Artifact – Antikythera Mechanism

Antikythera Mechanism

Featured Artifact the Antikythera Mechanism

The Antikythera Mechanism is an ancient analog computer designed to predict astronomical positions and eclipses. Antikythera Mechanism was recovered in 1900 from a shipwreck off the Greek island of Antikythera. The instrument has been designed and constructed by Greek scientists and dated to 150 to 100 BC. Technological artifacts approaching the Antikythera Mechanism’s complexity and workmanship did not appear again until the 14th century, when mechanical astronomical clocks began to be built in Western Europe.

 The Antikythera mechanism - Fragment A – front


The Antikythera mechanism – Fragment A – front

The Antikythera Mechanism was housed in a wooden box about 340 × 180 × 90 mm in size and comprised 30 bronze gears although, more could have been lost. The largest gear, clearly visible in fragment A, was about 140 mm in diameter and had 223 teeth. The mechanism’s remains were found as 82 separate fragments of which only seven contain any gears or significant inscriptions.

Since their discovery the fragments of the Antikythera mechanism are kept at the National Archaeological Museum of Athens.

Antikythera Mechanism

Antikythera Mechanism

The makers of the Antikythera Mechanism – from the Ancient World as they were! – seem to have accepted that the Sun was at the center of an orbital system, – anticipating Copernicus and Galileo by some fifteen hundred years.

On the front face of the Antikythera Mechanism there is a fixed ring dial representing the ecliptic, the twelve zodiacal signs marked off with equal 30 degree sectors. This matched with the Babylonian custom of assigning one twelfth of the ecliptic to each zodiac sign equally, even though the constellation boundaries were variable. Outside of that dial is another ring which is rotatable, marked off with the months and days of the Sothic Egyptian calendar, twelve months of 30 days plus five intercalary days. The months are marked with the Egyptian names for the months transcribed into the Greek alphabet. The first task, then, is to rotate the Egyptian calendar ring to match the current zodiac points. The Egyptian calendar ignored leap days, so it advanced through a full zodiac sign in about 120 years

Antikythera Mechanism

Antikythera Mechanism Internal View

The Antikythera Mechanism was operated by turning a small hand crank, now lost which was linked via a crown gear to the largest gear, the four-spoked gear visible on the front of fragment A, the gear named b1. This moved the date pointer on the front dial, which would be set to the correct Egyptian calendar day. The year is not selectable, so it is necessary to know the year currently set, or by looking up the cycles indicated by the various calendar cycle indicators on the back in the Babylonian ephemeris tables for the day of the year currently set, since most of the calendar cycles are not synchronous with the year. The crank moves the date pointer about 78 days per full rotation, so hitting a particular day on the dial would be easily possible if the mechanism was in good working condition. The action of turning the hand crank would also cause all interlocked gears within the mechanism to rotate, resulting in the simultaneous calculation of the position of the Sun and Moon, the moon phase, eclipse and calendar cycles, and perhaps the locations of planets.

Computer graphic Antikythera mechanism

Computer graphic Antikythera mechanism

The operator also had to be aware of the position of the spiral dial pointers on the two large dials on the back. The pointer had a “follower” that tracked the spiral incisions in the metal as the dials incorporated four and five full rotations of the pointers. When a pointer reached the terminal month location at either end of the spiral, the pointer’s follower had to be manually moved to the other end of the spiral before proceeding further.

More than 21 centuries ago, a mechanism of fabulous ingenuity was created in Greece, a device capable of indicating exactly how the sky would look for decades to come — the position of the moon and sun, lunar phases and even eclipses. But this incredible invention would be drowned in the sea and its secret forgotten for two thousand years.