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 Thursday 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, United Kingdom. “If they could do this, what else could they do?”
An even bigger question, according to science historian Francois Charette of Ludwig-Maximilians University of Munich, Germany, is why the technology disappeared for more than 1,400 years before reappearing in a less advanced form.
“Much of the mind-boggling technological sophistication available in some parts of the Hellenistic and Greco-Roman world was simply not transmitted further,” he wrote in an editorial accompanying the team’s report in the journal Nature.
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 site is on a major trade route between Rhodes and Rome.
Coins on the ship suggest it sank shortly after 85 B.C. Other artifacts indicate the ship carried a cargo of luxury goods, including statues and silver coins, that probably originated at the island Rhodes and was bound for Rome. The new study suggests that the Antikythera mechanism predates the sinking by 15 to 20 years.
The late British science historian Derek de Solla Price was the first to use modern technology to study the device. Over the course of 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’ interest in the device was piqued several years ago by a student who pointed it out to him, and he began studying the published literature, eventually producing a review article. But truly understanding it, he concluded, would require a more detailed knowledge of its encrusted gears.
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 Archeological 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.
The complicated meshing of the gears is a physical representation of the Callippic and Saros astronomical cycles. In the Callippic cycle, the sun, the moon and the Earth return to the same relative orientations four times in 76 years minus one day. The Saros cycle predicts that, following a solar or lunar eclipse, a similar eclipse will occur 223 lunar months later.
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