Impressions from the
5. Fachtagung "Geschichte der Astronomie" in Kassel

The historical section of the Vereinigung der Sternfreunde (German Amateur Astronomical Society) held its fifth annual conference in the Landesmuseum Kassel (left) and the Orangerie (right) on November 1 and 2, 2008.

Left: the first and the current face of astronomy in Kassel: Landgraf Wilhelm IV. von Hessen-Kassel (William IV, Landgrave of Hesse-Kassel, who ruled by day and performed fundamental star astrometry by night) and Karsten Gaulke, Leiter des Astronomisch-Physikalischen Kabinetts der Museumslandschaft Hessen Kassel. Right: an astronomical surprise - the Kasseler Musiktage, a music festival, uses a picture of a total solar eclipse (with maximum corona) as its eyecatcher. Even the detailled flyer doesn't say why and also doesn't credit this image, in contrast to all others ...

Partial group picture of the meeting participants in front of the Landesmuseum's lecture hall building.
Highlights from the talks given throughout November 1st:

Arnold Oberschelp surprised many with the insight that Copernicus' Commentariolus already contained the precise (often to better than 1%) relative distances of all planets from the Sun - this was not an achievement that only Kepler could arrive at! Copernicus didn't perform the necessary measurements (of elongation angles, plus throwing in the siderial revolution period) himself but seems to have deduced them from ancient tables, cleverly converting them from the geocentric to the heliocentric system. In 1596 Kepler wrote that he tried in vain to make sense of the relativ distances of the planets from the Sun, but he was the first one to actually plot the real distances in a diagram (Copernicus had done so only schematically).

Bernd Pfeiffer in his talk - all the visuals are here - explored the role of comet observations around 1600 (and the Great Comet of 1577 in particular) in reshaping astronomy's world view. While in the 15th century crappy distance "measurements" of comets had reinforced the ancient view of comets being "sublunar" non-astronomical entities, now Tychos's non-detection of a parallax clearly showed that the object was at least 4 times as far away as the Moon, shattering the "crystal spheres carrying the planets" in more than one sense. New physics became necessary to explain planetary motion.

Karsten Gaulke (see above) masterfully deconstructed the widely heard claim that Wilhelm had operated "the first fixed observatory in Europe in the early Modern Era" in Kassel. a) The observatory was not fixed; the angular measuring devices were out on the balcony of his - long-gone - castle only for the observations and were brought back inside after use (though the meridan was marked on the floor for easier setup). Tycho's Uraniborg instead was a real observatory with fixed instruments and continuous observational work done by many people while in Kassel astronomy was done only from 1560 til 1597, by only largely one observer at a time (Wilhelm himself: 1560-67) and with long gaps. b) The definition of "Europe" is all but clear - was the short-lived Istanbul Obs. European or Asian? Given strong cultural exchanges this distinction is of little use. And c) the Modern Era (Neuzeit) isn't well-defined either ... Whatever: Wilhelm eventually got 58 precise star positions which were incorporated e.g. in a famous clock (see below).

Olaf Kretzer from the Suhler Sternfreunde is in the process of going through tons of local and regional chronicles, scanning them for all things astronomical. It turns out that "observing reports" often are either based on calculations, not actual measurements - and that e.g. descriptions of total solar eclipses are frequently "imported" into locations where a partial eclipse at best could be seen. Old chronicles - some are now available on cheap CD-ROMs - are valuable sources, nonetheless: e.g. for comets which are mentioned frequently. Kretzer discovered several comets which are either missing from Kronk's vast collection completely or for which Kronk hadn't found European references but only information from East Asia. Aurorae are also frequently mentioned, and Kretzer sees a correlation with solar activity which would make old chronicles even useful as a proxy.

Stefan Binnewies reviewed the history of observatories on high mountains: The first temporary high-altitude telescope was installed by Piazzi Smyth in 1856 on the Teide volcano, the first permanent mountain observatory is Lick which saw 1st light in 1888. The first one in Germany was Wendelstein (1942), the first on in the Southern hemisphere the CTIO in 1967 - and the current record holder is a radio-astronomical test station near San Pedro de Atacama in Chile at an altitude of 5525 meters.

Joachim Ekrutt discussed the fact that the constellation Ophiuchus ist cut through by the ecliptic yet has never been part of the zodiac: Not only do the IAU constellation boundaries firmly put one foot of the serpent-holder on the other side (S) of the ecliptic but carefully drawn star maps back to at least the Uranometria of 1603 do the same. (So there is no evidence for a conspiracy by the IAU to introduce a 13th zodiacal constellation in order to show the ropes to astrologers ...) Ekrutt's talk (in which he also explained why most IAU boundaries have lots of kinks: stars referenced to a particular constellation in any catalog of the past were supposed to remain part of it whenever possible) led to an intense interest in the whereabouts of Ophiuchus' feet in every star chart or globe meeting participants encountered since, e.g. in the astronomy exhibition (see below)...

