The astronomer Johannes Kepler (1571–1630) was, along with Galileo and Isaac Newton, one of the founders of what nowadays we call science. In Kepler’s time those who practised science were known as natural philosophers, and theirs was largely a ‘pure’ discipline in which intellectual speculation was paramount and technology played only a small part – although Galileo was quick to point to the practical uses of the telescope in, for instance, seafaring and land surveying. Kepler’s three laws of planetary motion paved the way for Newton’s revolutionary celestial physics. Indeed, Kepler’s first law, which declares that the planets move not in circular but in elliptical orbits, was one of the boldest and most profound scientific propositions ever put forward: men, and women, had been burned at the stake for less.
Kepler was born in Weil der Stadt, a town near Stuttgart in the German duchy of Württemberg. His grandfather had been mayor of the town, but since his time the family’s fortunes had declined. Heinrich Kepler, the astronomer’s father, was a ne’er-do-well who earned his living, such as it was, as a mercenary and ran off to the wars when Johannes was five. He never returned, leaving his wife, Katharina, to bring up four children on her own.