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Tuesday, March 1, 2011

The First Computer?

The extant fragments of the Antikythera Mechanism.

Over 2,000 years ago, a Roman merchant vessel weighing probably 300 tons made a wrong turn and the ship crashed into coastal cliffs off the island of Antikythera near Crete.  The ship was carrying statues - life-size ones made of bronze and marble, other bronze sculptures, jewelry, coins, wine, and a unique instrument, now known as the Antikythera Mechanism.

Location of the island of Antikythera, relative to Crete
and Greece, showing the location of the wreck.

What exactly the device is has been debated since it was found in 1900 by a group of sponge divers.  Preserving items that have been underwater for long periods is difficult with today's knowledge and techniques, but little was known then about the necessary cautions and procedures.  When the device was brought to the surface it broke into several pieces.  It was initially ignored as the recovery teams were bent on sorting and identifying the other artifacts first.

The largest piece of mechanism as it exists today.
An x-ray of the piece above revealing the internal gears.

Researchers believe that this device was not built for astronomers, but may have been built to teach laypersons about astronomy.  A small dial inside the Metonic calendar (one of two used on the device)  spelled out locations where Panhellenic games were held, one of which was the Olympics.  A second dial on the back predicts eclipses.  This second dial, with its 18-year cycle, corresponds to the months in the Saros cycle, another ancient calendar system used for tracking eclipses.  There are 18 divisions marked with glyphs which were very accurate and matched the start dates of 100 eclipses occurring in the last 4 centuries BCE, as verified by NASA.

A model showing the gears of the reconstructed device.
Bronze parts are the ones researchers have evidence for;
copper parts are the ones researchers inferred.

The device was apparently built sometime between 150 and 100 BCE. Archimedes of Syracuse (he of "Eureka!" in the bathtub) is said to have constructed similar ones, and seven of the months inscribed on the device match a calendar used in Syracuse.  He died before this one was built, but he may have made a prototype to it.  Hipparchus, an astronomer, has also been proposed as the designer because of his theory that irregularities of the Moon's progression was caused by its elliptical orbit.  Cicero in the first century BCE (De Natura Deorum 2.34-35) mentions a device "recently constructed by our friend Posidonius, which at each revolution reproduces the same motions of the sun, the moon, and the five planets."

On right of each photo is a CT slice generated from x-ray data.
A diagram showing the complexity of the gear system.
The black ones are the ones visible from x-rays.  The red
ones are speculations for completion of the device.
Evidence suggests there may have been even more gears.

There is little doubt that the mechanism is of Greek origin, as the writing on the device is in ancient Greek.  It used a Metonic calendar, which was based on Babylonian mathematical progressions to address the fact that 12 lunar months only add up to 354 days, which is 11 days short of a solar year.  The names of the months on the device match those of calendars from the Corinthian colonies of ancient Greece, suggesting that the device may have come from there.

A computer-generated reconstruction of the Antikythera
Mechanism shows the back dials.  The upper one is a Metonic
calendar for fitting lunar months into solar ones.  The bottom
dial is an 18-year calendar for predicting solar and lunar eclipses.
Close-up of top dial in image above shows the right inner dial.  This one follows
the four-year cycles of the Panhellenic games.  Year 1 shows the Isthmian games
in Corinth and the Olympic games in Olympia.  Year 2, the Nemean games in Nemia
and the Naian games in Dodona.  Year 3, the Isthmian games in Corinth and the Pithian
games in Delphi.  Year 4, the Nemean games and a game as yet to be deciphered.
Close-up of the bottom dial in the top image.  This dial predicted eclipses based
on the Saros calendar.  The glyphs on the dial indicate the times, and the smaller
inner dial makes the necessary corrections to these times.

While the Antikythera Mechanism is the only known device of its kind, because of its precise design and engineering and the existence of contemporary accounts of similar devices, it is speculated that it is not unique.  However, it is very unique to the scientists and researchers of the Antikythera Mechanism Research Project. This group of international researchers are supported by some of the best international technology companies, and include personnel from one UK and two Greek universities.

The Antikythera Mechanism on display at the National Archaeological Museum in
Athens, being viewed by conservator Gerassimos Makris.  Image courtesy of the Museum.

The Antikythera Mechanism is currently kept in the Bronze Collection of the National Archaeological Museum in Athens.  There is a replica in Bozeman, Montana, for those who prefer local travel.  In 1978, Jacques Cousteau dove at the shipwreck site to search for any pieces that may have been overlooked, but found nothing.  Research is ongoing and a symposium is planned for this spring.  One can only hope other such devices will be discovered in the future.  Maybe even something more remarkable...

Unless otherwise noted, images are courtesy of Tony Freeth for the

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