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Terrestrial Time

Terrestrial Time (TT) is the modern time scale that is used instead of ephemeris time, which is obsolete. TT was introduced by the International Astronomical Union (IAU) in 1991 as the coordinate time scale consistent with the theory of general relativity for an observer on the surface of the Earth. For all practical purposes, it is equal to:

TT = TAI +32.184 s

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