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Apr9-10, 09:16 AM
P: 36
Do you mean mean retograde orbital motion or retrograde rotation?

Well if you mean rotation, that is the spinning movement of the planet on it's own axis, in our Solar System, all the planets, except for Venus and Uranus, rotate in the same direction as their orbital motion and Sun's rotation. Well if you accept the idea that all the planets and stars formed from the same molecular cloud, and due to angular momentum conservation it would be expected that their rotation and orbital movement would be in the same direction. Collisions with other objects is one possible explication for their different movements.

Now if you mean orbital retrograde motion, actually, all of the planets orbit in the same direction as the Sun's rotation. But there is an effect, that if you were in the Mercury's surface, when Mercury is at perihelion, it's angular orbital velocity exceeds it's rotation velocity, so the Suns appears to move in the retrograde direction. Note that this an observational effect if you were at Mercury's surface.