# Sidereal Month

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.

## Weblinks

*The Sidereal and Synodic Months - Animation*(Freedman and Kaufmann, 2004)*Sidereal and Synodic Periods of the Moon*(Illustration)

## Notes and References

- ↑ 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.