The most complex subsystem in this project, at least in terms of the numbers of wheels
(nearly 100), is the six-planet orrery which crowns the entire movement. In addition to
the planets orbiting the sun, the two outer planets of Jupiter and Saturn have their own
moons of four and five each respectively orbiting their parent planet. This adds a level
of difficulty rarely seen in a mechanical orrery. The ring dials just below the orrery are
the setting dials. Over all diameter of the orrery is just over 10". The model only
has the planets out to Jupiter, but the actual orrery is designed to include Saturn. This
orrery is based upon an astronomical clock made by Philipp Matthaus Hahn in 1780 as
described in the German language book Astrnomische Uhren und Welt-Modelle der
Priestermechaniker im 18. Jahrhundert vol. II Katalog, Ludwig Oechslin. I was very
lucky to have found this two volume set. Here are photographed and described astronomical
clocks, many with orrerys. Most importantly, however, is the fact that the author was
allowed to disassemble and make schematics of these clocks. Along with the two volume set
of books is a large folio containing these key schematics. It is this information that
allowed me to even attempt such project. It also cut much research time off the subsystem
making it affordable to add to the movement.
Below are photos of Hahn's astronomical clock of 1780, as well as the orrery assembly
out of the clock. Notice the tellurium on the left side of the clock. This clock having
both the orrery and tellurium influenced my design choices. It is interesting to note that
it also has a celestial sphere in the center. An item I had considered in my earlier designs before I ever saw this clock
but was later abandoned in favor of a planisphere.
Shown here is Hahn's original drawing for the orrery section of the clock. Next is the
contemporary schematic including all wheel / pinion tooth counts.
The pictures below show to scale the relative distances the planets orbit from the sun
as well as the planets relative sizes to each other. It becomes obvious, that to make the
orrery fit into a reasonable space, some compromises have to be made in bringing in the
two outer orbits toward the sun and to expand a bit away from the sun the three inner
planets. The planets will still reflect their ranking in sizes to each other, but not to
scale. And obviously the Sun is not to scale as it would be a s big as the entire orrery
if built to scale!