Antikythera mechanism

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The Antikythera mechanism
The Antikythera mechanism was a device which displayed the movements of the heavens that was recovered from an ancient shipwreck. The wreck was found near the Greek island of Antikythera in 1901.

Thought to be over two thousand years old, gamma ray analysis has revealed an intricate astronomical device utilising both a differential gear and a epicycle gear. Both of these gear types were once thought to be modern inventions.[1] It pre-dates instruments of similar complexity by around a thousand years.

Coins found at the wreck site suggest a date of 65 BC. The presence of Rhodian vases suggest that the vessel originated in the Aegean island of Rhodes.


Diving for sponges and black coral at a depth of 140 ft, Elias Stadiatos reported disturbing visions of "dead, naked women."[1] Subsequent dives discovered a treasure trove of ancient marble statues. The Greek government was informed of the find and many artifacts were recovered from the wreck the following year. The haul included the statues, jewelry, and what appeared to be several pieces of corroded bronze. Under the belief that these pieces were fragments of a larger statue, they were filed away in the depths of the National Archaeological Museum in Athens, while the rest of the artifacts were placed on display.

Cicero describes a mechanism of this type that was built by the Stoic philosopher Poseidonius (c. 135 – c. 51 BC) at a workshop in Rhodes, a Greek island near Anatolia:

Suppose a traveller carried into Scythia or Britain the orrery recently constructed by our friend Poseidonius, which at each revolution reproduces the same motions of the sun, the moon, and the five planets that take place in the heavens every day and night, would any single native doubt that this orrery was the work of a rational being?"[1]

Cicero was educated at Poseidonius's school of Stoic philosophy in Rhodes.

The shipwreck and cargo are dated to about 65 B.C. It sank off Antikythera while on a voyage from Rhodes.[2]

In 1974, Derek Price wrote a classic study of the mechanism called "Gears from the Greeks."[3] In 2005, the Antikythera Mechanism Research Project examined 82 fragments of the device with a recently developed technology called microfocus X-ray computed tomography. The new method allowed researchers to read about 3,000 characters from the mechanism. Price had been able to read about 1,000 characters. Many of Price's conclusions concerning how the mechanism worked have been overturned by more recent analysis.


The mechanism uses a calendar of the Corinthian family. It is most likely the calendar of Epirus, a region in northwestern Greece. The idea that the mechanism was intended for use in Rome was long popular with researchers. As Rome did not use a calendar of this type, the discovery of the calendar makes the city an unlikely destination.[4]

The dates of various sporting events were marked on a dial. This is less for the benefit of sports fans than to help the user specify an intended year. The four Panhellenic games, namely the Olympics, the Pythians, the Nemeans, and the Isthmians, were marked on this dial. The dial also gives the dates of two otherwise obscure games, one in Rhodes and the other in Epirus.

The mechanism may have been built in Rhodes and later modified for a client in Epirus. If so, the vender could have scratched the Haliea Games of Rhodes off the dial and added the Naia Games of Dodona in Epirus. This would explain why the word "Haliea" is now difficult to read.[4]

The Metonic cycle is used to synchronize solar and lunar cycles. A Metonic cycle is 254 sidereal months, 6,940 days, or 19 years. The gearing ratio between the dial for the months and the dial for the Metonic pointer is therefore 254/19. Nineteen turns of the solar pointer results in one turn of the Metonic pointer.

The mechanism also has a Callipic pointer. The Callipic cycle consists of four Metonic cycles and is therefore 76 years long. The Metonic cycle gives the length of a year as 365.26 days while the Callipic cycle gives 365.25 days. The correct value is 365.2422 days.

The E3 gear adjusts the speed of the moon pointer depending on the phase of the lunar cycle. This follows the lunar epicycle theory of Apollonius of Perga. Ellipses were not part of ancient astronomy. But in modern terms, the moon's elliptical orbit means that it moves across the sky more rapidly when it is closer to the Earth than when it is further away.


  1. 1.0 1.1 1.2 Rice, Rob S., "The Antikythera Mechanism: Physical and Intellectual Salvage from the 1st Century B.C."
  2. "Antikythera Mechanism – Reconstruction", September 13, 2011.
  3. Derek de Solla Price, Transactions of the American Philosophical Society, Vol. 64, No. 7 (1974), pp. 1-70 (70 pages)
  4. 4.0 4.1 Paul A. Iversen. “The Calendar on the Antikythera Mechanism and the Corinthian Family of Calendars.” Hesperia: The Journal of the American School of Classical Studies at Athens, vol. 86, no. 1, 2017, pp. 129–203. JSTOR, Accessed 12 Apr. 2021.