When I was confronted with the spectacular Trilogy of Time for the very first time, I started thinking about which one of the three watches I would like to own. At first the Tellurium was the prime candidate, because I considered the global day/night display with moonphase and eclipses the most useful of the three, in daily practice.
A little later, the Astrolabium gained attractivity in my eyes, just because it was so complicated. It was the manifold of lines, symbols and hands that made it so impressive.
As time passed by, I dedicated more and more energy in studying the Trilogy, getting deeper involved into their design and philosophy than I had ever anticipated. I even had the chance to spend several days with Dr. Ludwig Oechslin, the genius behind these watches. He is a true master of all sciences, and a fascinating personality.
It was him who opened my eyes, completely changing my attitude towards the one watch of the trilogy, which I had previously more or less ignored; the Planetarium.
This is the story as I learnt it from Dr. Oechslin, and which determined my final decision:
At the end of the 16th century, the Renaissance introduced massive changes and developments, not only in art and architecture, but especially in science. In both dimensions, microcosmos and macrocosmos, the view of the world that has hitherto dominated life, was completely turned over. Anatomical studies proved the human life being based a fascinating organism, but nowhere as mystical as most had thought before. And the Copernican system of the world replaced Earth as the centre of the known cosmos with the Sun. Suddenly, man as God's creation was removed from the centre, and given a place in a orbit around the Sun, among other planets. As the fate of Giordano Bruno, and Galileo Galilei's troubles show, it was even dangerous to publicly adopt the radical new view of the world. The problem was further enlarged by the fact that astrology, then considered an exact science, is based on the movement of the planets as they are seen from the Earth, so it formed a somewhat strange coalition together with the Church, which also defended the old system installed by Ptolomaeus, fighting against the new Copernican system.
In that time, a Swiss mathematician, astronomer and clockmaker, named Jost Bürgi, was torn between two emotions: on the one side, he was a scientist, and convinced of the Copernican system's truth, but on the other hand, he was pragmatic, and knew that his Catholic employers would not like him to express a view that was often considered heretical. Additionally, the old geocentric system was still needed as a base for astrological calculations.
Jost Bürgi (15521632)
When Bürgi started the construction of a new astronomical clock, he found an absolutely perfect compromise, combining the two disputing views of the world. He placed the Sun into the centre of his planetarium, as it should be according to Copernicus. Instead of letting the Earth circle around it, however, he placed the Earth into a fixed position, and re-calculated the planetary orbits in a way, that he could display them in reference to the fixed axis between Sun and Earth.
Jost Bürgi's marvelous clock, built in 1605, now held by the Museum of History of Art in Vienna
By means of that design, he was able to satrisfy both, the need for a astrological display, and his own self-understanding as a scientist. And to those criticizing that the Earth was not depicted in the centre of the system, he could point out that still all planets rotate around the Earth.
The dial of the Bürgi clock shows the Earth in a fixed location, with the other planets' positions being shown by hands
When working as a scholar, Dr. Ludwig Oechslin travelled through Europe, studying the astronomical timepieces made by Bürgi and his contemporaries. As soon as he was confronted with the clock held in Vienna, he was fascinated by the idea behind the planetary display, which he had never seen in an astronomical clock before. For Oechslin, it became a firm plan to design a watch, implementing the same unique display.
Besides the mathematical calculations, the real challenge was the fact that this watch would not have a "dial" in a conventional sense. Oechslin did not want to use a manifold of hands displaying the planets. This would add too much height, since it is necessary to stack at least seven hands (including hour and minute) on top of each other. Additionally, such a watch would be more difficult to read than the Astrolabium. Instead, the face should consist of several concentric rings, rotating around the watch's centre. Only the ring on which the Earth is placed is not moving, being the only place under which to hide the wheelwork. Oechslin invested huge amount of energy into this project, even more than he did before, with the Astrolabium.
this is how the planetary orbits are displayed on the Planetarium, in reference to the fixed axis between Sun and Earth: Since Earth is moving faster than the outer planets (Mars, Jupiter, Saturn), the referential system overtakes these planets. As a consequence, the watch displays them rotating clockwise, when in reality, they orbit the Sun counter-clockwise, like all other planets
Finally, Oechslin improved Bürgi's design by adding a unique moon display, rotating around the Earth.
The moonphase display on Ludwig Oechslin's Planetarium
Thus was Dr. Oechslin's admiration for Bürgi's genius, that he suggested the new and second timepiece of the marvelous UN Trilogy of Time should wear the name "Castello", Italian for "castle", which again is what "Burg" (Bürgi) is in German. However, the decision was made to call it "Copernicus", which, according to Oechslin, is not entirely correct, since the watch does not display the Copernican system, but a geocentric system with Copernican orbits.
This was what I learnt about the Planetarium, and being a (legal) historian myself, I was deeply impressed by the thoughts and personalities behind that watch. Of the Trilogy, this is the most unique piece, since that particular way to display the planetary orbits has been realized only a single time, 400 years ago, by Jost Bürgi, and has now been retrieved from the long forgotten by Ludwig Oechslin. My personal choice was clear now.
A small epilogue: Dr. Oechslin was aware of my original uncertainty of which watch to choose from the Trilogy. When I met him in Basel last year, he asked me which one I took. I raised my arm to show him my Planetarium. Spontaneously, he shook my hand and congratulated me.