AAS 98-151

THE INTERNATIONAL CELESTIAL REFERENCE SYSTEM

P. K. Seidelmann - U.S. Naval Observatory

Abstract

The International Astronomical Union (IAU) has adopted a new and much more accurate International Celestial Reference System (ICRS) based on extragalactic radio sources. The reference frame is essentially fixed in space and not tied to the dynamics of the solar system. The use of the new reference frame does involve the kinematics of the Earth rotation. The ICRS, its realization as an optical reference frame, and as a reference frame for dynamical applications are described. The differences from the FK5 reference frame, how to get from there to the new system, the magnitude of the transformations, and the internal accuracies of the past and new systems are provided.

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