The Conventional Fundamental Catalogue FK5

Abstract

A stellar fundamental catalogue compiled from absolute and differential observations of stellar positions at various epochs is the practical realization of a fundamental system of positions and proper motions of the stars. Utmost efforts are made to arrive at a catalogue of star positions that represents an inertial frame. The immediate purpose of the catalogue is to serve as the reference frame of positional astronomy. It should also fulfill the requirements of astronomical research in general, and of celestial mechanics, galactic and extragalactic research in particular. Until 1998 the FK5 constituted the IAU-sanctioned fundamental reference catalogue designed for meeting the aforementioned requirements. The following sections are intended to provide some insight into the lengthy process of constructing this catalogue. Nowadays, applications of stellar fundamental catalogues to the time and latitude service stay in the background, as is the case for geodesy and navigation, since radio interferometric and satellite laser techniques provide results far superior to the classical optical methods. A turning point in favour of optical methods may have been reached by the extension of the extragalactic reference frame to the optical wavelengths with the aid of the Hipparcos catalogue. Although the positions and proper motions of the Hipparcos stars were originally derived from differential astrometry, the connection of these positions and proper motions to the extragalactic reference frame (see Chaps. 6 and 7) promotes the status of the Hipparcos catalogue to that of a quasi-fundamental catalogue. Nevertheless, it is worth considering the principles of the FK5 construction.