the time scale used prior to 1984 as the independent variable in gravitational theories of the solar system. In 1984, ET was replaced by dynamical time.

Time kept by calculating the positions of the planets, and comparing the theoretical time used to make the calculation, to the time when the planets arrive at that position. Used for tables of planetary positions, such as in the "Astronomical Ephemeris". For a short time, the official time of astronomers, but now superseded by Atomic Time, as averaged in Coordinated Universal Time.

(astronomy) a measure of time defined by Earth's orbital motion; terrestrial time is mean solar time corrected for the irregularities of the Earth's motions

Determined in principle from the sun's apparent annual motion, ET is the numerical measure of uniform time, which is the independent variable in the gravitational theory of the earth's orbital motion, coming from Simon Newcomb's Tables of the Sun. In practice, ET was obtained by comparing observing positions of the Moon with gravitational ephemerides calculated from theories. In 1992, standard (apparent geocentric) ephemerides of comets and minor planets changed from using Ephemeris Time to Terrestrial Dynamical Time (TDT, or TT).

A measurement of time defined by orbital motions. Equates to Mean Solar Time corrected for irregularities in Earth's motions.

Time obtained from observing the motion of the moon around the earth.

Time based on the ephemeris second, i.e. based on the motion of the Earth around the Sun rather than on the rotation of the Earth ( Universal Time) or on an atomic clock ( atomic time).

Ephemeris Time (ET) is a now obsolete time scale used in ephemerides of celestial bodies, in particular the Sun (as observed from the Earth), Moon, planets, and other members of the solar system. This is distinct from Universal Time (UT): the time scale based on the rotation of the Earth around its axis. ET was replaced with the two time scales Terrestrial Dynamical Time (TDT) and Barycentric Dynamical Time (TDB) by the International Astronomical Union (IAU) in 1976.