Retrograde motion

Retrograde motion is in the direction opposite to the movement of something else, and is the contrary of direct or prograde motion. This motion can refer to the orbit of one body about another body or about some other point, or to the rotation of a single body about its axis, or other orbital parameters such as precession or nutation of the axis. In reference to celestial systems, retrograde motion usually means motion which is contrary to the rotation of the primary, that is, the object which forms the system's hub.

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