Sidereal Month

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B: Sidereal, C: Synodic

Synonym: Sidereal Lunar Month

The sidereal month is the time it takes for the moon to make one complete revolution around the earth; or the time it takes for the moon to reach the same position on the hour circle[1] 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 or typical calendar month.


Notes and References

  1. 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.