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        The Antikythera Mechanism: (Fossilised Astrolabe)

Discovered in 1900 AD in a shipwreck off the Greek islands, the Antikythera Mechanism contains over 30 geared wheels and dials and the remains are covered in astronomical inscriptions.

Potentially one of the most significant finds of modern time as it changes all pre-conceived ideas of our knowledge of the heavenly cycles. The 'Antikythera Mechanism' is now realised to have been designed specifically to calculate both the 'Metonic' cycle and the 'Saros' eclipse predictions:-

It dates from around the end of the 2nd century B.C. and is the most sophisticated mechanism known from the ancient world.

The device is currently displayed in the Bronze Collection of the National Archaeological Museum of Athens, accompanied by a reconstruction made and offered to the museum by Derek de Solla Price.


   Form and Function:

The Discovery:

The main fragments of the original device.

The device was first found over a hundred years ago (c. 1900) by sponge divers on a shipwreck at the bottom of the sea near the island of Antikythera. The gradual realisation that it was a sophisticated astronomical calculating device astonished experts around the world. For decades however, scientific investigation failed to yield much more about it, but modern equipment has begun to reveal its secrets. It dates from around the end of the 2nd century B.C. and is the most sophisticated mechanism known from the ancient world. Nothing as complex is known for the next thousand years. The Antikythera Mechanism is now understood to be dedicated to astronomical tool operating as a complex mechanical "computer" which tracks the cycles of the Solar System.


The Object - A Description.

The device contains a complicated arrangement of at least 30 precision, hand-cut bronze gears originally housed inside a wooden case covered with inscriptions which describe how to use it.

The device is remarkable for the level of miniaturization and for the complexity of its parts, which is comparable to that of 18th century clocks. It has over 30 gears with teeth formed through equilateral triangles. When a date was entered via a crank (now lost), the mechanism calculated the position of the Sun, Moon, or other astronomical information such as the location of other planets.

The mechanism has three main dials, one on the front, and two on the back. The front dial has two concentric scales. The outer ring is marked off with the days of the 365-day Egyptian calendar, or the Sothic year, based on the Sothic cycle. Inside this, there is a second dial marked with the Greek signs of the Zodiac and divided into degrees. The calendar dial can be moved to compensate for the effect of the extra quarter day in the year (there are 365.2422 days per year) by turning the scale backwards one day every four years. Note that the Julian calendar, the first calendar of the region to contain leap years, was not introduced until about 46 BC, up to a century after the device was said to have been built (and the leap year was implemented with errors until the early first century).

The front dial probably carried at least three hands, one showing the date, and two others showing the positions of the Sun and the Moon. The Moon indicator is adjusted to show the first anomaly of the Moon's orbit. It is reasonable to suppose the Sun indicator had a similar adjustment, but any gearing for this mechanism (if it existed) has been lost. The front dial also includes a second mechanism with a spherical model of the Moon that displays the lunar phase.

There is reference in the inscriptions for the planets Mars and Venus, and it would have certainly been within the capabilities of the maker of this mechanism to include gearing to show their positions. There is some speculation that the mechanism may have had indicators for all the five planets known to the Greeks. None of the gearing for such planetary mechanisms survives, except for one gear otherwise unaccounted for.

Finally, the front dial includes a parapegma, a precursor to the modern day Almanac, which was used to mark the rising and setting of specific stars. Each star is thought to be identified by Greek characters which cross reference details inscribed on the mechanism.

The upper back dial is in the form of a spiral, with 47 divisions per turn, displaying the 235 months of the 19 year Metonic cycle. This cycle is important in fixing calendars.

The lower back dial is also in the form of a spiral, with 225 divisions showing the Saros cycle; it also has a smaller subsidiary dial which displays the 54 year "Triple Saros" or "Exeligmos" cycle. (The Saros cycle, discovered by the Chaldeans, is a period of approximately 18 years 11 days 8 hours -- the length of time between occurrences of a particular eclipse.)

