The mysterious Antikythera Mechanism

By Faye J. Vasiliadis

A fascinating discovery, the Antikythera Mechanism was unearthed from the bottom of the sea off the coast of the island of Antikythera -on the southeastern tip of the Peloponnese-, by sponge divers, back in 1900. This complex device, which was made of bronze and recovered along with other items from a Roman shipwreck, intrigued the international scientific community who initially had no idea about its use. This sophisticated machine, which dates back to the end of the 2^nd century BC, is basically a clockwork mechanism with scales, pointers, and about 30 high precision gears with triangular teeth that rotate around multiple axles, exactly like in a mechanical watch. Its wooden case was securing both its front and rear side with metal plates that bear inscriptions with instructions for the instrument’s use. The most widely accepted theory regarding its operation is that it is an analog computer, calculating the motion of celestial bodies, and it is believed that it was designed and assembled by Rhodian astronomer Geminus. However, according to other theories, it was constructed by Hipparchus, another Rhodian astronomer, or even Archimedes.   

The Antikythera Mechanism has data appearing on both its sides, indicating the position of the Sun and Moon, as well as of the five planets that were known in antiquity, i.e. Mercury, Venus, Mars, Jupiter and Saturn. The device was allegedly used to predict the eclipses of the Sun and Moon, based on the Babylonian Saros cycle (the saros is a period of 223 synodic months, which means approximately 18 years, 11 days and 8 hours). The machine also depicted two separate calendars; one Egyptian and one based on a 19-year Metonic cycle, which was the basis for the Greek calendar. It was also used to determine the timing of all Panhellenic Games, including the Isthmian, Nemean, Pythian, and Naian Games, as well as the Olympics. 

The user, assisted by a manual rotor, could set in motion all the pointers through interlocking gears and axles. So, when a date was chosen on the front scale and the desired month and year on the upper back one, the other pointers would provide all available astronomical information. And vice versa, when a pointer would be shifted over to an astronomical phenomenon, its date of occurrence would appear. The most impressive feature of the Antikythera Mechanism, though, is that it can present the variable motion of the Moon through an amazing innovative -for its time- system of epicyclic drive (gears moving onto other gears). 

Based on the month names engraved on the Mechanism, it is believed that it was constructed in Corinth or one of its colonies, while gears -its main component- were already in use in ancient Greece since the 3^rd century BC, with the concept most likely developed by Aristotle. 

The 82 fragments of the Antikythera Mechanism found on the famous shipwreck are showcased in the National Archaeological Museum of Athens, and it is worth mentioning that in 2014 a group of marine archaeologists kicked off a mission to recover the remaining artifacts from that shipwreck and maybe -hopefully- the Mechanism’s missing parts, such as those driving the planetary pointers, or even its colored balls; red for Mars and gold for the Sun.