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Homework Help: Distance from one focus to the other

  1. Sep 15, 2007 #1
    Am I making this out to be too simple?

    I am given: The Sun's center is at one focus of Earth's orbit, how far from this focus is the other focus in meters and in terms of the solar radius?

    semimajor axis=a=1.5*10^11 meters.
    solar radius=R=6.96 *10^8 meters

    Now if c is the distance from the focus to the center of the ellipse,

    e=c/a implies c=ea.

    So the foci should just be 2ea meters apart...for which I am getting 5.01^9 meters. Which seems reasonable (I think:uhh:)

    Now I am having trouble with the latter part of the problem. I know it is just some sort of ratio. The text says 7.2 solar radii but does not give the answer in meters, so I cannot confirm that either.

  2. jcsd
  3. Sep 15, 2007 #2
    AGAIN I AM A JERK!! I got it.

  4. Sep 15, 2007 #3


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    Well, to find the ratio of the distance between foci to the "solar radius", you will need to know the solar radius! I take it that is the radius of the sun?
  5. Sep 15, 2007 #4
    Yes. I listed that in post #1. I figured it out, For some reason I was dividing wrong i.e, i had it inverted.

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