astronomical coordinate systems
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.
"astronomical coordinate systems." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (February 19, 2018). http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/astronomical-coordinate-systems
"astronomical coordinate systems." The Columbia Encyclopedia, 6th ed.. . Retrieved February 19, 2018 from Encyclopedia.com: http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/astronomical-coordinate-systems