After decades of research, a discreet discovery recovered from a Roman shipwreck has turned out to be a scientific sensation: the ancient Greeks had mechanical models of the cosmos with unimaginable precision. The so-called “Antikythera Mechanism” is an analog calendar computer.
Thomas Weibel/Swiss National Museum
In May 1902, when the Greek Minister of Education, Spyridon Stais, picked up a piece of heavily corroded bronze that had not yet been examined in detail at the National Archaeological Museum in Athens in May 1902, something unfortunate happened: a piece of the piece it broke – revealing a surprisingly well-preserved gear with teeth just 1.5 millimeters high, as you would expect from a modern watch.
However, the lump came from the wreckage of a Roman ship that sank around 70 BC. It sank in a bay on the island of Antikythera, in the far south of Greece, in 1900 and was discovered by sponge divers. The wreckage carried war spoils from the eastern Aegean and Asia Minor, marble and bronze statues, ceramic and glass vessels, jewelry and coins dating from 70 to 62 BC. Allowed.
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Precision equipment from antiquity was a real shock to science. What the hell was that? British physicist and historian of science Derek de Solla Price found the answer in the 1950s. “Price understood that the original device was flat and rectangular, the size of a modern desk clock, and had a knob or crank on the side,” says London mathematician Tony Freeth.
And further: “A complicated train of gears inside the case moved a series of hands over round dials on the front and back of the device. In this way, the positions of the sun and moon could be represented accurately. For any day and sometimes at exactly the time of day.” Because the names of celestial bodies are engraved on the mechanism, many researchers even speculate – even though no part of these gears survive – about position displays for the five planets known at the time: Mercury, Venus, Mars, Jupiter and Saturn.
It has long been known in the literature that the ancient Greeks built such gear trains. In the 1st century BC polymath Poseidonius worked on the island of Rhodes in 200 BC, and the lawyer and later Roman consul Cicero saw a device that «cuius singulae conversions idem efficiunt in sole et in luna et in quinque stellis errantibus quod efficitur in caelo singulis diebus et noctibus» (“whose individual revolutions produce the same thing in the Sun, the Moon, and the five planets as occurs in the actual sky in the individual days and nights”) as he did around 45 BC. AC at your work “De natura deorum” he wrote. No one thought it possible that this description could be taken literally.
If you want to understand what a mechanical transmission does, first examine the gears: their position, their circumference and, most importantly, the number of teeth. But even with the first X-ray images of the mechanism, it was not easy. The photos were not particularly clear, and the gears themselves were preserved only in fragments. There was a wheel on which radiologists thought they counted 128 teeth. 128 is a power of 2 and has no significance in astronomy.
Price, on the other hand, claimed that the wheel must have had 127 teeth. “127 is a prime number,” explains Freeth. «It refers to the orbit of the moon. If you watch the moon night after night, you will see that it moves across the starry sky once every 27.3 days throughout the zodiac. As early as the 5th century BC, the ancient Babylonians knew that the Moon travels through the zodiac almost exactly 254 times in 19 years.” 254 is twice 127 – and with that Price found this accurate Babylonian lunar calendar, embedded in an ancient gear more than 30 gears.
Today, after extensive examination of the total of 82 fragments found, including high-resolution CT scans and metal penetration, we know: The Antikythera mechanism was a complex mechanical calendar made of bronze, a gear-driven analog computer, with scales and text in Their circuit boards individual functions were recorded.
On one side was a solar calendar with date display. Embedded in one of his hands was a rotating silver ball that showed the phase of the moon. The dial had a static display with the 12 signs of the zodiac and a circular scale for the 365 days of the year, as provided for in the Egyptian calendar, with 12 months of 30 days plus five additional days. This scale was sliding to allow for the additional leap day that occurred once every four years.
The other side of the device showed two more displays: at the top, a large spiral-shaped lunar calendar with the 19-year lunar cycle, named after the Greek astronomer Meton. Below was the spiral-shaped display of a large eclipse calendar to show solar and lunar eclipses. And finally, within the lunar calendar display was a small display of four years of the Olympic calendar, which showed the Panhellenic Games, including the change of location.
Replica of the mechanism…Image: Ludwig Oechslin
… from Antikythera.Image: Ludwig Oechslin
Ludwig Oechslin, historian of technology and science and qualified master watchmaker, was director of the from 2001 to 2014 International Clock Museum in La Chaux-de-Fonds. In 2006, a new analysis of the Antikythera mechanism appeared in the journal “Nature” Oechslin caught his attention and decided to recreate the device himself. Using a computer-controlled milling machine, he made the gears and assembled them into a replica of the ancient mechanism.
“We know from the literature that such gear trains existed in antiquity,” says Oechslin, “but none of them have ever been found. According to the latest discoveries, one can now rightly say: The Antikythera mechanism is an analogue calendar computer and therefore a model of the cosmos of enormous precision.”
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