Orkney International Science Festival

AN ANCIENT GREEK COMPUTER

Phoenix Cinema, Pickaquoy, Kirkwall, September 8

by Eamonn Keyes

It used bronze gears to predict the position of sun, moon and planets – and eclipses as well. It was recovered from an ancient shipwreck, and over decades researchers have applied techniques to reveal its original form. Dr Vassilios Spathopoulos tells the story of the 2,000-year-old Antikythera mechanism and shows a working model of a machine that was in action at the time of Caesar and Cleopatra.

This enthralling talk was presented by Vassilios McInnes Spathopoulos, originally a Doctor in Aeronautical Engineering, but wearing his Astronomy outreach hat for his visit to Orkney.

The Antikythera Mechanism has now become famous due to its association in the latest and final Indiana Jones movie, where it is depicted as being invented by Archimedes during the siege of Syracuse in Sicily in 213 BC, and capable of locating fissures in time.

However, back here in reality the Mechanism is still an astonishing invention for the time, it is unlikely to have been invented in Syracuse, and was certainly meant for operation elsewhere, such as in Epirus or Pergamum.

The original remnants were recovered in 1901 from the wreck of a Roman ship off the island of Antikythera in Greece, giving it its name. Initially it looked just like a mass of bronze and wood, corroded after its time under the sea, and was largely ignored as it looked too complex to be contemporary with the other finds in the ship, and was thought to be from a much later period.

There were suggestions it might be an astronomical calculator, but more Interest in it was shown by the British science historian de Solla Price from 1951, and it was only in 1971, when it was x rayed, that the complexity of the item became evident. X Ray Tomography and then CT scans revealed more and more of the item and gave more information on what its likely purpose must have been.

Originating in the 2^nd or 1^st century BCE, this mechanism appears to have been the world’s first analogue computer. Of the 82 fragments found, around 37 appear to be gears, and when the likely construction was worked out it showed that the capabilities of this device were truly astonishing.

Whilst we know quite a lot about the scientific knowledge of the Greeks, the device pushed this far beyond the known boundaries, and instruments of similar complexity do not appear until the 14^th century, some 1500 years later. It is likely that it was build in Rhodes, from some of the information contained within its setup, and the astronomer Hipparchus may have been consulted during its manufacture.

It has a front and a rear face, all of which contain many scales covering many areas, from a calendar and list of days to the Zodiac, which when set could indicate the lunar cycle, predict eclipses and track the motion of the 5 other known planets across the sky. This included showing the actual moon phases presented on a small rotating ball. This, remarkably, would have necessitated differential gears. Other elements meant it would have been an almanac, showing the locations of specific stars. The main pointer was to indicate the sun position, for setting the date that everything else progressed from.

There were five dials on the back, showing the cycles of important games events, such as the Olympic games, and longer period cycles like the Metonic and the Saros cycle, used to calculate eclipses.

From the information gleaned it has been possible to recreate the Mechanism, and one of these was on display, showing both the beauty and complexity contained in the original, which would have been made of bronze and wood.

Although the instrument displays some inaccuracies, this is mainly due to the limitations of the knowledge of the times, and the quality and detail of the original construction, some 2200 years ago, was truly astonishing. It indicated that the Greeks knew that the lunar orbit was an ellipse, not a circle, and even took account of that speeding up and slowing down of the moon. It is also likely that some of the inaccuracy was due to the inability to be able to build instruments to the level of precision required to demonstrate the knowledge they were trying to demonstrate. For example, the teeth in the 37 gears would have needed to be done using manual processes with the inevitable flaws.

So, whilst not quite able to enable the time travel the movie suggested, it was an incredible capable machine for its time, and would not be equalled for many, many years.

An amazing insight into the people of the times, and an excellent and thought-provoking lecture by Dr. Vassilios McInnes Spathopoulos.