The ACT Reference Catalog

     The US Naval Observatory has completed the compilation of the ACT Reference Catalog, containing 988,758 stars covering the entire sky. The motivation behind the ACT was to provide accurate proper motions for the majority of the stars in the Tycho Catalogue. To do this, positions from new reductions of the Astrographic Catalogue (AC 2000) were combined with those of the Tycho Catalogue. The large epoch span between the two catalogs yields proper motions about an order of magnitude more accurate than those found in the Tycho Catalogue. The astrometric data contained in the ACT Reference Catalog include positions and proper motions and their corresponding errors. These are on the Hipparcos system (ICRS) for epoch J2000.0. Photometric and variability data from Tycho are included. In addition, cross-references to the Tycho, AC 2000, Bonner Durchmusterung (BD), Cordoba Durchmusterung (CD), Cape Durchmusterung (CPD), Henry Draper (HD), and Hipparcos catalogs are given. The ACT is now available at the international data centers and by contacting the authors via electronic mail.