1619

Events in 1619 1

• 1609 – 1619 Kepler's laws of planetary motion Elliptical orbits — planets move in ellipses, not circles Between 1609 and 1619, Johannes Kepler published three laws describing planetary motion: (1) planets move in elliptical orbits with the Sun at one focus; (2) a planet sweeps equal areas in equal times; (3) the square of a planet's orbital period is proportional to the cube of its distance from the Sun. Based on Tycho Brahe's meticulous observations, these laws replaced 2,000 years of circular orbit theory and gave Newton the data to derive universal gravitation.