Who discovered retrograde motion?

Retrograde motion was first described by Ptolemy as part of his solar system model. He described the motion of the planets in relation to the stars using the terms "retrograde" for westward motion and "prograde" for eastward motion.

Although Ptolemy's model of the solar system has since been discredited, the idea of retrograde motion is still widely used in astronomy. The modern use of the term "retrograde motion" refers to a celestial body's tendency to move in the opposite direction of other bodies in its system, such as the seven planets' movements and orbits in relation to the sun or their own moons.