Azimuth and Bearing

When you’re giving someone directions, odds are you’re doing so in relation to a separate location both you and the other person know. For instance, you might say something like “Go to the coffee shop on 5th Street and turn left.” This is because having an accepted position or reference point is extremely helpful in providing clear directions. This same concept is applied to astronomy, surveying, navigation, or any other related action.

Because the earth is a sphere, any location on the planet can be given using two separate angle measurements. These measurements are known as coordinates, and the system is referred to as the spherical coordinate system. Two coordinates used in the spherical coordinate system are called azimuth and bearing. This blog will explain both of these coordinates and how they are used in navigation.

Azimuth is more commonly defined as the angle between the horizontal projection of a vector from the origin to the point considered and the reference vector on the horizontal plane. In most applications, the reference vector is considered to be the line towards the north or north/south meridian. Because azimuth is an angular measurement, it is measured in units of angles such as degrees, grads, or angular mils. Azimuth is used throughout fields such as navigation, cartography, surveying, gunnery, and more.

The definition of azimuth varies slightly depending on the field to make it more useful to the context of a given subject or application. Azimuth can be determined by a number of factors such as solar observation, astronomical direction method, equal altitudes method, method of repetitions, micrometer method, hour-angle of Polaris, and hour-angle of crossing the almucantar.

Bearing is the horizontal angle between the direction of one object and another, or between one object and the direction of true north. Depending on the situation or application, forward direction can also be considered the reference direction. Azimuth is given as a plain angle, but bearing is given with the reference direction and direction of rotation as well. For example, while azimuth may be written as 45 degrees east or 320 degrees west, bearing would be shown as 45 degrees east of north or 22.5 degrees west of south.

Apart from this, there are six distinct differences between azimuth and bearing. They are as follows:

  • Azimuth is the angle from the north along the horizontal plane, representing one of the two basic coordinates of the spherical coordinate system.
  • Bearing is the angle along the horizontal plane and is relative to a reference direction defined by an observer.
  • When measuring azimuth, the reference direction is north and the rotation is clockwise, but while measuring bearing, both reference and the rotation are defined by the observer.
  • Azimuth is a standard measure, while bearing is a local measure, defined by the location of the observer.
  • Azimuth and bearing can be the same if the reference is north and rotation is clockwise.
  • When denoted, azimuth is put in degrees, while bearing is noted with the angle, reference direction, and the direction of rotation.

Although they have their differences, azimuth and bearing are both critical measurements in safe and accurate navigation.


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