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An Ancient Computer Surprises Scientists

By JOHN NOBLE WILFORD

Published: November 29, 2006

A computer in antiquity would seem to be an anachronism, like Athena ordering takeout

on her cellphone.

School of Physics and Astronomy, Cardiff University

Fragments of the Antikythera Mechanism, left, have now been examined with the latestin high-resolution imaging systems and three-dimensional X-ray tomography.

But a century ago, pieces of a strange mechanism with bronze gears and dials were

recovered from an ancient shipwreck off the coast of Greece. Historians of scienceconcluded that this was an instrument that calculated and illustrated astronomical

information, particularly phases of the Moon and planetary motions, in the secondcentury B.C.

The Antikythera Mechanism, sometimes called the worlds first computer, has now beenexamined with the latest in high-resolution imaging systems and three-dimensional X-ray

tomography. A team of British, Greek and American researchers was able to decipher

many inscriptions and reconstruct the gear functions, revealing, they said, an unexpected

degree of technical sophistication for the period.

The researchers, led by Tony Freeth and Mike G. Edmunds, both of the University ofCardiff, Wales, are reporting the results of their study in Thursdays issue of the journalNature.

They said their findings showed that the inscriptions related to lunar-solar motions andthe gears were a mechanical representation of the irregularities of the Moons orbital

course across the sky, as theorized by the astronomer Hipparchos. They established the

date of the mechanism at 150-100 B.C.

The Roman ship carrying the artifacts sank off the island of Antikythera around 65 B.C.

Some evidence suggests that the ship had sailed from Rhodes. The researchers speculated

that Hipparchos, who lived on Rhodes, might have had a hand in designing the device.

In another article in the journal, a scholar not involved in the research, Franois Charette

of the University of Munich museum, in Germany, said the new interpretation of theAntikythera Mechanism is highly seductive and convincing in all of its details. It is not

the last word, he concluded, but it does provide a new standard, and a wealth of fresh

data, for future research.

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Historians of technology think the instrument is technically more complex than any

known device for at least a millennium afterward.

The mechanism, presumably used in preparing calendars for seasons of planting and

harvesting and fixing religious festivals, had at least 30, possibly 37, hand-cut bronze

gear-wheels, the researchers reported. An ingenious pin-and-slot device connecting twogear-wheels induced variations in the representation of lunar motions according to the

Hipparchos model of the Moons elliptical orbit around Earth.

The functions of the mechanism were determined by the numbers of teeth in the gears.

The 53-tooth count of certain gears, the researchers said, was powerful confirmation of

our proposed model of Hipparchos lunar theory.

The detailed imaging revealed more than twice as many inscriptions as had been

recognized from earlier examinations. Some of these appeared to relate to planetary as

well as lunar motions. Perhaps, the researchers said, the mechanism also had gearings to

predict the positions of known planets.

Dr. Charette noted that more than 1,000 years elapsed before instruments of such

complexity are known to have re-emerged. A few artifacts and some Arabic texts suggestthat simpler geared calendrical devices had existed, particularly in Baghdad around A.D.900.

It seems clear, Dr. Charette said, that much of the mind-boggling technologicalsophistication available in some parts of the Hellenistic and Greco-Roman world was

simply not transmitted further, adding, The gear-wheel, in this case, had to be

reinvented.

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The Antikythera Mechanism is a unique Greek geared device, constructed around the end

of the second century bc. It is known1, 2, 3, 4, 5, 6, 7, 8, 9 that it calculated and displayedcelestial information, particularly cycles such as the phases of the moon and a luni-solar

calendar. Calendars were important to ancient societies10 for timing agricultural activity

and fixing religious festivals. Eclipses and planetary motions were often interpreted asomens, while the calm regularity of the astronomical cycles must have been

philosophically attractive in an uncertain and violent world. Named after its place of

discovery in 1901 in a Roman shipwreck, the Antikythera Mechanism is technically morecomplex than any known device for at least a millennium afterwards. Its specific

functions have remained controversial11, 12, 13, 14 because its gears and the inscriptions

upon its faces are only fragmentary. Here we report surface imaging and high-resolution

X-ray tomography of the surviving fragments, enabling us to reconstruct the gearfunction and double the number of deciphered inscriptions. The mechanism predicted

lunar and solar eclipses on the basis of Babylonian arithmetic-progression cycles. The

inscriptions support suggestions of mechanical display of planetary positions9, 14, 15,

now lost. In the second century bc, Hipparchos developed a theory to explain theirregularities of the Moon's motion across the sky caused by its elliptic orbit. We find a

mechanical realization of this theory in the gearing of the mechanism, revealing anunexpected degree of technical sophistication for the period.