Antikythera Mechanism

The Antikythera mechanism is an ancient mechanical computer designed to calculate astronomical positions. It was recovered in 1900–1901 from the Antikythera wreck. Its significance and complexity were not understood until decades later. Its time of construction is now estimated between 150 and 100 BC. Technological artifacts of similar complexity and workmanship did not reappear until the 14th century, when mechanical astronomical clocks were built in Europe.

The mechanism is the oldest known complex scientific calculator. It contains many gears, and is sometimes called the first known analog computer, although its flawless manufacturing suggests that it may have had a number of undiscovered predecessors during the Hellenistic Period. It appears to be constructed upon theories of astronomy and mathematics developed by Greek astronomers.

Consensus among scholars is that the mechanism itself was made in the Greek-speaking world. One hypothesis is that the device was constructed at an academy founded by the philosopher Posidonius on the Greek island of Rhodes, which at the time was known as a center of astronomy and mechanical engineering, and that perhaps the astronomer Hipparchus was the engineer who designed it since it contains a lunar mechanism which uses Hipparchus's theory for the motion of the Moon. However, the most recent findings of The Antikythera Mechanism Research Project, published July 31, 2008, alternatively suggest that the concept for the mechanism originated in the colonies of Corinth, which might imply a connection with Archimedes.

Discovery
The device was discovered in a shipwreck off Point Glyphadia on the Greek island of Antikythera. The wreck had been discovered in October 1900 and divers had retrieved numerous artifacts, most of them works of art. On 17 May 1902, archaeologist Valerios Stais was examining the finds and noticed that one of the pieces of rock had a gear wheel embedded in it. Stais initially believed it was an astronomical clock, but most scholars considered the device to be too complex to have been constructed during the same period as the other pieces that had been discovered.

The device is remarkable for the level of miniaturization and for the complexity of its parts, which is comparable to that of 19th-century clocks. It has more than 30 gears, although as many as 72 gears have been suggested, with teeth formed through equilateral triangles. When a date was entered via a crank (now lost), the mechanism calculated the position of the Sun and Moon or other astronomical information such as the locations of planets.

The mechanism has three main dials, one on the front, and two on the back. The front dial has two concentric scales. The outer ring is marked off with the days of the 365-day Egyptian calendar. Inside this, there is a second dial marked with the Greek signs of the Zodiac and divided into degrees. The calendar dial can be moved to compensate for the effect of the extra quarter day (there are 365.2422 days per year) by turning the scale backwards one day every four years.

The front dial probably carried at least three hands, one showing the date, and two others showing the positions of the Sun and the Moon. The Moon indicator is adjusted to show the first anomaly of the Moon's orbit. It is reasonable to suppose the Sun indicator had a similar adjustment, but any gearing for this mechanism (if it existed) has been lost. The front dial also includes a second mechanism with a spherical model of the Moon that displays the lunar phase.

There is reference in the inscriptions for the planets Mars and Venus, and there is some speculation that the mechanism may have had indicators for all the five planets known to the Greeks. None of the gearing for such planetary mechanisms survives, except for one gear otherwise unaccounted for.

Finally, the front dial includes a parapegma, a precursor to the modern day almanac, which was used to mark the rising and setting of specific stars. Each star is thought to be identified by Greek characters which cross-reference details inscribed on the mechanism.

It was announced in Athens on 21 October 2005 that new pieces of the Antikythera mechanism had been found. There are now 82 fragments. Most of the new pieces had been stabilized but were awaiting conservation.

Reconstruction
On 30 November 2006, a new reconstruction of the mechanism was made public by the Antikythera Mechanism Research Project, based on high resolution X-ray tomography. This work doubled the amount of readable text, corrected prior transcriptions, and provided a new translation. The inscriptions led to a dating of the mechanism to around 150 to 100 BC. It is evident that they contain a manual with an astronomical, mechanical and geographical section.

The new discoveries confirm that the mechanism is an astronomical analog calculator, used to predict the positions of celestial bodies. This work proposes that the mechanism possessed 37 gears, of which 30 survive, and was used for prediction of the position of the Sun and the Moon. Based on the inscriptions, the authors speculate that planetary motions may also have been indicated.

On the front face were graduations for the solar scale and the zodiac together with pointers that indicated the position of the Sun, the Moon, the lunar phase, and possibly the planetary motions.

On the back, two spiral scales (made of half-circles with two centers) with sliding pointers indicated the state of two further important astronomical cycles: the period of approximately 18 years separating the return of the Sun, Moon and Earth to the same relative positions and the more accurate cycle of 54 years and one day (essential in eclipse prediction).

It has further been discovered that the mechanism was based on computation methods used in Babylonian astronomy, not ancient Greek astronomy, implying that Babylonian astronomy inspired the Greek counterpart – including the mechanical constructs.