sidereal month

astronomy

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July 13, 2026

Quick Summary

A sidereal month is the time it takes for the Moon to complete one orbit around the Earth with respect to the stars. This period is approximately 27.32 days. It's important to distinguish this from a synodic month, which is the time it takes for the Moon to complete a cycle of phases as seen from Earth, averaging about 29.53 days. The difference arises because the Earth-Moon system is also orbiting the Sun during this time. The sidereal month is a fundamental astronomical measurement used in understanding lunar motion and in some calendrical calculations.123

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month
The sidereal month is the time needed for the Moon to return to the same place against the background of the stars, 27.321661 days (i.e., 27 days 7 hours 43 minutes 12 seconds); the difference between synodic and sidereal lengths is due to the orbital movement…
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The sidereal month is the time needed for the Moon to return to the same place against the background of the stars, 27.321661 days (i.e., 27 days 7 hours 43 minutes 12 seconds); the difference between synodic and sidereal lengths is due to the orbital movement…
Read More

Moon
Principal characteristics of the Earth-Moon system
322 days, the sidereal month, or sidereal revolution period of the Moon. Because the whole system is moving around the Sun once per year, the angle of illumination changes about one degree per day, so that the time from one full moon to the next is 29.531 days,…
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322 days, the sidereal month, or sidereal revolution period of the Moon. Because the whole system is moving around the Sun once per year, the angle of illumination changes about one degree per day, so that the time from one full moon to the next is 29.531 days,…
Read More