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The Antikythera mechanism (Template:Lang-el) is an ancient mechanical analog computer (as opposed to digital computer) designed to calculate astronomical positions. It was discovered in the Antikythera wreck off the Greek island of Antikythera, between Kythera and Crete, and has been dated to about 80 BCE.
The mechanism was found by chance in the remains of an ancient ship, discovered sometime before Easter 1900 at a depth of 42 m. Many statues and other artifacts were retrieved on site by Greek sponge divers. The wreck's most important discovery, however, came when, on May 17, 1902, archaeologist Spyridon Stais noticed that a piece of rock recovered from the site had a gear wheel embedded in it. Upon examination, it was found that the "rock" was in fact a heavily encrusted and corroded mechanism which had survived in three main parts and dozens of smaller fragments. The device was about 30 cm by 15 cm in size with the thickness of a book, made from bronze and originally mounted in a wooden frame. It was inscribed with a text of over 2,000 characters, of which about 95% have been deciphered. The full text of the inscription has not yet been published.
The device is displayed in the Bronze Collection of the National Archaeological Museum of Athens, accompanied by a reconstruction. Another reconstruction is on display at the American Computer Museum in Bozeman, Montana.
The origins of the mechanism are unclear, as are the circumstances in which it came to be on the Antikythera ship. The ship was a Roman one, though there is no doubt that the mechanism itself was made in Greece. One hypothesis is that the device was constructed at an academy founded by the ancient Stoic philosopher Poseidonios on the Greek island of Rhodes, which at the time was known as a centre of astronomy and mechanical engineering. Investigators have suggested that the ship could have been carrying it to Rome, together with other treasure looted from the island to support a triumphal parade being staged by Julius Caesar. 
Function and purpose
The Antikythera mechanism is one of the world's oldest known geared devices. It has puzzled and intrigued historians of science and technology since its discovery. Following decades of work in order to clean the device, systematic investigations were undertaken in 1951 by British Derek J. de Solla Price, professor of history of science at Yale University at that time. In June 1959, in a front-page article in Scientific American titled "An ancient Greek computer", he brought forth the theory that the Antikythera mechanism was a device for calculating the motions of stars and planets, which would make the device the first analog computer. Up until that time the function of the Antikythera mechanism was largely unknown, though it had been correctly identified as an astronomical device, perhaps being an astrolabe. In 1971 the Greek Institute of Nuclear Technology at the National Research Center for Physical Sciences Demokritos performed gamma-ray scans of the mechanism. In 1972 Price teamed up with Greek nuclear physicist Christoforos Karakalos, who carried out X-ray analysis of the mechanism, in this way revealing critical information concerning the device's interior configuration. In 1974 he authored "Gears from the Greeks: the Antikythera mechanism — a calendar computer from ca. 80 BCE.", where he presented a model of how the mechanism could have functioned. Recent research breakthroughs seem to give credence to Price's theory (see below).
The device is all the more impressive for its use of a differential gear—previously believed to have been invented in the sixteenth century—and for the level of miniaturization and complexity of its parts, which is comparable to that of clocks made in the eighteenth century. The differential gear arrangement is composed of 30+ gears with teeth formed through equilateral triangles. When past or future dates were entered via a crank (now lost), the mechanism calculated the position of the sun, moon or other astronomical information such as the location of other planets. The use of differential gears enabled the mechanism to add or subtract angular velocities. The differential was used to compute the synodic lunar cycle by subtracting the effects of the sun's movement from those of the sidereal lunar movement. It is possible that the mechanism is based on heliocentric principles, rather than the then dominant geocentric view espoused by Aristotle and others. This may indicate that the heliocentric view was more widely accepted at the time than was previously thought.
While the Antikythera mechanism was certainly remarkably advanced for its era, it was possibly not unique. Cicero, writing in the 1st century BCE, mentions an instrument "recently constructed by our friend Poseidonius, which at each revolution reproduces the same motions of the sun, the moon and the five planets." (Cicero was himself a student of Poseidonius.) Similar devices are mentioned in other ancient sources. It also adds support to the idea that there was an ancient Greek tradition of complex mechanical technology which was later transmitted to the Arab world, where similar but simpler devices were built during the medieval period. The early ninth century Kitab al-Hiyal ("Book of Ingenious Devices"), commissioned by the Caliph of Baghdad, records over a hundred mechanical devices described in Greek texts that had been preserved in monasteries. Such knowledge could have yielded to or been integrated with European clockmaking and ancient cranes.
The device's actual purpose still remains unclear, as we do not know its full range of capabilities. Some investigators believe that the Antikythera mechanism could have been used to track celestial bodies for auspicious occasions such as religious events or births. Price suggested that it might have been on public display, possibly in a museum or public hall in Rhodes. The island was renowned for its displays of mechanical engineering, particularly automata, which apparently were a speciality of the Rhodians; to quote Pindar's seventh Olympic Ode:
- The animated figures stand
- Adorning every public street
- And seem to breathe in stone, or
- move their marble feet.
