The Sloan Digital Sky Survey (SDSS) is a co-operative scientific project involving over 25 institutions worldwide including the University of Chicago Department of Astronomy and Astrophysics and Fermilab. During its eight years of operation (2000-2008) the survey mapped one-quarter of the entire sky (more than 930,000 galaxies and 120,000 quasars), producing high-resolution, five-color images of the entire area being captured, and spectrographic data for selected objects in the image area, captured in a second pass. It was preceded by a decade (1990-1999) of building the SDSS telescope and the data collection system. The 2.5 meter telescope is located at Apache Point Observatory, New Mexico.
Data were made available to the public in numbered, annual releases (DR1-DR7, "DR" for "Data Release"). Each release contains the data from the previous releases and adds newly collected data. The archiving project focussed on DR7, the last data release before the completion of the SDSS project in 2008.