Temporal Reference System Geocentric Coordinate Time https://www.commoncoreontologies.org/InformationEntityOntology TCG "TCG is a coordinate time standard intended to be used as the independent variable of time for all calculations pertaining to precession, nutation, the Moon, and artificial satellites of the Earth. It is equivalent to the proper time experienced by a clock at rest in a coordinate frame co-moving with the center of the Earth: that is, a clock that performs exactly the same movements as the Earth but is outside the Earth's gravity well. It is therefore not influenced by the gravitational time dilation caused by the Earth." From: (https://en.wikipedia.org/wiki/Geocentric_Coordinate_Time)