This page will discuss the retrograde rotation of Venus. Venus moves around the Sun in the same direction (considered to be eastward, or direct motion) as all the other planets, but its rotation is backwards relative to that orbital motion. This could be thought of as being due to some ancient collision which knocked it backwards, or simply due to the combined effects of all the random collisions which built it up just happening to cause it to rotate backwards, or there could be some completely different explanation, involving gravitational effects due to other bodies -- all of these ideas have been discussed at one time or another...

(refer to Rotation Period and Day Length for a detailed discussion of how rotation periods are related to day length)