What Is Retrograde Motion?

Retrograde motion refers to the apparent or actual motion of a heavenly body when it moves in the opposite direction of most of the other bodies in the solar system. As viewed from the North Pole, all major planets around the sun, with the exception of Uranus and Venus, revolve counterclockwise around the sun, states Encyclopaedia Britannica.

Although it baffled many ancient scientists, current astronomers have since established that retrograde motion is an illusion caused only by the Earth’s motion. According to Scienceu.com, it was practically unbelievable that a heavenly body would change its direction, only to reverse it a while later.

Of all the satellites known in existence, only a minority tend to display retrograde rotation. These include Phoebe, Saturn’s outermost moon; Jupiter’s four outermost moons; and Triton, Neptune’s largest moon. The revolution of all the asteroids around the sun is known to be direct. Of all the known periodic comets, only a few move in a retrograde orbit.

According to EarthSky, the planets show a slight shift towards the eastern direction from night to night. However, the direction changes from time to time. For a few months, they may head east before changing course and resuming their easterly direction. This is a typical example of a retrograde motion.