Why do the Planets in our Solar System Orbit the Sun Counter-Clockwise?

-- | March 18, 2013

Question: The planets in our solar system are orbiting the Sun counter clockwise, why? Do the laws of physics dictate that all planet orbit their respective stars counter clockwise or is it possible to have a solar system where the planets are in a clockwise motion around their star? — David

Answer: Most of the objects in our solar system, including the Sun, planets, and asteroids, all rotate counter-clockwise. This is due to the initial conditions in the cloud of gas and dust from which our solar system formed. As this gas and dust cloud began to collapse it also began to rotate. That rotation just happened to be in a counter-clockwise direction. There is nothing special about a counter-clockwise rotation, though. We could easily have found ourselves living in a solar system which was rotating clockwise about our Sun, if that was the initial state of rotation of the gas and dust cloud from which our solar system formed. Note, though, that there are two oddballs in our solar system that do not rotate in the same way as the rest of the planets. Uranus rotates about an axis that is nearly parallel with its orbital plane (i.e. on its side), while Venus rotates about its axis in a clockwise direction. These oddities are thought to be caused by events, such as collisions, which occurred during the formation of the solar system.

Jeff Mangum

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