sidereal month

noun

plural sidereal months

: the mean time of the moon's revolution in its orbit with reference to a star's position : 27 days, 7 hours, 43 minutes, 11.5 seconds of mean time

The Moon rotates on its axis once every 27.32166 days. This is the sidereal month and corresponds to the time taken for the average period of revolution of the Moon about the Earth.

—Stuart Ross Taylor

Word History

First Known Use

1833, in the meaning defined above