The AC 2000 Home Page
The Astrographic Catalogue (AC) was an international effort designed to photograph and measure the positions of all stars brighter than magnitude 11.0. (Actually, the brightest stars are missing due to their images being grossly over-exposed and, therefore, not being measured). In total, over 4.6 million stars were observed, many as faint as 13th magnitude. This project was started over 100 years ago. The sky was divided among 20 observatories, by declination zones. Each observatory exposed and measured the plates of its zone, subsequently publishing the plate measures.
The U.S. Naval Observatory has completed data entry of the printed volumes of the AC, has completed the data reduction of each zone, and has converted the positions to the system defined by Hipparcos. The resulting catalog, called AC 2000, is now available.
The positions derived from the published AC data are being used in combination with modern epoch positions to determine accurate proper motions. The first two catalogs of this type are the Twin Astrograph Catalog and the ACT Reference Catalog.
Those needing additional information than what is on this site
can contact Sean Urban at
This site was last updated March 5, 1998.
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