  With the Sixth Data Release of the Sloan Digital Sky Survey, the imaging of
the Northern Galactic Cap is now complete. The survey contains images and
parameters of roughly 287 million objects over 9583 deg^2, and 1.27 million
spectra of stars, galaxies, quasars and blank sky (for sky subtraction)
selected over 7425 deg^2. This release includes much more extensive stellar
spectroscopy than previously, and also includes detailed estimates of stellar
temperatures, gravities, and metallicities. The results of improved photometric
calibration are now available, with uncertainties of roughly 1% in g, r, i, and
z, and 2% in u, substantially better than the uncertainties in previous data
releases. The spectra in this data release have improved wavelength and flux
calibration, especially in the extreme blue and extreme red, leading to the
qualitatively better determination of stellar types and radial velocities. The
spectrophotometric fluxes are now tied to point spread function magnitudes of
stars rather than fiber magnitudes, giving a 0.35 mag change in the
spectrophotometric flux scale. Systematic errors in the velocity dispersions of
galaxies have been fixed, and the results of two independent codes for
determining spectral classifications and redshifts are made available.
(Abridged)
