Azimuth

In cartography/navigation, an azimuth is the angle (in the plane) formed by the line passing by the 2 points and the line of the two poles.

From 2 GPS points (Point 1: latitude $ lat_1 $, longitude $ long_1 $ and Point 2 latitude $ lat_2 $, longitude $ long_2 $), the formula to calculate an azimuth $ A $ is $$ A = \operatorname{atan2}(y, x) $$

with $ y = \cos(lat_1) \cdot \sin(lat_2) - \sin(lat_1) \cdot \cos(lat_2) \cdot \cos(long_2-long_1) $ and $ x = \sin(long_2-long_1) \cdot \cos(lat_2) $

Reminder: the arctan2 formula is $$ \operatorname{atan2}(y,x) = 2 \arctan \left( \frac{ y }{ \sqrt{x^2+y^2} + x } \right) $$

The angle is calculated by taking as base/reference the north geographic pole.

Every hour, the Earth rotates on itself about 15 degrees, so every hour on Earth, the sun is seen 15 degrees further west.

By knowing the azimuth of the sun, solar time can be calculated. At noon, the sun is 180 degrees. Each difference of 15 degrees is 1 hour.

Azimuth, with or without h, are 2 identical terms, despite the spelling variant, both spellings are accepted.