The ACT Reference Catalog

Obtaining the Catalog


The ACT Catalog has been superseded with the release of Tycho-2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 In early 2000, this catalog was all but superseded with the release of The Tycho-2 Catalogue, which contains 2.5 million stars compared to ACT's 1.0 million.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.


Please read the following disclaimer:

  1. The data provided herein are to be credited to the U.S. Naval Observatory in any application.
  2. The data are provided with no warranty as to usefulness or suitability for a given application.
  3. Data such as that provided here are available from the USNO to anyone who requests it, provided the request can be filled without impact on mission-related programs.

Please cite the following publication when utilizing the ACT Reference Catalog:

The data are currently being provided only through the data centers.

  • To download the data from NASA's Astronomical Data Center (ADC) directly, CLICK HERE (ACT Reference Catalog).
  • Those finding the links to Europe faster can find the data at the Centre de Donnes Astronomique de Strasbourg, CDS. To link directly to the catalog at the CDS, CLICK HERE.
  • Those finding the links to Japan faster can find the data at the Japanese Astronomical Data Analysis Center. To link directly to the catalog at the Japanese ADAC, CLICK HERE.


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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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