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Artikel XXXI

Antikythera mechanism

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Mystery of ancient astronomical calculator unveiled

An international team has unravelled the secrets of a 2,000-year-old computer which could transform the way we think about the ancient world. Professor Mike Edmunds and Dr Tony Freeth, of Cardiff University led the team who believe they have finally cracked the workings of the Antikythera Mechanism, a clock-like astronomical calculator dating from the second century BCE.

The remains of the device were first discovered in 1902 when archaeologist Valerios Stais noticed a heavily corroded gear wheel amongst artefacts recovered by sponge divers from a sunken Roman cargo ship. A further 81 fragments have since been found containing a total of 30 hand-cut bronze gears. The largest fragment has 27 cogs.

Researchers believe these would have been housed in a rectangular wooden frame with two doors, covered in instructions for its use. The complete calculator would have been driven by a hand crank. Although its origins are uncertain, the new studies of the inscriptions suggest it would have been constructed around 100-150 BCE, long before such devices appear in other parts of the world.

The new research suggests it is more sophisticated than anyone previously thought. Using bespoke non-invasive imaging systems, such as three-dimensional X-ray microfocus computed tomography, the team was able to take detailed pictures of the device and uncover new information. Detailed work on the gears in the mechanism show that it was able to track astronomical movements with remarkable precision.

The calculator was able to follow the movements of the moon and the sun through the Zodiac, predict eclipses and even recreate the irregular orbit of the moon. The team believe it may also have predicted the positions of some or all of the planets. The findings suggest that Greek technology was far more advanced than previously thought. No other civilisation is known to have created anything as complicated for another thousand years.

Professor Edmunds said: "This device is just extraordinary, the only thing of its kind. The design is beautiful, the astronomy is exactly right. The way the mechanics are designed just makes your jaw drop. Whoever has done this has done it extremely well." The team was made up of researchers from Cardiff, the National Archaeological Museum of Athens and the Universities of Athens and Thessaloniki.

Remarkably, scans showed the device uses a differential gear, which was previously believed to have been invented in the 16th century.

The level of miniaturisation and complexity of its parts is comparable to that of 18th century clocks.

There are three dials on the device. The front dial displays the position of the sun and the moon in the zodiac and a corresponding calendar of 365 days, which could be adjusted for leap years. The back dials track the long-term lunar cycle, including the Metonic (Maansknopen!) cycle of 19 years, when the same phase of the moon returns on the same date of the year. The dials also track the Callippic cycle of 76 years, when the moon returns to the same position in the sky relative to the zodiac and its monthly lunar phase.

Francois Charette, an astronomer at Ludwig-Maximilian University in Munich, said finding such a complicated computer in Ancient Greece was like finding the plans for a steam engine in Renaissance Italy.

The mechanism is in over 80 pieces and stored in precisely controlled conditions in Athens where it cannot be touched.

Recreating its workings was a difficult, painstaking process, involving astronomers, mathematicians, computer experts, script analysts and conservation experts. The researchers are now hoping to create a computer model of how the machine worked, and, in time, a full working replica. It is still uncertain what the ancient Greeks used the mechanism for, or how widespread this technology was.

One of the remaining mysteries is why the Greek technology invented for the machine seemed to disappear. No other civilisation is believed to have created anything as complex for another 1,000 years. One explanation could be that bronze was often recycled in the period the device was made, so many artefacts from that time have long ago been melted down and erased from the archaelogical record.

The fateful sinking of the ship carrying the Antikythera Mechanism may have inadvertently preserved it.

Sources: BBC News, EurekAlert! (29 November 2006), Telegraph, The Guardian, The Independent (30 November 2006)

http://news.bbc.co.uk/2/hi/science/nature/6191462.stm

http://www.eurekalert.org/pub_releases/2006-11/cu-moa112806.php

http://www.telegraph.co.uk/news/main.jhtml?xml=/news/2006/11/29/ugreek129.xml

http://www.guardian.co.uk/science/story/0,,1960316,00.html

http://news.independent.co.uk/world/science_technology/article2026794.ece

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Antikythera mechanism

From Wikipedia, the free encyclopedia

The Antikythera mechanism (main fragment)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.

Contents

1 Discovery

2 Origins

3 Similar devices in ancient literature

4 Function and purpose

5 Possible uses

6 First investigations and reconstructions

6.1 Price

6.2 Bromley and Percival

6.3 Wright

6.4 Antikythera Mechanism Research Project

7 New discoveries

8 See also

9 Notes

10 References

11 External links

Discovery

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[1] 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.

Origins

The origins of the mechanism are unclear, as are the circumstances by which it came to be on the cargo ship. The ship was Roman, but 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 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.[1]

Similar devices in ancient literature

Cicero mentions two separate machines similar to the Antikythera mechanism.

The first was built by Archimedes and brought to Rome by the Roman general Marcellus after Archimedes' death at the siege of Syracuse in 212 BC. Marcellus had a high respect for Archimedes and this was the only item he kept from the siege. The device was kept as a family heirloom, and Cicero was shown it by Gallus about 150 years later. The motions of the sun, moon and five planets were shown by the device. Gallus gave a 'learned explanation' of it and demonstrated it for Cicero. "And when Gallus moved the globe, it was actually true that the moon was always as many turns behind the sun on the bronze contrivance as would agree with the number of days it was behind in the sky. Thus the same eclipse of the sun happened on the globe as would actually happen". Cicero, De Re Publica I 21-22 If Cicero's account is correct, and there is no reason to doubt it, then this technology existed as early as the 3rd century BC. There are several mentions by later Roman writers of Archimedes' device.[citation needed]

Cicero also says that another such device was built 'recently' by his friend Posidonius, "... each one of the revolutions of which brings about the same movement in the sun and moon and five wandering stars [planets] as is brought about each day and night in the heavens..." Cicero, De Natura Deorum II.88 (or 33-34)

It is unlikely that either of these machines was the Antikythera mechanism found in the shipwreck, because both the devices mentioned by Cicero were located in Rome. So we know of at least three such devices. The modern scientists who have reconstructed the Antikythera mechanism also agree that it was too sophisticated to have been a one-off device.

Function and purpose

Schematic of the artifact's mechanismThe 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 the History of Science 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,[2] 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.[citation needed]

It is probable that the Antikythera mechanism was not unique, as showed by Cicero's words. This 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."

Possible uses

This article or section does not cite its references or sources.

You can help Wikipedia by introducing appropriate citations. This article has been tagged since December 2006.

Possible practical uses of this device were:

Astrology was commonly practised in the ancient world. In order to create an astrological chart, the configuration of the heavens at a particular point of time is needed. It can be very difficult and time-consuming to work this out by hand, and a mechanism such as this would have made an astrologer's work very much easier.

Calculating solar and lunar eclipses. However, the device would probably only have indicated days when eclipses might occur, and a more accurate calculation of the time of day would have to be done by hand.

Setting the dates of religious festivals connected with astronomical events

Adjusting calendars, which were based on lunar cycles as well as the solar year

First investigations and reconstructions

Reconstruction of the Antikythera mechanism in the National Archaeological Museum, Athens (made by Robert J. Deroski, based on Derek J. de Solla Price model)

Price

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.

2005 X-ray image of the Antikythera mechanism

Wright

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 [2] 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.

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, 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.