ephemeris time

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The time-scale that was used in calculating orbits within the Solar System from 1960 to 1984. Its fundamental unit was the ephemeris second which was defined by the statement that the tropical year at the epoch 1900.0 was precisely 31 556 925.9747 ephemeris seconds. Ephemeris Time was in many ways inconvenient, and in 1984 it was replaced by Terrestrial Dynamical Time (now known as Terrestrial Time) which has the SI second as its fundamental unit.

Subjects: Astronomy and Astrophysics — Physics.

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