Saturday science subject: Hipparchus' Apple II

— 12:19 PM on December 9, 2006

It turns out the ancient Greeks were just a little bit more advanced than everyone thought. Not content with harboring geniuses like Archimedes, they had apparently devised a calculating machine almost two millennia before Schickard and Pascal. Dating back to around 100 BC, the so-called Antikythera Mechanism "computed and displayed the movement of the Sun, the Moon and possibly the planets around Earth, and predicted the dates of future eclipses," according to Nature.

The mechanism is contained in a squarish wooden case a little smaller than a shoebox. On the front are two metal dials (brass, although the original was bronze), one inside the other, showing the zodiac and the days of the year. Metal pointers show the positions of the Sun, the Moon and five planets visible to the naked eye. I turn the wooden knob on the side of the box and time passes before my eyes: the Moon makes a full revolution as the Sun inches just a twelfth of the way around the dial. Through a window near the centre of the dial peeks a ball painted half black and half white, spinning to show the Moon's changing phase. . . . To show me what happens inside, Wright opens the case and starts pulling out the wheels. There are 30 known gear-wheels in the Antikythera Mechanism, the biggest taking up nearly the entire width of the box, the smallest less than a centimetre across. They all have triangular teeth, anything from 15 to 223 of them, and each would have been hand cut from a single sheet of bronze. Turning the side knob engages the big gear-wheel, which goes around once for every year, carrying the date hand. The other gears drive the Moon, Sun and planets and the pointers on the Metonic and Saros spirals.
The Antikythera Mechanism is attributed to either Hipparchus, a Greek astronomer who lived between 190 BC and 120 BC, or his followers. An article in the New York Times says the mechanism was actually rediscovered a hundred years ago after lying in a shipwreck off the coast of Greece for two thousand years. However, only recent techniques, including high-resolution imaging and 3D X-ray tomography, have permitted researchers to uncover the full extent of the device's sophistication.
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