Kepler's third law announced, 1619.
© Science Museum / Science & Society Picture Library
Page from 'Harmonices mundi' (The harmony of the world) by German astronomer Johannes Kepler (1571-1630) published in Linz, Austria in 1619. In this book Kepler announced his third law of planetary motion, stating that the square of a planet's periodic time is proportional to the cube of its mean distance from the sun. Kepler became a follower of Copernicus whilst studying theology and later worked with Tycho Brahe in Prague where he worked out the orbit of Mars. This led him to discover the laws of planetary motion. Kepler's three laws formed the basis of Isaac Newton's discoveries. Wilhelm Schickard designed the woodcut diagrams and illustrations for this work.