Tycho Brahe

Danish nobleman-astronomer who built Uraniborg, the most precise observatory of its age, and made the best naked-eye measurements ever taken.

In 1572 a 'new star' (a supernova) blazed out in the constellation Cassiopeia. Tycho measured its position so precisely that it had to be far beyond the Moon - shattering the ancient idea of an unchanging heaven of perfect spheres. His 1577 comet did the same to the solid crystalline spheres. Then his decades of Mars observations - accurate to about an arc-minute - became the raw data that Kepler turned into the laws of planetary motion.

Built on the medieval astronomical tradition and his own instrument-making (his quadrants and sextants were the state of the art). Enabled Kepler's laws (1609) - the foundation of every orbit in this bot, from the ISS to GPS. He also catalogued the stars, including Polaris, whose position his measurements help anchor.