The Catalogue of Fundamental Stars is a series of six astrometric catalogues of high precision positional data for a small selection of stars to define a celestial reference frame, which is a standard coordinate system for correlation of star positions.
Fourth Fundamental Catalogue (FK4) was measured and published in 1963 to contain 1535 stars in various equinoxes from 1950.0 to 1975.0.
Fourth Fundamental Catalogue's Supplement (FK4S) is an amendment to FK4 containing further 1987 stars.
Fifth Fundamental Catalogue (FK5) was an update of FK4 in 1988 with new positions for the 1535 stars. It was obsoleted when the quasar based International Celestial Reference Frame (ICRF) was introduced.
Examples: Iota Arietis is located at FK5 2132, Alpha Arietis is at FK5 74, Kappa Aurigae at FK5 1168.
Fifth Fundamental Catalogue Extension (FK5) was an addition of 3117 new fundamental stars, published in 1991.
Sixth Fundamental Catalogue (FK6) is a 2000 update of FK5 correlated with the ICRF through the Hipparcos satellite. It comes in two parts, FK6(I) and FK6(III) containing respectively 878 and 3272 stars. Both are updated and amended versions of FK5, using Hipparcos catalogue data.
Astronomical Calculation Institute
1. ^ ReadMe for Sixth Catalogue of Fundamental Stars (FK6) at VizieR Service at Centre de Données astronomiques de Strasbourg
* Fifth fundamental catalogue part I Basic FK5 (1988)