coordinate system

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Related to Astronomical coordinate: Celestial coordinates
The Four Main Coordinate Systemsclick for a larger image
The Four Main Coordinate Systems
coordinate systemclick for a larger image
coordinate system

coordinate system

() A system, resembling that of latitude and longitude on the Earth, by which the direction of a celestial body or a point in the sky can be specified. The direction is defined and determined by two spherical coordinates, referred to a fundamental great circle lying on the celestial sphere and a point on the fundamental circle (see illustration). One coordinate (a) is the angular distance of the celestial body measured perpendicular to the fundamental circle along an auxiliary great circle passing through the body and the poles of the fundamental circle. The other coordinate (b) is the angular distance measured along the fundamental circle from a selected zero point to the intersection of the auxiliary circle.

There are four main coordinate systems: the equatorial, horizontal, ecliptic, and galactic coordinate systems (see table). They are all centered on the Earth. Transformations can be made from one system to another by means of the relationships between the angles and sides of the relevant spherical triangles. The astronomical triangle, for example, relates equatorial and horizontal coordinates; the triangle formed by the celestial body and the poles of the equator and ecliptic relates equatorial and ecliptic coordinates. See also heliocentric coordinate system.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006
References in periodicals archive ?
Finally, astronomical coordinates may be calculated as an equivalent to equatorial coordinates of the zenith:
Symbolized by a crescent Moon and evening star, Islam is intertwined with astronomical phenomena: a new Moon ushers in the beginning of the holy month of Ramadan, and astronomical coordinates are used to determine the direction of Mecca, where the Kaaba holds the sacred (and possibly meteoritic) Black Stone.
Every month, our gatefold celestial chart cinches the sky in a star-sequined corset of astronomical coordinates. With hoops that girdle the night and ribs that radiate from the north celestial pole, this halter keeps everything in place with a web of reference circles tied to the Earth's spin and orbital motion.

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