Investigations and reconstructions
Price's model, as presented in his "Gears from the Greeks: the Antikythera mechanism — a calendar computer from ca. 80 BCE", was the first, theoretical, attempt at reconstructing the device. According to that model, the front dial shows the annual progress of the sun and moon through the zodiac against the Egyptian calendar. The upper rear dial displays a four-year period and has associated dials showing the Metonic cycle of 235 synodic months, which approximately equals 19 solar years. The lower rear dial plots the cycle of a single synodic month, with a secondary dial showing the lunar year of 12 synodic months. A British orrery maker named John Gleave, constructed a replica based hereupon, though with some very slight modifications of his, in order for it to be functional. The following link gives an idea of the internals of this device, though later researchers have doubts as to whether Price's model is an accurate representation of the original Antikythera mechanism.
A partial reconstruction was built by Australian computer scientist Allan George Bromley (1947–2002) of the University of Sydney and Sydney clockmaker Frank Percival. This project led Bromley to review Price's X-ray analysis and to make new, more accurate X-ray images that were studied by Bromley's student, Bernard Gardner, in 1993. His model differed significantly from Price's earlier proposition, though it wasn't considered satisfactory either.
Another reconstruction was made in 2002 by Michael Wright, mechanical engineering curator for The Science Museum in London, working with Allan Bromley. He analyzed the mechanism using linear tomography, which can create images of a narrow focal plane, and thus visualized the gears in great detail. In Wright's reconstruction, the device not only models the motions of the sun and moon, but of all the classical planets.
Antikythera Mechanism Research Project
The Antikythera mechanism is now being studied by the Antikythera Mechanism Research Project, a joint program between Cardiff University, the National and Kapodistrian University of Athens, the Aristotle University of Thessaloniki, the National Archaeological Museum of Athens, X-Tek Systems UK and Hewlett-Packard USA, funded by the Leverhulme Trust and the Cultural Foundation of the National Bank of Greece.
The mechanism's fragility precluded its removal from the museum, so the Hewlett-Packard research team built a large 3-D X-ray imaging scanner, known as the "PTM Dome", around the device. The images are processed using 400kV microfocus computerised tomography. It was announced in Athens on October 21, 2005 that many new pieces of the Antikythera mechanism had been found. There are now more than 70 fragments. Most of the new pieces had been stabilized but were awaiting conservation. On June 6, 2006 it was announced  that the imaging system had enabled much more of the Greek inscription to be viewed and translated, from about 1,000 characters that were visible previously, to about 2,000 characters, representing about 95% of the complete text. The team's findings might shed new light concerning the function and purpose of the Antikythera mechanism. Research is ongoing.
- Armillary sphere
- Astronomical clock
- Classical planets
- Horoscopic astrology
- Orrery, a free-standing solar system model
- Prague Orloj
- Reverse engineering
- American Mathematical Society's The Antikythera Mechanism I and The Antikythera Mechanism II (Java Animation by Bill Casselman)
- Fortunat F. Mueller-Maerki's Geartrain diagram
- Manos Roumeliotis's Antikythera Mechanism MOV files
- Rupert Russell's The Antikythera Mechanism
- Price, Derek J. de Solla, "An Ancient Greek Computer". Scientific American, June 1959. p. 60–67.
- Rice, Rob S., "The Antikythera Mechanism: Physical and Intellectual Salvage from the 1st Century BCE". USNA Eleventh Naval History Symposium.
- The Economist, "The Antikythera mechanism: The clockwork computer". September 19, 2002.
- Rice, Rob S., "Gears, Galleys, and Geography The Antikythera Mechanism's Implications". Text of the 1993 APA Abstract.
- Rosheim, Robot Evolution: The Development of Anthrobotics. Wiley-IEEE, 1994
- Lienhard, John H., Antikythera Mechanism. "The Engines of Our Ingenuity". KUHF-FM, Houston.
- Wright, M T. "A Planetarium Display for the Antikythera mechanism". Horological Journal, 144 No. 5, 169–173, May 2002.
- Derek De Solla Price. Gears from the Greeks: The Antikythera Mechanism—A Calendar Computer from ca. 80 BCE. Science History Publications, New York, 1975, ISBN 0871696479; originally published in Transaction of The American Philosophical Society, New Series, Volume 64, Part 7, 1974.
- Russo, Lucio, "The Forgotten Revolution : How Science Was Born in 300 BCE and Why it Had to Be Reborn". Springer , 2004, ISBN 3540203966.
- The Antikythera Mechanism Research Project