Apple

A surface of revolution defined by Kepler. It consists of more than half of a circular arc rotated about an axis passing through the endpoints of the arc. The equations of the upper and lower boundaries in the - plane are

(1)

for  and . It is the outside surface of a spindle torus.

It is also a quartic surface given by Cartesian equation

(2)

or

(3) Ref: mathworld.wolfram.com