On this day, in 1571, the German astronomer Johannes Kepler was born. Kepler broke with the long standing tradition of explaining the motion of the planets with a combination of circular motions. He created a successful mathematical model of how the planets move around the Sun, summarised in his three laws of planetary motion. The first of these laws states that planets follow elliptical orbits, with the Sun located at one of the foci of this ellipse. These laws would later be explained by the Physics of the 17th century, namely by Isaac Newton.