The time-scale used in the Geocentric Celestial Reference System, the unit of which is the SI second. TCG differs from Terrestrial Time because a clock on the Earth's surface is moving with respect to the geocentric frame and feels the gravitational field of the Earth. Terrestrial Time is in effect a conveniently scaled TCG that differs from International Atomic Time (TAI) only by a fixed offset. The rate difference between TCG and Terrestrial Time is about 22 ms per year.
Subjects: Astronomy and Astrophysics.