![Photograph of an illustration in Johannes Kepler, Mysterium Cosmographicum (1596)[Credits : By permission of the British Library]](http://media-2.web.britannica.com/eb-media/80/65980-004-06E52DAB.jpg)
Kepler used this illustration to help explain his first model of the cosmos, based on assigning the orbit of each of the known planets to a different, concentric sphere. The Platonic solids (tetrahedron, cube, octahedron, dodecahedron, and icosahedron) just fit between the concentric spherical shells within which, Kepler supposed, the six known planets revolved around the Sun. The cube stands between the shells of Saturn and Jupiter, the pyramid between those of Jupiter and Mars, and so on.
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