The Birthday of Johannes Kepler (1571)

Kepler discovered three laws of planetary motion: (1) ellipses with Sun at focus; (2) equal areas in equal times; (3) T² ∝ a³. He used Tycho’s data and geometry. Kepler’s second law is a consequence of conservation of angular momentum (mathematics of motion). His third law led Newton to inverse‑square gravity. Kepler also wrote on the polyhedral model of the solar system (Platonic solids), a beautiful but incorrect theory. He is the father of celestial mechanics – mathematics as the language of the heavens.