太阳方位角即太阳所在的方位，指太阳光线在地平面上的投影与当地子午线的夹角，可近似地看作是竖立在地面上的直线在阳光下的阴影与正南方的夹角。方位角以正南方向为零，由南向东向北为负，由南向西向北为正，如太阳在正东方，方位角为负90°，在正东北方时，方位为负135°，在正西方时方位角为90°，在正北方时为±180°。

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.

[edit] True north-based azimuths

[edit] 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.

[edit] 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.

[edit] 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.

[edit] Other systems

[edit] 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).

[edit] 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.

[edit] 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, theta θ is almost universally used to represent the azimuth in mathematical applications, whereas physical applications may denote the azimuth using the symbol phi, φ. Although there are several conventions in spherical coordinates, the azimuth is usually denoted by either theta, θ or phi, φ.