Geocentric Coordinate Time

The Geocentric Coordinate Time ( TCG short of French temps coordonné géocentrique ) was defined by the International Astronomical Union in 1991 as the time that would measure a clock that moves with the earth, but it is far enough away from Earth that the gravitational field can be ignored. It is a variant of the dynamic time.

It passes 0.7 billionth faster than the time to the surface.

Physical background

The influence of gravity on the passage of time describes the theory of relativity. An extreme example is the environment of a black hole. Near the black hole, the time is stretched so much that an outside observer the actual entry into collapsing matter never experienced in the black hole, while the emitted radiation from the matter it appears redshifted.

Weak gravitational fields like the earth will have less, but measurable effects. The potential difference between the surface and "infinitely far away" is ( according to classical mechanics)

Here, the radius of the earth and the gravitational acceleration at the earth's surface.

A clock on the Earth's surface is thus compared to a clock far away from the earth by following factor slower:

That's about 0.7 billionth. Here, the measured time difference and the speed of light. In this makes 0.022 seconds from, in 45 years a second, and the history of the earth for three years difference have accumulated.