Tycho & Kepler

Kitty Ferguson

Read July-August 2007

All science writing should be this good.

Ferguson's book is ostensibly a biography of Tycho Brahe and Johannes Kepler. That itself warrants applause: whereas previous authors have focused on one or the other (often exaggerating their personalities or surroundings), there are fewer accounts of the interaction between the two. Their interaction is strangely coincidental (two of the greatest astronomers also happened to be at the peak of their powers during rare visible supernovae), fraught (the much-older Brahe was deeply concerned by a foolish supplication by Kepler to Brahe's competitor), dangerous (as deeply-religious Protestants caught amidst some of the worst religious turmoil), symbiotic (Brahe the brilliant “experimentalist” and Kepler the phenomenal theoretician each critically depended on the other), and ultimately foundational in shaping our views of the cosmos.

Had Ferguson done just that, it would suffice to make this book valuable. But she does three more things. First, she does not shy away from a little geometry; this book is illustrated with numerous drawings and appendices that explain basic astronomical concepts as well as you could possibly imagine without mathematics (or, perhaps, better than you could with only a little math). Second, she plunges Brahe and Kepler into the social turmoil of their times, so this is also a sliver of an account of the late Reformation and early Counter-Reformation; her sympathies are obviously with her long-suffering heroes, leaving us with a sense of just how arbitrary life was in those times. The heavy irony of two men who studied the stars out of a profoundly religious conviction, even as society surged and seethed around equally strongly-held religious convictions, can't be lost on many readers (but to Ferguson's credit, she leaves each reader to form their own views of such matters).

The third is perhaps most subtle but also the most important: this is a work of intellectual history. In the very best sense of historicist writing, Ferguson takes us into the mind of their contemporaries, and treats Ptolemy with the respect he deserves. Indeed, this book's subtley lies in Ferguson's unwillingness to buy into a mainstream view of “Copernicus right, Ptolemy wrong”, a position further complicated by Brahe's own take on planetary motion (which, Ferguson takes pains to point out, cannot be distinguished from the Copernican one purely on the grounds of mathematics). Instead of villifying past beliefs, Ferguson even makes a slight case (p. 63) for why astrology might be considered reasonable, but at all times keeps her own head level.

What Ferguson most crisply illustrates is how Brahe and then Kepler forced changes to our theories of the cosmos. Brahe's experiments with the nova's parallax demonstrate that the heavens must be changing, a radical departure from the long-standing belief that life on earth was temporal but the heavens were immutable: a revolutionary (ha!) revision that she takes pains to elaborate. And she stays at least a half-step ahead of her reader: at the crucial juncture of the story, she asks whether Kepler's calculation of Mars's orbit was merely curve-fitting (“the discovery that Mars's orbit was elliptical would not come—as one might naively suspect—from Kepler's simply plotting a number of points where Tycho had found Mars and then failing in the attempt to draw a circle whose rim would pass through all of them”, p. 299)—and then proceeds to spend a chapter explaining why not, and what Kepler in fact did, which was much more subtle (though it still depended critically on Brahe's extraordinary data). Even her throw-away remarks are insightful: for instance, she notes (p. 149) that Brahe's comet monograph included an overview of related work, a practice that is now routine and expected but was well ahead of its time.

Amidst all this experimental labor, mathematical insight and social turmoil, Ferguson does not lose the light touch. We get a glimpse of the practical genius behind Brahe when, having difficulty getting his instruments transported to Prague from Magdeburg, he successfully convinces the latter town's officials to use the return trip to import Bohemian wines (p. 265). And when Ferguson has finally laid out Kepler's triumph over Ptolemy, she proclaims “Kepler sent that ancient genius bumping off on a trick unicycle with the wheel attached off-center to nothing at all”. (By limiting herself to just one such caustic remark in the book, she offers a path that Berlinski might profitably have followed.)

There are a few small disappointments. Her account of Kepler's discovery of the laws of planetary motion are a little hasty, especially when it comes to deconstructing the Ptolemaic and Tychonic worlds. She tells us that Brahe could only observe his comet “for an hour or so just after sunset”, yet he “made observations three hours and five minutes apart” (p. 96). And finally, there is a extremely tantalizing digression into Kepler's study of optics (p. 292), but it is hasty and full of bald, unexplained declarations—just for one paragraph, Ferguson resembles a traditional science writer. But fortunately the moment passes and she returns to firm ground.

Then there are production values. In addition to the astronomy illustrations, there are two sets of color plates (even in the paperback edition!). Ferguson rightly appreciates Brahe's outstanding instruments enough to reproduce many of their original illustrations, which adds to the book's charm, and takes pains to explain them (as in her description of his quadrant, p. 121-5). Even the index is thorough. If only more authors cared as much!