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Calculating semi major axis

  1. Feb 7, 2012 #1
    need help please in calculating semi major axis(SMA) of a binary star..
    if for example
    the orbital distance of star A is 50AU and star B is 100 AU from the centre of mass what would the SMA be?

    is it as simple as the half way point ? ie 75AU?

    thanks in advance
  2. jcsd
  3. Feb 7, 2012 #2


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  4. Feb 8, 2012 #3
    thanks for the link, i have had good rethink re. this..
    can a binary system that has a circular orbit have a SMA?
    or is that called a radii when it is not elliptical?
    so for the question concerned would the SMA simply be 100AU?
  5. Feb 8, 2012 #4
    if the speeds of the 2 stars are constant, would r ( distance between M and m fig. b ) remain the same .

    if so would r be the SMA? and not the distance between the centre of mass and the orbit of m (fig. a)?

    oh i am getting confused!!!!!!!

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  6. Feb 8, 2012 #5


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    From the article I linked above :

    If this is a simple two body problem with no other objects then the distance between M and m would stay the same.
  7. Feb 8, 2012 #6
    many thanks for your guidence!!!
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