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.
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. 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
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 θ is almost universally used to represent the azimuth. Although there are
several conventions in spherical coordinates, the azimuth is usually denoted by either theta, θ or
phi, φ.
See also
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