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Geo-Joint: The Antikythera Mechanism

Posted on January 13 2015

Antikythera Mechanism
Image: Tom Hall
People have been staring at the night sky for as long as there have been people.  By the time the Greeks had built their civilization, things had gotten pretty advanced.  They knew not only the phases of the moon and the travels of the five visible planets (Jupiter, Mars, Mercury, Saturn and Venus), but also the phenomenon of solar eclipses.  These things all had their periodicities, and their timing could be calculated.
In 1900, sponge divers off the Greek island of Antikythera found a strange clockwork-like mechanism made of bronze in the wreck of an ancient ship.  It had wheeled gears and inscriptions and was quite corroded and broken and was lacking some parts.  There was speculation as to whether it was some sort of early astolabe or other kind of navigational instrument.  Eventually, however, researchers realized that the Antikythera Mechanism, as it came to be called, was a device meant to track moon phases, the travel of the five known planets, and the occurrence of solar eclipses.
As early as the 1930s, working models of this ancient computer  had been constructed, and they continue to be built. The accuracy of these facsimilies has been aided by the use of CT scan technology which allows a view of the mechanism’s inaccessible interior.  This ability has shown that there is also a dial tracking the four-year cycle of the Olympic Games.  The Greeks had developed very advanced mathematics but used Babylonian systems to design the Antikythera Mechanism.  The Babylonians had determined that there was an 18-year cycle to solar eclipses, which they called the Saros Cycle.  Of course the cycle wasn’t exactly 18 years, so there are gears that make corrections for the extra time.  Moon cycles are similarly adjusted for, using ingenious gearing inside the mechanism.  While the raw data of astronomical movements had been known for some time, this predictive device was 1,000 years ahead of its time in technology. It was apparently built sometime before 205 BCE, as astronomers and other researchers have determined that a solar eclipse in that year was the apparent designed starting point for the gear movements.
Its functions are now known, but the mystery of who built it remains.  There are inscriptions on the device that point to it having originated in Syracuse, the home of Archimedes, the famous Greek astronomer and inventor.  He probably didn’t have a hand in its construction though, given that he was killed in 212 BCE, before the assumed 205 BCE starting date.  The ship that carried the ancient computer is thought to have sunk sometime between 85 BCE and 60 BCE.  So the exact origins and the ingenious mind or minds that puzzled the design out are probably lost to antiquity.  But it is humbling to know that some very clever people were doing some very complicated science and mathematics in order to better understand the universe, so long ago.

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