Astrographic Catalogue History
and Zone Information


The AC 2000 has been superseded with AC 2000.2. Please see the AC 2000.2 home page for more details.


History of the the Carte du Ciel and Astrographic Catalogue

The Carte du Ciel was an international effort begun more than a century ago to determine accurate positions for all stars brighter than 11th magnitude using photographic plates and, using another set of plates, to publish charts representing the relative positions of all stars of 14th magnitude and brighter. The charts proved to be very expensive to photograph and reproduce, so about half of the institutions did not complete this part of the work. However, the astrographic program designed to measure all stars to 11th magnitude was completed. Actually, the original goal of 11th magnitude was generally surpassed. In fact, some observatories routinely measured stars as faint as 13th magnitude. One should be aware that some of the brightest stars were over-exposed on the plates and not measured. Therefore, these stars are missing from the published data and, hence, missing in the resulting catalogs. The plate measures, as well as the formulae used to transform them to standard coordinates, have been published in what is known as the Astrographic Catalogue (AC).

In total, 20 observatories from around the world participated in exposing and measuring the plates. Each was assigned a specific zone, between two parallels of declination, to photograph. In order to compensate for any plate defects, each area of the sky was to be photographed twice, using a two-fold, corner-to-center overlap pattern. This pattern was continued even at the zone boundaries; each observatory's plates would overlap with those of the adjacent zones. The participating observatories agreed to use a standardized telescope so each plate photographed had a similar scale of approximately 60 arcsecs/mm. The measurable areas of the plates were 2 x 2 degrees, so the overlap pattern consisted of plates that were centered on every degree band in declination, but offset in right ascension by two degrees. The first plates in the even degree bands were centered at right ascension 0 hours 0 minutes; the first plates in the odd degree bands were centered with right ascension several minutes higher (corresponding to approximately one degree). In addition to a standardized overlap pattern and type of telescope to use, the observatories also agreed to expose a grid, called a reseau, on each plate to facilitate its measurement. The reseau orientation defined the plate's x,y coordinate system. Many factors, such as reference catalog, reduction technique and printing formats were left up to the individual institutions. The positional accuracy goal was 0.5 arcsec per image.

The following table lists information regarding zones observed by participating observatories.

Zone Information

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Zone Declination Range Epochs Number of Stars*
Greenwich +65 +90 1892-1905 179,000
Vatican +64 +55 1895-1922 256,000
Catania +54 +47 1894-1932 163,000
Helsing +46 +40 1892-1910 159,000
Hyderabad North +39 +36 1928-1938 149,000
Uccle +35 +34 1939-1950 117,000
Oxford II +33 +32 1930-1936 117,000
Potsdam +39 +32 1893-1900 108,000
Oxford I +31 +25 1892-1910 277,000
Paris +18 +24 1891-1927 253,000
Bordeau +17 +11 1893-1925 224,000
Toulouse +5 +11 1893-1935 270,000
Algiers +4 -2 1891-1911 200,000
San Fernando -3 -9 1891-1917 225,000
Tacubaya -10 -16 1900-1939 312,000
Hyderabad South -17 -23 1914-1929 293,000
Cordoba -24 -31 1909-1914 309,000
Perth -32 -37 1902-1919 229,000
Perth-Edin. -38 -40 1903-1914 139,000
Cape -41 -51 1897-1912 540,000
Sydney -52 -64 1892-1948 430,000
Melbourne -65 -90 1892-1940 218,000

* Note: the sum of the number of stars in each zone is more than that in the project. The reason is that there is a 1 degree overlap between adjacent zones; these stars effectively belong to both zones, hence for the purposes of this chart, are counted twice.

The AC 2000.2 catalogue is the result of reducing the Astrographic Catalogue measures. It was produced by the U.S. Naval Observatory and the Copenhagen University Observatory. CDs are available through the U.S. Naval Observatory by contacting Sean Urban using seu AT Please include a mailing address.


AC 2000.2 Home Page | History and Zone Facts | Reductions
Publications | Obtaining the Data | USNO Home


Those needing additional information than what is on this site can contact Sean Urban using seu AT

This site was last updated November 16, 2006.

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