The celestial and terrestrial departure points and their various aspects in geodesy and astrometry

Summary Based on the 127th Colloquium Report of the subgroup on coordinate frames and origins of the IAU working group on reference systems, in this paper, the possibility of taking the Celestial Departure Point as the origin of right-ascension on the instantaneous true equator is analysed in view of high-precision geodesy and astrometry. The properties and the applications of the celestial and terrestrial departure points in various aspects of practice and theory are generally reviewed. We have found that, referred to the ideal barycentric reference system proposed in the 127th IAU Colloquium, the Celestial Departure Point of a Quasi-Inertial Geocentric Equatorial Coordinate System may be a matchable origin on the moving geocentric true equator. Presented at the Seminary on Physical Geodesy, Faculty of Mathematics and Physics of the Charles' University, Prague, March 1993; Contribution to the Special Commission on Fundamental Constants of the I.A.G. On leave from Shanghai Observatory, China