hour angle, in astronomy, a coordinate in the equatorial coordinate system. 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 of the object being located. The hour angle is used in measuring astronomical time; local sidereal time is equal to the hour angle of the vernal equinox.
"hour angle." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (September 21, 2018). http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/hour-angle
"hour angle." The Columbia Encyclopedia, 6th ed.. . Retrieved September 21, 2018 from Encyclopedia.com: http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/hour-angle