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Johannes Kepler and the New Astronomy - On Tycho's Island
June 23, 2000

Jay Pasachoff assesses books on two highly influential astronomers.

Copernicus to Tycho to Kepler to Galileo to Newton. The main line of progress in understanding our universe has long been clear. But the role of Tycho Brahe has been more shadowy and obscure than those of the others. He is more often identified merely with providing the observations that Kepler transformed into the important laws of planetary orbits that we now know govern not only the planets and comets in our solar system but also at least 30 planets around stars other than our sun. In On Tycho's Island , John Robert Christianson culminates a long-standing interest by analysing the key period of Tycho's life and showing that his was the first to set up a modern scientific institution, with colleagues and assistants as well as a lasting structure.

Tycho and his family ranked high in the nobility, and it was this rank that enabled him to receive the substantial support from the Danish king, Frederick II, that allowed him to take over the island of Hven, not far from the royal castle at Elsinore. Christianson's book is really about the sociology of science, and readers who are not familiar with the astronomical work of Tycho and its importance will not find in it the reasons why they should be interested. The book is in two parts, a 248-page section about Tycho's life and work and then a 132-page section of short biographies of the dozens of assistants whose names have been singled out each time they appear (distractingly) in bold in the first section.

Christianson concentrates on the Hven years of 1576 through 1597, from the dedication of Uraniborg to the time when Tycho and his large entourage left for the Continent, eventually winding up in Prague. He deals only briefly with the two incidents perhaps best known from Tycho's life: first,how "the bridge of his nose" was hacked off in a traditional student duel and, second, how he died. In connection with the latter, Christianson does not mention the traditional story of Tycho's death from an infection of the bladder, which either burst or became infected by his having remained too long at table at a dinner because of etiquette, and states baldly "his body heavy with quicksilver from numerous Paracelsian elixirs, Tycho Brahe died on 24 October 1601".

Some of the most interesting discussion covers the relations of Tycho with his family. Since he was of the nobility, his marriage with Kirsten Jorgensdatter, a commoner, could never be made official, in spite of their children. Indeed, many of his actions in later years were aimed at finding ways for his children to inherit his wealth. The sad story of how his daughter Magdalene Tygesdatter (who could not have the noble name of Brahe) was jilted, and how resulting court cases coloured Tycho's interactions with the powers that be, is told at great length and gives spirit to the narrative.

Those looking for female scientists will seize on the mentions of Tycho's sister Sophie, who helped him with some early observations, such as the lunar eclipse of 1573, when she was 14. However, it is her unfortunate chasing of a no-good astronomer-alchemist husband that is discussed at length. Sophie Brahe's work on genealogy, not astronomy, took up her later years. Less interesting for a general reader would be such technical discussions as the following: "Rosencrantz opened his heart and laid out his orthodox, German-inspired religious views, while Tycho listened with care and gently replied with his own philosophical theology of Hermetic and Platonic Philippism, touched with Ramism and unified by an emblematic world view."

Though some terms are described in a glossary, such basic and important terms as "lunar theory" and "solar theory" are not defined. I awaited a discussion of the translation of the title of Tycho's important book, Astronomiae Instauratae Progymnastmata , but Introduction to the Instauration of Astronomy did not help. Neither does Christianson discuss just what numerous named instruments did or how they were used. For example, what was involved when "Christian Riber used his portable radius to observe a lunar eclipse of 1592 in Wittenberg and a solar eclipse of 1593 in Zerbst"? How were "the trigonal sextant, the tripartite arc" and the four parallel sights along pinnules used? (I suspect the author meant that the first of these had to be mounted vertically as shown in a drawing and, as would be reasonable, not horizontally as it is stated, to measure altitudes.) In the discussion of real estate on Hven, why should we not be told what a "hundred baliff" or a "demesne" is, or be able to refer to the terms in the glossary?

Tycho's relations with young Christian IV were not good, and some of the support he had previously received for Uraniborg was taken away. With hindsight, if Tycho had tended more to his responsibility to maintain a certain royal chapel, the need to leave Denmark might have been averted. In any case, the temporary exile Tycho foresaw turned into a permanent one.Science benefited from the circumstances that brought the young Johannes Kepler to Tycho's entourage in Prague and left Kepler with the observations he needed to formulate his theory. (Kepler receives a seven-page mini-biography in part two of the book.) So though I was glad to learn that normal consumption of beer in Denmark at the time was four to eight quarts a day, and that "in 1589, his dwarf jester tried to flee and was beaten", I would have liked more discussion of how the sociology of Tycho's Uraniborg tied in with the science that resulted. The fact that Victor Thoren's book The Lord of Uraniborg (1990) is a thorough biography should not have prevented Christianson, if he wanted to appeal to general readers, from discussing Tycho and his scientific importance more comprehensibly, even in the context of his sociological book.

James Voelkel's short biography of Kepler is a wonderful book. Voelkel carefully but expeditiously leads the reader through Kepler's life, describing the long-term importance of events. And the events span not only science but also Kepler's three unfortunate encounters with the Counter-Reformation and a variety of political and religious events in Europe, all explained so that the reader can readily see how they fit together. As Voelkel felicitously writes: "The meeting of Johannes Kepler and Tycho Brahe on February 4 1600, is extraordinarily significant in the history of science. The two men could not have been more different. Tycho was a nobleman, self-assured, domineering and combative. Kepler was a commoner, sincere, reflective, peace-loving and unassuming. Yet they fit together like a lock and key."

This book, like others in the Oxford Portraits of Science series, is officially meant for young adults but is, in effect, a readable survey for anyone. We learn about Kepler's search for harmonies in the universe as well as side investigations of optics and even the capacity of wine barrels. We see how he was led to the discovery first of the law of equal areas, that the line joining the Sun and a planet sweeps out equal areas in equal times, and then of what we now call Kepler's first law, that the planets orbit the sun in ellipses with the sun at one focus. Kepler's third law, linking the cube of the radii of planets' orbits with the square of their periods, is justified simply and worked out numerically in an inset box. Throughout, we learn how Kepler had to fit in his scientific studies with his search for a secure and safe position for himself and for his family in the face of religious persecution and turmoil. And we see that in his triumphant Rudolfine tables, 50 times more accurate than the Ptolemaic and Prutenic tables that preceded them, he had himself drawn in the frontispiece as the architect of the achievement. So, at least, Kepler appreciated his own worth, as we are led to do in this brief, fascinating biography.

Jay M. Pasachoff is professor of astronomy and director, Hopkins Observatory, Williams College, Massachusetts, United States.

Johannes Kepler and the New Astronomy

Author - James R. Voelkel
ISBN - 0 19 511680 1
Publisher - Oxford University Press
Price - $22.00
Pages - 141

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