In astronomy, a celestial coordinate system is a system for specifying positions of celestial objects: satellites, planets, stars, galaxies, and so on. Coordinate systems can specify a position in 3-dimensional space, or merely the direction of the object on the celestial sphere, if its distance is not known or not important.
The coordinate systems are implemented in either spherical coordinates or rectangular coordinates. Spherical coordinates, projected on the celestial sphere, are analogous to the geographic coordinate system used on the surface of the Earth. These differ in their choice of fundamental plane, which divides the celestial sphere into two equal hemispheres along a great circle. Rectangular coordinates, in appropriate units, are simply the cartesian equivalent of the spherical coordinates, with the same fundamental (x,y) plane and primary (x-axis) direction. Each coordinate system is named for its choice of fundamental plane.
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A star's galactic (yellow), ecliptic (red) and equatorial (blue) coordinates, as projected on the celestial sphere. Ecliptic and equatorial coordinates share the vernal equinox (magenta) as the primary direction, and galactic coordinates are referred to the galactic center (yellow). The origin of coordinates (the "center of the sphere") is ambiguous; see celestial sphere for more information. |
Read more about Celestial Coordinate System: Coordinate Systems, Converting Coordinates
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