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The orbit of the earth

  1. Mar 15, 2005 #1
    i want to know why the orbit of the earth is not circular. is it becasue to the rotation axis of earth is not inclined. can anyone explain it?
    thx for kind attendion
  2. jcsd
  3. Mar 15, 2005 #2


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    All orbits are elliptical, not just Earth's. Elliptical is the "default" - a circular orbit is merely a unique case of elliptical where the apgoee and perigee are the same.

    Some bodies have very nearly circular orbits - and all will, (if left to their own devices) become circular after eons have passed.
  4. Mar 15, 2005 #3


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    It also depends on what tolerance you will accept and still call it circular. Earth's eccentricity is 0.0167. Expressed as only 2 digits, its 0.0. If you drew a perfect circle and an ellipse with an eccentricytiy of 0.0167 on a piece of paper, you'd never be able to tell the difference just looking at it.

    But what about a planet whose orbit is circular. Is it's eccentricity 0.0000? Maybe. But how about if you examine further to the right of the decimal. Is it's eccentricity 0.00000000000000? Probably not. So there's probably no such thing as a circular orbit.

    Earth's eccentricy varies over time. Sometimes it is much more circular than it is now. Jupiter is the main culprit in causing the pertabutions that cause Earth's eccentricity (and inclination, and longitude of nodes, and SMA) to periodically change. And Jupiter does the same thing to Mars, only to a greater extreme. But Mars' orbit goes through phases where at times it is nearly circular. Theories exist that this is what leads to ice ages.
  5. Mar 16, 2005 #4
    thank for your kind reply
  6. Mar 16, 2005 #5


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    With all the gravitational nudging that goes on in the universe, maintaining a perfectly circular orbit would be difficult.
  7. Mar 16, 2005 #6


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    Since most of the planets' orbits are *roughly* circular, fitting with the idea that all of the planets condensed from a spinning disk of gas and dust, a more interesting question may be: what happend to Pluto to make its orbit more eccentric...?
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