophysicist who studies gamma rays in the Laboratory for High Energy Astrophysics. He helped build, test, and analyze data from EGRET on the Compton Gamma Ray Observatory, and he is now helping build part of the Gamma Ray Large Area Space Telescope (GLAST), scheduled for launch in 2006. His particular scientific interest is gamma-ray pulsars.