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# Why is earth orbit elliptical?

I want perfect reasoning !

Please help me out!

### 4 Answers

- Anonymous1 decade agoFavorite Answer
Orbits are the natural outcome of two phenomena: momentum and gravity. Combining these as vector quantities produces geometrical constructions that are equivalent both topologically and mathematically to conic sections. Thus we expect the geometry of orbits to follow the geometry of conic sections.

A circle is a conic section, but there is only one arrangement of the conic-section criteria that produces it. An ellipse is a conic section as well, but many more combinations of the conic-section parameters produce it. Therefore we expect elliptical orbits to prevail in nature. Parabolic and hyperbolic orbits are also possible, naturally, since they complete the set of conic sections. But they are not generally closed orbits and therefore do not persist long enough for us to observe them.

Therefore the ellipse is the orbital shape most likely to arise in nature and to persist for long enough to characterize it.

- 1 decade ago
A perfectly circular orbit is too hard (rare) to achieve randomly. Imagine you want to put a satellite into the orbit and make it circular. For every distance from Earth, there is only one exact speed that will make the orbit circular - if you deviate from that speed even by a margin of one inch per year, the orbit will be elliptical (or spiral) - only slightly, but still. Now the solar system bodies were distributed more or less randomly. There was just no chance that they would hit the perfect combination of speed and distance to create circular orbits.

- 1 decade ago
There are three reasons actually:

1 gravitational pull of the sun is constant, so does not pull harder in one section of orbit than another

2 the earth spins on a tilted axis (hence it is already out of alignment with a perfect circle)

3 the moon has a very minor pulling effect, but can be seen during orbit

there are other reasons too, but this is the easiest way to explain