altazimuth coordinate system definition of altazimuth coordinate system in the Free Online Encyclopedia.

altazimuth coordinate system (ăltăz`əməth) or horizon coordinate system, astronomical coordinate system in which the position of a body on 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. is described relative to an observer's celestial horizon celestial horizon, one axis of the altazimuth coordinate system . It is the great circle on the celestial sphere midway between the observer's zenith and nadir; it divides the celestial sphere into two equal hemispheres.
..... Click the link for more information. and zenith zenith, in astronomy, the point in the sky directly overhead; more precisely, it is the point at which the celestial sphere is intersected by an upward extension of a plumb line from the observer's location.
..... Click the link for more information. . The coordinates of a body in this system are its altitude altitude, vertical distance of an object above some datum plane, such as mean sea level or a reference point on the earth's surface. It is usually measured by the reduction in atmospheric pressure with height, as shown on a barometer or altimeter .
..... Click the link for more information. and azimuth azimuth (ăz`əməth), in astronomy, one coordinate in the altazimuth coordinate system .
..... Click the link for more information. . Altitude is measured from the celestial horizon along the vertical circle through the body and the zenith of the observer. Azimuth is measured along the celestial horizon from the observer's south point (the point on the horizon directly south of him) to the point where the body's vertical circle intersects the horizon. Because the earth rotates on its axis, the altitude and azimuth of a celestial body are constantly changing.