# Spheroidal Foci

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Spheroids are the surfaces of revolution of ellipses: a *prolate* spheroid is obtained by rotating about the major axis, while an *oblate* spheroid is obtained by rotating about the minor axis. When both axes are equal the spheroid becomes a sphere. In the prolate case, the foci of the ellipse are invariant under the revolution, while in the oblate they give rise to a "focal circle". This Demonstration shows how the foci vary with the shape of the spheroid.

Contributed by: Peter Falloon (March 2011)

Open content licensed under CC BY-NC-SA

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"Spheroidal Foci"

http://demonstrations.wolfram.com/SpheroidalFoci/

Wolfram Demonstrations Project

Published: March 7 2011