Ephemeris Time
Related Category: Astronomy: General
(ET), astronomical time defined by the orbital motions of the earth, moon, and planets. The earth does not rotate with uniform speed, so the solar day is an imprecise unit of time.
Ephemeris 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.
ephemeris time
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ephemeris time (abbr E.T.) The uniform measure of time defined by the laws of dynamics and determined in principle from the orbital motions of the planets, specifically the orbital motion of the earth as represented by Newcomb's Tables of the Sun.
Ephemeris Time (ET). 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, ...
Ephemeris Time
(a) Time based on the ephemeris second. Ephemeris time is determined primarily from observations of the Moon against the background of stars, ...
Ephemeris Time [LLM96]
Eta Aquilae
A pulsating star in the constellation Aquila. It was the first Cepheid variable star discovered, in 1784. [C95]
Etalon ...
Ephemeris time is used by astronomers for the greatest degree of accuracy. Ephemeris are tables giving the computed positions of celestial bodies for every day of a given period. It is an astronomical almanac containing positional tables.
Ephemeris time
The term ephemeris time is in itself apt to refer to time in connection with any Astronomical Ephemeris. It has been used more specifically to refer:-...
(ET).
ET -- Ephemeris time, a measurement of time defined by orbital motions. Equates to Mean Solar Time corrected for irregularities in Earth's motions. Obsolete, replaced by TT, Terrestrial Time.
Duffett-Smith, P. "Ephemeris Time (ET) and Terrestrial Dynamical Time." §16 in Cambridge, England: Cambridge University Press, pp. 22-23, 1992.
The small tidal effect can not be observed in a short period but the cumulative effect of the Earth's actual daily rotation occurring in less than 24 hours as measured on a stable clock (ephemeris time, atomic time) even a few milliseconds every day, ...
dynamical ~: [or Terrestrial Dynamical Time, TDT] 'scientific time' - it superseded ephemeris time in 1984, and is based on a uniform scale of time derived from atomic clocks (i.e. not subject to fluctuations in the Earth's rate of rotation).
It includes routines for conversions between Universal Time (UTC), Atomic Time (TAI), and Ephemeris Time (ET). It also performs conversions between calendar dates and Julian dates, and interprets or formats dates and times in a variety of styles.
Compare ephemeris time.
In the years preceding 1960 the arguments of the ephemerides in the American Ephemeris and Nautical Almanac were designated as universal time.
 See also: Ephemeris, Time, Earth, Second, Rotation
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