AZIMUTH

'Azimuth' 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.

Contents

Navigation

True north-based azimuths

Mapping

Astronomy

Other uses

Other systems

Declination

Horizontal coordinate

Polar coordinate

See also

Navigation

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

From North
North	0° or 360°
North North East	22.5°
North East	45°
East North East	67.5°
East	90°
East South East	112.5°
South East	135°
South South East	157.5°
South	180°
South South West	202.5°
South West	225°
West South West	247.5°
West	270°
West North West	292.5°
North West	315°
North North West	337.5°

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.

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

In aviation, 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 magnetic tape drives, azimuth refers to the angle between the tape head(s) and the tape medium.

Other systems

Declination

If instead of measuring from and along the horizon the angles are measured from and along the celestial equator, the angles are called declination and right ascension (hour angle).

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 from the origin to the point onto the xy-plane (the component of the vector in the xy-plane). In cylindrical coordinate, theta $heta$ is almost universally used to represent the azimuth. Although there are several conventions in spherical coordinates, the azimuth is usually denoted by either theta, $heta$ or phi, $phi$.

See also

★ Azimuthal quantum number

★ Longitude

★ Magnetic declination

★ Zenith