Hour Angles to Degrees (h to °)

1 hour angle equals 15 degrees exactly.

How to convert hour angles to degrees

To convert hour angles to degrees, multiply the number of hour angles by 15. This factor is exact. To go the other way, multiply degrees by 0.06666666667 (rounded).

degrees = hour angles × 15

Example: 10 hour angles = 150 degrees.

About these units

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.

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.

1 hour angle = 0.04166666667 turns (approximately).

Sources: Wikipedia: Hour angle; Wikipedia: Right ascension

Degree (°)

General & non-SICurrent unit

One 360th of a full turn. The everyday unit of angle, inherited from the ancient Babylonians' base-60 counting.

Dividing the circle into 360 parts traces back to the astronomers of ancient Babylon, who counted in base 60. Why 360 in particular is still debated. One explanation points to Persian and Babylonian calendars, which used a year of about 360 days, so the Sun seemed to advance roughly one degree each day. Another says the Babylonians started from the angle of an equilateral triangle and split it into 60 pieces, and a third credits early chord-based trigonometry, where a chord equal to the radius made a natural base. Greek astronomers such as Aristarchus and Hipparchus were among the first to use Babylonian astronomical knowledge systematically.

The number also divides well. 360 has 24 divisors and splits evenly by every whole number from 1 to 10 except 7, which suits a world cut into 24 time zones of 15 degrees of longitude each. Each degree breaks into 60 arcminutes, and each of those into 60 arcseconds. The SI Brochure lists the degree among the widely used non-SI units, equal to π/180 radian, about 0.01745. For scale, the Moon and the Sun each look about half a degree wide, and a little finger held at arm's length covers roughly one degree of sky.

1 degree = 0.002777777778 turns (approximately).

Sources: BIPM SI Brochure, 9th edition (2019); Wikipedia: Degree (angle); Wikipedia: Angular diameter

Related conversions

See all angle units.