Planets’ Rotation and Revolution

Posted: November 9, 2009 in Astronomy, Science
How do our planets rotate and revolve?

There is a difference between an object that is ‘rotating‘ and one that is ‘revolving‘: for example, planets rotate on their axes, but revolve around the Sun in their orbits. On that score, seen from above its North Pole, the Earth both rotates and revolves in an anti-clockwise direction.

As it turns out, almost everything in the Solar System revolves and rotates in anti-clockwise direction. Even the Sun spins on its axis in anti-clockwise motion, taking 25.4 days to complete one rotation (but slightly more at its poles).

There are, however, a few exceptions to the ‘everything goes anti-clockwise’ rule: Venus, Uranus and Pluto have ‘clockwise’ motion.

Why doesn’t the rotation slow down?

Well, actually, it is slowing down, but very slowly. The moon’s rotation, for instance, has already slowed to match its period of revolution around the Earth. Owing to tidal friction, the same process is taking place throughout the Solar System. however, there is so much rotational energy stored in the Solar Syatem that the spin-down period is measured in tens of billions of years, so there is no need to panic yet.

(pgs. 140-141, “Why is Uranus Upside Down?” by Fred Watson)

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