altazimuth coordinate system

[ăl-tăz′ə-məth]

The coordinate system in which a celestial object's position is described in terms of its altitude and azimuth. Like celestial latitude and longitude, and declination and right ascension, the altitude and azimuth coordinates are used to map objects in the sky. Unlike the other two systems, which are oriented to fixed features of the celestial sphere, the altazimuth system is based solely on an observer's location on the Earth, making it the most practical system for use in celestial navigation or surveying. Altitude can be determined using a sextant, and calculation of an observer's geographic location can then be determined using a chronometer and tables of star positions contained in a special almanac. Compare ecliptic coordinate system equatorial coordinate system.