Johannes Kepler-
Johannes Kepler was born on December 27, 1571, in Weil der Stadt, Württemburg, in the Holy Roman Empire of German Nationality. Johannes Kepler died in Regensburg in 1630. He thought this might be the key to the solar system. He truly believed in the Copernican system, so he saw the planetary orbits as six concentric circles. A natural question to ask is: why did the Creator make the orbits the particular sizes they are? He felt the universe would somehow show mathematical beauty or symmetry. Arguing in a way that Pythagoras and Plato would have sympathized with, he suggested that the orbits might be arranged so that regular polygons (triangles, squares, etc.) would just fit between adjacent ones, and maybe somehow this reflected some invisible underlying structure holding it all together. Disappointingly, he found it just didn't work out---the ratios were wrong. Then he had a real inspiration. The universe was really three-dimensional, and instead of thinking about circles, he should be thinking about spheres, with the planetary orbits being along the equators. Thinking in three dimensions, the analogue of the above diagram would be two concentric spheres with a tetrahedron between them, so that the outer sphere passes through the vertices of the tetrahedron, and the inner sphere touches all its sides, but is completely contained in the tetrahedron. Now came the really exciting part-there were just six planets, so five spaces between spheres, and there are just five regular solids! Thus, if the distances came out right, the theory provided a complete explanation, in terms of an elegant geometric model, of why there are just six planets, and why they are spaced as we find them. Actually, the distances still don't come out right, especially for Jupiter, but Kepler was so sure of the rightness of his scheme, that he blamed the discrepancies on errors in Copernicus' tables. He modestly titles his work Mysterium Cosmographicum--the mystery of the universe (explained). The crucial illustration from his book is shown below, the outer sphere being the orbit of Saturn, and the central part is shown magnified at top right.
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