Kepler (Johannes Kepler)

Johannes Kepler was a 17th-century mathematician and astronomer who discovered that planets move in elliptical, not circular, orbits around the Sun, challenging earlier ideas of perfect circles. He formulated three famous laws: (1) planets orbit the Sun in ellipses with the Sun at one focus, (2) a planet's speed varies depending on its distance from the Sun, moving faster when closer, and (3) there is a precise mathematical relationship between a planet's orbit size and its orbital period. Kepler's work greatly advanced our understanding of planetary motion, laying the groundwork for Isaac Newton's theory of gravity.