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The Antikythera mechanism (Greek: O μηχανισμός των Αντικυθήρων transliterated as O mēchanismós tōn Antikythērōn) 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 150-100 BC.
Sometime before Easter 1900, Elias Stadiatos, a Greek sponge diver, discovered the wreck of an ancient cargo ship off Antikythera island at a depth of 42 m. Sponge divers retrieved several statues and other artifacts from the site. The mechanism itself was discovered on May 17, 1902, when archaeologist Valerios Stais noticed that a piece of rock recovered from the site had a gear wheel embedded in it. Examination revealed that the "rock" was in fact a heavily encrusted and corroded mechanism that had survived the shipwreck in three main parts and dozens of smaller fragments. The device itself was surprisingly thin, about 33 cm (13in) high, 17 cm (6.75in) wide and 9 cm (3.5in) thick, made of bronze and originally mounted in a wooden frame. It was inscribed with a text of over 2,000 characters, all of which 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.
One hypothesis is that the device was constructed at an academy founded by the ancient Stoic philosopher Posidonius 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. Posidonius as the creator is further supported by accounts of Cicero (see "Function and Purpose," below). After indepth x-ray analysis had been completed it was noted that the device's "Metal pointers show the positions in the zodiac of the sun, moon and five planets known in antiquity."
Another hypothesis is that the mathematician Archimedes constructed the mechanism. Archimedes developed the advanced geometry needed for the Antikythera mechanism's construction. However, there is little to link Archimedes directly with the machine. 
 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 cleaning the device, in 1951 British science historian Derek J. de Solla Price undertook systematic investigation of the mechanism. In June 1959, Price's "An Ancient Greek Computer" was the lead article in Scientific American. Price advanced the theory that the Antikythera mechanism was a device for calculating the motions of stars and planets, which would make the device the first known analog computer. Until that time, the Antikythera mechanism's function was largely unknown, though it had been correctly identified as an astronomical device, perhaps being an astrolabe.
In 1971 Price, by then the first Avalon professor of science history at Yale University, teamed up with Charalampos Karakalos, professor of nuclear physics at the Greek National Centre of Scientific Research "DEMOKRITOS". Karakalos had gamma- and X-ray analysis carried out on the mechanism, which revealed critical information about the device's interior configuration. In 1974 Price wrote "Gears from the Greeks: the Antikythera mechanism — a calendar computer from ca. 80 B.C.", where he presented a model of how the mechanism could have functioned. Recent research breakthroughs confirm Price's theory.
The device uses a differential gear, previously believed to have been invented in the 16th century, and is remarkable for the level of miniaturization and complexity of its parts, which is comparable to that of 18th century clocks. It has a differential gear arrangement with over 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.
It is probable that the Antikythera mechanism was not unique. Cicero, writing in the 1st century BC, mentions an instrument "recently constructed by our friend Posidonius, which at each revolution reproduces the same motions of the sun, the moon and the five planets." 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 that was later transmitted to the Muslim world, where similar but simpler devices were built during the medieval period. The early 9th 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 medieval cranes.
The functions provided by the device include:
- A 365-day calendar, which ingeniously factored in the leap year every four years
- The Metonic cycle
- The Callippic cycle, which is four Metonic cycles minus one day and reconciles the solar year with the lunar calendar
- Predict lunar and solar eclipses under the Saros cycle, a 223-month repetitive interplay of the Sun, Earth and Moon
- A star almanac, showing the times when the major stars and constellations of the Greek zodiac would rise or set
- (speculatively) may also have shown the positions of the planets
- Includes the main lunar anomaly (the Moon appears to move across the heavens at different speeds at different times)
Price suggested that it might have been on public display, possibly in a museum or public hall in Rhodes. The island was known for its displays of mechanical engineering, particularly automata, which apparently were a specialty of the Rhodians. Pindar, one of the nine lyric poets of ancient Greece, said this of Rhodes in his seventh Olympic Ode:
- "The animated figures stand
- Adorning every public street
- And seem to breathe in stone, or
- move their marble feet."
 First investigations and reconstructions
Price's model, as presented in his "Gears from the Greeks: the Antikythera mechanism — a calendar computer from ca. 80 BC", 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 own 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.
 Bromley and Percival
An ingenious variant on Price's reconstruction was built by Australian computer scientist Allan George Bromley of the University of Sydney and Sydney clockmaker Frank Percival. Bromley went on to make new, more accurate X-ray images in collaboration with Michael Wright. Some of these were studied by Bromley's student, Bernard Gardner, in 1993.
