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3 December 2006
Mystery of ancient astronomical calculator unveiled

An international team has unravelled the secrets of a 2,000-year-old computer which could transform the way we think about the ancient world. Professor Mike Edmunds and Dr Tony Freeth, of Cardiff University led the team who believe they have finally cracked the workings of the Antikythera Mechanism, a clock-like astronomical calculator dating from the second century BCE.
     The remains of the device were first discovered in 1902 when archaeologist Valerios Stais noticed a heavily corroded gear wheel amongst artefacts recovered by sponge divers from a sunken Roman cargo ship. A further 81 fragments have since been found containing a total of 30 hand-cut bronze gears. The largest fragment has 27 cogs. Researchers believe these would have been housed in a rectangular wooden frame with two doors, covered in instructions for its use. The complete calculator would have been driven by a hand crank. Although its origins are uncertain, the new studies of the inscriptions suggest it would have been constructed around 100-150 BCE, long before such devices appear in other parts of the world.
     The new research suggests it is more sophisticated than anyone previously thought. Using bespoke non-invasive imaging systems, such as three-dimensional X-ray microfocus computed tomography, the team was able to take detailed pictures of the device and uncover new information. Detailed work on the gears in the mechanism show that it was able to track astronomical movements with remarkable precision. The calculator was able to follow the movements of the moon and the sun through the Zodiac, predict eclipses and even recreate the irregular orbit of the moon. The team believe it may also have predicted the positions of some or all of the planets. The findings suggest that Greek technology was far more advanced than previously thought. No other civilisation is known to have created anything as complicated for another thousand years.
     Professor Edmunds said: "This device is just extraordinary, the only thing of its kind. The design is beautiful, the astronomy is exactly right. The way the mechanics are designed just makes your jaw drop. Whoever has done this has done it extremely well." The team was made up of researchers from Cardiff, the National Archaeological Museum of Athens and the Universities of Athens and Thessaloniki. Remarkably, scans showed the device uses a differential gear, which was previously believed to have been invented in the 16th century. The level of miniaturisation and complexity of its parts is comparable to that of 18th century clocks.
     There are three dials on the device. The front dial displays the position of the sun and the moon in the zodiac and a corresponding calendar of 365 days, which could be adjusted for leap years. The back dials track the long-term lunar cycle, including the Metonic cycle of 19 years, when the same phase of the moon returns on the same date of the year. The dials also track the Callippic cycle of 76 years, when the moon returns to the same position in the sky relative to the zodiac and its monthly lunar phase.
Francois Charette, an astronomer at Ludwig-Maximilian University in Munich, said finding such a complicated computer in Ancient Greece was like finding the plans for a steam engine in Renaissance Italy.
     The mechanism is in over 80 pieces and stored in precisely controlled conditions in Athens where it cannot be touched. Recreating its workings was a difficult, painstaking process, involving astronomers, mathematicians, computer experts, script analysts and conservation experts. The researchers are now hoping to create a computer model of how the machine worked, and, in time, a full working replica. It is still uncertain what the ancient Greeks used the mechanism for, or how widespread this technology was.
     One of the remaining mysteries is why the Greek technology invented for the machine seemed to disappear. No other civilisation is believed to have created anything as complex for another 1,000 years. One explanation could be that bronze was often recycled in the period the device was made, so many artefacts from that time have long ago been melted down and erased from the archaelogical record. The fateful sinking of the ship carrying the Antikythera Mechanism may have inadvertently preserved it.

Sources: BBC News, EurekAlert! (29 November 2006), Telegraph, The Guardian, The Independent (30 November 2006)

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