AGK3
The AGK3 for Astronomical Society Catalog 3 is a photographic star catalog of about 200,000 fixed stars , on the initiative of the Astronomical Society in 1960 originated years. For the sky survey, around 10,000 precisely tracked photo plates were exposed from observatories around the world , the star locations of which were measured using standardized methods.
The AG and its star catalogs
The Astronomical Society, one of the oldest scientific associations in Europe, was founded in 1800 by two German astronomers - the Gotha "Astro-Manager" Franz Xaver von Zach (1754–1832) and the Bremen moon specialist Hieronymus Schröter (1745–1816) . Around 1860 , the AG, as it is called in specialist circles, initiated the most important star catalog of that time, the AGK. From 1929 onwards it was equipped with new measurements and v. a. more precise self-movements to the AGK2 , which with the newer version AGK3 represents an important database for astronomy , celestial mechanics and orbit determination to this day .
Meaning of exact asterisk words
Such directories of precise star locations are important for almost all measurements in astronomy , especially for direction measurements and the derivation of stellar proper motions . Most of the star positions are determined relative to one another (e.g. with a meridian circle or a photographic zenith telescope PZT), but they have to be "hooked" into an absolute coordinate frame . This is provided by so-called fundamental catalogs (see FK4 or FK5 ). Star catalogs are also essential for the precise orbit determination of the earth , moon and planets . In addition, they allow the observation of system changes such as precession or nutation , which go back to periodic moon influences on the earth's axis and influence all star locations by shifting the coordinate lines. The earth's rotation and geophysical influences on it can be precisely determined and monitored through measurements of the connection to the earth, which rotates as a stable top in this coordinate frame .
The star catalog AGK3 (approx. 1955–1970)
The initiative for the transition from AGK2 to AGK3 came from the Hamburg astronomers Otto Heckmann and Dirk Brouwer from the US Naval Observatory after the IAU General Assembly in Rome in 1952 . While the AGK2 was essentially only created through the work of three observatories (Hamburg, Bonn and St.Petersburg?), It was now clear that the increased number of reference stars (AGK3R, Corbin 1978) was being observed through modern meridian circles in as many observatories as possible should be (reference stars give the photographic recordings, with which the "mass work" takes place, the necessary parameters for precise linkage and coordinate transformation ).
The review of the FK3 (Kopff 1937–38) to the FK4 (Fricke et al. 1963), which was in progress, was already in progress and should provide an improved reference system. In addition, some of the instruments used for AGK2 (Schorr & Kohlschütter 1951–53) should also contribute to AGK3, for which u. a. the Hamburg astro camera with a focal length of about 2 m came into question.
Eleven observatories instead of just three before
The IAU Commission 8 formally recommended it at the 1955 IAU General Assembly in Dublin . As a result, the circle of participating observatories expanded to the following: Babelsberg , Bergedorf , (Bonn), Bordeaux, Greenwich, Heidelberg , Nikolajev, Ottawa, Paris, Pulkovo, Strasbourg and Washington ( United States Naval Observatory ), where Scott made the meridian circle measurements of the AGK3 -Stars should coordinate.
Working in Hamburg-Bergedorf
The Hamburg-Bergedorf and Bonn observatories were supposed to share the recording and evaluation of the photo plates , but later it was decided to leave the recordings of the "Bonn AGK2 zone" (each observatory processed a certain declination area ) to the Hamburgers. Between August 1956 and June 1964 , the same number of AGK3 plates were exposed with 1939 as in the earlier project - from a declination range from the celestial pole down to δ = 2.5 °.
Recording technology and photo emulsions
Special attention was paid to the type of recordings - on both sides of the pier in order to avoid systematic errors from the camera lens. The two plate sets were evaluated in opposite directions on the stereo comparator and the image coordinates x and y averaged. As with the AGK2, there was again the problem of obtaining suitable photo material - but less the glass (again from Grünenthaler Spiegelglas AG ), but the emulsions . Three companies were considered for them ( Kodak Co. in London, Agfa- Wolfen in East Germany and Perutz & Co. in Munich), but the situation in post-war Germany was difficult even with such competition. Long delivery times, customs formalities and the beginning of the Cold War ultimately favored the plates from Munich ; Agfa and Kodak combined were only about 30 percent. Perutz had to experiment with the sensitivity of the emulsions for a long time in order to achieve sufficient sensitivity. Scientific record production was discontinued when Perutz later merged into the new company Agfa-Gevaert . Around 1990 Kodak stopped producing astro plates .
Measurement and reductions
From 1957 Bergedorf worked again on three plate knives because Bonn loaned its machine. After eight years of work, all panels were measured. The subsequent calculation of the data was faster this time because the university data center received one of the first modern computers , an IBM 650 , in 1956. The manual punching of 400,000 punch cards was faster than the calculations with the crank calculating machines . 1967 the observatory even got its own YAW computer Danish Regnecentralen . Nevertheless, the first AGK3 volume could not appear until 1975 . The frequent changing of the magnetic tapes caused problems, and Washington, DC did not send the magnetic tape with the supplementary stars of the AGK3R until 1967.
Only after lengthy discussions (Dieckvoss et al.) Were the correction procedures for the influences of the star colors established. The connection to the AGK3 stars (reference catalog AGK2A) or the FK4 and the re-evaluation of the AGK2 locations were negotiated because the quality of improved own movements (EB) strongly depends on it. The mean error was ± 0.13 ″ for the positions and ± 0.009 ″ / year for the own movements. Stars with noticeably greater contradiction have been omitted; if it only affected AGK2, EB was eliminated.
Result and outlook
As with AGK2, the intensive phase lasted about 10 years. The result was around 250,000 stars down to the 9th to 10th magnitude with significantly higher precision, v. a. because of better EB through new reduction and longer periods of time. The AGK3 is still widely used today, although the internal accuracy of the 1997 Hipparcos catalog is almost 50 times higher. With the systematic influences this is obviously more favorable, which is probably also due to the quality of the modern, partially automated meridian circles. While "Hipparcos" achieved an astonishing positional quality (approx. ± 0.003 ″) in its 3 to 4 years of observation in space, the proper movements were naturally much more poorly determined, so that the catalog increasingly loses its accuracy. The advantages and disadvantages of the AGK3 are exactly the opposite , so that a well-modeled combination means further advantages.