Reproduction of 2,100-year-old calculator deepens mystery
The model of the Antikythera Device is based on the latest discoveries of the mysterious mechanism
By John Cox , Network World , 12/17/2008
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A new working model of the mysterious 2,000-year-old astronomical calculator, dubbed the Antikythera Device, has been unveiled, incorporating the most recent discoveries announced two years ago by an international team of researchers.
The new model was demonstrated by its creator, former museum curator Michael Wright, who had created an earlier model based on decades of study. He demonstrates how the more complete device works in a video originally created on the New Scientist Website. (It's part of an update story by Jo Marchant, author of Decoding the Heavens, an account not only of the device itself but also the century-old scientific quest to recover its meaning.)
The added details and precision of the new model are based on the breakthrough research by The Antikythera Mechanism Research Project, a joint effort by researchers from Greece and the United Kingdom. They were able to plumb the depths of the device, comprised of 81 separate pieces (including several fused together over time), and decipher many more of the inscriptions by using high-tech hardware and software from HP Laboratories and X-Tek Systems, a U.K.-based manufacturer of high-resolution X-ray inspection equipment. The 2006 slideshow on the device, and the technology used by the researcher to decipher it, is online.
Though often dubbed the "first computer," the device doesn't meet the fundamental requirement of computing. One of the project members, Michael Edmunds, a professor in the School of Physics and Astronomy at Cardiff University in Wales, prefers the term "calculator." "It multiplies, divides and subtracts, but you can't program it," he says.
But it's a highly advanced calculator: the complexity of its gearing was not seen again until the rise of European clock-making in the Middle Ages, 1,000 years later.
About the size of a shoebox, the Antikythera Device is crammed with an astoundingly complex and precise arrangement of 27 fine-toothed bronze gears and dials, turned by a hand-operated knob on one side. On the front and back, dials and pointers show the relative positions of the sun and moon in the sky over periods of time (and possibly of the five then-known planets), a black-and-white ball showed the moon's changing phases, and inscriptions showed the times of rising and setting of stars.
On the back, two spiral dials tracked the relative positions of the sun and moon, and the dates of solar and lunar eclipses, and showed the dates of the Olympic games.
The ancient Greeks believed that celestial orbits were circular, instead of the elliptical ones we know them to be today. To account for the discrepancies in the moon's movements, the Greek astronomer Hipparchus developed a mathematical model superimposing the motions of overlapping circles, each with a different center. The Antikythera Device uses a "pin and slot" arrangement to exactly reproduce this anomalous motion, so it accurately represents the observed celestial motions and times.
Reflecting this complexity, the 2006 research team included astrophysicists, radio astronomers, mathematicians and philologists (philology is the study of ancient texts and original documents).
They made use of two advanced technologies to make their discoveries.
HP Labs supplied a technology to bring out surface details previously unseen. Tom Malzbender, a senior research scientist with HP Labs, and colleagues Dan Gelb and Hans Wolters had developed a digital technique, called reflectance imaging, for re-imaging how light is reflected from a surface. Essentially, it's a computerized version of what most of us have done with the oil dip stick in our car: you hold it up to the light and twist and turn it, until the light shows up the oil film and the inscribed markings.
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The HP researchers do it by putting an object inside a dome that's fitted with a camera, scores of light bulbs, and a laptop computer to control it. A separate laptop runs a program to create a polynomial texture map (PTM) of the captured images, letting the researchers then change the lighting and surface characteristics.
The second technology was 3-D computer tomography, based on X-ray gear from X-Tek weighing nearly 8 tons. But unlike medical X-rays, these are real-time and digital, taking super-thin slices through an object and then recreating them into a 3-D image that can be manipulated. One result: The tomography not only showed new details of the gearing and teeth but also uncovered inscriptions never before seen.
Based on these results, the researchers discovered the following:
* The device was built between 150 and 100 B.C., somewhat earlier than previously thought. The shipwreck took place about 65 B.C. The date is significant, as is the assumption (based on some circumstantial evidence) that the ship, traveling a busy sea route, was heading to Rome from Rhodes, where one of the greatest of Greek astronomers, Hipparchus, lived and worked from about 140 to 120 B.C. Researchers speculate that he or one of this students could have influenced the design, and possibly the building, of part of the mechanism.
* The pin-and-slot gearing, as mentioned above, which creates an anomalous motion for the moon, simulating visually the mathematics created by Hipparchus to account for moon's observed, irregular orbit around the Earth.
* One of the two back spiral dials on the back of the device is now shown to simulate what's called the Saros eclipse cycle, in which a given solar or lunar eclipse will be repeated 223 lunar months later.
* The second back spiral dial is now confirmed to have 235 teeth, demonstrating it simulates the Metonic lunar cycle, which over 19 years (235 lunar months) represents the return of the moon to the same phase on the same date in the year.
* Researchers now believe the device had 37 gear wheels; seven of those are deduced from the now more-visible details of the surviving wheels and from the new understanding of their relationships and functions.
* Researchers agree with Wright's speculation that some of the missing gears were likely used to simulate the movement of the known planets, making the Antikythera Mechanism one of the earliest and most complex planetariums.
Even deciphered, the Antikythera Device retains its power to fascinate us.
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