Orbit of the Moon
The Moon makes one circle around Earth, called the sidereal month, in 27.3 days. But in this time, the Earth continues to move forward, so the Moon will be in a different place relative to the Sun, and the phase of the Moon will be different. To reach the same phase, the Moon must travel a bit farther. The time for the Moon to reach the same phase, called the synodic month, is 29.5 days.