Johannes Kepler (1571–1630)

The German mathematician and astronomer Johannes Kepler, who developed laws of planetary motion, was born in Weil der Stadt, now part of Germany. When he was 18 he began to study theology at Tübingen. All students studied geometry, astronomy, arithmetic and music, and it was here that Kepler first encountered Nicolaus Copernicus’s theory of a Sun-centred cosmos.

Kepler’s first astronomical work, Mysterium cosmographicum (The Cosmic Mystery), published in 1595 while he was teaching at Graz (now in Austria), explained the orbits of the planets in terms of a series of nested regular solids. This attracted the attention of Tycho Brahe, Imperial Mathematician to the Holy Roman Emperor Rudolf II, who invited Kepler to work with him in Prague. The move was timely for Kepler, who had been banished by the Catholic authorities in Graz for refusing to convert from Lutheranism.

In Prague, Kepler’s tasks included casting horoscopes for the emperor and working with Tycho on a star catalogue and astronomical tables which, on their eventual publication decades later, became known as the Rudolphine Tables after their patron. On Tycho’s sudden death in 1601, Kepler became Imperial Mathematician and obtained full access to Tycho’s jealously guarded data. He used Tycho’s detailed observations of Mars to work out its orbit, but he had to make thousands of calculations, describing the experience as ‘my war with Mars’. Eventually he realised that Mars’s orbit must be an ellipse rather than a circle, and published his discovery in Astronomia nova (The New Astronomy) in 1609. Kepler began a correspondence with Galileo, and made improvements to Galileo’s telescope design to make it better suited to astronomical use.

The ongoing political and religious upheaval of 17th-century Europe brought an end to this phase of Kepler’s career. He was forced to leave Prague after Rudolf’s abdication, and moved to Linz (now in Austria). His work was further interrupted when his mother Katharina was accused of witchcraft, a common persecution in Europe at the time. Kepler managed to appeal against the charges and his mother was released. Despite the disruptions, Kepler managed to publish Harmonices mundi (The Harmony of the World), which further expanded his studies of planetary motion, in 1619. His final years were largely spent on the move.

Web links:
Kepler biographical resources from the NASA Kepler mission,