Azimuth means the bearing of a direction—such as that toward a particular point on the horizon from a given place—measured clockwise around from due north. Thus the azimuth of due north is 0°, that of due east is 90°, that of due south 180°, and that of due west 270°. The azimuth of a point one degree to the west of north is 359°. Azimuth is measured in the horizontal plane through the observer. To fully specify the direction of an observed point, one must also specify the vertical angle or altitude of the point.

It is possible to specify the position of a star or other object in the sky by its azimuth and altitude, but this will change with time owing to the diurnal motion of the celestial sphere. Even at a given moment, the azimuth and altitude values of a particular star will be different for observers at different places on the earth.

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