MAST Digitized Sky Survey DSS

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About the MAST Digitized Sky Survey (DSS)


The Catalogs and Surveys Group of the Space Telescope Science Institute has digitized the photographic Sky survey plates from the Palomar and UK Schmidt telescopes to produce the "Digitized Sky Survey" (DSS).

These images support ground and space-based telescope operations and provide a valuable scientific resource to the astronomical community.

Each plate covers 6.5 x 6.5 degrees of the sky and have been digitized using a modified PDS microdensitometer with a pixel size of either 25 or 15 microns (1.7 or 1.0 arcsec respectively). These images are 14000x14000 (0.4GB) or 23040x23040 pixels (1.1GB) in size and are difficult to access quickly.

To provide convenient access to these data, the images have been compressed using a technique based on the H-transform to reduce the data volume. Although the technique is lossy, it is adaptive so that it preserves the signal very well. We typically compress the data by a factor of 7, but much higher compression ratios are possible. These compressed data are archived locally on a 1 terabyte RAID array for rapid access.

Users can then easily retrieve image data for any part of the sky.

The first epoch images have already been published on CDROM, and the second epoch POSS-II and SES surveys have been distributed on CDROM to a small number of institutions who are supporting our effort to digitize and compress these survey plates. All of the data is available to the community through web sites at most of these centers.

Please note that all these data are copyrighted - see the Acknowledgements link for specific information.

Access the Data

Contents of the Data

The Digitized Sky Survey comprises a set of all-sky photographic surveys in E, V, J, R, and N bands conducted with the Palomar and UK Schmidt telescopes. The Catalogs and Surveys Branch (CASB) is digitizing the photographic plates to support HST observing programs but also as a service to the astronomical community.

The 6.5-degree x 6.5-degree plates are scanned using a modified PDS microdensitometer to a pixel scale of about 1.7 arcseconds per pixel for the POSS, SERC, and Palomar Quick-V surveys, and to about 1.0 arcseconds per pixel for the POSS-II surveys.

Images of any part of the sky may be extracted from the DSS, in either FITS or GIF format.