Hubble Guide Star Catalog – Astrographic Catalog/Tycho

The Hubble Guide Star Catalog – Astrographic Catalog/Tycho (GSC-ACT) is an astronomical catalog which records the twenty million stars of the Hubble GSC, version 1.1, recalibrated using the U.S. Naval Observatory's ACT (Astrographic Catalog/Tycho). By 2009 it was considered obsolete, superseded by such catalogues as GSC-2.2, B1.0, A2.0, and especially UCAC-3.