What is the Greenwich Hour Angle used to measure?

The Greenwich Hour Angle is used to determine the angular measurement west of the Greenwich Meridian, which is essential in navigation and astronomy. It quantifies how far a celestial body has moved from the observer's location compared to the Greenwich Meridian, expressed in degrees. For instance, if a celestial object is at an hour angle of 15 degrees, it indicates that the body is positioned 15 degrees west of the prime meridian.

Understanding this concept allows navigators to calculate their local time in relation to GMT (Greenwich Mean Time) and helps them identify the position of celestial bodies at various times. By knowing the hour angle, one can determine when celestial bodies will be at their highest point in the sky, which is crucial for celestial navigation.