An Etymological Dictionary of Astronomy and Astrophysics
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The proper time experienced by a clock at rest in a coordinate frame co-moving with the center of the Earth, i.e. a clock that performs exactly the same movements as the Earth but is outside the Earth's gravity well. TCG was defined in 1991 by the International Astronomical Union as one of the replacements for Barycentric Dynamical Time (TDB).

→ geocentric; → coordinate; → time.