The sidereal month is the time it takes for the Moon to complete one orbit of the Earth relative to the fixed stars.
Synodic month: 29.530589 days (29 days, 12 hours, 44 minutes, 2.9 seconds)
The synodic month is the time it takes for the Moon to return to the same phase, as seen from Earth (i.e., from New Moon to New Moon, or from Full Moon to Full Moon). The difference between the sidereal and synodic months is due to the Earth's motion around the Sun during the course of a lunar orbit.
