SOLUTION: Suppose that the orbit of a planet is in the shape of an ellipse with a major axis whose length is 500 million km. If the distance between the foci is 400 million km, what is the

So, the major semi-axis length is a = 500/2 = 250 millions kilometers.


The focal distance is 400 millions kilometers; so the linear eccentricity "c" is half of it, i.e. c = 200 millions kilometers.


Then for the minor semi-axis of the ellipse "b" you have


    b =  =  = 150 millions kilometers.


The canonical equation of the ellipse is


     +  = 1,


where x a y are coordinates of the orbit in millions of kilometers.