Why is the time between two successive full moons different from the lunar synodic month?
We all know that the length of the synodic lunar month is 29.53 days. But if we calculate the time separating two successive New Moons from lunar ephemerides,we always get a different value. Could you please explain why? That is an excellent question! The answer is a bit complicated: The Moon moves around the Earth in a slightly elliptical orbit (the ellipse is close to a circle, but not quite a circle). As a result, the Moon moves faster near pericenter (where it is closest to Earth). Also, the orientation of the pericenter relative to Earth’s axis is fixed. However, new moon occurs when the Moon is in between Earth and Sun, and location of new moon with respect to the Earth’s axis varies as the Earth goes around the Sun. Let me give an example to try to make this clear: Assume that at some position, the pericenter occurs between Earth and the Sun and as a result, new moon occurs when the Moon is at the pericenter. Now, if the Earth was not going around the Sun, then the next new moon
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