O.M.Smirnov
Inst.Astr., Russian Acad.Sci.
ZGSC is a losslessly compressed version of the Guide Star Catalog. The total size is just over 200 Megabytes (compression ratio about 6:1), which allows the catalog to be kept on fast media, for drastic improvements in access times. We have developed a suite of IDL software (called ZGUIDARES) for retrieving samplings of the catalog. XSKYMAP is a graphical application based on IDL widgets that provides access to the ZGSC. It is a tool for both producing skymaps (e.g., finder charts), and for statistical studies of the GSC. Skymaps, including hard copies, may be produced with a variety of options and in different visualization modes. Each object's full catalog entry can be accessed instantly by pointing the mouse at its image on the map. One recent application of XSKYMAP/ZGSC is at the Italian National Galileo Telescope (TNG), inaugurated this summer. XSKYMAP is integrated into the telescope control software, to be used as a charting tool.