Ellipse
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An ellipse in a shape that looks like an oval or a flattened circle. A circle has one center, called a focus, but an ellipse has two foci. For example, an ellipse can be made by putting two pins into cardboard and a circle of string around those two, then putting a pencil in the loop and pulling as far as possible without breaking the string in all directions. The orbits of the planets are ellipses, with the sun at one focus and nothing at the other.
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