This video compares and contrasts three different types of Geometries:

o Spherical Geometry

o Euclidian Geometry (the one we all know)

o Hyperbolic Geometry

With the wonderful property that

Spherical Geometry is sort of the opposite of Hyperbolic Geometry...

(Note to self, have to do more research on this!), i.e.,

Circumference of a circle:

Spherical: 2 x pi x sin(r)

Euclidian: 2 x pi x r

Hyperbolic: 2 x pi x sinh(r)