astronomical coordinate systems

rectangular coordinates A system for specifying the position of an object relative to two or three mutually perpendicular axes from some specified origin. The axes are identified as x, y, and (where a third axis is used) z. Cartesian coordinates are rectangular coordinates. In astronomy, rectangular coordinates are sometimes used for Solar System objects, with the length of each axis given in astronomical units. They are usually heliocentric or geocentric in origin, but other points of origin can be used.

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 , the altazimuth coordinate system , the celestial or ecliptic coordinate system , and the galactic coordinate system . These systems are based on three common principles: (1) all stars are considered to be located on the inner surface of the celestial sphere , 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.