Ik had niet gedacht dat dit zou lukken...
Ik moet jullie helaas teleurstellen, maar mijn meest recente project is GEEN gitaar. Zelfs geen vage benadering van een gitaar.
Maar toch heb ik er een hoop lol aan gehad, en ik vond het wel iets om met de rest van de wereld te delen.
https://www.youtube.com/watch?v=iuvbwdbbQJM
Nadere toelichting in het Engels (geknipt uit de beschrijving bij het Youtube-filmpje):
I recently took a course in clock repair, where I learned some of the basics about clocks and gears and stuff. After that, I decided to take a swing at building something with gears myself. Not a clock, but something more fun, and something that doesn't need to run as smoothly and precisely as a clock should, because I don't have the machinery you need to make something as accurate as that. I need to be able to make all the bits and pieces by hand. So I tried to think of a quirky project to experiment with...
I am also a big fan of the Discworld series, by Terry Pratchett. If you don't know what I'm talking about: Look it up! Read the books! Wear the lilac!
The basic premise is explained in the first book of the series, The Colour Of Magic: "Through the fathomless depths of space swims the star turtle Great A'Tuin, bearing on its back the four giant elephants who carry on their shoulders the mass of the Discworld. A tiny sun and moon spin around them, on a complicated orbit to induce seasons [...]"
You can probably guess where this is leading: I wanted to make a Discworld Orrery. It has taken half a year, and since about a week or so, it looks like it's finished! It feels a bit rickety in places, and I am very careful when I use it, but so far, everything seems to work.
I have tried to incorporate as many facts from the books as I could. Some facts about Discworld astronomy can be found in the books from the Discworld Series itself, and also in some of the additional publications such as the Compleat Discworld Atlas and the Discworld Almanak. Not all details are covered however, and not everything makes sense when you actually do the math. As far as I know, Terry Pratchett never completely specified the way Discworld astronomy works, and a lot of the discrepancies should probably be explained away as "Because... well, magic!"
Still, we can try...
The disc's tiny orbiting sunlet maintains a fixed orbit while the majestic disc turns slowly beneath it. The disc itself revolves once every eight hundred days. This is a Celestial Year, which consists of eight seasons. The summers are those times when the sun rises or sets at the nearest point on the Rim, the winters those occasions when it rises or sets at a point around ninety degrees along the circumference. A Celestial Year is usually divided into two Common or Agricultural Years of 400 days, containing one of every season.
The mechanism is powered by turning the handle. The orbit of the sun is fixed, in the vertical plane along the spine of Great A'Tuin. The handle should be turned counterclockwise, so that the sun rises on the side of Great A'Tuin's head, and the disc spins Turnwise (clockwise, when seen from above). One turn of the handle represents one day. The sun orbits the disc once a day, and the disc makes a full turn every 800 days, one Celestial Year.
Underneath the disc, the calendar ring rotates once every Common Year, 400 days, which is divided into 13 months, consisting of 32 days each, except for the month of Ick, which only has 16 days. The months are shown on the ring, the arrow indicates the current date.
The moon also spins around the disc, approximately once a day. According to the Discworld Almanak: "The orbits of the Sun and Moon about the World, passing over and beneath it in an ellipse or flattened circle, are very similar and periodically the Moon passes so close to the Sun that one face of it is scorched. By the great foresight of the Keeper of the Geometries, the Moon spins in its path so that this is always the same face, which by now is quite blackened. And thus, when this face revolves towards the world, are the Phases or Aspects of the Moon caused."
In my model, the lunar orbit lies in a vertical plane that rotates once every 63.6(...) days. The indicator on the base of the orrery shows the phase of the moon. Full moon occurs when the lunar orbit plane coincides with the solar orbit plane, which is when the moon may be close to the sun for an extended period of time. New moon occurs when the lunar orbit is perpendicular to the solar one. This way, the time between two full moons comes to 31.8(...) days: almost, but not exactly one month. I didn't want it to be exactly 32 days, otherwise the lunar and solar orbits would match up too perfectly. Similarly, the moon orbits the disc in almost, but not exactly one day, to cause some variation in the relative positions of the sun and moon.
I have made several other considerations, concessions and choices during the build, but I won't go into all of that here. I only hope I won't come across some detail that doesn't fit my model the next time I reread the series...
