Antikythera Mechanism

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"The Antikythera mechanism is an ancient mechanical calculator (also described as the first "mechanical computer") designed to calculate astronomical positions. It was discovered in the Antikythera wreck off the Greek island of Antikythera, between Kythera and Crete, in 1900. Subsequent investigation, particularly in 2006, dated it to about 150-100 BC, and hypothesised that it was on board a ship that sank en route from the Greek island of Rhodes to Rome, perhaps as part of an official loot. Technological artifacts of similar complexity did not appear until a thousand years later.

Antikythera MechanismSometime before April of 1900, a Greek sponge diver named Elias Stadiatis discovered the wreck of an ancient large cargo ship off Antikythera island at a depth of 42 m (138 ft) to 60 m (200 ft). Sponge divers retrieved several statues (including the famous Antikythera Ephebe, and the Philosopher) and other artifacts from the site, known as the Antikythera wreck. The mechanism itself was discovered on 17 May 1901, 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 (13 in) high, 17 cm (6.7 in) wide, and 9 cm (3.5 in) thick, made of bronze and originally mounted in a wooden frame (a very small part of it is still in the museum). It was inscribed with a text of over 3,000 characters, most of which have only recently been deciphered. These characters were part of a manual, which describes how to set up the instrument and how to use it for observations, with references to the Sun, the motion of the planets (stationary points), Aphrodite (Venus), Hermes (Mercury), and eclipses.

Jacques-Yves Cousteau visited the wreck for the last time in 1978, but found no more remains of the Antikythera Mechanism. Professor Michael Edmunds of Cardiff University who led the study of the mechanism 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 carefully." and added: "in terms of historic and scarcity value, I have to regard this mechanism as being more valuable than the Mona Lisa."

The mechanism is the oldest known scientific instrument. It has several accurate scales, and is essentially an analog computer made with gears. It is based on theories of astronomy and mathematics developed by Greek astronomers. Based on the shape of the Greek letters used in the manual of the instrument, it is estimated that it was constructed around 150 to 100 BC. The circumstances under which it came to be on the cargo ship are unclear. The ship is estimated to have sunk between 80 to 60 BC and was a Roman or Greek ship with cargo for Rome, perhaps part of official loot. It contained more than 100 statues similar to the ones the Romans took to Italy after their conquest of Greece. Consensus among scholars is that the mechanism itself was made in Greece. All the instructions of the mechanism are written in Greek.

The device is remarkable for the level of miniaturization and complexity of its parts, which is comparable to that of 18th century clocks. It has over 30 gears, although some have suggested as many as 70 gears, with teeth formed through equilateral triangles. When a date was 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. It is possible that the mechanism is based on heliocentric principles, rather than the then-dominant geocentric view espoused by Aristotle and others. The heliocentric view proposed by Aristarchus of Samos (310 BC - c. 230 BC) did not receive widespread recognition, but provides for the possibility of the existence of such a system at this time.

The mechanism has three main dials, one on the front, and two on the back.

The front dial is marked with the divisions of the Egyptian calendar, or the Sothic year, based on the Sothic cycle. Inside this there is a second dial marked with the Greek signs of the Zodiac. This second dial can be moved to adjust, with respect to the Sothic dial, to compensate for leap years. Note that the Julian calendar, the first calendar of the region to contain leap years, was not invented until about 50 B.C., up to a century after the device was said to have been built.

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 ingeniously 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 it would have certainly been within the capabilities of the maker of this mechanism to include gearing to show their positions. There is some speculation that the mechanism may have had indicators for the 5 planets known to the Greeks. None of the gearing, except for one unaccounted gear, for such planetary mechanisms survives.

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.

The upper back dial is in the form of a spiral, with 47 divisions per turn, displaying the 235 months of the 19 year Metonic cycle. This dial contains a smaller subsidiary dial which displays the 76 year Callippic cycle. (There are 4 Metonic cycles within 1 Callippic cycle.) Both of these cycles are important in fixing calendars.

The lower back dial is also in the form of a spiral, with 223 divisions showing the Saros cycle; it also has a smaller subsidiary dial which displays the 54 year "Triple Saros" or "Exeligmos" cycle. (The Saros cycle, discovered by the Chaldeans, is a period of approximately 18 years 11 days 8 hours -- the length of time between occurrences of a particular eclipse.)

While a century of research is finally answering the question of what the mechanism did, we are actually no nearer to answering the question what it was for."[1]

New Discoveries

"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. This work doubled the amount of readable text, corrected prior transcriptions, and provided a new translation. The new discoveries confirm that the mechanism is an astronomical analog computer or orrery used to predict the positions of heavenly bodies in the sky. This work proposes that the mechanism possessed 37 gears, of which 30 survive, and was used for prediction of the position of the sun, moon, and probably planets, as the manual implies as it contains so many references to the planetary motions.

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, and the lunar phase. Based on the inscriptions, which mention the stationary points of the planets, the authors speculate that planetary motions may also have been indicated here. The inscriptions lead to a new dating of the Mechanism, as they were written between 150 to 100 BC. It is evident that they contain a manual with an astronomical, mechanical and geographical section. The name ISPANIA (ΙΣΠΑΝΙΑ, Spain in Greek) in these texts is the oldest reference to this country.

On the back, two spiral scales (simple Archimedean spirals, with two centers) with sliding 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 and the more accurate exeligmos cycle of 54 years and one day (essential in eclipse prediction, see Eclipse cycle). It also contains another spiral scale for the Metonic cycle (19 years, equal to 235 lunar months) and the Callippic cycle that proposed a more accurate periodicity of 940 lunar months in approximately 76 years.

The Moon mechanism, using an ingenious train of gears, two of them linked with a slightly offset axis and pin in a slot, shows the position and phase of the Moon during the month. The velocity of the Moon varies according to the theory of Hipparchus, and to a good approximation follows Kepler's second law for the angular velocity, being faster near the perigee and slower at the apogee (see Kepler's laws of planetary motion)."[2]

Note from the webmaster: I have found that no scientists or skeptics actually argue about the validity of the Antikythera mechanism. The sole debate seems to be over what it was FOR.