  The Sloan Digital Sky Survey has validated and made publicly available its
Second Data Release. This data release consists of 3324 square degrees of
five-band (u g r i z) imaging data with photometry for over 88 million unique
objects, 367,360 spectra of galaxies, quasars, stars and calibrating blank sky
patches selected over 2627 degrees of this area, and tables of measured
parameters from these data. The imaging data reach a depth of r ~ 22.2 (95%
completeness limit for point sources) and are photometrically and
astrometrically calibrated to 2% rms and 100 milli-arcsec rms per coordinate,
respectively. The imaging data have all been processed through a new version of
the SDSS imaging pipeline, in which the most important improvement since the
last data release is fixing an error in the model fits to each object. The
result is that model magnitudes are now a good proxy for point spread function
(PSF) magnitudes for point sources, and Petrosian magnitudes for extended
sources. The spectroscopy extends from 3800 A to 9200 A at a resolution of
2000. The spectroscopic software now repairs a systematic error in the radial
velocities of certain types of stars, and has substantially improved
spectrophotometry. All data included in the SDSS Early Data Release and First
Data Release are reprocessed with the improved pipelines, and included in the
Second Data Release. The data are publically available as of 2004 March 15 via
the web sites http://www.sdss.org/dr2 and http://skyserver.sdss.org .
