Tycho & Kepler: The Unlikely Partnership That Forever Changed Our Understanding of the Heavens

Natural History, April, 2003 by Laurence A. Marschall

by Kitty Ferguson Walker & Company, 2003; $28.00

When Copernicus first proposed a universe with the Sun at its center in 1543, most of his sixteenth-century contemporaries regarded the idea as interesting but hardly revolutionary. Geometrically, it made little difference whether the Sun or the Earth stood still, and the crude observations of the time offered precious little evidence for telling one case from the other. Even those partial to a sun-centered scheme hedged their bets by harrumphing, at least in public, that, yes, this Copernicus was a clever fellow, but whatever the merits of his model, it was, after all, only a model. God could have chosen to make the Earth revolve around the Sun--but simply didn't.

In private, though, some of his contemporaries believed He did. Tycho Brahe, a Danish nobleman and amateur astronomer, thought Copernicus might be on to something. Tycho had seen a new star appear in the heavens in 1572, and he determined that it lay far beyond the Moon, in a region of the firmament where, according to the conventional astronomy of his day, nothing ever changed. Convinced that the old picture of the Earth-centered universe needed repair, Tycho proposed a hybrid system in which the Sun carried the orbiting planets around a stationary Earth. But Tycho knew that his proposal would be just another clever model without the support of careful astronomical measurements--measurements Tycho, with the right resources, would be happy to make.

King Frederick II of Denmark provided the money Tycho needed for his purposes, and granted him the little island of Ven (formerly Hven), at the mouth of the Baltic Sea, within view of Hamlet's fabled castle, Elsinore. There Tycho erected a battery of precise sighting devices (the telescope had not yet been invented); for almost thirty years, he and a staff of assistants compiled nightly observations of the positions of the planets.

As the data accumulated, however, Tycho found he lacked the mathematical skills, not to mention the time away from his aristocratic lifestyle, to make the calculations he needed to prove his point. By the last decade of the sixteenth century, the fifty-year-old astronomer was facing a midlife crisis, afraid that immortality was slipping from his grasp. Nicolaus Reimers Bar, a former assistant, had written a scurrilous book claiming Tycho's system as his own. Worse, Denmark had a new king, who was not inclined to continue his father's royal indulgence of Tycho's expensive hobby.

So Tycho packed up and wandered through Europe, eventually stopping in Prague. There he found a patron in Rudolph II, the Holy Roman Emperor--and, just as important, a new assistant named Johannes Kepler. Twenty-five years Tycho's junior, Kepler was an impoverished German mathematician on a quest to prove his own pet theory about the motions of the planets.

Science writer Kitty Ferguson begins her book with this meeting of Kepler and Tycho, and continues in flashbacks of the lives of the two great figures viewed against the unsettled backdrop of post-Reformation Europe. Taken separately, as many earlier biographers have done, the stories of the two astronomers seem merely eccentric: Tycho's artificial nose and Kepler's mother's trial for witchcraft are the only details my students usually remember. But Ferguson's approach, enlivened with the dramatic pacing of a mystery novel, shows beautifully how the obsessions of the pragmatic, imperious Brahe meshed perfectly with the obsessions of the idealistic, pensive Kepler.

They were an odd couple, indeed, and Tycho, weary and wary of the world by the time they met, resisted full collaboration with the young Kepler to the very end. As it was, he died scarcely a year after their meeting, and Kepler became heir to the finest observations of the planets ever made. From those, he showed conclusively that the Earth and the planets orbited the Sun--though in elliptical orbits, not the circular ones Copernicus preferred. Kepler's laws led, in turn, to Newton's laws of motion, which laid the groundwork for modern physics and cosmology. If the story of Tycho and Kepler was, as Kitty Ferguson's subtitle states, an "unlikely partnership," it was nonetheless a marriage made in heaven.

Laurence A. Marschall, author of The Supernova Story, is the W.K. T. Sahm professor of physics at Gettysburg College in Pennsylvania, and director of Project CLEA, which produces widely used simulation software for education in astronomy.