1.26 The retrograde motion of Mars according to the heliocentric model

When planets orbit the Sun, those nearer the Sun orbit faster than those farther out. Thus, a planet will overtake and pass a more distant one. During most of its orbit, we see Mars moving eastward against the background stars, but when we pass it, Mars will for a period of several months appear to move "backwards" (that is, westward) against the stars. Astronomers call this backward drift "retrograde motion."