AGK

(AG Catalog) Abbrev. for Astronomische Gesellschaft Katalog . A general catalog of star positions originally proposed by the Prussian astronomer Friedrich Argelander in 1867. Argelander was the founder (in 1863) of the Astronomische Gesellschaft (Astronomical Society), which gave its name to the AGK. The first version, known as AGK1, covered the northern sky and by 1912 declination zones between +90° and –18° had been published. A revision, known as AGK2, was based on photographic measurements begun in the 1920s and was published 1951–58. A further set of photographic plates was produced in the 1950s to determine proper motions, which appeared in the AGK3 version; this lists 183 145 stars and was distributed on magnetic tape from 1969, finally appearing in print in 1975. AGK3R (1977–78) gave more accurate positions of 20 194 northern-hemisphere reference stars, while an updated version, AGK3U (1992), using photographic plates supplied for the HST Guide Stars Catalog in 1983, provided refinements to the positions of 170 464 stars.