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Round and Round

December 5, 2009 Leave a comment Go to comments

It’s amazing to think that effects of the big bang are still around. Each time we witness the sun rise or set it’s because of the big bang.  Well, technically the sun the planet and us are all here because of the big bang, but the main point I’m trying to get at here is the rotation of the planet.  All of the planets in the solar system and even the sun rotates. With the exception of Venus and Uranus, they all rotate in the same direction, and it’s assumed that Venus and Uranus are all wonky because of a massive collision which caused them to change direction.

In very, very simple terms stars are formed by collapsing gas clouds and planets are formed by collapsing dust clouds.  When they start out they’re rather large. And by large, I mean up to a  light year across. As these clouds collapse, their rotations, no matter how slight, speed up. This is because angular momentum is conserved. The classic example of this is a figure skater with outstretched arms spinning faster and faster as she brings her arms closer to her body. As the cloud spins faster and faster, it tends to flatten out. This is because a disc is the best way to balance rotational momentum and gravitational collapse.

That’s why all of the planets in the solar system exist in the same plane and why accretion discs form around black holes, and why spiral galaxies are relatively flat. What’s so crazy awesome about this is that it’s intuitive and counter intuitive at the same time. Being on Earth and subject to Earth’s gravity (damn her!) we tend to think of things relatively flatly. While we may change our elevation by going up or down in a building, we still mostly move around in only two dimensions. In this sense, it’s only natural that all the planets in the solar system would exist in the same plane. However, outside of the steely, unyielding  grip of Earth’s gravity thing can move around in whatever dimension they damn well please (as long as it’s one of the main three). You’d think not being constrained would cause havoc on the rotational orbits of planets.

So what causes the sun and all the planets to rotate and all the planets to orbit in the same plane and all of the rings of those planets to orbit in a coplanar fashion is that billions of years ago when everything in the solar system was spread out across a cloud that was a light year across, that cloud was rotating. That rotation might’ve been slight, nearly imperceptible, but ti was definitely there. If it wasn’t there, all of the matter in the cloud would’ve just collapsed within the star. There would be no rotation to the star, but there would also wouldn’t be any planets that formed either.

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