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The astronomical computer of the Greeks

Archeology / Remains of ancient machinery testify to complex technology

Antikythera mechanism. He probably knew how to predict the position of the celestial bodies on any given date

When the Greek diver Elias Stadiatos discovered in 1900 the remains of a cargo ship off the coast of the tiny island of Antikythera, it was the sculptures that were scattered on the bottom that left the main impression on him. He came up to the surface, took off his helmet and told enthusiastically that he had found a pile of dead naked women. The ship's luxury cargo also included jewelry, fine furniture, and bronze vessels, some of which dated to the first century BC. But it turned out that the most important finds were some lumps of food and green from rust. These were the remains of a complex mechanical mechanism.

The Antikythera Mechanism, as it is now known, was originally housed in a small wooden box, with dials on the outside and a set of gears inside. X-rays of the remains, in which about 30 different wheels could be distinguished, led the late Derek Price, a historian of science at Yale University, to conclude that the device was an astronomical computer, with which it was possible to predict the position of the sun and moon on any given date. But a new analysis of the findings shows that the device was more sophisticated than Price thought.

Michael Wright, curator of the Department of Mechanical Engineering at the Science Museum in London, based his new analysis on detailed X-rays of the mechanism, using a method known as linear tomography. This method makes it possible to move the x-ray source, the photographic film and the object being studied so that only the details of one plane are visible at a time. By analyzing the photographs received, the exact location of each and every wheel was determined.

Wright noticed a nut fixed in the center of the mechanism's main wheel. From this he concluded that it was a central wheel, around which all the others moved. This structure raised the hypothesis that the device was designed to reproduce a certain type of "epicyclic" movement. The Greeks believed in an earth-centered universe, and explained the movements of the heavenly bodies using elaborate models based on epicyclic movements. In these movements, each body circles a point that itself circles the Earth. Wright found evidence that the Antikythera Mechanism served as an accurate model of the movements of the Sun and Moon and of the planets Mercury and Venus.

Admittedly, there is not much logic in building a device to predict the movements of the sun, the moon and two planets only. But if, as Wright surmised, the mechanism included an upper layer that was lost, the extra wheels might have served as a model for the other three planets known to the Greeks - Mars, Jupiter and Saturn. That is, it is possible that the device could predict the positions of the known celestial bodies on any given date with a reasonable degree of accuracy.

Wright built an approximate model of the clock, in which the mechanisms of each celestial body are arranged on top of each other in layers. The complete reconstruction, the details of which were described in an article that appeared last May in the Horological Journal, is now on display at the Technopolis Museum in Athens. By turning a knob on the side of the device, you can make the celestial bodies advance and recede, so that you can determine their positions on any given date.

The origins of much of modern technology, from locomotives to robots, have their roots in the elaborate mechanical toys that were refined in the 18th century. These toys evolved from the art of watchmaking. Now it seems that the roots of this art reach back to ancient Greece.

Economist, published in "Haaretz"

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