The circumcircle of an ellipse, i.e., the circle whose center concurs with that of the ellipse and whose radius is equal to the ellipse's semimajor axis.
Auxiliary Circle
See also
Circle, Eccentric Angle, EllipseExplore with Wolfram|Alpha
References
Gallatly, W. The Modern Geometry of the Triangle, 2nd ed. London: Hodgson, p. 75, 1913.Montenbruck, O. and Pfleger, T. Astronomy on the Personal Computer, 4th ed. Berlin: Springer-Verlag, p. 62, 2000.Referenced on Wolfram|Alpha
Auxiliary CircleCite this as:
Weisstein, Eric W. "Auxiliary Circle." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/AuxiliaryCircle.html