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planetary orbital rotation [Q&A]


Vigneshwar of Poornaprajna College asks, what is the reason that the Earth and other planets revolve anti-clockwise around the Sun?

The interesting thing is not that they revolve anti-clockwise, but that they all go in the same direction. The sense of the rotation is a convention decided upon simply for the sake of definiteness. If one looks at the solar system from the other side, so to speak, it will appear as though the planets are revolving clockwise.

The fact that all the planets share the same sense of rotation is a pointer to their common origin in a single dust cloud. If the Sun and the planets are formed at different locations and then brought together, they would be expected to have random initial angular momenta and would be going around in every which way. On the other hand, if they condensed out of a large dust cloud, they would all share the same sign of the angular momentum, and barring some catastrophic dynamical events, would all be rotating in the same direction. As they indeed do.