Newly Decoded Text on Antikythera Mechanism Gives New Insights Into the Functions of an 'Ancient Computer'

Antikythera Mechanism (Brett Seymour / WHOI)

The enigmatic 'Antikythera Mechanism' has been back in the news recently, with researchers unveiling the results of a decade-long project to decipher tiny inscriptions on the device. Previous research had largely focused on the mechanics of the 'ancient computer' that was salvaged from a shipwreck in 1901 by sponge divers.

The approximately 2100-year-old clock-like device could be used to calculate the movements of the Sun, Moon and planets, as well as predict eclipses, using a system of gearwheels, with the user able to 'travel' backwards and forwards in time by winding a handle.

In a special issue of the journal Almagest, researchers have broken down the various sections of the mechanism. Firstly, the front:

The bronze plate known as the “Front Cover” of the Antikythera Mechanism had inscriptions on its outside face... The texts give data on synodic cycles for the five planets, and it may be conjectured that lost lines described the behaviour of the Sun and Moon. The data strongly support the idea that planetary motions were displayed on the front face of the Mechanism using simple epicyclic or eccentric models. Previously unattested long and accurate period relations are given for Venus and Saturn, which are favourable for geared representation and probably of Greek, rather than Babylonian, origin.

The dial at the center of the front face of the Antikythera Mechanism was surrounded by two scales, one representing the zodiac, the other the Egyptian calendar year. The Zodiac Scale was inscribed with the names of the zodiacal signs as well as series of index letters in alphabetic order, while the Egyptian Calendar Scale was inscribed with the Greek names of the Egyptian months. In addition, two rectangular plates, the remains of which survived displaced from their original positions, bore an inscription, called the Parapegma Inscription, comprising an alphabetically indexed list of annually repeating astronomical events relating to the Sun and to fixed stars.

The new discoveries about the mechanism were made possible by modern imaging technologies ("computed tomography and polynomial textual mapping") being applied to the tiny engraved text found on it - some of which were barely 1mm in height!

Antikythera Mechanism text

On the back of the mechanism they found dials showing lunar calendars, a 'Games' (i.e. an athletic competition, such as the Olympic Games) calendar, and information about predicting eclipses:

The rear face of the Mechanism consisted of a rectangular "Back Plate" dominated by two large spiral dials. The upper five-turn Metonic Dial represented a 235-lunar-month calendrical cycle while the lower four-turn Saros Dial represented a 223-lunar-month eclipse prediction cycle. A subsidiary quadrant "Games" dial was situated inside the Metonic Dial, and a subsidiary three-sector Exeligmos Dial inside the Saros Dial. Preserved text inscribed around the dials (from the lower right quarter of the plate), probably representing about a quarter of the original inscription, provided further information associated with the predictions of eclipses.

The Metonic Dial inscriptions imply a calendrical scheme similar to that described by Geminos. It was intended to be a version of the calendar of Corinth as it was practiced either at Corinth itself or in some locality of Epirus. The Games dial shows six competitions, four Panhellenic (Olympics, Pythian, Isthmian, and Nemean) plus Naa (Dodona) and very probably Halieia (Rhodes).

On the Saros dial there were probably originally about 50 or 51 month cells with a lunar and/or solar eclipse prediction, each carrying a "glyph" and an index letter. Predicted eclipse times (in equinoctial hours) on the glyphs were calculated as times of true syzygy according to solar and lunar models that both involved anomaly, with the simple Exeligmos dial extending the predictions over three or more Saros cycles.

The additional information referred to by index letters from the Saros dial was grouped into paragraphs; that for lunar eclipse prediction probably ran down one side of the plate, and that for solar eclipse prediction down the other. Statements about direction may imply a meteorological aspect by referring to predictions of winds attending the eclipses. Five references to colour and size at eclipse are the only Greco-Roman source known to us that suggests prediction of eclipse colors, and might conceivably be linked with astrology.

The press have run with this 'astrology' attribution, but it's just a small part of what this research has uncovered, and even then I think it's still just a 'possibility' (note the wording above, "might conceivably").

The researchers also translated text that was inscribed on a plate - possibly a protective cover - that was found lying against the rear face of the Antikythera Mechanism in situ on the shipwreck. Only small fragments remain of this plate, but some of the text was, amazingly, preserved "as offsets on a layer of accreted matter that built up against it". It was found that the text on this plate provided "a systematic description of the dials, pointers, and other external features of the Mechanism, beginning with the front face and continuing with the rear face."

The best preserved passages include descriptions of features on lost parts of the Mechanism: a display of pointers bearing small spheres representing the Sun and planets on the front dial, and a dial on the upper back face representing a 76-year "Kallippic" calendrical cycle.

Lastly, the research team was able to use the 'data' that drove the device to guess at the likely location of the person who compiled it, finding that it corresponded to observations from a latitude of around 35 degrees - that ruled out Egypt the north of Greece, but matches the island of Rhodes.

It is hoped that ongoing excavation of the shipwreck will uncover more fragments of gears and inscriptions that could shed further light on this amazing contraption.

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