Site Map

Data Access for SDSS DR8


We provide data access for Data Release 8 (DR8) through two main sources: the Science Archive Server (SAS) and the Catalog Archive Server (CAS). In general, SAS is designed for access to the full dynamic range FITS images and the actual spectra, whereas CAS is designed for access to the catalog-level results through an SQL database interface. This page summarizes the tools; more information is given in the image data access and spectroscopic data access pages.

Data access tools for CAS:

DR8 CASJobs CAS SQL advanced user interface (use DR8 context)
DR8 SkyServer Interactive query tools for CAS
SkyServer Imaging Query Form Simple image query form interface
SkyServer Spectroscopic Query Form Simple spectroscopic query form interface
SkyServer Cross-ID Match list of RA/Dec or IDs to imaging or spectroscopic catalog
Image List Generate JPGs for a large set of objects
SkyServer Navigate Point-and-click interface to JPG image of SDSS sky
SDSS Command Line Query Tool (sqlcl) Python module for interfacing with CAS at the command line

Data access tools for SAS:

The Science Archive Server provides an interface to interactively view and download SDSS spectra, images of SDSS fields, and to generate mosaics of those fields. In addition, SAS contains directory structures with the data in flat file formats. The links below lead to these directories. To navigate these directories successfully, please study the detailed data model as well as the basics of SDSS spectroscopy and SDSS imaging.

SAS Spectra Tool to view spectra and retrieve FITS
SAS Images Tool to view images and retrieve FITS
SAS Mosaic Tool to create larger-scale mosaic FITS images
Imaging catalogs Directories of full image catalog files BOSS_PHOTOOBJ data model
Corrected frames Directories of full corrected image frames BOSS_PHOTOOBJ/frames data model
Datasweep catalogs Directories of reduced "sweep" imaging catalog data files PHOTO_SWEEP data model
Spectroscopic catalogs Directories of SDSS spectra and catalogs SPECTRO_REDUX data model

Occasionally users require quick access for analysis to essentially all of the objects detected in the images. For this purpose, we provide a subset of the objects and the quantities associated with them in the so-called "datasweep" files. The datasweep catalogs require for each object that it have a solid detection in at least one band; in addition, not all of the quantities are reported for each object. While they therefore form a subset of the full dataset, for many purposes they are sufficient. For example, the BOSS galaxy and quasar target selection is performed on the basis of the sweeps.

The 'corrected' frames have been flat-fielded and bias-subtracted; bad columns and cosmic rays have been interpolated over, and sky has been subtracted.

Essentially all of the data input into CAS is included in some form in the SAS. However, there are some small changes in naming convention (for example, "resolve_status" in SAS flat files is referred to as "resolveStatus" in CAS).

Value-Added Catalogs


In addition to the primary SDSS-III photometry and spectroscopy, there are a few extra catalogs created by our collaborators that are distributed through the SAS.


Bovy et al. (2011) describes a technique for QSO target selection based on an extreme deconvolution method. The associated catalog is available here. The files in the catalog are described in the data model.

Photometric Redshift Distributions

Sheldon et al. (2011) have created a set of photometric redshift probability distributions for SDSS-III objects. The catalog is available here. The files in the catalog are described in the data model.

Data Volume

The table below lists the sizes of the various data products in DR8. Note that the total data volume is 49.6 TB. However, a substantial fraction (~50%) of this is raw or intermediate data that is primarily of interest to experts. If your institution requires most or all of this data you may email us at the helpdesk to contact a data transfer expert.

Directory Description SizeRunning Total
common/sdss-spectro/plates Matches to photometry 11.55 GB 11.55 GB
common/sdss-spectro/raw Raw spectroscopy files 1.335 TB 1.346 TB
common/sdss-spectro/redux 2d & 1d spectro reductions 3.933 TB 5.280 TB
common/sdss-target Legacy targeting files 9.373 GB 5.289 TB
common/sdss-tiling Legacy tiling files 11.31 GB 5.300 TB
common/segue1/target SEGUE-1 targeting files 88.91 GB 5.387 TB
groups/boss/calib Photometric calibration files 1.003 GB 5.388 TB
groups/boss/photo/data Raw imaging data 11.57 TB 16.95 TB
groups/boss/photo/redux Photometric reductions 10.15 TB 27.10 TB
groups/boss/resolve Photo resolve files 225.7 GB 27.64 TB
groups/boss/sweeps Photometric sweep catalog 326.7 GB 27.64 TB
groups/boss/photoObj/301 Complete photometric catalog 3.411 TB 31.05 TB
groups/boss/photoObj/astromqa QA files for astrometry 93.65 GB 31.15 TB
groups/boss/photoObj/external Matches to other catalogs 633.8 GB 31.76 TB
groups/boss/photoObj/frames Corrected frame files 16.94 TB 48.71 TB
groups/boss/photoObj/photoz-weightPhotometric redshift distributions12.91 GB 48.72 TB
groups/boss/photoObj/xdqso XDQSO catalog 39.20 GB 48.76 TB
groups/segue2/sspp SSPP files 450.4 GB 49.20 TB
groups/segue2/target SEGUE-2 target files 65.21 GB 49.26 TB
groups/segue2/targetAll SEGUE-2 targeting on all data 351.8 GB 49.60 TB


Data can be downloaded directly using the rsync ( tool. Subsets of the data can be selected either by accessing sub-directories or using the advanced filtering features of rsync. The following example bash script shows how to sync a file to the current local directory.

# Classic rsync form
rsync -av "$host::$remotefile" .
# Alternate URL form
# rsync -av "rsync://$host/$remotefile" .

Any path to data (i.e. part of a http URL) in the dr8 tree will commence with '/sas/dr8'. However, that same path is visible to rsync by removing '/sas'. For example, these two URLs would retrieve the same file:


Note there are many terabytes of data under the /sas/dr8 hierarchy, please use the rsync command with care. If your institution needs this much data you may email us at the helpdesk to contact a data transfer expert.