Monty's Book Of Why: Why Does The Earth Spin In The Direction It Does?

Monty's Book Of Why question for Tuesday is a big one, as big as the earth itself and as old as time.

A KMPH viewer who wants to know wrote in to ask, "why does the earth spin in the direction it does?"

So why does it spin as it does?

Frederick Ringwald, professor of physics at Fresno State, says that it is a "neighborhood" thing that started a long, long time ago.

The earth spins in the direction it does because that's the overall direction that all the planets orbit around the sun, counterclockwise, as viewed from over the north pole.

The sun and most of the planets rotate in this direction, too, although Venus is an exception.

The reason is because, when the sun and the planets formed 4.6 billion years ago, the cloud of gas and dust from which they condensed by gravity compressed by a factor of a trillion, trillion (that's a 1 with 24 zeroes after it), the chances of everything falling exactly radially inward was therefore about 1 in a trillion trillion: in other words, about zero.

An overall spin was therefore put on the solar system, and this is preserved in the spins and orbits of the sun and the planets.

Professor Ringwald also says, no one knows why Venus spins backwards: one idea was that it once had a moon that crashed into it, and reversed its rotation.

Now you know.

If you have one of those nagging questions for which you would like us to help you find an answer, include the title "Monty's Book Of Why," and send me your question.

You can e-mail it to, or post it onto our KMPH Fox 26 Facebook page.

So send us your questions and we'll have more answers for you in the next Monty's Book Of Why.