Full name: sidereal month
Plural form: months
Symbol: mo
Alternate spelling: sidereal months
Category type: time
Scale factor: 2360591.6
The SI base unit for time is the second.
1 second is equal to 4.2362262070237E-7 sidereal month.
Valid units must be of the time type.
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The sidereal month is defined as the Moon's orbital period in a non-rotating frame of reference (which on average is equal to its rotation period in the same frame). It is about 27.32166 days (27 days, 7 hours, 43 minutes, 11.6 seconds). The exact duration of the orbital period cannot be easily determined, because the 'non-rotating frame of reference' cannot be observed directly. However, it is approximately equal to the time it takes the Moon to pass twice a "fixed" star (different stars give different results because all have proper motions and are not really fixed in position).