As the Moon orbits Earth, it rotates at such a rate as to keep the same face aiming our way… but not exactly the same face, as shown in this excellent video from NASA’s Goddard Space Flight Center (lovingly annotated by the Bad Astronomer himself, Dr. Phil Plait.)

The Moon has a slight wobble to its axial rotation, and over the course of a month its orientation shifts slightly — an effect known as…

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