What does the Sidereal Hour Angle measure?

The Sidereal Hour Angle measures the angle between a celestial body, such as a star, and the observer's local meridian or a reference point in the sky. Specifically, it quantifies the difference in time since the celestial body last crossed the observer's meridian, expressed in angular measurement (degrees). When a star is positioned directly on the meridian, its hour angle is 0 degrees. As time progresses, the hour angle increases up to 360 degrees in a complete rotation of the Earth.

This measurement is critical in navigation as it helps in locating celestial bodies in the sky and determining the local time based on their position. Understanding the Sidereal Hour Angle is essential for astronomers and navigators alike to precisely calculate positions and navigate effectively using celestial references.