New Celestial Reference System

Abstract

The IAU (1976) System of Astronomical Constants, the FK5 and new lunar and planetary theories are being introduced in 1984. The investigation and planning for the transition has revealed the complex interdependencies between observational techniques and the reference systems, and their strong link to the rotating and orbiting Earth. The inaccuracies in our knowledge of the star positions, astronomical constants and the rotation and motion of the Earth are embedded in subtle ways in the observations and the reference coordinate systems. For example, the FK4 reference system in 1950.0 coordinates rotates with respect to an inertial system. Details are given for the conversion to the new system.

The concepts for a future reference system are developed, based on separating the real motions involved such that observations from various moving platforms can be related to the appropriate coordinate system, without involving motions which are not intrinsically involved in the observations. Therefore, reference systems determined or utilized in space, while affected by aberration and parallax, would logically be defined with no dependence on precession, nutation, polar motion, or Universal Time, which are all concerned with motions of the Earth’s surface.