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Orbiting planets

  1. Dec 6, 2013 #1
    I am not so good in astronomy but i had desire to know what was in there right from my childhood. can you please clear me the following questions i have in my life about space..
    1.Why does planets follow the same path or trajectory to orbit around the sun and why do they revolve around the sun?
    2.Is there any force that governs the movement of planets orbiting around the sun?
  2. jcsd
  3. Dec 6, 2013 #2

    Simon Bridge

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    Can't say why - that would involve metaphysics - but there are lats of ways that the situation we see could have come about.
    The established model involves most of the planets and the Sun forming from the same base material a long time ago - long enough for almost all those objects that do not orbit the Sun to have left. Studies of exoplanets are challenging the details of these ideas though.

    Yes. The Sun and the Planets move about each other according to the Law of Gravity.
    http://solarsystem.nasa.gov/yss/display.cfm?ThemeID=28 [Broken]
    Last edited by a moderator: May 6, 2017
  4. Dec 6, 2013 #3
    Because the gravity of the Sun is the major force governing their motion. All other forces are minor. Any body in motion near the Sun feels the pull of its gravity, and little else. Because that force is directed at the Sun, the path tends to curve around the Sun. As there is little or no force to pull the body out of that curve (for instance, perpendicular to the plane of the curve), the curve tends to remain in the same plane.

    They revolve around the Sun because they are in motion - if they were at rest relative to the Sun, they would fall straight into it. If you work out the equations of gravitational motion, any object in motion around a massive body goes into an orbit about it, of one sort or another.
  5. Dec 6, 2013 #4

    Simon Bridge

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    Not all free fall trajectories are cyclic though...
    The trouble with answering the questions like this is that the answer tends to beg the question:
    how come the planets all go around the Sun?
    because all other forces are minor.
    how come all the other forces are minor?
    Because, if they were major, then the planets involved would no longer be here
    ... and so on.

    There are probably a lot of bodies in the solar system that are just passing through like this... orbit for a while in a highly eccentric fashion for a while then get kicked out when they come too close to a planet.

    It's not entirely clear what would constitute a satisfactory answer here.
    I'm hoping the reading will help OP clear up some concepts, then, if the questions remain, they can be asked again in a way that makes it easier to work out where the confusion lies.
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