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Homework Help: Ratio of Sun's Diameter to the Moon's

  1. Jun 6, 2009 #1
    1. The problem statement, all variables and given/known data
    During a total solar eclipse, your view of the Sun is almost exactly replaced by your view of the moon. Assuming that the distance from you to the sun is about 400 times the distance from you to the moon. Find the ratio of the Sun's diameter to moon's diameter.

    2. Relevant equations

    3. The attempt at a solution
    I started by drawing a diagram with the sun of diameter D1 to the left of the moon, which has a diameter D2, to the left of the Earth which has no relevant numbers attached to it like this:


    The distance from the moon to Earth is AU/400, and the distance from the Sun to the moon is AU-AU/400. This is where I get stuck. I don't see how you can say anything meaningful about the ratio of the Sun's diameter to the moons without knowing the distance from the top of the sun to the top of the moon, thus having a trapezoid to work with. Any tips or other ways of going about solving this would be helpful.
  2. jcsd
  3. Jun 6, 2009 #2


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    Homework Helper

    Don't you simply have similar triangles?

    Won't the ratio of the bases be in the same proportion to the ratio of their heights?
  4. Jun 6, 2009 #3
    I see what you mean. I'll post again if I have any more trouble.
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