Sidereal Month
From Astrowiki-en
Synonym: Sidereal Lunar Month
The sidereal month is the time it takes for the Moon to make one complete revolution around the Earth, in other words, the time it takes for the Moon to reach the same position on the hour circle with respect to the fixed stars. The sidereal month is 27 days, 7 hours and 43 minutes and is therefore slightly shorter than the synodic month. The hour circle is a circle which is projected onto the celestial sphere which passes through the celestial poles and intersects the celestial equator at right angles.
