hour angle

Hour angle.

The hour angle is indicated by a greenarrow on the celestial equator plane. The arrow ends at the hour circle of an green dot indicating the apparent place of an astronomical object on the celestial sphere.

An hour angle (HA) is the angle between the hour circle of a celestial object and the observer's meridian, measured anticlockwise along the celestial equator. It is sometimes used as a coordinate in place of right ascension. See also equatorial coordinates.


The local hour angle (LHA) is the hour angle of a celestial object measured with respect to the observer's local meridian.