|Hour Angle||close window|
The hour angle is an expression describing the difference between local solar time and solar noon. Although it is calculated directly from measurements of time, it is expressed in angular units (degrees).
The hour angle measures time after solar noon in terms of one degree for every four minutes, or fifteen degrees per hour. Time after solar noon is expressed using a positive hour angle, and time before solar noon, a negative hour angle. Therefore, at two hours before solar noon, the hour angle is -30 degrees, and at two hours after solar noon it is +30 degrees.
This diagram depicts the relationship between the hour angle and local solar time in the Northern Hemisphere:
Note again that the hour angle does not directly correspond to the spatial position of the sun like the altitude and azimuth angles; it's a measurement of time.