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<title>USNO AC 2000 Home Page</title>
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Sean E. Urban
Astrometry Dept.
U.S. Naval Observatory
Washington, DC
seu@pyxis.usno.navy.mil
Revised: 03 Feb 1998
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<td align=center><h1>The AC 2000 Home Page</h1></td>
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<p>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.
<p>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
<a href="./cite.html"> AC 2000, is now available.</a>
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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
<a href="../TAC/tac.html" target="_top"> Twin
Astrograph Catalog </a> and the
<a href="../ACT/act.html" target="_top"> ACT Reference Catalog.</a>
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[<a href="http://ad.usno.navy.mil/proj/AC/home.html">AC 2000 Home Page</a> |
<a href="http://ad.usno.navy.mil/proj/AC/hist.html">History and Zone Facts</a> |
<a href="http://ad.usno.navy.mil/proj/AC/reduce.html">Reductions</a> ]
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[<a href="http://ad.usno.navy.mil/proj/AC/pubs.html">Publications</a> |
<a href="http://ad.usno.navy.mil/proj/AC/cite.html">Obtaining the Data</a> |
<a href="http://www.usno.navy.mil/" target="_top">USNO Home</a>]</center>
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Those needing additional information than what is on this site
can contact Sean Urban at
<a href="mailto:seu@pyxis.usno.navy.mil"><i>seu@pyxis.usno.navy.mil</i></a>.
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This site was last updated March 5, 1998.
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<a href="http://ad.usno.navy.mil/proj/AC/disclaim1.html">Disclaimer for external links</a>
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