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In other words, the celestial equator is an abstract projection of the terrestrial equator into outer space. [1] Due to Earth's axial tilt , the celestial equator is currently inclined by about 23.44° with respect to the ecliptic (the plane of Earth's orbit ), but has varied from about 22.0° to 24.5° over the past 5 million years [ 2 ] due ...
For example, the north celestial pole has a declination of +90°. The origin for declination is the celestial equator, which is the projection of the Earth's equator onto the celestial sphere. Declination is analogous to terrestrial latitude. [6] [7] [8]
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".
The equatorial coordinate system is centered at Earth's center, but fixed relative to the celestial poles and the March equinox. The coordinates are based on the location of stars relative to Earth's equator if it were projected out to an infinite distance.
At their intersections with the celestial sphere, these form the celestial equator, the north and south celestial poles, and the ecliptic, respectively. [8] As the celestial sphere is considered arbitrary or infinite in radius, all observers see the celestial equator, celestial poles, and ecliptic at the same place against the background stars.
It is on the celestial equator at both the left and right extremes of the sky chart, with the ecliptic (the orange dotted sine curve) passing through it. The first point of Aries , also known as the cusp of Aries , is the location of the March equinox (the vernal equinox in the northern hemisphere, and the autumnal equinox in the southern ...
Right ascension and declination as seen on the inside of the celestial sphere. The primary direction of the system is the March equinox, the ascending node of the ecliptic (red) on the celestial equator (blue). Right ascension is measured eastward up to 24 h along the celestial equator from the primary direction.
The ecliptic intersects the celestial equator within this constellation and Pisces. Underlying these technical two definitions, the sun passes directly overhead of the equator, within this constellation, at the September equinox. Virgo can be easily found through its brightest star, Spica.