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Apogee and perigee

  1. Jan 11, 2005 #1
    i know the equation for both, apogee=a(1+e) perigee=a(1-e). i know the e stands for eccentricity, but what does the a stand for? thanks.
     
  2. jcsd
  3. Jan 11, 2005 #2

    Galileo

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    Since the sum of the apogee and the perigee will give you the length of the major axis of the ellipse, consider a(1+e)+a(1-e)=2a.
    So a is the length of the semi-major axis of the ellipse.

    It's the same 'a' as in the equation for an ellipse:

    [tex]\frac{x^2}{a^2}+\frac{y^2}{b^2}=1[/tex]
    (if b<a).
     
  4. Jan 11, 2005 #3
    thank you.
     
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