Thaddeus Hagecius ab Hayek, a Czech physician and astronomer, died Sep. 1, 1600, at age 75. Hagecius was the personal physician and astrologer for the Holy Roman Emperor, Rudolf II, and he was probably the most important mathematical scientist of his generation in eastern Europe. In 1572, a nova or new star became visible in the constellation of Cassiopeia. It attracted the attention of Hagecius, in Prague, and also of young Tycho Brahe, in Denmark. Both men made careful measurements of the star, found that it did not move relative to the stars around it, and concluded that it really was a star, and not some nearby celestial object. Both men wrote treatises on the new star, and since their measurements and conclusions were similar, they greatly impressed each other. When, twenty years later, Tycho lost his position in Denmark, it was Hagecius who convinced Emperor Rudolf to invite Tycho to come to Prague as the Imperial Mathematician. And it was there, in Prague, that Tycho met young Johannes Kepler, who would become the next Imperial Mathematician when Hagecius and Tycho died in quick succession in 1600 and 1601.

Tycho Brahe’s De stella nova of 1573 is of legendary rarity, and there is no copy here at the Library. Hagecius’ Dialexis de novae et prius incognitae stellae (1574) is nearly as scarce, but this one we do have in the History of Science Collection, along with two other treatises on the nova of 1572 by Thomas Digges and John Dee (both published in 1573). And although we lack Tycho’s original treatise on the nova, we do have his much expanded edition of 1602, and a scarce English translation of 1632. Now if only some generous soul would donate Tycho’s 1573 pamphlet to the Library, we would have the one of the world’s premier collection of treatises on the nova of 1572.

The maps above of the constellation Cassiopeia and its stellar intruder, the nova of 1572, are from: Hagecius (1574; first image), Digges (1573; third image), and Tycho Brahe (1632; fourth image). The second image is a portrait of Hegecius, and the last is the title-page of our copy of Hagecius’ Dialexis de novae.

Dr. William B. Ashworth, Jr., Consultant for the History of Science, Linda Hall Library and Associate Professor, Department of History, University of Missouri-Kansas City. Comments or corrections are welcome; please direct to