TCG – Terrestrial Coordinated Time (Fr. Temps-Coordonnee Geocentrique)

TCG (Geocentric Coordinate Time) is a relativistic coordinate time scale defined for a reference system centered at the Earth’s center of mass. It is one of the time scales recommended by the International Astronomical Union (IAU) for high-precision applications in celestial mechanics and space science. TCG runs at a constant rate that differs slightly from Terrestrial Time (TT) due to relativistic effects related to the Earth’s gravitational potential.

In geodesy, TCG is relevant for precise modeling of satellite orbits, Earth rotation, and the transformation between terrestrial and celestial reference frames. Consistent use of relativistic time scales such as TCG ensures the accuracy of space-geodetic observations and global reference frame realizations.