This Demonstration shows the stereographic projection of the five Platonic solids.

To understand stereographic projection, imagine that on top of the unit sphere there is a light and that the sphere is sitting on a plane. Any point on the surface of the sphere casts a shadow onto this plane, which is called the stereographic projection of the point. Now take a Platonic solid and blow up its edges until they lie on the sphere's surface. The stereographic projection of the Platonic solid is the shadow these lines cast onto the plane.