Kepler, Johannes (1571–1630)

Kepler’s mathematical analysis of Brahe’s observations of the motions of Mars enabled him to formulate the descriptive ‘laws’ of planetary motion, thus giving heliocentric astronomy an empirical basis far more accurate than it had before. He insisted that astronomy had to discover the causes of the motions that the laws described, in this way becoming a ‘physics of the sky’. In the pursuit of this goal, he formulated the notion of distance-dependent forces between sun and planet, and guessed that gravity could be explained as an attraction between heavy bodies and their home planets, analogous to magnetic action, thus pointing the way for Newton’s theory of gravity.