About 2,200
years ago an unknown genius in ancient Greece built a mechanical computer. It
calculated and displayed astronomical events. The device had a level of
engineering skill 1,500 years ahead of its time.
In 1900 Greek
sponge divers, blown off course by a storm, took their chances in deep water.
They were off the island of Antekythera and instead found a Roman shipwreck
from 85BC, loaded with Greek artefacts. The haul contained curious wood and
bronze fragments. About the size of a roof tile, the largest piece had gear
wheels visible. Archaeologists were baffled but with modern scanning techniques
and rigorous science, over a period of about 60 years of painstaking work, the
puzzle has been solved.
The Antekythera
Mechanism Research Project, set up by Cardiff University in 2000, used CT scans
(microfocus X Ray Computer Tomography) to produce 3D structural images and
advanced photography (polynomial texture mapping) to search for markings.
This revealed hidden gears, lines, text
and markings on the fragments. They confirmed the ancient Greeks had arranged
precision gears so accurately the device could model the motion of astronomical
objects far into the future. It was operated by handle and individual pointers
on the front face, driven by 30 intermeshed gears, indicated the astronomical
position of the sun, moon and planets. On the rear face is the ancient Greek
calendar with pointers to predict lunar eclipses, solar eclipses and the
Olympic games dates between their four games venues.
To predict lunar position and phase is very complicated. The moon shifts position, speed and angle on
it's elliptical orbit of the earth. Also a year is 365.25 days so to make any
daily calendar work regular corrections are needed. This complexity means a
complete lunar cycle, where the moon ends up at the same phase and position in
the sky, takes about 19 years. This is called the Metatonic cycle. However an
even more accurate 76 year cycle, discovered and used by the Greeks, called the
Callipic cycle confirms an astonishing level of technical and scientific skill.
Thought to be
invented in the middle ages the mechanism had differential (variable speed)
gears yet the calendar start date was 205BC.
The first scientist to reconstruct a machine is Dr Michael Wright previously of the
Science Museum here are the workings of
his model: https://m.youtube.com/watch?v=MqhuAnySPZ0
The maker is
unknown but are there clues? There are several philosophers possibly involved
and such a complex device would have evolved over time. Archimedes (287 -
212BC) as an engineer used gears and the astronomy is based on theories of
Hipparchus(190 - 120BC). An intriguing clue about a mechanism can be found in a
surviving letter. Hipparchus is thought to have founded a school on Rhodes. One
of his students Posidonius, who knew the Roman diarist Cicaro,
later ran the school. In 79BC, Cicero mentions, in one of his letters a
device “recently constructed
by our friend Posidonius, which at each revolution reproduces the same motions
of the sun, the moon, and the five planets that take place in the heavens every
day and night.”
The Antekythera
Mechanism was lost for 2000 years. Bronze was very valuable to the Roman
military and melted much down, so other devices may have been destroyed.
However, the technology was not lost and appeared later in the Arabian geared
Islamic Astrolabe and then in Europe in the first clocks, leading to our modern
geared machines. Yes, the ancestor of the gearbox in your car could well be a
2200 year old computer!
and here is a
Lego version!.....
- John Faulkner
