Thursday 29 August 2013

The Antikythera Mechanism

The Antikythera Mechanism at the Archaeological Museum in Athens.

The Fragments

Fragments of the Antikythera Mechanism were recovered from the ancient shipwreck in 1901. The Antikythera Mechanism is the earliest preserved portable astronomical calculator and the earliest known modular mechanism in the world. Its calculations are closely related to the social and religious institutions of ancient Greece. It was used for astronomical observations, for predicting solar and lunar eclipses, for keeping an accurate calendar of many years, for predicting the date of Pan-Hellenic celebrations, and much more.

Fragment A

When discovered, the Mechanism was a compact mass of copper, corroded and covered with marine concretions and remained unnoticed for approximately six months. On May 1902, when the pieces were already separated under unknown circumstances, the numismatist I. Svoronos described the fragments as 'an unusual find... a bronze device consisting of several bronze gears, some of them very fine which resemble those of a modern clock'.

Fragment C

Despite its fragmentary condition it bears 30 bronze gear-wheels with teeth which were operated manually by a handle attached onto one of the short sides, enabling the mechanism to make calculations based on two cycles of the Solar System, the Metonic cycle and the Soros cycle, both known to the ancient Babylonians and the Greeks. The mechanism was placed inside a wooden case.

The smaller fragments

The Mechanism's front and back metal plates were covered with densely incised inscriptions, which contained astronomical information and instructions on how to use the device.

Fragment B

A small part of two concentric annuli with subdivisions is retained on the front side of the Mechanism. The outer dial bears an Egyptian calendar containing 12 months of 30 days each and five extra days which add up to 365 days of the solar year. The inner dial corresponds to the Zodiac cycle. The upper back dial is arranged as a five-turn spiral which forms a 19-year calendar based on the Metonic cycle. Twelve months of the Corinthian calendar can be read on the Metonic disc: two smaller subsidiary dials are shown inside the Metonic dial, the Olympic dial, which is a four-year dial predicting the dates of the Pan-Hellenic games and the hypothetical Callippic dial, which is a 76-year cycle, an 18-year calendar, which predicts the solar and lunar eclipses. Inside the Saros dial there is a smaller subsidiary dial, the Exeligmos dial - this is a 54-year triple Soros dial.

(Another photograph of the fragments, with hologram suspended above. Seven large fragments and 75 of much smaller size are preserved).

The mechanism is an application of the teachings of Hipparchus who developed a theory to explain the irregularities of the moon's motion across the sky caused by its elliptic orbit.

A number of models have been designed and constructed in an attempt to fully understand how the Mechanism works. This is Price's model.

This is the Auth model - the front


The Auth model - the back.

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