On his deathbed in 1601, the greatest naked-eye astronomer, Tycho Brahe, told his young colleague, Johannes Kepler, "Let me not have lived in vain." For more than thirty years, Tycho had made meticulous observations of planetary movements and the positions of the stars, from which he developed his Tychonic system of the universe-a highly original, if incorrect, scheme that attempted to reconcile the ancient belief in an unmoving Earth with Copernicus's revolutionary re-arrangement of the solar system. Tycho knew that Kepler, the brilliant young mathematician he had engaged to interpret his findings, believed in Copernicus's formation, in which all the planets circled the Sun; and he was afraid his system-the product of a lifetime of effort to explain how the universe worked-would be abandoned. In point of fact, it was. From his study of Tycho's observations came Kepler's stunning Three Laws of Planetary Motion-ever since the cornerstone of cosmology and our understanding of the heavens. Yet, as Kitty Ferguson reveals, neither of these giant figures would have his reputation today without the other; and the story of how their lives and talents were fatefully intertwined is one of the most memorable sagas in the long history of science. Set in a turbulent and colorful era in European history, at the turning point when medieval gave way to modern, Tycho & Kepler is both a highly original dual biography and a masterful recreation of how science advances. From Tycho's fabulous Uraniborg Observatory on an island off the Danish coast, to the court of the Holy Roman Emperor, Rudolph II, to the religious conflict of the Thirty Years' War that rocked all of Europe, to Kepler's extraordinary leaps of understanding, Ferguson recounts a fascinating interplay of science and religion, politics and personality. Her insights recolor the established personalities of Tycho and Kepler, and her book opens a rich window onto our place in the universe.