“THE FIRST EUROPEAN OBSERVATORY OF THE SIXTEENTH CENTURY, AS FOUNDED BY LANDGRAVE WILHELM IV OF HESSE-KASSEL”: A SERIOUS HISTORIOGRAPHIC CATEGORY OR A MISLEADING MARKETING DEVICE?

Karsten Gaulke

1—Introduction

This paper examines a centre of astronomy in Germany shortly after the death of Nicolaus Copernicus in 1543: the so-called “observatory of Landgrave Wilhelm IV of Hesse-Kassel”.1 Wilhelm was born in 1532, the son of Philipp the Noble, one of the leaders of the Protestant resistance against the Habsburg Emperor Charles V. Philipp and his Protestant allies (e.g., Johann, the Elector of Saxony) were defeated in the Schmalkald war. Philipp was arrested, and his young son became the regent for several years—thereby learning an important lesson about the geo-strategic weakness of the Hessian territory.2 Fascinated by astronomy, Wilhelm had a balcony-like platform (the Aldaun or Altanen) erected on the royal castle in Kassel around 1560. A little bit earlier he had begun astronomical observation and came to see the errors in the traditional Ptolemaic star-catalogue. Consequently, he formulated his further programme of research: to map the stars with the help of precision instruments. His fi rst catalogue of 1562 contained the positions of 58 stars. It served as a pattern for the brass globe on the top of the famous Wilhelmsuhr made by the instrument maker Eberhard Baldewein of Marburg—a planetary clockwork that showed not only

1 For more detailed information concerning the astronomical activities of Wilhelm IV see: Karsten Gaulke, “Scrutinising a legend—a new look at the mathematical instruments and clocks of Wilhelm IV of Hesse-Kassel and the ‘Wissenschaftskam- mer’” in Bart Grob, Hans Hooijmaijers, Who Needs Scientifi c Instruments—Conference on Scientifi c Instruments and Their Users, Leiden, 2005, pp. 37–49. 2 Wilhelm Ernst Winterhager, “Philipp als politische Persönlichkeit”, in Ursula Braasch-Schwersmann et alii (eds.), Landgraf Philipp der Großmütige 1504–1567. Hessen im Zentrum der Reform: Begleitband zu einer Ausstellung des Landes Hessen, Marburg—Neustadt an der Aisch, 2004, pp. 12 ff. 88 karsten gaulke the mean motion of the planets according to Ptolemaic theory, but also their true anomalies, thus refl ecting the equations, the positions of the apogees, the declinations and their positions with regard to the Sun (Aux). This splendid automaton made Wilhelm famous among his fellow princes. Elector August of Saxony was especially inspired by it and so ordered a similar automaton from Wilhelm, which was completed in 1567, and today is preserved in the Mathematisch-Physikalischen Salon in Dresden. Subsequently, Wilhelm came to be seen as the German princely authority for astronomical and astrological expertise (e.g., the Gregorian reform of the calendar) and also as an agent of fi ne scien- tifi c instruments and clockwork. This position served Wilhelm in ways beyond merely promoting his purely scientifi c reputation—it was a new way to gain infl uence and power in the diversifi ed political landscape of the Holy Roman Empire. Concerning the Aldaun, in older publications several authors labelled this location for astronomical activities “the fi rst European observatory in modern times”, as if this description were self-evident. This paper will shed some critical light on this label: to what extent is it a serious historiographic category and to what extent a rather clever marketing device designed to stress the importance of the Kassel collection of scientifi c instruments?

2—The astronomical activities in Kassel

The period of mapping the stars in Kassel lasted from 1558 until 1597, fi ve years after the death of Wilhelm IV in 1592. There were three main periods of observational research: 1560–1567, 1567–1584 and 1584–1592. But a key question is to determine at what time can we really speak of an “observatory”? I would propose that there are four main conditions defi ning an observatory in the early modern era. First of all, a long period of uninterrupted research should be detectable. Second, something like a constant working group should exist to implement the observations. Third, the instruments should be at one fi xed place, with some of them possibly stationary in order to have comparable conditions of measure- ment. And fourth, the place of observations should be noticed by the scientifi c community as an important centre of astronomical activity. The fi rst observations of the early period date from the year 1558 and concern the famous comet seen in that year. It is possible that the