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Sidereal month = the moon’s revolution time Synodic month = the moon’s phase cycle. A Note on Terminology:
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Sidereal month = the moon’s revolution timeSynodic month = the moon’s phase cycle
A Note on Terminology: Sidereal is derived from the Latin word for star (sidus). A Sidereal Period denotes the time it takes for an object (for example, the Moon) to return to the same place as seen with respect to the stars. Synodic is derived from the Greek word synodos, meaning a "coming together" (e.g., a Church "Synod"). The Synodic Period of the Moon is therefore the time between the apparent coming together of the Sun and Moon on the same side of the sky at successive New Moons. Synodic periods always require you to combine two Sidereal periods. In this case, we are combining the orbit of the Moon around the Earth (the Moon's Sidereal Period), and the Earth's orbit around the Sun (the Earth's Sidereal Period) together to compute the Synodic Period.