Retrograde Motion

Since the Earth travels faster in its orbit that do the superior planets, it overtakes and passes them at times during their mutual orbits around the Sun. As the Earth begins to overtake Mars, for example, Mars will appear to slow its eastward motion among the stars. Then just as the Earth overtakes it, Mars will appear to loop slightly westward for a short time. Once the Earth is well past Mars, that planet will resume its eastward motion among the stars.

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