Guide Star Catalog

The Guide Star Catalog (GSC or Hubble Space Telescope Guide Catalog or HSTGC) is a catalog of stars compiled for use with the Hubble Space Telescope, as guide stars, recognizable stars with locations, to be used when refining the aim at objects near these stars in the celestial sphere. To make the catalog so-usable for accurate aiming, it favors stars over other astronomical objects, and favors non-binary stars. GSC-I has 20 million stars of magnitudes +6 through +15, and GSC-II (aka GSC2) has nearly a billion to magnitude +21.

The Guide Star Photometric Catalog (GSPC) is a catalog including calibrated photometry of a smaller set (fewer than 2000) of stars. Two major editions have been produced, GSPC-I and GSPC-II.