Mysterium Cosmographicum

Johannes Kepler's Mysterium Cosmographicum is Kepler's own first published statement of his youthful theory that the spacing of the six known planetary orbits reflects the geometry of the five Platonic solids nested between them, in the order Mercury, octahedron, Venus, icosahedron, Earth, dodecahedron, Mars, tetrahedron, Jupiter, cube, Saturn. As Kepler's own primary text, it is the direct and authoritative source for what he actually proposed and in what order, rather than a later paraphrase of it. Its limit is that it records an early hypothesis Kepler himself later replaced with the three laws of planetary motion that made his lasting reputation; he did not abandon the polyhedral model outright, republishing it with notes in a 1621 second edition, but the astronomy of his own later work superseded its predictive claims. Cite it for what Kepler proposed and when, not as a functioning astronomical model.