The Antikythera mechanism, built in Greece, is the oldest mechanical ancient computer to be discovered worldwide, and was created for accurate calculations of astronomical positions. It was discovered in the Antikythera shipwreck on the Greek island of Antikythera in a wooden box by Valerios Stais on May 17, 1902.
The importance and complexity of the mechanism was understood only a few decades after the discovery.
This advanced computer from 200 BC is currently found at the National Archeology Museum in Athens, with its mechanism, gears and inscriptions on it, forcing researchers to reconsider their view of the level of complexity of ancient Greek science. The mechanism comes in a shape of a box with a few dials on the outside and inside it has an assembly of gears similar to a mechanical clock of the eighteenth century.
After the initial discovery, 20 more gears were recovered, including a sophisticated set of gears mounted on a rotary plate acting as an epicyclic system. All of the components appear to be cut from a single sheet of bronze about 2 millimetres thick. The gears have teeth at an angle of 60 degrees and the sizes are identical which makes the wheels combine perfectly.
The Antikythera mechanism is one of the most ancient and complex scientific computers. Although its constructions without any flaws suggest that there were other mechanisms before it, these mechanisms were not discovered. Its design was made on the basis of astronomical and mathematical theories developed by Greek astronomers, somewhere between 200-100 BC. The level of miniaturization is remarkable and the complexity of it is at the level of 18th century clocks.
The mechanism is composed from three dials. The one in front is the largest one showing 365 segments. Each segment represents a day from the Egyptian solar calendar. Inside the dial, a second circle shows the 12 signs of the zodiac. By tuning a handle (which was never found) one could position the two needles to indicate for each day of the year the exact position of the Sun and Moon with a small sphere indicating the phase of the moon.
The back of the mechanism was composed by two dials in order to guarantee its exactitude. Whatever the day and year was chosen on the front dial, one dial from the back of the mechanism shows the Metonic cycle. This indicates the lunar and solar over a period of 19 years corresponding to 235 lunar months. The second dial from the back indicates eclipses of the Sun and Moon.
Several writers from antiquity mention the existence of similar machines, but the Antikythera mechanism is the only one which has been recovered. Also recent discoveries showed that the mechanism was used to indicate which cities would host future Olympic Games every four years.
In the inscriptions of the mechanism are some references to the planets Mars and Venus. It is speculated that the mechanism would have been able to represent and calculate the position of all five planets known to Greeks.