# Azimuth

Azimuth

Azimuth (Audio-IPA|lang=US English|en-us-azimuth.ogg|ˈæzɪməθ) is a mathematical concept defined as the angle, usually measured in degrees (°), between a reference plane and a point. This concept is used in many practical applications including navigation, astronomy, mapping, mining and artillery. The word "azimuth" is derived from the Arabic السمت "('as-sumūt')" which means "the ways", referring to the ways or directions a person faces.

In navigation, the reference plane is typically true north and is considered 0° azimuth. Moving clockwise, a point due east would have an azimuth of 90°, south 180°, and west 270°. Some navigation systems use south as the reference plane. However, any direction can serve as the plane of reference, as long as it is clearly defined for everyone using that system.

True north-based azimuths

Mapping

There are a wide variety of azimuthal map projections. They all have the property that directions (the azimuths) from a central point are preserved. Some navigation systems use south as the reference plane like in the Philippine practice. However, any direction can serve as the plane of reference, as long as it is clearly defined for everyone using that system.

Astronomy

Azimuth is often, some consider incorrectly, referred to as a bearing. However, in modern astronomy azimuth is nearly always measured from the north. In former times, it was common to refer to azimuth from the south, as it was then zero at the same time the hour angle of a star was zero. This assumes, however, that the star (upper) culminates in the south, which is only true for most stars in the Northern Hemisphere.

Other uses

Azimuth is used to determine headings or the direction in which to fly. In artillery, it is the direction of fire.

Azimuth is also terms used in mining for a similar, but slightly different angle: "azimuths" and "meridian angles" are used to name any angle measured clockwise from any meridian.

For tape and cassette tape decks, azimuth refers to the angle between the tape head(s) and tape. For magnetic tape drives, azimuth refers to the angle between the tape head(s)

In sound localization experiments and literature, the azimuth refers to the angle the sound source makes compared to the imaginary straight line that is drawn from within the head through the area between the eyes.

An azimuth thruster in shipbuilding is a propeller that can be rotated horizontally.

Other systems

Right Ascension

If instead of measuring from and along the horizon the angles are measured from and along the celestial equator, the angles are called right ascension if referenced to the Vernal Equinox, or hour angle if referenced to the Prime Meridian.

Horizontal coordinate

In the horizontal coordinate system, used in celestial navigation and satellite dish installation, azimuth is one of the two coordinates. The other is altitude, sometimes called elevation above the horizon. See also: Sat finder.

Polar coordinate

In three-dimensional polar coordinate systems, including cylindrical coordinates and spherical coordinates, the azimuth of a point is the angle between the positive x-axis and the projection of the vector onto the xy-plane (the component of the vector in the xy-plane). In cylindrical coordinates, phi $phi$ is almost universally used to represent the azimuth in mathematical applications, whereas physical applications may denote the azimuth using the symbol phi, $phi$. Although there are several conventions in spherical coordinates, the azimuth is usually denoted by either theta, $heta$ or phi, $phi$. elec 4503

* Panning (camera)
* Altitude (astronomy)
* Azimuthal quantum number
* Inclination
* Longitude
* Magnetic declination
* Zenith

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### Look at other dictionaries:

• Azimuth — Az i*muth, n. [OE. azimut, F. azimut, fr. Ar. as sum?t, pl. of as samt a way, or perh., a point of the horizon and a circle extending to it from the zenith, as being the Arabic article: cf. It. azzimutto, Pg. azimuth, and Ar. samt al r[=a] s the… …   The Collaborative International Dictionary of English

• Azĭmuth — (arab., Astr.), der Winkel (Azimuthalwinkel), den sein Vertical am Zenith mit dem Meridiane macht; das Maß desselben ist ein Bogen des Horizonts. Je nachdem dieser Bogen vom Mittagspunkte ab nach O. od. W. auf dem Horizonte bis 180° fortgezählt… …   Pierer's Universal-Lexikon

• Azimuth — Azimuth, nennt man in der Astronomie die Entfernung des Höhenkreises eines Sterns vom Südpunkte des Horizonts. Das A. kann östlich oder westlich sein, je nachdem der Stern östlich oder westlich vom Südpunkte des Horizonts steht. Das A. und die… …   Herders Conversations-Lexikon

• azimuth — (n.) distance of a star from the north or south point of the meridian, late 14c., from O.Fr. azimut, from Arabic as sumut the ways, plural of as samt the way, direction (see ZENITH (Cf. zenith)) …   Etymology dictionary

• azimuth — ► NOUN Astronomy ▪ the horizontal direction of a celestial object, measured from the north or south point of the horizon. DERIVATIVES azimuthal adjective. ORIGIN Arabic, the way, direction …   English terms dictionary

• azimuth — [az′ə məth] n. [ME & OFr azimut < Ar as sumūt < as < al, the + sumūt, pl. of samt, way, path] Astron. Surveying etc. an angular measurement used to locate an object, star, etc.: it is measured clockwise around the horizon from the north …   English World dictionary

• azimuth — i. A direction expressed as a horizontal angle, usually in degrees, measured clockwise from a reference datum or direction, usually north. The azimuth will be a true zenith, grid azimuth, magnetic azimuth, or relative azimuth, depending upon… …   Aviation dictionary

• azimuth — noun /ˈæzɪməθ/ a) An arc of the horizon intercepted between the meridian of the place and a vertical circle passing through the center of any object; as, the azimuth of a star; the azimuth or bearing of a line surveying. b) The quadrant of an… …   Wiktionary

• azimuth — UK [ˈæzɪməθ] / US noun [countable] Word forms azimuth : singular azimuth plural azimuths astronomy the angle of the imaginary line between the position of a plane, ship etc and the position of another object …   English dictionary

• azimuth —   n. angular distance, measured along horizon, of object from north or south points; angle between meridian and the great circle which passes through both zenith and heavenly body.    ♦ azimuth compass, magnetic compass having sights for taking… …   Dictionary of difficult words