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Homework Help: What am I doing wrong?

  1. Nov 23, 2006 #1
    It is given that the perihelion for a certain comet is [tex]r_{per} = 0,2301 AU[/tex] and the eccentricity is [tex]e = 0,999846[/tex].
    My mission is to find the aphelion.
    I know that this is given by

    [tex]r_{aph} = a(1+e)[/tex]

    And I have used that

    [tex]a = \frac{r_{per} + r_{aph}}{2}[/tex]

    This gives me

    [tex]r_{aph} = \frac{r_{per}(1 + e)}{1-e}[/tex]

    and then I get that [tex]r_{aph} = 2988 AU[/tex]. This all seems very simple so what am I doing wrong?

    The correct answer should be [tex]r_{aph} = 4698 AU[/tex]
  2. jcsd
  3. Nov 23, 2006 #2
    Ok, I got it. Small variations in [tex]e[/tex] and [tex]r_{per}[/tex] will give a big difference in the aphelion. ;)
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