This description covers the phenomenon of retrograde motion of planets, which occurs when a planet appears to move backwards in its orbit around the Sun. This phenomenon occurs due to the relative motion of the planet and Earth, and can be observed from Earth. During this period, the planet appears to move
Retrograde motion in astronomy is, in general, orbital or rotational motion of an object in the direction opposite the rotation of its primary, that is, the central object. It may also describe other motions such as precession or nutation of an object's rotational axis. Prograde or direct motion is more normal motion in the same direction as the primary rotates. However, "retrograde" and "prograde" can also refer to an object other than the primary if so described. The direction of rotation is determined by an inertial frame of reference, such as distant fixed stars.