Walter Oberschelp, being from Aachen, is particularly interested in astronomical thinking of Carolingian times, i.e. roughly around 800 C.E. - few in the audience had ever contemplated that era. The material available, esp. the 7-Bücher-Computus written after the Reichssynode in Aachen in 809 (1200 years ago next year; it will be celebrated bigtime) had unveiled a disastrous state of science in Germany, contains some fascinating insights, e.g. possibly the first-ever depiction of a heliocentric Universe in its 5th volume and deep insights into planetary orbits (while still clinging to the geocentric view, of course). Many ideas from antiquity can be recovered here, albeit seen through Carolingian eyes.

Daniel Fischer, i.e. the author of this report, reviewed the complicated pre-history of the telescope, based largely on Willach's 2007 paper and some further 'investigations' on location in the Netherlands this fall. References given for good - general - sources on the early history of the telescope were The Galileo Project from the U.S., 400 years invention of the telescope from the Netherlands, Galileo's Telescope from Italy, History of the Telescope from the English Wikipedia and The History of Astronomy in tabular form: the crucial quarter millennium 1500 to 1750 CE, a living document by myself - which is already being revised with new insights garnered from this very productive meeting!

Kassel at night, November 1st: The Orangerie (left; with the Sun of large Planetenweg) and other museums are "linked" by green laser beams, "nicely" visible in the foggy air ...

In the Astronomisch-Physikalisches Kabinett on November 2nd: Waiting for a Foucault pendulum marker to fall (which it does in the moment the right image was taken).

One of the showpieces of the collection: the "Great Planetary Clock" or Wilhelmsuhr from 1560-61. It was built after plans drafted by Wilhelm IV. himself, and the 27 cm-sized rotating sky globe makes use of the 58 star positions the Landgraf had measured from his balcony.

A sky globe made by Joost Bürgi (a later observer at Kassel's "observatory") between about 1582 and 1586; it once moved driven by a clock mechanism. The detail on the right shows Ophiuchus' foot being cut through by the ecliptic, again proving that the constellation was in the ecliptic all the time.

A sky globe made by Willem Blaeu in Amsterdam after 1621. The way the constellations are depicted was adapted from copper-plate engravings by Jan Saenredam which were widely used in such globes throughout the 17th century.

A specutacular Arabic astrolabe from islamic Spain, made by Ibrahim ibn Said al-Sahli in 1086 - it comes with many exchangeable dials and is amazingly well preserved. It was probably given as a gift to Wilhelm IV. by some nobleman who wanted his political support.

Left: a table torquetum made in Prague around 1600 - too small for actual measurement use, it was nonetheless employed to demonstrate the use of the much larger real torqueta for angular measurements in the sky. This one was made with such care, though, that its likely destination was an art collection or Wunderkammer. To the contrary the azimuthal quadrant on the right from around 1560 was used for astronomical measurements, probably even by Wilhelm IV. himself! Copies of this specimen - which features several innovations in fine mechanics - can be found in museums around the world, but this is the real thing!

Left: Detail of a table clock with calendrical and astronomical displays, from around 1565. Right: an armillary sphere by Simon Duchesne, Delft, before 1592.

A particularly complex little astronomical clock (technically a Stutzuhr), made by Bürgi in 1590-91 - it is also the first equation watch in the world. And another novely: reliefs on the outside show, among other astronomy celebrities, Mr. Copernicus himself!

Life was hard for observational astronomers in the 16th century: Here two meeting participants try to measure the angle between two artificial stars with a 2-person-sextant, a working replica of an instrument used for pre-telescopic astrometry ...

An 72 cm-sized sky globe Bürgi began to construct in 1582 but finished with lots of artistic detail only 111 years later. 1180 stars are shown!

A Copernican tellurium by Blaeu, 1628-34.

Some of the larger telescopes on display in Kassel: on the upper left (and lower left) a very long one from around 1700, on the upper right (and also lower left in the background) a Newtonian made by Edwared Scarlett around 1740, on the lower left in the front a Gregory by James Short from 1741, and on the lower right a wooden telescope made by Giuseppe Campani in 1699/1700; the original mounting was lost but has been reconstructed from a photograph.

On the left a golden astronomical pocket watch, made by Fromanteel & Clarke in London around 1695, on the right a "planetolabium", showing the solar system out to Mars, made by Lothar Zumbach von Koesfeld in Kassel before 1700. The planets had to be place onto their orbits.

On the left the objective lens (diameter 11 cm, focal length 30 meters!) and eyepiece of an "aerial telescope" which Campani made in 1684. How these bizarre telescopes in the late 17th century worked is demonstrated by a setup shown on the right - with a much shorter focal length, of course ...

Page prepared hours after returning from Kassel by Daniel Fischer (all texts and pictures, with special
thanks to Mr Gaulke for the permission to photograph in the exhibition)