In January, the SDSS collaboration released Data Release 8, including a much larger area of sky, with photometric data for nearly 500 million sky objects, and spectra for more than 1.5 million.

A small part of the sky as seen by Data Release 8

As always, data from all previous releases is still available also. New this week is the ability to cross-match sky objects between Data Release 7 and Data Release 8. If you have object IDs and parameters for a specific object from DR7, you can query for the same object in DR8.

The cross-matching is available three different ways:

SpecDR7: This is a unique match between a DR8 SpecObjAll and a DR7 photoprimary within 1 arcsec. DR7 PhotoTag columns and relevant DR7 ProperMotions are also included for convenience.

PhotoPrimaryDR7: This is a unique match between a DR8 photoprimary and a DR7 photoprimary, and matches between different run/camcol/field are allowed. The match radius is 1 arcsec. The table contains the DR8 and DR7 objids, the distance between them and the DR7 PhotoTag quantities.
PhotoObjDR7: This is a unique match between a DR8 photoobj and a DR7 photoobj, and matches are restricted to the same run/camcol/field are allowed. The match radius is 1 arcsec, and within this radius preference is given to a photoprimary match over a secondary. If no primary match exists, the nearestsecondary match is chosen. If more than one match of a given mode exists, the nearest one is chosen. The table contains the DR8 and DR7 objids and modes, the distance between them, and the DR7 phototag quantities.