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Why do planets revolve around the sun in an elipical orbit, instead of circular?

Because nothing in the universe is exact. I mean, to put something in a perfect circular orbit (which is possible), everything about the release has to be perfectly exact. When you are talking about bits of rock that fell into the suns orbit or were spun off from the surface or whatever, this is highly unlikely. Add in factors like other random bits of rock coming in from nowhere and running into the orbiting bits, and the likelihood of a perfect cicular orbit is, well, impossible.

A circle is just a very special ellipse, one that you probably won't find in a giant body orbiting another. A stable orbit is fairly easy to acheive, all the object has to have is enough velocity in a rougly correct direction, and it'll stay orbiting in a more or less stable manner.
 
Originally posted by: LordMorpheus
Because nothing in the universe is exact. I mean, to put something in a perfect circular orbit (which is possible), everything about the release has to be perfectly exact. When you are talking about bits of rock that fell into the suns orbit or were spun off from the surface or whatever, this is highly unlikely. Add in factors like other random bits of rock coming in from nowhere and running into the orbiting bits, and the likelihood of a perfect cicular orbit is, well, impossible.

A circle is just a very special ellipse, one that you probably won't find in a giant body orbiting another. A stable orbit is fairly easy to acheive, all the object has to have is enough velocity in a rougly correct direction, and it'll stay orbiting in a more or less stable manner.
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are you serious?
 
A circle is a special case of an ellipse. Given the right set of circumstances, an orbit could be circular (but it was still be elliptical). Technically, a planet orbit can be any form of conic section. But for the orbit to be closed, it'll be an ellipse. For example, parabolic "orbits" are possible but the object will only pass the Sun once before being flying off into space never to return.

The real answer to your question, though, requires you to derive Kepler's First Law (the one that says orbits are ellipses) using conservation of energy and Newton's Law of Gravitation. Basically a conic section is the result of an inverse square law...

 
Originally posted by: LordMorpheus
Because nothing in the universe is exact. I mean, to put something in a perfect circular orbit (which is possible), everything about the release has to be perfectly exact. When you are talking about bits of rock that fell into the suns orbit or were spun off from the surface or whatever, this is highly unlikely. Add in factors like other random bits of rock coming in from nowhere and running into the orbiting bits, and the likelihood of a perfect cicular orbit is, well, impossible.

A circle is just a very special ellipse, one that you probably won't find in a giant body orbiting another. A stable orbit is fairly easy to acheive, all the object has to have is enough velocity in a rougly correct direction, and it'll stay orbiting in a more or less stable manner.
Click to expand...

And you have the nerve to question God's abilities? :roll:

It's elliptical because He made it so.
 
Originally posted by: mwtgg
Originally posted by: LordMorpheus
Because nothing in the universe is exact. I mean, to put something in a perfect circular orbit (which is possible), everything about the release has to be perfectly exact. When you are talking about bits of rock that fell into the suns orbit or were spun off from the surface or whatever, this is highly unlikely. Add in factors like other random bits of rock coming in from nowhere and running into the orbiting bits, and the likelihood of a perfect cicular orbit is, well, impossible.

A circle is just a very special ellipse, one that you probably won't find in a giant body orbiting another. A stable orbit is fairly easy to acheive, all the object has to have is enough velocity in a rougly correct direction, and it'll stay orbiting in a more or less stable manner.
Click to expand...

And you have the nerve to question God's abilities? :roll:

It's elliptical because He made it so.
Click to expand...

Yep. He knows.
 
It's a government conspiracy. It's not even possible under the laws of physics for a planet to orbit a "star" (I bet you believe that one, too).

The truth is out there.
 
Cuz space is all rubber-bandy-like. The planets fly out then they snap back like volleyballs on bungie cords.


Um, yeah God did it.
 
Let's say for argument's sake that all of the planets started in a perfectly circular orbit for some reason (they didn't).

You know that the sun exerts a gravitational attraction on the planets, allowing them to have a nice circular orbit. However, there are other planets in the system that also exert gravitational forces on all of the other planets in the solar system. How does one maintain a perfectly circular orbit with so many forces acting on every planet? It's almost impossible.

In fact, the sun feels the attraction of these planets slightly, but the total of this force is not significant enough to make the sun move in a noticable way.
 


I think that both these answers, below, have correct info,
and also there is the problems of the angle of the moment of inertia,
the not exact mass of the center of gravity of each planet/moon
and much more Physics, and Calculus needed to be exact than I know.

Originally posted by: JulesMaximus
The universe is an imperfect place.
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Originally posted by: LordMorpheus
Because nothing in the universe is exact. I mean, to put something in a perfect circular orbit (which is possible), everything about the release has to be perfectly exact. When you are talking about bits of rock that fell into the suns orbit or were spun off from the surface or whatever, this is highly unlikely. Add in factors like other random bits of rock coming in from nowhere and running into the orbiting bits, and the likelihood of a perfect cicular orbit is, well, impossible.

A circle is just a very special ellipse, one that you probably won't find in a giant body orbiting another. A stable orbit is fairly easy to acheive, all the object has to have is enough velocity in a rougly correct direction, and it'll stay orbiting in a more or less stable manner.
Click to expand...

 
Originally posted by: PhoenixOrion
too technical and that's why i visit Highly Technical forum from time to time.
Click to expand...



its not really, read up on keplars laws of planetary motion, the math is pretty simple and straight forward, any highschooler can sort it out.
 
Originally posted by: dethman
because god said so. seriously i that's what they tell me on sunday mornings in that big pointy building.
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P&N is that way, jackass. religion gets bashed enough as is, no need to stoop down to P&N levels - every possible opportunity
 
Well, there are other gravitational forces and also that the planets have not been orbitting long enough to correct their orbit completely. That is why the moon is moving away from earth like an 1.5 inches per year. The moom used to be 40k miles from earth, now it is 250k.
 
Let's assume that the earth's orbit was circular, at least for a relatively short amount of time. As soon as the first meteor "becomes smashed into us", we have an elliptical orbit. That simple enough to understand without a long mathematical explanation of why an ellipse is a stable orbit?

Other things to look at: objects can have a parabolic or a hyperbolic "orbit" - that is, we see them entering the solar system once, and they swing around the sun and head out, never to return.

 
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