About how long does it take the moon to rotate on its axis?

Answer 1

The moon takes 29.5 days to complete one synodic cycle. This cycle is what we observe from earth, and it is the cycle we would measure from, say, one full moon to the next. However, by the time a synodic cycle ends, the moon has rotated a little more than 360 degrees. This is hard to grasp and takes some time and thought. The rotation of bodies that are orbiting other bodies always presents a need to distinguish between synodic and sidereal rotation. The true, 360 degree sidereal rotation of the moon takes 27.32 earth days. See links on the moon, and on synodic and sidereal periods. Note: Many erroneously conclude that since the same face of the moon always orients toward earth this means that the moon cannot be rotating. However, if you imagine observing from the north the orbiting of the moon around the earth (the moon does orbit the earth-- another idea that some people don't believe), the only way that the same face orients toward earth is for the moon's orbital and rotational periods to be the same. The moon is tidally locked with earth, and this is what causes the orbital and rotational periods to be the same. The face of the moon does in fact change a little due to the phenomenon called libration, a topic beyond the scope of the question. == ==
Jeremiah Deem Tulsa - 27.322 days