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jgreen1124
2007-Oct-05, 09:57 PM
What makes the planets orbit the Sun in the same direction?
Better yet. It seems like everything in our Galaxy travels (orbits)around the center the same direction. What causes this to happen? If I'm wrong please correct me. I'm here to learn. :lol:

Thanks
Jay

Hornblower
2007-Oct-05, 10:19 PM
What makes the planets orbit the Sun in the same direction?
Better yet. It seems like everything in our Galaxy travels (orbits)around the center the same direction. What causes this to happen? If I'm wrong please correct me. I'm here to learn. :lol:

Thanks
Jay
According to our best theories, the planets condensed out of a slowly rotating mass of dust and gas, and inherited its direction of rotation. It would take a colossal disturbance by a massive interloper to flip any of them into retrograde orbits.

When you get out into the reputed Oort cloud, where the Sun's gravity is much weaker and the motions slower, relatively mild perturbations could result in retrograde objects such as Halley's comet.

I would make a strongly educated guess that a similar thing happened on a much larger scale to form a spiral galaxy.

EvilEye
2007-Oct-06, 02:24 AM
Aside from being tidally locked, planets while orbiting in the same direction do not have to always rotate in that direction. Heck. Even our moon does not orbit us in the same direction. It actually orbits backward, but we spin faster than its orbit, so it looks like it moves east to west.

Ken G
2007-Oct-06, 03:42 AM
Hang on, our Moon does not orbit backward, nor rotate backward, and indeed its rotation is tidally locked to its orbit. Also, a nitpick on Halley's comet-- it is not really an Oort cloud comet, which are long-period comets, but it is indeed a retrograde comet so it should have come from the Oort cloud and gotten perturbed into a special short-period orbit that is presumably quite rare and is really its own class. The point is, it's true that the weak gravity makes Oort cloud comets susceptible to perturbations, but they started as Kuiper belt comets where they formed, much closer to the Sun, so it took more significant perturbations to coax them out into the Oort cloud in the first place, in the process ruining their prograde orbits.

George
2007-Oct-06, 04:00 AM
What makes the planets orbit the Sun in the same direction?
As stated above, the planets most likely formed from a rotating disk, an accretion disk. This idea goes back to 1734 and later promoted by Kant, then formulated by LaPlace. More on this "nebular hypothesis" -- shouldn't this be of "theory" status? -- can be found here (http://en.wikipedia.org/wiki/Solar_nebula).

Looking down on our system, almost all objects in the solar system will travel counter-clockwise, unless seen from the southern hemisphere where they are moving clockwise. [Friday corn]Seen from the equator, therefore, they aren't moving at all. [/corn]

EvilEye
2007-Oct-06, 04:16 AM
Hang on, our Moon does not orbit backward, nor rotate backward, and indeed its rotation is tidally locked to its orbit. Also, a nitpick on Halley's comet-- it is not really an Oort cloud comet, which are long-period comets, but it is indeed a retrograde comet so it should have come from the Oort cloud and gotten perturbed into a special short-period orbit that is presumably quite rare and is really its own class. The point is, it's true that the weak gravity makes Oort cloud comets susceptible to perturbations, but they started as Kuiper belt comets where they formed, much closer to the Sun, so it took more significant perturbations to coax them out into the Oort cloud in the first place, in the process ruining their prograde orbits.

You know what? You are correct, and I was drinking....and feel stupid now.

If the moon truly traveled from east to west THAT would be retro.

I am sorry.

But it IS true that is not orbiting us the way it appears.

Ken G
2007-Oct-06, 12:32 PM
But it IS true that is not orbiting us the way it appears.

That's true, it's why the Greeks thought the Sun was orbiting us, but of course it isn't really.

George
2007-Oct-06, 01:39 PM
That's a relatively good point. ;)