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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 ]
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".
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, 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.
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 ...
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 ...
TT differs from Geocentric Coordinate Time (TCG) by a constant rate. Formally it is defined by the equation = +, where TT and TCG are linear counts of SI seconds in Terrestrial Time and Geocentric Coordinate Time respectively, is the constant difference in the rates of the two time scales, and is a constant to resolve the epochs (see below).
Create and develop a requested astronomy article. Copyedit : Check for proper usage of "equinox" vs. "epoch" when discussing the coordinates of astronomical objects. Equinox refers to the precession of the coordinate system used. Epoch refers to the timing of an event such as an observation. Verify :