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.
This artist's illustration represents the variety of planets being detected by NASA's Kepler spacecraft. Scientists now say that one in six stars hosts an Earth-size planet. CREDIT: C. Pulliam & D. Aguilar (CfA)