Fundamental Catalogues of Extragalactic Radio Sources

Abstract

As pointed out in Sect. 1.8 an alternative to the conventional stellar reference system of the FK5 is presented by extragalactic reference systems. The advantages of an extragalactic system rest, first, upon the observed positions of extragalactic objects (EGOs) whose rotation, when averaged over a large number of objects, would be representative of the rotation of the Universe, which, however, is assumed to be zero according to the discussion in Sect. 4.1.2. Second, these advantages rest upon the possibility of introducing explicitly the General Theory of Relativity for the definition of the celestial space-time reference frame, thereby meeting better the accuracy requirements of modern astrometry.