Kepler's model of the universe, 1619.
© Science Museum / Science & Society Picture Library
A plate from 'Mysterium cosmographicum' (The cosmic mystery) by Johannes Kepler (1571-1630) published in 1596. The different spheres represent the orbits of the planets, their ratios being equivalent to the distances to the planets. The outer sphere represents the orbit of Saturn. Kepler suggested that distances between the planets could be explained if different regular solids were drawn within the spheres. Although incorrect, this was the first mathematical cosmological model.