The Sloan Digital Sky Survey is the first CCD photometric survey of the North Galactic hemisphere and the most ambitious astronomical survey ever undertaken. When completed, the Sloan Digital Sky Survey (SDSS) will provide detailed optical images covering more than a quarter of the sky, and a 3-dimensional map of about a million galaxies and quasars.

 

While the SDSS was originally designed to study the distant universe, its wide area, high precision maps of faint stars have made it an invaluable tool for studying the Milky Way and its immediate neighborhood. As the survey progresses, its data are released to the scientific community and the general public in annual increments.

 

The SDSS uses a dedicated, 2.5-meter telescope at Apache Point Observatory, New Mexico, equipped with two powerful special-purpose instruments. The 120-megapixel camera can image 1.5 square degrees of sky at a time, about eight times the area of the full moon. A pair of spectrographs fed by optical fibers can measure spectra of (and hence distances to) more than 600 galaxies and quasars in a single observation. A custom-designed set of software pipelines keeps pace with the enormous data flow from the telescope.

 

The SDSS completed its first phase of operations, known as SDSS-I, in June 2005. Over the course of five years, SDSS-I imaged more than 8,000 square degrees of the sky in five bandpasses, detecting nearly 200 million celestial objects, and it measured spectra of more than 675,000 galaxies, 90,000 quasars, and 185,000 stars. These data have supported studies ranging from asteroids and nearby stars to the large scale structure of the Universe.

 

The next phase, SDSS-II, will continue until June 2008. With a consortium that now includes 25 institutions around the globe, SDSS-II will carry out three distinct surveys – the Sloan Legacy Survey, SEGUE, and the Sloan Supernova Survey – to address fundamental questions about the nature of the Universe, the origin of galaxies and quasars, and the formation and evolution of our own Galaxy, the Milky Way.