Mysterious old Greek gadget turns out to be early computer

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After a century of study, scientists have unlocked the secrets of a mysterious 2,100-year-old device known as the "Antikythera mechanism," showing it to be a complex and uncannily accurate astronomical computer.

The mechanism, recovered in more than 80 highly corroded fragments from a sunken Roman ship, could predict the positions of the sun and planets, show the location of the moon and even forecast eclipses.

The international team of scientists reported today in the journal Nature that the first-century B.C. device, the earliest known example of an arrangement of gear wheels, shows a technological sophistication that was not seen again until clockwork mechanisms were introduced in the 14th century.

The results "imply that Greek technology was much more advanced in this area than was previously thought," said the team's leader, physicist Mike Edmunds of Cardiff University in Wales. "If they could do this, what else could they do?"

The device was found in 1901 by Greek sponge divers working in 120 feet of water off the coast of the Greek island of Antikythera, midway between the southern tip of Greece and Crete.

The late British science historian Derek de Solla Price was the first to use modern technology to study the device. Over two decades beginning in the 1950s, he used X-ray and gamma-ray images to reveal gears inside the corroded pieces.

He concluded, correctly, that it was an astronomical calculator. But the device as he reconstructed it was unduly complicated, and there were many gaps in his explanation of how it worked.

Edmunds' team brought a 7.5-ton X-ray tomography machine — similar to that used to perform CT scans on human patients — into the National Archaeological Museum in Athens, Greece, to examine the fragments in greater detail than was possible before.

They were able to image the bronze gears more clearly and double the number of deciphered inscriptions on the casing.

They concluded the device contained 37 separate gears, about 30 of which still survive. It was originally housed in a wooden case slightly smaller than a shoebox.

Two dials on the front show the zodiac and a calendar of the days of the year that can be adjusted for leap years, while metal pointers show the positions in the zodiac of the sun, moon and five planets known in antiquity. Two spiral dials on the back show the cycles of the moon and predict eclipses.

By turning the gears with a hand crank, the user could select a specific day in the past or future and observe the positions of the heavenly bodies on that day.

"The design is beautiful; the astronomy is exactly right," Edmunds said. "The way the mechanics are designed just makes your jaw drop. Whoever has done this has done it extremely well."