All previous reconstructions rely on data taken from the description by Derek J. de Solla Price. Michael Wright, formerly Curator of Mechanical Engineering at The Science Museum, London, and now of Imperial College, London, made a completely new study of the original fragments together with Allan Bromley. For this, Wright designed and made apparatus for linear tomography, allowing resolution of radiographic images in three dimensions.
The new data from this survey supersedes that of Price. Working from it, Wright has, between 2002 and 2005, developed an entirely different reconstruction. The arrangement of the surviving gearing is not as Price described. The function of both back dials is changed. There is evidence that further mechanism has been lost from under the front dial and that this dial display was more elaborate than previously supposed. Wright’s working model demonstrates the possibility that it might have been a fully-elaborated orrery, corresponding to those mentioned in ancient literature. (Follow external link.)
Wright points out that the detail of the instrument is less important than its significance as artifactual evidence for an established tradition of geared mechanism in Hellenistic antiquity that is otherwise known only through literary references. A line of development may be traced from these devices, through similar ones described in Arabic sources, to the medieval rise of the mechanical tradition of Western Europe.
 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 supported by 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 and X-Tek systems had to bring their devices to Greece. HP built a 3-D surface imaging device, known as the "PTM Dome," that surrounds the object under examination. X-Tek systems developed especially for the Antikythera Mechanism a 12 ton 450kV microfocus computerised tomographer. It was announced in Athens on 21 October 2005 that many new pieces of the Antikythera mechanism had been found. There are now more than 80 fragments. Most of the new pieces had been stabilized but were awaiting conservation. On 30 May 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 non-lost text. The team's findings might shed new light concerning the function and purpose of the Antikythera mechanism. Research is ongoing. The first results will be announced at an international conference in Athens (Greece), November 30 and December 1, 2006.
 New discoveries
According to one recent article, it appears that the device was more complex than originally thought, containing 37 gears. The inscriptions on the device have been deciphered but the complete text does not appear to be available. The new discoveries confirm that the mechanism is an astronomical computer or orrery used to predict the positions of heavenly bodies in the sky.
On 30 November 2006, the science journal Nature published a new reconstruction of the mechanism based on the high resolution X-ray tomography described above, together with expanded versions of the text and its translation where possible. This work proposes that the mechanism possessed 37 gears, of which 30 still survive, and was used for prediction of the position of the sun, moon and probably planets. On the front face were graduations for the solar cycle and the zodiac together with pointers that indicated the position of the sun and the moon, and the lunar phase: based on the inscriptions, the authors speculate that planetary motions may also have been indicated here, based on mention of the stationary points. On the back, two spiral pointers indicated the state of two further important astronomical cycles: the Saros cycle, the period of approximately 18 years separating the return of the sun, moon and earth to the same relative positions (essential in eclipse prediction); and the Callippic cycle that proposed 940 cycles in approximately 76 years.
 See also
- Armillary sphere
- Astronomical clock
- Classical planets
- Horoscopic astrology
- Orrery, a free-standing solar system model
- Prague Orloj
- Reverse engineering
- ^ Solla Price (1959: 60). The name has been confused in some recent publications with that of the politician Spyridon Stais.
- ^ The American Mathematical Society site has a page describing the differential gear of the Antikythera mechanism: The differential in the Antikythera Mechanism.
- "Decoding the ancient Greek astronomical
calculator known as the Antikythera Mechanism"
T. Freeth1, Y. Bitsakis, X. Moussas, J. H. Seiradakis, A. Tselikas, H. Mangou, M. Zafeiropoulou, R. Hadland, D. Bate, A. Ramsey, M. Allen, A. Crawley, P. Hockley, T. Malzbender, D. Gelb, W. Ambrisco and M. G. Edmunds.
Nature 444, 587-591 (30 November 2006) | doi:10.1038/nature05357;
- American Mathematical Society's The Antikythera Mechanism I and The Antikythera Mechanism II (Java Animation by Bill Casselman)
- Marchant, J., "In search of lost time", Nature, Vol.444, No.7119, (30 November 2006), 534-538.
- 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., papers:
- “Simple X-ray Tomography and the Antikythera Mechanism”, PACT (Revue du groupe européen d'études pour les techniques physiques, chimiques, biologiques et mathématiques appliquées à l'archéologie or Journal of the European Study Group on Physical, Chemical, Biological and Mathematical Techniques Applied to Archaeology), vol.45 (1995), pp. 531 – 543.
- “Current Work on the Antikythera Mechanism”, Proc. Conf. Αρχαία Ελληνική Τεχνολογία (Ancient Greek Technology), Thessaloniki, 4 – 7 September 1997, pp. 19 – 25.
