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Astronomy
Planetary Science
The Moon

How fast does the moon spin?

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May 12, 2009 8:11PM

== The Moon rotates once in about 27.32 days, and its radius is 1080 miles or 1738 km. The rotational speed starts at zero at either geographic pole (the two places where the axis of rotation intersects the surface) and increases (but not at a constant rate) as you head toward the lunar equator, where it reaches its maximum of about 10.3 mi/hr (or 16.7 km/hr). Pretty slow!

The fact that the moon rotates (spins) on its axis once per lunar cycle (orbit around earth) gives rise to the observation that the same side of the moon always faces earth. If the moon did not rotate at all relative to the fixed stars, we would observe most of the surface of the moon over the course of a year or so. It would take some time for all the dark 'new moon' surfaces to be exposed to us in sunlight.