The Antikythera mechanism is an artifact from ancient Greece, discovered in a shipwreck off the coast of the island of Antikythera in 1901. Investigations and analysis have shown that it is an analogue model of the solar system, used to predict positions of astronomical bodies and eclipses, together with a calendar and with several additional indicators. There are many popular and scholarly publications about it on the web. Two good introductory articles are the one in Wikipedia and Tony Freeth's article in Scientific American from 2022. The heart of the mechanism consists of several gear trains, ultimately driven by a single crank. A person would have turned this crank, and the gear trains translate it into the motion of various outputs: the Metonic cycle (a sun-moon calendar), the Saros cycle of possible eclipses, the positions of the planets, sun and moon as seen from Earth, the phase of the moon, and others. Of the many videos on the web, I recommend Freeth's one and Jo Marchant's Darwin lecture.
The scholarly research is wide ranging, and the parts of it that I find most interesting are the ones which deduce the mechanical characteristics. There is a great deal of detective work. CT scans and image processing have allowed the size and configuration of many of the gears to be determined, although some parts of the mechanism are damaged or missing entirely. Comparison of gear ratios with astronomical cycles led to an understanding of what parts of the mechanism are for. A "user manual" in the form of inscriptions on the external surfaces of the mechanism provides further information about its purpose and operation. In some of the more recent work, hypotheses have been put forward for the missing parts of the mechanism, notably the gears that drove the planet positions, by looking at possible mechanisms and deducing what would fit the physical constraints of the surviving parts. Some of the research has been largely settled for a while, such as the gear trains for the Metonic and Saros cycles, while other parts have been updated more recently, such as the planet mechanism. The astronomical model is centered on Earth, and so it has to account for the motions of the planets, sun and moon as seen from Earth. They appear to speed up and slow down and even to reverse direction. This motion can be modelled to some degree of accuracy with two gears, one off center with respect to the other, coupled by a pin and slot. The references above give more detail.
Several published papers include detailed diagrams of the gear trains and tables listing the number of teeth and size of the gears (or equivalently, their modules). Two of Tony Freeth's articles are particularly useful:
- Freeth, T. and A. Jones (2012) The cosmos in the Antikythera Mechanism. ISAW Papers 4, available at http://dlib.nyu.edu/awdl/isaw/isaw-papers/4/. Includes gear schematics. There are measurements for the planet gear trains, but not for the Metonic/Saros part of the mechanism.
- Freeth et al. (2021). A Model of the Cosmos in the ancient Greek Antikythera Mechanism. Nature (Scientific Reports). https://www.nature.com/articles/s41598-021-84310-w. Presents a revised version of the planet mechanisms. The supplement (linked from the same page) has videos showing the assembly, and a table with the sizes of many of the gears. A very valuable resource.
There have been a number of projects to reproduce the mechanism, either as computer models or actually manufactured. Michael Wright made a replica in the 1970s, and Mogi Vincentini made a computer model from it. Freeth has used computer models to illustrate his published papers and to show that his proposed mechanism fits together. There is a lengthy series by Clickspring in which he builds a replica using original tools; at the time of writing it is not yet complete. A bronze version was made by Nicholas Andronis. He has also made a scaled up wooden version. Spencer Conner has another version made out of brass. He made a number of changes to modernize the design. There is a 3-D printable version, for which plans can be purchased, and a rather magnificent wooden version. I have also seen videos generated from other CAD models which may or may not have been made physically, and a 3-D printed version which even goes so far as to reproduce the damage to the casing.
There are plenty of YouTube videos with misleading information. It did not come from aliens or time travel. It's not an ancient mystery. It is an archaeological relic and scientific enquiry by thoughtful people has elucidated its structure and functioning. If you see a video which is an episode of someone's podcast or which employs AI, you should probably skip it. Unless you like that kind of thing, of course.
.jpg)
Dr. Andronis's site at https://www.amclock.net/ deserves further mention. He has detailed instructions and engineering drawings for his bronze version. The instructions include assembly and operating instructions, and many notes on practical issues such as adjusting the size of the parts to make them fit. He includes a table giving the tooth counts and sizes of all the gears, pulling together information from multiple sources. There are a couple of errors: some entries in the table quote the diameter of a gear under a column marked as radius and then also have an (incorrect) radius which is half of this, while others have the correct values; and there is one gear which I could not find on the engineering drawings, but can be reconstructed from the table.
I have been looking for a substantial new 3-D design and printing project, and the Antikythera mechanism is it. At the time of writing, I have prototypes for most of the mechanism, but still have a way to go before it operates smoothly. Perhaps I will succeed, perhaps it will end up in the Closet Of Abandoned Projects. What I want to make is a functional reconstruction: it should work, and use modern design techniques when that makes it work better, even if this means departing from the original mechanism in appearance.
The manual on Dr. Andronis's site says Warning: The only thing you learn from designing and building Antikythera Mechanisms is how to build a better Antikythera Mechanism next time. Well, perhaps, but as in many of my previous projects, the journey may turn out to be the destination.
