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sidereal monthThe time taken by the Moon to complete one revolution around the Earth, measured with respect to a background star or stellar group considered fixed in position. The average time is 27.321 66 days.
Sidereal Month(religion, spiritualism, and occult)
A sidereal month is the period of time it takes the Moon to complete an orbit of Earth with respect to a fixed point in space, specifically, with respect to a fixed star (hence the designation sidereal, from the Greek sidus, meaning “star”). Because of the motion of Earth around the Sun, sidereal months are shorter than months measured from one new moon to the next. A sidereal month is 27 days 7 hours 43 minutes and 11.5 seconds in length.
the period of time between two successive arrivals of the moon, in its apparent orbital motion, at the same place (with respect to the stars) on the celestial sphere. Because of the irregularities of the moon’s motion—that is, deviations from the motion prescribed by Kepler’s laws—the length of a sidereal month is not constant and can vary by a few hours. The mean value of a sidereal month is 27.321661 mean solar days. The sidereal month is equal to the moon’s period of revolution around the earth, with respect to the stars. Because of the earth’s motion in its orbit, the sidereal month is shorter than the synodic month.