Hi. Unfortunately, it looks like my first ever PhysicsForums post isn't even about Physics. I'll think of a Physics-related question later. :) Anyway, I know that each ellipse has an inscribed circle and a circumscribed circle, but I was wondering about a third circle associated with an ellipse. Specifically, I'm thinking of the circle whose circumference is equal to that of the given ellipse. Is there a name for this circle? I swear I've been Googling this for hours now, but all I could find are pages showing how difficult it is to calculate the circumference of an ellipse. Thank you guys in advance!