The emergence of modern astronomy – a complex mosaic: Part XIII

In the initial phase of its reception the thing that most interested the readers of De revolutionibus were the planetary tables and ephemerides that Copernicus’ new mathematical models delivered. There was great enthusiasm for this aspect of his work in the hope that it would deliver more accurate celestial data for cartography, navigation and astrology the principle reasons why people, during this period, were interested in astronomy. It was not long before that initial enthusiasm began to wain, as people realised that although they were different inaccuracies the new sets of table were as error strewn and inaccurate as the old ones based on the works of Ptolemaeus. The problem was that the tables produced from De revolutionibus were based on the same star catalogue, the one in Ptolemaeus’ Mathēmatikē Syntaxis. This star catalogue had over the years become very corrupted through errors that crept in by repeated manuscript copying and recalculating the values for new locations.

We can find this very clearly expressed by the English mathematicus Thomas Harriot (c. 1560–1621) a true polymath, who produced significant scientific discoveries in cartography, navigation, mathematics, astronomy, chemistry, physics and linguistics.


Portrait often claimed to be Thomas Harriot (1602), which hangs in Trinity College, Oxford. Source: Wikimedia Commons

He was also one of those early Copernican, who accepted Copernicus’ cosmology. Unfortunately Harriot’s only publication was a brief account of his voyage to North America With Walter Raleigh (c. 1552–1618) in 1585–86, where he became viewed historically North America’s first scientist, so all of his scientific advances had little or no impact. In chapter 3 of an unpublished navigation manual that he wrote for the captains of Raleigh’s fleet he discussed taking the declination of the sun. He says sailors used two different methods. The Spanish and Portuguese sailors used one based on the Alfonsine tables derived from Ptolemaeus in 1252 but first published in the 15thcentury and the other based on the theory of certayne notable mathematicians & especially of one Nicolaus Copernicus of Cracow in poland. He writes that the Alfonsine tables lead to obvious errors in the determination of latitudes.

The latter were Reinhold’s Prutenic Tables and Harriot say that declination tables were usually made from Stadius’ Ephemerides; he adds these should be better tables but:

it falleth out they are worse; our owne men find faults, as also the Spaniardes but know not where the fault is, nether is it to be tried, found, or decerned by there manner of experiments.

He goes on the explain that the work of Tycho Brahe (1546-1601) at Huaena (Hven) and the Landgrave of Hesse had shown that: ‘Copernicus his tables; the prutenickes, & all ephimerides made out of them’ were half a degree or more out of the sun’s place, and the Alfonsine about a quarter of a degree. Although living withdrawn from society on the outskirts of London Harriot was well aware that both Tycho Brahe and the Landgrave of Hesse knew of the inaccuracies in the tables based on De revolutionibus and as we shall see undertook programmes to correct the problem; aiming to fulfil the aims of Regiomontanus when he moved to Nürnberg about a hundred years earlier.

Harriot’s Landgrave of Hesse was actually Wilhelm IV, Landgrave of Hesse-Kassel (1532–1592).


Wilhelm IV Source: Wikimedia Commons

He was born the eldest son of Philipp I, Landgrave of Hesse (1504–1567) (known as Philip the Magnanimous) and his first wife Christine of Saxony (1505–1549). Philip was one of the earliest Lutheran Protestant rulers in Germany and founded the Protestant University of Marburg in 1527. Wilhelm was introduced to astronomy by his mathematics teacher Rumold Mercator (1541–1599), the son of Gerhard Mercator, in the form of Peter Apian’s Astronomicum Caesareum (1540). Wilhelm was fascinated by the volvelle in Apian’s masterwork, rotating paper calculators used to determine the position of celestial object. In 1559/1560 together with Andreas Schöner (1528-1590), the son of the Nürnberger mathematicus Johannes Schöner (1477-1547), Wilhelm conceived the idea of designing and constructing a clock that would display all the celestial movements given by the volvelle in Apian’s book. This mechanical masterpiece was to be crowned with a celestial globe giving the position of all of the principle fixed stars.


The so-called Wilhelmsuhr or planet clock

On comparing the star tables in both Ptolemaeus and Copernicus with his own actual observations Wilhelm realised that both star catalogues were woefully inaccurate. This would lead him to his programme of re-determining the position of all of the fixed stars.

The earliest recorded observation that we have made by Wilhelm and Andreas Schöner dates from 1558 but most of the records of his early astronomical activities were lost during WWII. Wilhelm is credited with having established the first European observatory but this claim is very dependent on how you define observatory. All of his instruments, which were designed and constructed by the clockmaker Eberhard Baldewein (c. 1525–1593), who was also responsible for the construction of the celestial clock together with the clockmaker Hans Bucher and the case-maker Hermann Diepel, were portable instruments. These were stored in a room in his palace


The Landgrave’s palace in Kassel on an old postcard based on a painting from about 1800 Source: Wikimedia Commons

from where they were carried out onto a balcony to make observations.


