title: The Sloan Digital Sky Survey-II

abstract: The SDSS is an optical imaging and spectroscopic survey originally designed to address problems in large-scale structure such as the dependence of galaxy bias on environment and the clustering properties of quasars. Such questions require very large, uniformly selected samples. All of the SDSS systems - the telescope, the instruments, and the data system - were designed from the beginning to handle large volumes of data and to apply precise calibrations.

In the course of undertaking the extragalactic programs it became evident that SDSS also has much to offer Galactic astronomy, for example the detection of low-surface-brightness stellar structures in the Galactic halo and the discovery of candidate very-low-metallicity stars. Another promising direction is the time-domain, available from repeated scans of the same strip of sky (and also some repeat spectroscopy). SDSS-II is the new funding cycle, 2005 - 2008, that features continuing the original extragalactic surveys; a new survey to detect structures in the Milky Way and to discover unusual stars; and a survey for intermediate-redshift Type Ia supernovae. sdss.org