How long is the moons period of orbit?

Answer 1

There are a lot of ways of looking at this depending on your relation to the Earth/moon system:

1. The Moon's orbital period in a non-rotating frame of reference is 27.32 days (27 days, 7 hours, 43 minutes, 11.6 seconds). This is the sidereal month. It is measured by observing how long it takes the Moon to pass a fixed star.
2. A synodic month is 29.53 days (29 days, 12 hours, 44 minutes, 2.8 seconds) It is measured from New Moon to New Moon. This is the most common way of expressing the lunar cycle.
3. An anomalistic month is the Moon's orbital period measured from perigee to perigee - the point in the Moon's orbit when it is closest to Earth. An anomalistic month is about 27.55 dayson average.
4. The tropical month is the time for the Moon to return to the same ecliptic longitude, i.e. measured from the equinox; it is slightly shorter than the sidereal month because of precession of the equinoxes.
5. The draconic month or nodal month is the period in which the Moon returns to the same node of its orbit (one of the two points where the Moon's orbit crosses the plane of the Earth's orbit). Its duration is about 27.21 days on average.