The Antikythera Mechanism Research Project, with experts from Britain, Greece and the United States, detected in July 2008 the word "Olympia" on a bronze dial thought to display the 76 year Callippic cycle, as well as the names of other games in ancient Greece, and probably used to track dates of the ancient Olympic games. According to BBC news:

"The four sectors of the dial are inscribed with a year number and two Panhellenic Games: the 'crown' games of Isthmia, Olympia, Nemea, and Pythia; and two lesser games: Naa (held at Dodona) and a second game which has not yet been deciphered."

One of the remarkable proposals made by Price was that the mechanism employed differential gears, which enabled the mechanism to add or subtract angular velocities. The differential was used to compute the synodic lunar cycle by subtracting the effects of the Sun's movement from those of the sidereal lunar movement.

It was announced in Athens on 21 October 2005 that new pieces of the Antikythera mechanism had been found. There are now 82 fragments.

All the gear wheels have been made with teeth of just the same angle (60 degrees) and size, so that any wheel could mesh with any other. There are signs that the machine was repaired at least twice; a spoke of the driving wheel has been mended, and a broken tooth in a small wheel has been replaced. This indicates that the machine actually worked.


The Purpose of the Mechanism.

Following decades of work in order to clean the device, systematic investigations were undertaken in 1951 by British historian of science Derek J. de Solla Price. In June 1959, in a front-page article in Scientific American titled "An ancient Greek computer", he brought forth the theory that the Antikythera mechanism was a device for calculating the motions of stars and planets.

The purpose was to position astronomical bodies with respect to the celestial sphere, with reference to the observer's position on the surface of the earth.

The device has a series of plates attached to it that contain over 2000 characters and appear to act as an instruction manual for the user. The discovery of this had heralded the notion that the mechanism was created by a trained scientist and mechanic for use by a non-expert, possibly a navigator or traveller.

However, the device is unlikely to have been intended for navigation use because:

a) Some data, such as eclipse predictions, are unnecessary for navigation.

b) The harsh environment of the sea would corrode the gears in a short period of time, rendering it useless.


Similar Devices in Ancient Literature

Cicero's 'De republica', a 1st century BC philosophical dialogue, mentions two machines that some modern authors consider as some kind of planetarium or orrery, predicting the movements of the Sun, the Moon, and the five planets known at that time. They were both built by Archimedes.



 Article: Nature July, 2008.

A new paper from the Antikythera Mechanism Research Project (AMRP) was published in the prestige science journal Nature on July 31st 2008. It reveals surprising results on the back dials of the Antikythera Mechanism - including a dial dedicated to the four-year Olympiad Cycle of athletic games in ancient Greece. The research team has also deciphered all the months on the Mechanism’s 19-year calendar, revealing month names that are of Corinthian origin, probably from a Corinthian colony of the western Hellenic world - overturning the previous idea that the Mechanism was from the eastern part of the Mediterranean. For the first time we have direct evidence of its cultural origins.

'The upper back dial is a 19-year calendar, based on the Metonic cycle, arranged as a five-turn spiral. The lower back dial is a Saros eclipse-prediction dial, arranged as a four-turn spiral of 223 lunar months, with glyphs indicating eclipse predictions. Here we add surprising findings concerning these back dials. Though no month names on the Metonic calendar were previously known, we have now identified all 12 months, which are unexpectedly of Corinthian origin. The Corinthian colonies of northwestern Greece or Syracuse in Sicily are leading contenders—the latter suggesting a heritage going back to Archimedes. Calendars with excluded days to regulate month lengths, described in a first century bc source, have hitherto been dismissed as implausible. We demonstrate their existence in the Antikythera calendar, and in the process establish why the Metonic dial has five turns. The upper subsidiary dial is not a 76-year Callippic dial as previously thought, but follows the four-year cycle of the Olympiad and its associated Panhellenic Games'.

(Link to full Article)



Reproduction of the Antikythera Mechanism.

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