The Antikythera Mechanism 2000 years on
Modern graphic of the Antikythera Mechanism. Credit: Nikon

The Antikythera Mechanism 2000 years on

16/05/2018Written by Tori Tasker

The enduring puzzle of an ancient astronomical computer.

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Antikythera Mechanism (front dial) at the National Archaeological Museum, Athens.
Greek island of Antikythera. Credit: Google maps

The world’s first computer was discovered on 17 May 1902 in a shipwreck off the Greek island of Antikythera, to the great puzzlement of archaeologists at the time. Since then, we have learnt a great deal more about the sophistication of this ancient astronomical computer, known as the Antikythera Mechanism.

At over 2000 years old, the very existence of the Antikythera Mechanism was a surprise. Its technological sophistication seems out of place from a time when there was a lull of astronomical discoveries. Although exact history of the Antikythera Mechanism is speculative, the possibilities are exciting. It was likely created in Greek city of Rhodes during the 2nd century B.C., with a design influenced by ancient mathematicians and astronomers. This may have included the famous Greek astronomer Hipparchus of Rhodes, whose work on the complex motion of the Moon seems to feature in the mechanism. At some point, this ancient computer was loaded onto a cargo ship bound from Rhodes to Rome, perhaps for a parade organised by Julius Caesar. But by some misfortune, the ship sunk off the coast of the island Antikythera and remained under the sea until it was discovered in 1902 by a Greek archaeologist.

At the time of discovery, scholars didn’t know what to make of the mechanism and its inscriptions, and so later generations of researchers were left to uncover its secrets. In the 1970s and 1990s, X-ray imaging revealed that the mechanism was used to look at the sky. However, as the X-ray images were hard to read, not many scholars took this as credible information. It wasn’t until the early 2000s that the mechanism was really understood. In 2006, detailed 3D X-ray scans revealed the inner workings and inscriptions of the mechanism.

How it works

How it works
Modern graphic of the Antikythera Mechanism. Credit: Nikon
How it works
Antikythera Mechanism (rear dial) at the National Archaeological Museum, Athens.

At a basic level, the Antikythera Mechanism is just a clock. However, instead of telling time as we know it today, it tells celestial time. Wooden pieces on the mechanism suggest it was cased in a wooden box. This case, the size of an A4 piece of paper, had front and back doors. These doors are inscribed with astronomical and mechanical markings, most of which are too damaged to decipher. On the case there are also two dial systems which form a calendar and predict lunar and solar eclipses.

On the mechanism itself, there are seven hands representing the Sun, the Moon, and each of the five planets visible to the naked eye: Mercury, Venus, Mars, Jupiter, and Saturn. These hands likely moved at different speeds. There is also a rotating ball – half black and half silver – to show the phases of the Moon. There are at least 30 known gears in the mechanism which combined to create a geocentric model. A geocentric model of the Solar System is one that puts Earth at the centre, with the other planets, stars, the Moon, and the Sun all orbiting the Earth. This was how ancient astronomers understood the Solar System until Copernicus proposed the Sun-centred model in 1543.

On the back face of the mechanism there are two large dials which track cycles of the Sun and Moon such that it’s possible to predict upcoming eclipses when the Earth, Moon, and Sun align. Inscriptions reveal which stars rose and on what date.

The Antikythera Mechanism was ahead of its time in both technology and astronomy. The technological sophistication of the Antikythera Mechanism does not appear in the archaeological record again until the invention of astronomical clocks in 14th century Europe. This could suggest that there are predecessor mechanisms yet to be found.

Currently the Antikythera Mechanism is on display in the National Archaeological Museum of Athens. It is still the subject of much research and debate.

To learn more about this astonishing astronomical computer, watch this session of expert talks about the Antikythera Mechanism from the Computer History Museum in California.

About the author: Tori Tasker is the Public Programmes Team Leader at the National Space Centre.