Question

Calculate hour angle for local apparent time at 6am, 9am

Answer 1

In astronomy and celestial navigation, the hour angle is one of the coordinates used in the equatorial coordinate system to give the direction of a point on the celestial sphere. The hour angle of a point is the angle between two planes: one containing the Earth's axis and the zenith (the meridianplane), and the other containing the Earth's axis and the given point (the hour circlepassing through the point).
The angle may be expressed as negative east of the meridian plane and positive west of the meridian plane, or as positive westward from 0° to 360°. The angle may be measured in degrees or in time, with 24h = 360° exactly.

In astronomy, hour angle is defined as the angular distance on the celestial spheremeasured westward along the celestial equator from the meridian to the hour circlepassing through a point. It may be given in degrees, time, or rotations depending on the application. In celestial navigation, the convention is to measure in degrees westward from the prime meridian(Greenwich hour angle, GHA), from the local meridian (local hour angle, LHA) or from the first point of Aries (sidereal hour angle, SHA).

The hour angle is paired with the declinationto fully specify the location of a point on the celestial sphere in the equatorial coordinate system.