The sloan digital sky survey

Astronomy is about to undergo a major paradigm shift, with data sets becoming larger and more homogeneous, designed for the first time in a top-down fashion. In a few years, it might be much easier for astronomers to "dial-up" a part of the sky, when they need a rapid observation, rather than wait for several months to access a (sometimes quite small) telescope. With several projects in multiple wavelengths underway-such as the SDSS, Galex, 2MASS, GSC-2, POSS2, Rosat, First, and Denis projects, each surveying a large fraction of the sky-the concept of having a digital sky, with multiple, terabyte-size databases interoperating seamlessly no longer seems outlandish. As more and more catalogs are added and linked to the existing ones in coming years and query engines become more sophisticated, astronomers will have to be just as familiar with mining data as with observing on telescopes.As a major part of that effort, the Sloan Digital Sky Survey will digitally map about half of the northern sky in five filter bands from ultraviolet to near infrared; we expect it to detect over 200 million objects in this area. Simultaneously, the project will measure redshifts for the brightest 1 million galaxies. (A redshift is the spectral displacement of a celestial body toward longer wavelengths caused by the Doppler effect or the source's gravitational field; the higher the redshift value, the more distant the object from Earth, hence the farther back in time.) In doing so, the SDSS will revolutionize astronomy, increasing the amount of information made available to researchers by several orders of magnitude. The resultant archive available for scientific research will be large (exceeding several terabytes) and complex-including textual information, derived parameters, multiband images, and spectra. The catalog will let astronomers study the universe's evolution in greater detail and should serve as the standard reference for the next several decades. As this article describes, the potential scientific impact of the survey is stunning, but to realize its potential, data must be turned into knowledge. As I'll indicate, this is not easy, for the survey's information content will be several times larger than the entire text contained in the Library of Congress.