- “A Planetarium Display for the Antikythera Mechanism”, Horological Journal, vol. 144 no. 5 (May 2002), pp. 169 – 173, and vol. 144 no. 6 (June 2002), p. 193.
- “Towards a New Reconstruction of the Antikythera Mechanism”, ed. S.A. Paipetis, Proc. Conf. Extraordinary Machines and Structures in Antiquity (Ancient Olympia, August 2001), Peri Technon, Patras 2003, pp. 81 – 94.
- “In the Steps of the Master Mechanic”, Proc. Conf. Η Αρχαία Ελλάδα και ο Σύγχρονος Κόσμος (Ancient Greece and the Modern World) (Ancient Olympia, July 2002), University of Patras 2003, pp. 86 – 97.
- “Epicyclic Gearing and the Antikythera Mechanism, part 1”, Antiquarian Horology, vol. 27 no. 3 (March 2003), pp. 270 – 279.
- “The Scholar, the Mechanic and the Antikythera Mechanism”, Bulletin of the Scientific Instrument Society, no. 80 (March 2004), pp. 4 – 11.
- “The Antikythera Mechanism: a New Gearing Scheme”, Bulletin of the Scientific Instrument Society, no. 85 (June 2005), pp. 2 – 7.
- “Ο Μηχανισμός των Αντικυθήρων” (The Antikythera Mechanism), Αρχαιολογία & Τέχνες 95 (June 2005), pp. 54 – 60.
- “Il meccanismo di Anticitera: l’antica tradizione dei meccanismi ad ingranaggio” (The Antikythera Mechanism: evidence for an ancient tradition of the making of geared instruments), in: E. Lo Sardo (ed.), Eureka! Il genio degli antichi, Naples, July 2005 – January 2006), Electa Napoli 2005, pp. 241 – 244.
- “Epicyclic Gearing and the Antikythera Mechanism, part 2”, Antiquarian Horology, vol. 29 no. 1 (September 2005), pp. 51 – 63.
- “Counting Months and Years: the Upper Back Dial of the Antikythera Mechanism”, Bulletin of the Scientific Instrument Society, no. 87 (December 2005), pp. 8 – 13.
- “The Antikythera Mechanism and the early history of the Moon Phase Display”, Antiquarian Horology, vol. 29 no. 3 (March 2006), pp. 319 – 329.
- “Understanding the Antikythera Mechanism” Proc. Conf. Αρχαία Ελληνική Τεχνολογία (Ancient Greek Technology), Athens, October 2005; in preparation (Preprint).
- Mr Michael Wright, staff page at Imperial College, London
- 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 0-87169-647-9; originally published in Transaction of The American Philosophical Society, New Series, Volume 64, Part 7, 1974.
- James, Peter and Thorpe, Nick. Ancient Inventions. Ballantine, 1995, ISBN 0-345-40102-6.
- Pastore, Giovanni, Antikythera E I Regoli Calcolatori, Rome, 2006, privately published 
- Russell, Rupert, "The Antikythera Mechanism" 
- Russo, Lucio, "The Forgotten Revolution: How Science Was Born in 300 BCE and Why it Had to Be Reborn". Springer , 2004, ISBN 3-540-20396-6.
- Edmunds, Mike & Morgan, Philip, "The Antikythera Mechanism: Still a Mystery of Greek Astronomy", Astronomy & Geophysics, vol. 41, pp. 6–10. (The authors mention that an "extended account" of their researches titled "Computing Aphrodite" is forthcoming in 2001, however it does not seem to have appeared.)
- News.com.com Decoding an ancient computer
 External links
- Irish Independent News Ancient Greek star calculator finally yields up its secrets.
- http://www.nature.com/nature/journal/v444/n7119/full/444534a.html - Nature news feature on the Mechanism.
- BBC News - Ancient Moon 'computer' revisited
- Preview of research results to be announced at Athens conference beginning 30 November 2006. Report includes six slides, indexed. (22 November, 2006)
- The Antikythera Mechanism Research Project
- Discovery Channel website article (8 June, 2006)
- Google Maps satellite image of relevant part of Mediterranean
- New York Times  Article "An Ancient Computer Surprises Scientists"
- Nature article
- Nature news feature
- New York Times  Article "Early Astronomical ‘Computer’ Found to Be Technically Complex"
- Ancient Calculator Was Ahead of Its Time
- San Francisco Chronicle HP imaging helps scientists figure out world's oldest mechanical calculator (Nov. 30, 2006)