Hour Angle (h)

AstronomicalCurrent unit

One twenty-fourth of a turn (15 degrees), the angle the Earth rotates in one hour. Right ascension is measured in hours.

1 hour angle = 0.04166666667 turns (approximately).

About the hour angle

Hour angle measures how far an object has moved west of the local meridian, expressed in time instead of degrees. A full circle is exactly 24 hours, so one hour equals 15 degrees, one minute of time equals 15 arcminutes, and one second of time equals 15 arcseconds. Astronomers use the same scheme for right ascension, the sky's equivalent of longitude, which is measured eastward from the March equinox in hours, minutes, and seconds.

Local hour angle equals local sidereal time minus an object's right ascension. Zero means it is crossing the meridian, a negative value means it is still approaching, and a positive value means it has passed. The Sun's hour angle advances about one hour per clock hour, but a fixed star's advances roughly 1.0027 hours per clock hour, so an hour of hour angle takes about 59 minutes 50 seconds for stars. The same 15 degrees per hour underlies the division of the globe into 24 time zones.

Sources: Wikipedia: Hour angle; Wikipedia: Right ascension

Hour Angle conversion chart

1 hour angle expressed in every other angle unit:

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