Terrestrial time

Terrestrial time is a time scale used for apparent geocentric ephemerides with the SI second as unit of time. On 1 January 1977 0 h IAT, TT had the value of 1 January 1977, 0 h 0 min 32.184 s. This is an ideal time scale that in practice is linked to International atomic time IAT, by TT = IAT + 32.184 s.