Apparent motion is used in at least two senses. First, it is used to refer to the motion of an object observed by someone who may also be moving relative to some rest frame. It is often used in this way in astronomy to describe planetary motions as seen by an observer on Earth. Second, it is used to refer to the perceived motion of an object when all that has been presented to the eyes is a series of stills. This is the principle that makes movies and TV possible.