The ACT Reference Catalog

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The ACT Catalog has been superseded with the release of Tycho-2

The ACT Reference Catalog was a primary source of astrometric information following the release of Tycho-1. In early 2000, this catalog was all but superseded with the release of The Tycho-2 Catalogue, which contains 2.5 million stars compared to ACT's 1.0 million. Copies of Tycho-2 on CD-ROM are still available by contacting either Erik Hoeg at or Sean Urban at With that said, this webpage and its links will continue to give information regarding the ACT Reference Catalog, even if only for historical reasons.


Brief Description of the ACT Reference Catalog

The U.S. 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 (ESA SP-1200). 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, proper motions and error estimates. These are on the Hipparcos System (J2000.0) for epoch J2000.0. Photometric data (B and V) from Tycho are included. Additionally, cross references to the Tycho, AC 2000, Bonner Durchmusterung (BD), Cordoba Durchmusterung (CD), Cape Durchmusterung (CpD), Henry Draper (HD) and Hipparcos Catalogues are given.


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Those requiring additional information may contact Sean Urban at

This page was last updated November 27, 2001.

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