What is retrograde motion? | EarthSky 2/6/17, caused by Earth’s passing these slower-moving outer worlds. But there’s a real retrograde motion, too. A photomosaic from Voyager 2 of Neptune’s largest moon, Triton. The moon orbits Neptune opposite the direction that the planet rotates. Does this mean that Triton came from the Kuiper Belt and was eventually captured by the ice giant? NASA / Jet Propulsion Lab / U.S. Geological Survey.
Venus is one unique planet when it comes to rotational motion. It takes Venus 243 Earth days to completely rotate on its axis, but just 225 days to orbit the sun. Venus also is one of two planets that rotates in reverse, a phenomenon called retrograde motion, which according to most theories is due to an ancient planetary collision.