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.
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