Why does the planets take an eliptical orbit around the sun?

Question

ie.why is it not taking a circular path?and also wat is the reason of this rotation ?

Answer 1

the gravitational pull of the planets on each other plus the general chaos that the solar system was born from prevents perfectly circular orbits.

Answer 2

This is due to the sun's gravity...the reason the path is eliptical is because earth is moving at a velocity that is perpendicular to the suns gravitational pull.

Answer 3

A circular path *is* an elliptical path.  It just happens to be an ellipse in which each point is equidistant from the center.  So given that a circle is just a special case of an ellipse, it's hardly surprising that elliptical orbits are the order of the day.

Suppose you're on the Moon, where there is essentially zero air resistance.  If you drop a ball, it falls down to the surface, although it takes longer to do so than you're used to, because the gravity on the Moon is only one-sixth of that on the Earth.

If you throw it forward, on the other hand, it arcs downward, and the harder you throw it, the further out it goes before it hits the ground.  If you throw it just hard enough--much harder than you could physically throw it with just your arm strength--it would go so far out that the downward arc of the ball matches the downward arc of the Moon's surface (as seen by you).  The ball is then in a circular orbit around the Moon, and this speed is often called the "orbital velocity."

If, instead, you throw the ball just a little bit less hard, it goes a long way around the Moon before striking it.  What curve describes the arc of that ball?  If you've taken elementary physics, you might guess that it takes a parabolic path, which is almost right, but in fact, it is an ellipse.  The only reason the ball doesn't come back to you is because the Moon "gets in the way."  In fact, even if you don't throw it very hard at all, it still takes an elliptical path--albeit one that's quickly interrupted by the Moon's surface.

If you throw the ball just a little bit *harder* than you would need in order to maintain a circular orbit, then it goes further out before arcing "downward."  But the ball still returns to you after going around the Moon, provided you haven't thrown it so hard as to escape the Moon's gravity altogether (the "escape velocity").  That orbit stretches further from the Moon's center than the circular orbit; it is also elliptical.

In short, at any speed up to the Moon's escape velocity, a thrown ball will take an elliptical orbit, but only at one speed--the orbital velocity--will that orbit be circular.  In other words, a circular orbit is a very special case of the elliptical orbit, and that's the case whether you're talking about a ball in orbit around the Moon, or the planets in orbit around the Sun.

So instead of being somewhat surprised that planetary orbits are all elliptical and not circular, maybe you should be surprised that they are so close to being circular!  The reason for that is that elliptical orbits are not very stable dynamically.  If a planet were in a very elliptical orbit, other planets would tend to yank on its orbit to make it even more elliptical, and eventually eject it out of the solar system entirely.  This probably even happened, very early in the solar system's history, and there is a small chance it could still happen: Recent simulations have suggested there is about a 1 to 2 percent chance that Mercury, Venus, or Mars could be ejected from the inner solar system, sometime before the Sun becomes a red giant and engulfs Mercury and Venus (and possibly the Earth).

EDIT: If you're curious about why the orbits are ellipses and not some other non-elliptical oval, that's a different and much deeper question.  The short answer is that Newton showed, in his Principia Mathematica, that an inverse-square law of gravity always leads to planets orbiting in conic sections (circles, ellipses, parabolas, or hyperbolas).  There is no easy answer as to just why it must be a conic section, other than the mathematics, although I try to give a simpler demonstration here:

http://astro.isi.edu/notes/gravity.html

A somewhat more rigorous (but also more geometrical, dense, and opaque) demonstration can be found here:

http://astro.isi.edu/notes/newton.pdf

Answer 4

A circular orbit is a precise mathematical concept which can't be realised in practice. To orbit the sun in a circular orbit, a planet would have to maintain exactly constant distance and speed. Tbe solar system has settled down from an intially chaotic system so that the major planets are nicely spaced out and never approach one another, but the chances of a planet ending up in a perfectly circular orbit out of this original chaos are vanishingly small.

Moreover, this overlooks the gravitational attractions of the planets on one another, which ensures that even a circular orbit would have been disturbed into an ellipse before very long.

Answer 5

A circle is a "perfect" geometric shape.  Perfection is only a concept, nothing is really perfect.  Of all of the orbits of all objects in the universe, somewhere there is probably an orbit which is really close to perfectly circular.  If there were two, and only two objects in the universe, then you might be able to have this perfection.

Orbits can also be parabolic, like most comets.  These are conic sections, geometrically speaking, which also includes hyperbolic.  This would not be an orbit, as it is an open ended shape, it won't return to orbit again.

As for rotation, I don't understand the question in this context, but pretty much every astronomical object rotates, it is a form of motion, everything is in motion.

Answer 6

Aristotle believed that all orbs in space are perfectly spherical and the path of all orbs is circular; may be this wrong presumption is due to the fact that circle is regarded as the most perfect geometric figure, and that he expected that everything in the universe is perfect.

The reason for elongated circular path, perhaps, is due to the change in the gravitational pull exerted on the orbs by the sun. While a moving object tends to  escape from its path the centre which holds it keeps pulling it back. That is the reason why planets and satellites keep revolving round some centre. Thus elliptical orbits are formed.