Retrograde Motion of Planets

as seen from the earth, the motion of the planets from east to west relative to the stars, that is, opposite to the direction in which the planets revolve about the sun. The reason for retrograde motion is the terrestrial observer’s movement in space as a result of the earth’s revolution about the sun; this motion causes the observer to view a complex motion formed by the orbital motions of the observed planet and of the earth. Retrograde motion is observed for the superior planets near opposition and for the inferior planets near inferior conjunction.