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Thread: Precession

  1. #1

    Precession

    We all know that the Earth's axis precesses like a top spinning down. Someone asked me the other day, and I couldn't find the answer, whether the Earth's ORBIT precesses around the sun?

    If the question isn't clear, I'll try to explain...

    The orbits of all the planets, including ours, are ellipses with major and minor axes. The axes of these ellipses has a configuration (if you could step out of the plane of the solar system and draw the lines). So the question boils down to: Is that configuration static, or do the axes themselves change configuration relative to each other over time (i.e. do the foci of the orbital path, themselves ever move).

    I've attached a graphic to explain what I mean. The little circle in the middle of the three orbits would be the central star, and the red/green/blue ellipses are orbital paths. "Before" would be the "non-precessed" orbits, and "After" would be orbits precessed with passage of time. Obviously the diagram is exaggerated, but I think it conveys the meaning better than my writing skills.

    So does this happen or do orbits more or less remain static?

    Does it happen in our solar system?

    And finally, if it does happen, are there any noticeable effects?
    Attached Images Attached Images

  2. #2
    Join Date
    Nov 2002
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    Quote Originally Posted by peco
    We all know that the Earth's axis precesses like a top spinning down. Someone asked me the other day, and I couldn't find the answer, whether the Earth's ORBIT precesses around the sun?

    snip...

    Obviously the diagram is exaggerated, but I think it conveys the meaning better than my writing skills.

    So does this happen or do orbits more or less remain static?

    Does it happen in our solar system?
    Yes, precession happens. It is mostly due to the perturbations of other planets. However, Mercury's orbit was found to be precessing more than predicted. Here is the amount of precession in GR for each of the planets.

    Quote Originally Posted by peco
    And finally, if it does happen, are there any noticeable effects?
    No, there are no noticeable effects, if you discount the fact that we can measure it. There are some ideas out there that it could have effected Earth enough to cause ice ages. But, there is no hard evidence of this.

  3. #3
    Earth = 3.839 arcsec/century
    Cool. They aren't exactly rocketing around I guess, but that was a good read.

    Thanks.

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