Release 1009 of 1,082

STScI Preparing a Desktop Universe For Astronomers

Release date: Jun 7, 1993 12:00 AM (EDT)
Release type: American Astronomical Society Meeting

Astronomers at the Space Telescope Science Institute (STScI) in Baltimore, Maryland report that their ambitious program to make a digitized survey of the entire sky available to astronomers around the world will debut by the end of this year. At that time, STScI plans to have the survey of the southern sky digitally compressed and stored on a set of 60 CD-ROMs (compact disk read-only memory) which is a widely used computer media.

The Full Story
Release date: Jun 7, 1993
STScI Preparing a Desktop Universe For Astronomers

Astronomers at the Space Telescope Science Institute (STScI) in Baltimore, Maryland report that their ambitious program to make a digitized survey of the entire sky available to astronomers around the world will debut by the end of this year. At that time, STScI plans to have the survey of the southern sky digitally compressed and stored on a set of 60 CD-ROMs (compact disk read-only memory) which is a widely used computer media.

At the meeting of the American Astronomical Society in Berkeley, California it was announced that STScI has completed the compression of the southern sky and is about to begin compressing digital scans of the northern sky. The northern images will be distributed on 40 CD-ROMs in 1994. The STScI began the compression project in June 1992.

"Photographic sky surveys have had a tremendous impact on astronomy. The sky survey CD set will be one of the most important astronomical research tools ever created," said Project Scientist Dr. Marc Postman. "It will afford astronomers rapid access to images of the sky in a format that is readily digested by modern computers."

Postman explained that two versions of the entire sky are being produced - one at a compression factor of 10 that is nearly indistinguishable from the original data, and one at a compression factor of about 100. The latter will fit on just ten CD-ROMs.

"While the higher compression is not suitable for professional research activity," Postman emphasized that the ten CD-ROM set will provide an invaluable tool for the educational and amateur communities.

The original sky survey photographs were taken with wide-angle Schmidt telescopes - the Oschin Telescope on Mount Palomar (California) and the United Kingdom Schmidt Telescope at Siding Spring in New South Wales, Australia. The Oschin Telescope is operated by the California Institute of Technology; the UK Schmidt was operated by the Royal Observatory Edinburgh until 1988 and subsequently by the Anglo-Australian Observatory.

The surveys being compressed are the southern J band survey (894 plates; epoch 1975- 1984) and the northern Palomar E band survey (583 plates; epoch 1950-56).

These photographic surveys were first digitized during an intensive eight-year effort by STScI astronomers to prepare the Guide Star Catalog (GSC) which provides the coordinates of target stars that are used by NASA's Hubble Space Telescope for acquiring and locking onto celestial targets.

To construct the catalog and to support planning for HST observations, astronomers spent five years scanning 2100 photographic plates of the sky (including the 1500 deepest ones being used for the present CD project), and converting them into a huge computer data base.

The digitized scans represent a huge quantity of data. Each of the 1500 plate scans is 14,000 picture elements on a side. This adds up to 600 billion bytes of data in all.

The raw scans were initially stored on 4,500 magnetic tapes and then converted to 400 double sided 12-inch diameter optical disks.

To make the digitized sky survey more accessible to researchers, STScI astronomers identified and extensively tested an algorithm that can compress the data by a ratio of 10:1 without significantly degrading the accuracy of stellar positions and brightnesses.

When the sky survey CD-ROMs are released, all astronomers will have a powerful resource for doing a wide range of research: galaxy counts, supernova and variable star searches, identification of optical counterparts to sources of invisible radiation, multi-object spectroscopy and preparation of finder charts.

"One of the very exciting scientific projects that will be greatly aided by this database is the mapping of the three-dimensional distribution of galaxies 900 million light-years away," said Postman.

The first release of the compressed data is expected late in 1993. A distribution plan is being worked out to make the compressed sky survey sets affordable to libraries, astronomy departments, and amateurs around the world. The 100 CD-ROM set will take up only two linear feet of bookshelf space!

The compressed digitized sky survey project is being led by Dr. Marc Postman, and co- investigators Drs. Michael Shara, Barry Lasker, Michael Meakes, Flavio Mendez, Jesse Doggett, Rick White, and Brian McLean. The three-year compression project is being funded by the Science Operations Branch of NASA's Office of Space Science and Applications (OSSA). The initial digitization of the photographic sky surveys was funded by the NASA Hubble Space Telescope Project.