n pl , ephemerides
1 a table giving the future positions of a planet, comet, or satellite
2 an annual publication giving the positions of the sun, moon, and planets during the course of a year, information concerning eclipses, astronomical constants, etc.
3 Obsolete a diary or almanac (C16: from Latin, from Greek: diary, journal; see ephemeral)
n time that is based on the orbit of the earth around the sun rather than the axial rotation of the earth, one ephemeris second being 1/31556925.9747 of the tropical year 1900. It was used from 1960 to 1983 as an astronomical timescale but has been replaced by terrestrial dynamical time and barycentric dynamic time
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