astronomical coordinate systems definition of astronomical coordinate systems in the Free Online Encyclopedia.

astronomical coordinate systems. A coordinate system is a method of indicating positions. Each coordinate is a quantity measured from some starting point along some line or curve, called a coordinate axis. There are four basic systems of astronomical coordinates: the equatorial coordinate system equatorial coordinate system, the most commonly used astronomical coordinate system for indicating the positions of stars or other celestial objects on the celestial sphere . The celestial sphere is an imaginary sphere with the observer at its center.
..... Click the link for more information. , the altazimuth coordinate system altazimuth coordinate system (ăltăz`əməth) or horizon coordinate system,
..... Click the link for more information. , the celestial or ecliptic coordinate system ecliptic coordinate system, an astronomical coordinate system in which the principal coordinate axis is the ecliptic , the apparent path of the sun through the heavens.
..... Click the link for more information. , and the galactic coordinate system galactic coordinate system, astronomical coordinate system in which the principal axis is the galactic equator (the intersection of the plane of the Milky Way with the celestial sphere ) and the reference points are the north galactic pole and the zero point on the
..... Click the link for more information. . These systems are based on three common principles: (1) all stars are considered to be located on the inner surface of the celestial sphere celestial sphere, imaginary sphere of infinite radius with the earth at its center. It is used for describing the positions and motions of stars and other objects.
..... Click the link for more information. , the imaginary sphere centered on the earth and representing the entire sky; (2) each coordinate axis is a great circle on the celestial sphere; and (3) coordinate measurements of an object to be located are made along two great circles, one a coordinate axis and the other perpendicular to it and passing through the object. Measurements are made either in degrees or in hours.