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A fragment of the 2,100-year-old Antikythera Mechanism, believed to be the earliest surviving mechanical computing device, is seen at the National Archaeological Museum in Athens on Thursday. ((Thanassis Stavrakis/Associated Press))

Scientists have unlocked the secret of an ancient device recovered from a Roman shipwreck, saying the complex mechanism was used to track the movements of the stars and moon.

The machine, believed to be about2,000 years old,was discovered in 1901 on a shipwreck off the coast of the Greek island of Antikythera and embedded in rock. The strange wheel-like device with complex gears had baffled researchers attempting todetermine its purpose.

But a recent study in the journal Nature has revealed the device, known as the Antikythera Mechanism, wasactually a complex means of tracking the movements of astronomical bodies for use in navigation.

A team of researchers led by Mike Edmunds and Tony Freeth at Cardiff University in Wales used X-rays to peer through the deposits covering the mechanism,to uncover ancient script and clueson how the mechanism worked.

"This device is just extraordinary, the only thing of its kind," said Edmunds in announcing the results. "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 researchers will bereleasing their full findings of what they areregarding as a 2,000-year-old computer at a two-day international conference in Athens on Thursday and Friday.

Created between 150 BC and 100 BC, the mechanism contained 37 gear wheelsina case of wood and bronze in a contraptionthat resembled a clock. The gear wheels were designedto track the movements of the sun and moon, and even track eclipses and the irregular orbit of the moon. It may also have been able to follow some of the planets.

Also astonishing is the machine's use of a differential gear, a device known to have beenused in the 17th century but often speculated to have been invented years earlier.

The device is an arrangement of gears that permits the rotation of two shafts at different speeds. It is most commonly associated in modern usage with automobiles, which use a differential gear on their rear axle to allow different rates of wheel rotation on curves. The intricacy of the device is also comparable to that of 18th-century clocks.

'State of the art in astronomy'

"I'm very surprised to find a mechanical representation of this," Alexander Jones, an astronomy historian who works at the University of Toronto, told Nature.

Jones predicts the mechanism will have a profound impact on our view of the history of science.

"This was absolutely state of the art in astronomy at the time."

The greater question puzzling scientists is how such a useful device could have disappeared entirely from the archeological record, so much so that no record of anything as complex appears for another 1,000 years. One explanation is that the recycling of bronze in ancient times melted down older versions and caused any archeological record to disappear.

But as London Science Museum's curator, Michael Wright, told Nature in a subsequent article, a more likely possibility is that the device or plans of the device migrated in some form to the Muslim world after the fall of Rome, and reappeared years later in Europe.

"I find it as easy to believe that this technology survived unrecorded, as to believe that it was reinvented in so similar a form," said Wright.

Edmunds and Freeth worked alongside researchers from universities of Athens and Thessaloniki and the National Archaeological Museum of Athens, where themore than80 pieces of the mechanism are being held in precisely controlled conditions.