hour angle definition of hour angle in the Free Online Encyclopedia.

hour angle, in astronomy, a coordinate in the equatorial coordinate system equatorial coordinate system, the most commonly used astronomical coordinate system for indicating the positions of stars or other celestial objects on the celestial sphere . The celestial sphere is an imaginary sphere with the observer at its center.
..... Click the link for more information. . The hour angle of a celestial body is the angular distance, expressed in hours, minutes, and seconds (one hour equals 15 degrees), measured westward along the celestial equator from the observer's celestial meridian to the hour circle hour circle, in astronomy, a secondary axis in the equatorial coordinate system . The hour circle of a celestial body is the great circle on the celestial sphere that passes through both the body and the north celestial pole.
..... Click the link for more information. of the object being located. The hour angle is used in measuring astronomical time; local sidereal time sidereal time (ST), time measured relative to the fixed stars; thus, the sidereal day is the period during which the earth completes one rotation on its axis so that some chosen star appears twice on the observer's celestial meridian .
..... Click the link for more information. is equal to the hour angle of the vernal equinox.