altazimut

Altazimut, also known as the alt-azimuth coordinate system, is a two-dimensional, local-horizon based system used to specify the position of celestial and terrestrial objects. The two coordinates are altitude and azimuth. Altitude is the angle above the observer’s horizon, ranging from 0 degrees at the horizon to 90 degrees at the zenith. Azimuth is the compass direction of the projection of the object onto the horizon, typically measured clockwise from a reference direction such as north, giving values from 0 to 360 degrees.

The altazimut system is observer-centered and fixed to the observer’s position. Because the sky appears to rotate as the Earth turns, altitude and azimuth depend on the viewer’s geographic latitude and the current time. To relate altazimut coordinates to the more universal equatorial system, one uses the observer’s latitude and local sidereal time to convert between right ascension and declination and between altitude/azimuth and the equatorial frame. In practice, conversions are performed with established formulas or, more commonly, with software and telescope control systems.

Altazimut mounts are widely used in astronomy due to their straightforward mechanical design: two perpendicular axes allow motion in altitude and azimuth, enabling easy manual pointing and broad motion ranges. They are common in small portable telescopes and in many modern observatories. A limitation for long-exposure astrophotography is field rotation: while the object remains at fixed altitude and azimuth, the field of view rotates, which is mitigated by software correction or additional hardware, such as a derotator.

Beyond astronomy, the altazimut frame is also employed in navigation, surveying, and educational contexts to illustrate how objects rise, move across the sky, and set with the observer’s horizon as a reference.