azimuth

Azimuth is a directional measure used in the horizontal plane to specify the direction of a celestial or terrestrial object relative to a reference direction. In most contexts, the reference is true north, and azimuth is measured clockwise from north. As a result, azimuth values range from 0° to 360°, with 0° (or 360°) indicating north, 90° east, 180° south, and 270° west. A complementary coordinate is altitude (or elevation), which indicates the angle above the horizon; together, azimuth and altitude locate an object on the celestial sphere or in the local sky.

Conventions and references may vary. Azimuth can be defined relative to true north, magnetic north, or grid north, and the choice affects the numeric value unless corrections are applied for magnetic declination or grid convergence. In practice, field measurements often state the reference direction used.

Applications span astronomy, navigation, surveying, and meteorology. In astronomy and celestial navigation, azimuth helps locate stars, planets, and the Sun by combining with altitude to specify position in the horizontal coordinate system. Modern instruments—such as compasses, theodolites, and telescopes with computerized trackers—use azimuth to point accurately, sometimes converting coordinates between horizontal, equatorial, and other systems. In surveying, azimuth denotes the angle between a baseline and the line to a surveyed point, measured clockwise from a chosen reference direction, and is fundamental to map making and construction.

The term bearing is often used synonymously with azimuth, though some contexts distinguish bearing as a general direction. In meteorology and winds, wind direction may be expressed as an azimuth indicating the origin direction of the wind.