GCRS – Geocentric Celestial Reference System

The Geocentric Celestial Reference System (GCRS) is a relativistic reference system centered at the Earth’s center of mass, defined within the framework of General Relativity. It is kinematically non-rotating with respect to distant extragalactic objects and serves as the theoretical geocentric counterpart to the Barycentric Celestial Reference System (BCRS).

In geodesy, the GCRS provides the fundamental celestial reference system used for modeling Earth rotation, satellite motion, and the transformation between terrestrial and celestial reference frames. It is essential for the precise interpretation of VLBI observations, satellite orbit determination, and the consistent realization of Earth orientation parameters within the IERS conventions.