Azimuth System
Synonym for horizontal system, one of the coordinate systems used to locate the position of celestial bodies.
An azimuth is the angular measurement in a spherical coordinate system which represents the horizontal angle from a cardinal direction, most commonly north.
Mathematically, the relative position vector from an observer to a point of interest is projected perpendicularly onto the horizontal plane; the angle between the projected vector and a reference vector on the reference plane is called the azimuth.
When used as a celestial coordinate, the azimuth is the horizontal direction of an astronomical object. The reference vector points to true north. The azimuth is the angle between the north vector and the celestial object's vector on the horizontal plane.
Azimuth is usually measured in degrees (°).
Etymology and History
The word azimuth originates from medieval Arabic السموت (al-sumūt, pronounced as-sumūt), meaning "the directions" (plural of Arabic السمت al-samt = "the direction"). The Arabic word entered late medieval Latin in an astronomy context and in particular in the use of the Arabic version of the Astrolabe astronomy instrument. The first known record in any Western language is in Spanish in the 1270s in an astronomy book that was largely derived from Arabic sources, the Libros del saber de astronomía commissioned by King Alfonso X of Castile. In Arabic the written al-sumūt is always pronounced as-sumūt.
Astronomy
Azimuth is one of the two coordinates. The other is altitude, sometimes called Elevation above the horizon.
Tohe reference plane for an azimuth is true north, measured as a 0° azimuth. Moving clockwise on a 360 degree circle, east has azimuth 90°, south 180°, and west 270°.
The latitude which measures the vertical angle of a planet is not to be confused with the - positive (north) or negative (southern) - Declination, i.e. a planet's deviation from the Ecliptic.
See also
Weblinks
Notes and References
- ↑ Formed between a reference direction (in this example north) and a point of interest