What is the formula for calculating true azimuth in an afternoon observation?

The formula for calculating true azimuth in an afternoon observation involves adjusting the observed horizontal angle relative to the true north direction. In the afternoon, the sun is typically located in the southern hemisphere of the sky, which means that if the observed horizontal angle is measured, it must be adjusted to find the true azimuth.

By taking A, which represents the initial azimuth angle, and adding (360 degrees minus the observed horizontal angle), you are effectively converting the angle measured into a true azimuth that accounts for the sun's position. This adjustment properly aligns the measurement within the 360-degree framework of azimuth, allowing the observed angle to be converted correctly to true azimuth with respect to north.

This approach is particularly relevant during afternoon observations when the local coordinate systems can differ significantly from true geographic directions, thereby necessitating such calculations for accurate mapping and navigation purposes.