A table of computed positions occupied by a celestial body over successive intervals of time such as daily; plural ephemerides.
From L. ephemeris "day book, diary," from Gk. ephemeris "diary, account book," from ephemeros "short-lived, lasting but a day," from → epi "on, upon" + hemerai, dative of hemera "day."
Ruzij, from ruz, → day + zij "astronomical table," from Mid.Pers. zig "astronomical table," originally "string," since the lines of a table were compared to strings used on a weaver's instrument, variant zih, meaning "cord, string" (Modern Persian zeh "cord, string"); Av. jiiā- "bow-string;" cf. Skt. jiyā- "bow-string;" PIE base *gwhi- "thread, tendon" (from which derive also Gk. bios "bow;" L. filum "thread;" Russ. žca "thread").
Fr.: jour des éphémérides
86,400 → ephemeris seconds.
Fr.: méridien des éphémérides
A fictitious meridian that rotates independently of the Earth at the uniform rate implicitly defined by → Terrestrial Dynamical Time (TDT).
Fr.: seconde des éphémérides
The length of a tropical second (1/31,556,925.97474 of the tropical year) on 1900 January 0.5 → ephemeris time.
ephemeris time (ET)
Fr.: Temps des éphémérides
The uniform time-scale used as the independent variable
to calculate the orbits in the solar system prior to 1984. Ephemeris Time was adopted in
1960 to deal with irregularities in the → Earth's rotation
that had been found to affect the
course of mean solar time. The definition of Ephemeris Time is based on Newcomb's analytical
theory of the Earth's motion around the Sun (Newcomb 1898), according to which the geometric
mean longitude of the Sun with respect to the Earth-Moon barycenter is expressed by:
Fr.: transit au méridien des éphémérides
The passage of a celestial body or point across the → ephemeris meridian.