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.
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.