Sternwarte im Astronomisch-Physikalischen Kabinett, Foto: MHK, Arno Hensmanns Reconstruction of Wilhelm’s observatory

Wilhelm’s early astronomical activities were supported by Andreas Schöner and Victorinus Schönfeldt (1525–1592), a graduate of Wittenberg, who on Philipp Melanchthon’s recommendation became professor for mathematics on the University of Marburg in 1557, as well as various unnamed assistants. Due to the pressure of his work as heir and then following the death of his father as landgrave his programme to re-determining the position of all of the fixed stars didn’t get started until the 1580s.

In 1578 Wilhelm appointed the twenty-seven year old Swiss clock and instrument maker Jost Bürgi (1552–1632) as clock maker to his court to replace Hans Bucher, who had been Eberhard Baldewein assistant, and who had died in 1578.


Bürgi was a very inventive clock maker and probably the best at his craft living in Europe at the time. Although he was very famous in his lifetime it is not known where or when and from whom he learnt the craft of clock making. In 1584 Wilhelm added the astronomer Christoph Rothman to his staff. Rothmann is a frustrating figure for the astronomy historian. Even by the normal level paucity of knowledge about Renaissance scientific figures, our knowledge about the life of Rothmann, an important figure in the reception of Copernican heliocentrism, is almost non-existent. His date of birth is not known but estimated to be between 1550 and 1560 and it is assumed that he was born in Bernburg, Saxony-Anhalt because later in life he signed himself Mathematicus Christophorus Rothmannus Bernburgensis when he matriculated at the University of Wittenberg in 1575, where he studied theology and mathematics.

Between 1584 and 1589 Rothmann and Bürgi, with the active support of Wilhelm, produced a catalogue containing the newly determined positions of 387 stars, determined to a, for the time, very high level of accuracy. Unfortunately this catalogue first saw the light of day in 1618, as the Hesse-Kassel astronomical team disintegrated starting in 1590. In 1590 Rothmann was sent off on a journey to Hven by Wilhelm to study the instruments and methodology of Tycho Brahe. He never returned from that journey although still under contract to Wilhelm in Kassel. Why he went AWOL is simply not known. It is known that he returned to Bernburg, where he seems to have abandoned astronomy, writing instead theology tracts that he never published. His date of death is not known but was probably around 1600 but not later than 1608. In 1592 Wilhelm presented his nephew Rudolph II, the German Emperor, with one of Bürgi’s mechanical globes and Bürgi was sent to Prague with the globe to demonstrate it to Rudolph. Not long after Bürgi moved into the Emperor’s employment in Prague, as during his absence Wilhelm had died. Wilhelm’s son Moritz (1572–1632), like his father an academic, turned his attention from the study of astronomy to the study of alchemy, the court in Kassel becoming an important centre for alchemy along with the Marburg University, which from this period claims the oldest chair for chemistry, in reality a chair for Paracelsian alchemical medicine.

Although Wilhelm’s efforts to produce a new reliable star catalogue rather fizzled out, he played a major roll in inspiring and promoting another parallel effort to do the same, that of the Danish aristocrat Tycho Brahe.



Filed under History of Astronomy, Renaissance Science

5 responses to “The emergence of modern astronomy – a complex mosaic: Part XIII

  1. A good example how the dramatic fun breakthroughs rest on a foundation of boring tedious scut work. Without the dull task of compiling an accurate star catalogue, no Kepler’s laws!

    Didn’t Owen Gingerich illustrate Tycho’s work with a thick stack of papers containing his star catalogue, and a thin sheaf with the star positions accurately determined before Tycho? Or something like that.

    • There was a lot of boring tedious scut work involved in the emergence of modern astronomy. The Prutenic Tables, the ephemerides based on them by Feild, Stadius and others, the star catalogues of Wilhelm & Tycho and most importantly the Rudolphine Tables based on Tycho’s work. They are actually very much the key ingredients of the story.

      I’m not aware of any such illustration from Gingerich but he has written a vast amount and whilst I have read an awful lot of it, I haven’t read everything he has published. Actually measured Tycho’s star catalogue is about twice the size of Wilhelm’s. He only plotted the position of somewhat more than 700 stars and then filled his catalogue up to 1000 stars with ones from Ptolemaeus’ catalogue. What Tycho did have, which Wilhelm didn’t, was extensive highly accurate tables of planetary positions, which of course in what enabled Kepler to determine the elliptical orbit of Mars.

  2. DCA

    As usual, thanks, this was interesting and illuminating. I’ve read a fair amount of history of astronomy but now have a much clearer pciture of the Landgrave. Also, I hadn’t realized (though i should have) that the errors in the Ptolemaic catalog meant that the resulting planetary positions (and hence theories) would inevitably be pretty inaccurate–which would make it hard to develop any planetary theory (as it did precession). I think most historians focus on the theoretical side (how many epicycles?) and rather neglect the (as noted) dull and tedious work of observation and computation needed just to provide the data needed. We owe Brahe a lot!

  3. John Kane

    An interesting article but as a bit of a side note the volvelle fascinates me.

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