Question 548404
 I have an astronomy program that provides information on known comets. They provide only two pieces of information: Perhelion and eccentricity. 
I have gone through a number of books and web pages both for astronomy problems and math problems trying to find out how to find out the length of the major axis.
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Draw an ellipse with major axis = 2a
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Put in the center, the focus, and the object at perigee.
If the focus is the sun:
perihelion = distance from focus to object = p
distance of focus from center = c
Eccentricity = c/a
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a = p + c
a = p + ae
a-ae = p
a(1-e) = p
a = p/(1-e)
2a = 2p/(1-e)
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You are given p and e so you can determine major axis = 2a
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Cheers,
Stan H.
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