Kepler’s work Astronomia Nova and Harmonices Mundi provided the mathematical foundation for the heliocentric model of the solar system. He discovered that planets move in elliptical, rather than circular, orbits and that their speed varies with their distance from the sun. A key figure of the Scientific Revolution, his laws provided the essential groundwork for Isaac Newton's theory of universal gravitation. Kepler was also a pioneer in the field of optics and a deeply religious man who sought to understand the 'divine geometry' of the universe through mathematics.