Ellipses are found in both natural and artificial objects. The paths of the planets and some comets around the Sun are approximately elliptical, with the sun at one of the foci. The seam where two cylindrical pipes are joined is an ellipse. Artists drawing circular objects such as the tops of vases use ellipses to render them in proper perspective. In Salt Lake City the roof of the Mormon Tabernacle has the shape of an ellipse rotated around its major axis, and its reflective properties give the auditorium its unusual acoustical properties. (A pin dropped at one focus can be heard clearly by a person standing at the other focus.) An ellipsoidal reflector in a lamp such as those dentists use will, if the light source is placed at its focus, concentrate the light at the other focus.
Because the ellipse is a particularly graceful sort of oval, it is widely used for esthetic purposes, in the design of formal gardens, in table tops, in mirrors, in picture frames, and in other decorative uses.
Finney, Thomas, Demana, and Waits. Calculus: Graphical, Numerical, Algebraic. Reading, MA: Addison Wesley Publishing Co., 1994.
J. Paul Moulton