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In astronomy and celestial navigation, an ephemeris (/ ɪ ˈ f ɛ m ər ɪ s /; pl. ephemerides / ˌ ɛ f ə ˈ m ɛr ɪ ˌ d iː z /; from Latin ephemeris 'diary', from Ancient Greek ἐφημερίς (ephēmerís) 'diary, journal') [1] [2] [3] is a book with tables that gives the trajectory of naturally occurring astronomical objects and artificial satellites in the sky, i.e., the position ...
A fundamental ephemeris of the Solar System is a model of the objects of the system in space, with all of their positions and motions accurately represented. It is intended to be a high-precision primary reference for prediction and observation of those positions and motions, and which provides a basis for further refinement of the model.
For example, orbital elements, especially osculating elements for minor planets, are routinely given with reference to two dates: first, relative to a recent epoch for all of the elements: but some of the data are dependent on a chosen coordinate system, and then it is usual to specify the coordinate system of a standard epoch which often is ...
The Astronomical Almanac for 1984 through 2002 were based on JPL ephemeris DE200, and from 2003 to 2014 the Astronomical Almanac was based on JPL ephemeris DE405. [9] As of 2022, the Almanac is derived from DE430. [15] The JPL ephemerides are widely used for planetary science; some examples are included in the Notes and References.
The JPL ephemeris time argument T eph is within a few milliseconds of TT. TT is slightly ahead of UT1 (a refined measure of mean solar time at Greenwich) by an amount known as Δ T = TT − UT1. Δ T was measured at +67.6439 seconds (TT ahead of UT1) at 0 h UTC on 1 January 2015; [ 16 ] and by retrospective calculation, Δ T was close to zero ...
Ephemeris time (ET), adopted as standard in 1952, was originally designed as an approach to a uniform time scale, to be freed from the effects of irregularity in the rotation of the Earth, "for the convenience of astronomers and other scientists", for example for use in ephemerides of the Sun (as observed from the Earth), the Moon, and the planets.
This is a visual example of the official date change from the Julian calendar to the Gregorian ... Explanatory Supplement to the Astronomical Ephemeris. London ...
Two sample pages of the 2002 Nautical Almanac. The Nautical Almanac has been the familiar name for a series of official British almanacs published under various titles since the first issue of The Nautical Almanac and Astronomical Ephemeris, for 1767: [1] this was the first nautical almanac to contain data dedicated to the convenient determination of longitude at sea.