- The time taken for the Moon to orbit the Earth. Several types of month are defined for different purposes, including the draconitic month, the time the Moon takes to reappear at the same node of its orbit on the celestial equator, which is the most realistic measure and totals 27.21 days, and the sidereal month of 27.32 days, the time the Moon takes to reappear at the same point in the sky relative to the fixed stars. This differs from the draconitic month because of the motion of the Earth and Moon around the Sun. The Anomalistic month of 27.55 days is the total time needed for the Moon’s cycle of slowing and speeding up in its orbit as it is carried nearer and farther from the Earth.
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