The isoazimuth is of use when navigating with respect to an object of known location, such as a radio beacon.
A straight line called the azimuth line of position is drawn on a map, and on most common map projections this is a close enough approximation to the isoazimuth.
Let X be a fixed point on the Earth of coordinates latitude:
In a terrestrial spherical model, the equation of isoazimuth curve with initial course C passing through point S(B, L) is:
In this case the X point is the illuminating pole of the observed star, and the angle Z is its azimuth.
The equation of the isoazimuthal [2] curve for a star with coordinates (Dec, GHA), - Declination and Greenwich hour angle -, observed under an azimuth Z is given by: where LHA is the local hour angle, and all points with latitude B and longitude L, they define the curve.