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Brightness of Mars as observed from earth

  1. Aug 26, 2006 #1
    it is observed that Mars is somewhat brighter when in opposition (ie. sun- earth - mars in that order) that at other times. How can this be explained using
    a) The Ptolemaic model and
    b) The Copernican model of the solar system.
    (Assume that Ptolomy's construction describes the actual motion of the planet)

    can some one give me some sites and also an explanation
  2. jcsd
  3. Aug 26, 2006 #2


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    These sound an awful lot like homework problems. If so, you need to show some attempts before we can help you.
  4. Aug 26, 2006 #3
    In both models Mars is closest to Earth at opposition
    and i know that ptolemaic model use epicycles
    also that earth is always in the middle of the sun and mars which makes it brighter i think i m really confused on this question
  5. Aug 26, 2006 #4


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    In the Ptolemaic (actually Apollonian/Hipparchan) model the deferent of mars is just a circle around the earth as center(did they do deferents in your class?). So the position of the mars's epicycle on its deferent can't be the reason mars is closer to the earth at opposition (why? Draw a diagram.). What other degree of freedom does the deferent/epicycle system have? Whatever it might be it's a good place to look for the answer.
  6. Aug 26, 2006 #5
    thanks iv got it now, the retrograde causes mars to get brighter when in oppostion of the sun and earth
    Last edited: Aug 26, 2006
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