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ANTIKYTHERA Mechanism

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Author Topic: ANTIKYTHERA Mechanism  (Read 3880 times)
Bianca
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« Reply #30 on: August 15, 2008, 08:44:09 pm »










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The device is remarkable for the level of miniaturization and for the complexity of its parts, which is comparable to that of 18th century clocks. It has over 30 gears, although Michael Wright has suggested as many as 72 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 has two concentric scales. The outer ring is marked off with the days of the 365-day 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 and divided into degrees. The calendar dial can be moved to adjust, to compensate for the effect of the extra quarter day in the year (there are almost 365.25 days per year) by turning the scale backwards one day every four years.

Note that the Julian calendar, the first calendar of the region to contain leap years, was not introduced until about 46 B.C., up to a century after the device was said to have been built (and it was implemented with errors until the early first century).

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 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 all the five 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.)



The Antikythera Mechanism Research Project, with experts from Britain, Greece and the United States, detected in July 2008 the word "Olympia" on a bronze dial thought to display the 76 year Callippic cycle, as well as the names of other games in ancient Greece, and probably used to track dates of the ancient Olympic games.



According to BBC news,

"The four sectors of the dial are inscribed with a year number and two Panhellenic Games: the "crown" games of Isthmia, Olympia, Nemea and Pythia; and two lesser games: Naa (held at Dodona) and a second game which has not yet been deciphered".
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