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In astronomy, an epoch or reference epoch is a moment in time used as a reference point for some time-varying astronomical quantity. It is useful for the celestial coordinates or orbital elements of a celestial body , as they are subject to perturbations and vary with time. [ 1 ]
Coordinate systems in astronomy can specify an object's relative position in three-dimensional space or plot merely by its direction on a celestial sphere, if the object's distance is unknown or trivial. Spherical coordinates, projected on the celestial sphere, are analogous to the geographic coordinate system used on the surface of Earth.
In astronomy, an equinox is either of two places on the celestial sphere at which the ecliptic intersects the celestial equator. [1] [2] [3] Although there are two such intersections, the equinox associated with the Sun's ascending node is used as the conventional origin of celestial coordinate systems and referred to simply as "the equinox".
In astronomy, there is also a heliocentric rectangular variant of equatorial coordinates, designated x, y, z, which has: The origin at the centre of the Sun. The fundamental plane in the plane of the Earth's equator. The primary direction (the x axis) toward the March equinox.
The epoch for which M 0 is defined is often determined by convention in a given field or discipline. For example, planetary ephemerides often define M 0 for the epoch J2000, while for earth orbiting objects described by a two-line element set the epoch is specified as a date in the first line. [5]
In astronomy literature, I have never seen the word equinox refer to a time basis; the word epoch is always used as a basis for the coordinate system itself, i.e. precession and nutation changing the celestial equator used for declination and right ascension. The epoch (astronomy) article seems to indicate that using equinox in this sense is ...
The Experiment to Detect the Global EoR Signature (EDGES) is an experiment and radio telescope located in a radio quiet zone at the Murchison Radio-astronomy Observatory in Western Australia. It is a collaboration between Arizona State University and Haystack Observatory, with infrastructure provided by CSIRO. [1]
In astronomy, the ecliptic coordinate system is a celestial coordinate system commonly used for representing the apparent positions, orbits, and pole orientations [1] of Solar System objects. Because most planets (except Mercury ) and many small Solar System bodies have orbits with only slight inclinations to the ecliptic , using it as the ...