Transcript: We always see the same features on the surface of the Moon.  This means that the Moon's rotational period equals the time that it takes to orbit the Earth.  This is called synchronous rotation.  The time that it takes for one phase of the Moon to recur in the night sky is called the Moon Synodic period.  It's twenty-nine and a half days.  This is different from the Moon's sidereal period which is the time that it takes for a fixed phase of the Moon to reappear amongst the fixed stars; this is only 27.3 days.  The phases of the Moon are one of the most prominent patterns in the night sky. They have been known to civilizations and fairly accurately measured for tens of thousands of years.