In 1596 a young Johannes Kepler thought he had found the secret plan of the cosmos: the six known planets were spaced by the five perfect solids, nested one inside the other. Turn the model, zoom from Saturn down to Mercury, and see how close he came.
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Kepler's model
Thin spheres put each planet at its mean distance. Kepler gave each sphere a thickness, from the planet's nearest to its farthest point from the Sun, and fit the solids between the shells.
Mercury fit badly, so Kepler let its sphere touch the edges of the octahedron instead of its faces.
How close did he come?
| Solid | Between | Kepler | Real | Off by |
|---|
| Planet | Kepler | Real | Off by |
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The real ratios use today's mean distances and eccentricities. Within 5% is green, within 12% amber. Kepler, working from Copernicus's tables, found errors of the same size and blamed the tables at first. It was Tycho Brahe's better data that finally showed him the cup could not fit, and led him instead to elliptical orbits.