Find eccentricity of orbit of comet

[moondawg]

Homework Statement

Find eccentricity for: a comet with mass 1.2x10¹⁰kg moves in an elliptical orbit around the sun. Its distance from the Sun ranges between .5AU and 50 AU.

Homework Equations

The Attempt at a Solution

I drew it out to try and viualize it and i know eccentricity is the distance between the foci divided by length of major axis but how do i find the foci?! So confused and I know this problem is probably extremely easy please help!

 

[Delphi51]

You need a different formula for eccentricity, involving the information given here. Check this out:
http://en.wikipedia.org/wiki/Eccentricity_(mathematics)#Values
The row for ellipses has eccentricity as a function of the a and b that you are given.

 

[tiny-tim]

hi moondawg!

Its distance from the Sun ranges between .5AU and 50 AU.
…
¬ i know eccentricity is the distance between the foci divided by length of major axis but how do i find the foci?! So confused and I know this problem is probably extremely easy please help!

yes, https://www.physicsforums.com/library.php?do=view_item&itemid=96" = f/a …

hint: what are perihelion and aphelion in terms of f and a ?