Relativity in Celestial Mechanics and Astrometry

The driving idea, in organizing this Symposium on "Relativity in Celestial Mechanics . and Astrometry" was that, in recent years, the ac curacy of several Astrometric techniques has so much increased that re lativistic effects are no more marginally mentioned in academic presen tations but have become an intrinsic part of the interpretation of all the positional data. Techniques such as V. L. B. I. , space probes, lunar lasers, etc . . . have greatly contributed to reduce the accuracy level to an angular equivalent of a few milliarc-seconds. HIPPARCOS will extend this trend to stellar astrometry and new proposals aim at gaining ano ther one or two orders of magnitude in observing precision. In paral lel, great progress has also been made in the theories of motion of ce lestial bodies and more rigourous treatments within the frame of general relativity become necessary. The definition of reference frames and of various coordinate times become also a major problem in the intercompa rison of observations produced by different methods. This Symposium gave to people using relativistic corrections in reducing their measurements or in constructing various theories of mo tion a chance to exchange their experience in the field and to confront it with theoreticians in general relativity. The Symposium was approved by the IAU in 1983 and it was organi zed by the Institute of Theoretical Astronomy of the USSR Academy of Sciences on May 28-31, 1985.