Ask A Scientist© Astronomy Archive

Question:  Why does Venus rotate in a direction opposite the other planets?
Mr. Kiper's 5th period class

Answer 1:  Class, this is a very good question.  There is no good reason for the 
direction of rotation of any of the planets except what the motion of the matter 
locally that formed the planet.
It is actually surprising that so many of the other planets have similar
rotations directions.  Since there are only very small forces that slow planets
down, the rotations we see tell us something about the early motion of the
matter in the local region.  It is really fun to ask interesting questions. This  is what scientists spend
most of their time doing. Keep up the good work.
samuel p bowen

Answer 2:  The latest ideas I have read about are that planets from dust
particles and similar things hitting each other and sticking together till they
get bigger and bigger.  A planet like Venus probably got to be it's present size 
from the collision of smaller "planets".  The last two small planets to collide  in forming the planets
we see today determine it's rotation by how they happen to hit each other.  This 
is the best idea we have right now, but maybe someday you or someone like you
will come up with a better one.
Dan Koury
daniel n koury jr