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.
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|Zone||Declination Range||Epochs||Number of Stars*|
* 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 usno.navy.mil. Please include a mailing address.
Those needing additional information than what is on this site
can contact Sean Urban using seu AT usno.navy.mil.
This site was last updated November 16, 2006.
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