FK3

The FK3 (abbreviation for Third Fundamental Catalog of the Berlin Astronomical Yearbook) was the first astronomical fundamental catalog that referred to a precisely defined inertial system .

It was created by the Heidelberg Astronomical Computing Institute in the interwar period and published in 1937. This basic star catalog represented the heavenly (celestial) coordinate system until 1963/64 . Its addition to the then valid FK4 was called FK3 Sup and comprised around 600 supplement stars .

Like its successors up to today's FK6, the FK3 serves (e) as an exact reference system for astronomy , geodesy and space travel . The coordinate frame consists of the exact positioning and orientation of the coordinate axes right ascension and declination . With its underlying constants - which were defined in cooperation with the IUGG - it also provided a precise model for tasks in the planetary system , as well as a quasi-inertial system for the extragalactic astronomy that was developing at the time .

The FK3 contains about 900 fundamental stars (i.e. stars that are measured to within 0.1 "). The star locations were determined from relative and absolute methods of astrometry and their different epochs were transformed to a common point in time (see also B1950.0 ).

The system also contains the proper motions of each star (which were relatively accurate at the time) , so that their positions could be converted a few decades into the future and into the past. They relate with about ½ "accuracy to a stationary (" inertial ") system, whereas today about 0.02" is reached for this (see also VLBI ).

Characteristic values of the FK3 and its successors FK4 , FK5 and FK6 as well as the satellite-based (relative) Hipparcos catalog
Short name	Number of stars	title	Published	Measurement places	Measurement of own movements	Overlap
Auwers, A., 1879	539	Fundamental catalog for zone observations on the Nördl. sky	1879	Ø 1860	≈1850-1870	up to dec. = −10 ° ^{Note 1}
Peters, J., 1907	925	New FK Berliner Astr. Yearbook based on the principles of Auwers	1907	Ø 1880	1745-1900	up to dec. = −89 °
FK3	873	Third fundamental catalog of the Berlin Astronomical Yearbook	1937	1912-1915		from here over the whole sky, with epochs 1900, 1950, 2000
FK3sup	662	(Additional stars, Volume II)	1938	Ø 1913	1845-1930
FK4	1,535	Fourth Fundamental Catalog	1963	Ø 1950
FK4sup	1,111	Supplement Stars FK4 / 5	≈1965
FK5	1,535	Fifth Fundamental Catalog	1988	Ø 1975
FK5sup	3.117	Supplement Stars of FK5	1991
Hipp. ^{Note 2}	118,000	Hipparcos catalog	1998	1989-1993	1989-1993
FK6	4,150	Sixth Catalog of Fundamental Stars	1999, 2000	Ø 1992

^{Note 1}The first FK (Auwers 1879) covered only 60% of the starry sky (up to declination −10 °).

^{Note 2}Hipparcos is not an FK in the strict sense of the word, but has only been precisely adapted to the FK5 system and has 'stiffened' it. However, the new system (FK6) has gained significantly in accuracy thanks to the measurements made by the astrometric satellite ( Hipparcos , 1989–1993).

FK3

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