Johannes Kepler

German astronomer and mathematician (1571 to 1630) best known for his three laws of planetary motion, which described the elliptical shape of planetary orbits and became foundational to modern astronomy and orbital mechanics. His 1609 book Astronomia Nova established the first two laws: that planets move in elliptical orbits with the Sun at one focus, and that a planet sweeps out equal areas in equal times. His 1619 book Harmonices Mundi established the third law, relating a planet's orbital period to its distance from the Sun. In October 1604 he began systematically observing a bright new star in the sky, an event now called Kepler's Supernova (SN 1604), one of the last supernovae observed in the Milky Way with the naked eye. The Kepler Space Telescope, launched by NASA in 2009, was named in his honor and used the transit method his own orbital laws help describe to catalogue thousands of exoplanets.