A is also for Altitude and Azimuth

Altitude

The ALTITUDE of an object is its angle along an arc extending from the horizon (0 degrees) to the zenith (+ 90 degrees), the point directly overhead. Its AZIMUTH is the compass direction of the altitude of the object in degrees. Usually due North is considered 0 and also 360 degrees.

Altazimulth

Serious amateur astronomers used to consider the ALTAZIMUTH mount to be generally inferior to the EQUATORIAL mount because the equatorial mount easily "tracks" an object under study by moving in only one axis while the altazimuth mount requires constant movement in both axes. However, the advantage of the altazimuth mount over the equatorial mount is its great rigidity.

Two fairly recent developments began changing the prejudice against the altazimuth mount: the appearance of relatively inexpensive computer controlled drive motors and the development of very large Dobsonian (a form of altazimuth) mounted telescopes with apertures of from 20 to 30+ inches. It would be prohibitively expensive to construct equatorial mounts rigid enough to support such instruments.

Today even some of the relatively inexpensive small telescopes of the "go to" variety are mounted altazimuthly.