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International Earth Rotation and Reference Systems Service

What is the difference between TT and TCG?

TT (Terrestrial Time) is the coordinate time at the surface of the Earth. TCG (Geocentric Coordinate Time)is the coordinate time at the center of mass. It is computed by TCG = TT + LG (MJD - 43144) x 86400 s, where LG is defined to be 6.969290134 x 10-10.