REFERENCE CATALOGS - PRESENT STATUS AND FUTURE-PROSPECTS

The present celestial reference frame is represented by the positions and proper motions of the 4500 stars in the Fifth Fundamental Catalogue (FK5). For practical applications it is extended by the catalogues IRS (International Reference Stars) and PPM (Positions and Proper Motions). According to resolutions of the IAU the FK5 system will be replaced by a purely kinematically defined reference system defined by extragalactic radio sources in the near future. At optical wavelengths, the forthcoming Hipparcos Output Catalogue will be linked to the extragalactic system.