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The Sloan Digital Sky Survey (see www.sdss.org for general information) will map one-quarter of the entire sky and perform a redshift survey of galaxies, quasars and stars. The DR2 is the second major data release and provides images, imaging catalogs, spectra, and redshifts for download.

As of September 27, 2004, Data Release 3 (DR3) is available, with substantially larger sky coverage. This DR2 site will be kept online for some time for historical reference.

About DR2 explains what is new in DR2, and lists remaining or new caveats and subtleties in the data.

Please refer to the credits page for our sources of funding, participating institutions, how to acknowledge the use of SDSS data in your publications. Please also note how to refer to SDSS sources in your publications using the proper IAU nomenclature for SDSS sources.


Footprint area 3324 sq. deg.
Imaging catalog 88 million unique objects
Data volume
images5.0 TB
catalogs (DAS, fits format)0.7 TB
catalogs (CAS, SQL database)1.4 TB
Average wavelengths and magnitude limits
(95% detection repeatability for point sources)
u g r i z
3551Å 4686Å 6165Å 7481Å 8931Å
22.0 22.2 22.2 21.3 20.5
PSF width 1.4" median in r
Photometric calibration
r u-g g-r r-i i-z
2% 3% 2% 2% 3%
Astrometry < 0.1" rms absolute per coordinate


Spectroscopic area 2627 sq. deg.
Resolution 1800
Signal-to-noise >4 per pixel at g=20.2
Redshift accuracy 30 km/sec rms for main galaxy sample (from repeat observations)
Target magnitude limits for main samples Galaxies: Petrosian r <17.77
Quasars: PSF i <19.1
Spectroscopic catalog 367,360 spectra, classified into
260,490 Galaxies
32,241 Quasars (redshift <2.3)
3,791 Quasars (redshift >2.3)
34,998 Stars
13,379 M stars and later
18,767 Sky spectra
3,694 Unknown class
Data volume
calibrated spectra ("2d")27 GB
spectra, redshifts, line measurements ("1d")73 GB

Previous data releases

For reference, we provide links to earlier data releases. The current data release always provides both the largest sky coverage and the highest-quality data and reductions.

This is version v2_20080930_1913 .

If you are using Netscape 4.x and see oversized fonts, please look at the workaround on the Credits page.

News DR3 now released!
Imaging Sky Image
SDSS DR2 Imaging Sky Coverage (Aitoff projection of Equatorial coordinates)

Spectral Sky Image
SDSS DR2 Spectral Sky Coverage (Aitoff projection of Equatorial coordinates)