c. 1619-1641

English astronomer among the first to accept Johannes Kepler's theory of elliptical orbits. Having corrected Kepler's Rudolphine tables, Horrocks predicted and became the first to observe a transit of Venus (1639). He calculated an improved solar parallax value that challenged then-current estimates of the solar system's size, undertook the first continuous series of tidal observations, demonstrated the Moon's orbit is elliptical, and made tentative steps towards universal gravitation by recognizing the Sun's perturbing influence on the Moon's orbit.