Fundamental catalogues,past, present and future

Presented is a review of the main achievements of fundamental astrometry from earliest times through the present century. At all times the construction of a celestial reference coordinate system has tormed an important task for describing motions in the sky. The positions of fundamental stars and their centennial variations have been laid down in fundamental catalogues which-beginning with the 18th century-have facilitated famous discoveries and have given rise to the improvement of the techniques of observation. This review culminates in the documentation of the observational achievements of the latest 25 years where in a world-wide campaign of about 50 observatories considerable contributions have been made to the improvement of the current conventional reference coordinate system given in the Fourth Fundamental Catalogue (FK4). The observations analysed in an ambitious program at Heidelberg will yield the FK5 which also will introduce the System of Astronomical Constants adopted by the IAU in 1976. This report ends with an outlook on contributions of space techniques and of radioastrometry of extragalactic sources to progress in fundamental astrometry.Dedication: This review is an extended version of the Dirk Brouwer Lecture 1983 of the Division on Dynamical Astronomy of the American Astronomical Society. With the topics of this lecture the author honors Dirk Brouwer's contributions to astrometry and gratefully acknowledges the support given to astronomy by Ministerialdirigent Karl Otto Schlau in the Government of Baden-Württemberg, Stuttgart, Federal Republic of Germany.