Kepler’s Platonic solid model of the Solar System from Mysterium Cosmographicum (1596)

Plato believed the four earthly elements (earth, air, fire, and water) were formed from geometrically regular polyhedra. He argued that earth was a cube, air an octahedron, fire a tetrahedron, and water an icosahedron.

Kepler attempted to relate the Platonic solids not to the elements but to the five extraterrestrial planets. In his diagram below, the six spheres correspond to the six known planets — Mercury, Venus, Earth, Mars, Jupiter, and Saturn — with the solids set between them, thus explaining the distance relationships between the planets. The innermost polyhedron is the octahedron, then the icosahedron, dodecahedron, tetrahedron, and last the cube.

Kepler later abandoned the idea, but out of his work on this model came his three laws of orbital dynamics and the notion that the orbits of the planets are ellipses, rather than circles, which would change astronomy forever. Also, we got this pretty diagram out of it, so that’s cool too.