Antikythera Mechanism: The technology behind the worlds oldest computer

The Antikythera mechanism, one of the world's oldest known geared devices, is an ancient mechanical calculator, also described as the first known mechanical computer, designed to calculate astronomical positions, that has puzzled and intrigued science and technology historians since its it was recovered from an 80 BC wreck off the island of Antikythera in 1901.

Dated to about 150-100 BC, the intricacy of the way in which the Mechanism works was so startling to scientists that initially they often the device's dating, doubting it could be as old as it really was. Technological artifacts of similar complexity did not reappear before the 14th century, when mechanical astronomical clocks appeared in Europe.

A lecture on the Mechanism was recently delivered by Professor Robert Hannah of the Classical Studies Department at New Zealand's Otago University to a packed audience at Sydney University in Australia, who tried to analyse the workings of the Mechanism and, more importantly, to explain how the ancient Greeks were able to create such a complex, precise and sophisticated instrument more than 2,000 years ago, stressing that scientists are still studying and trying to decipher the device.

Sometime before Easter 1900, Elias Stadiatis, a Greek sponge diver, discovered the wreck of an ancient cargo ship off Antikythera Island at a depth of 42 m (138 ft). Sponge divers retrieved several statues and other artifacts from the wreck. The mechanism itself was discovered on May 17, 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. It was inscribed with a text of over 2,000 characters, many of which have only just recently been deciphered.

The mechanism is the oldest known complex scientific calculator, and is sometimes called the first known analog computer, although its flawless construction suggests that it may have had a number of predecessors during the Hellenistic Period that have not yet been discovered.

It appears to be constructed upon theories of astronomy and mathematics developed by Greek astronomers, and one hypothesis is that the device was constructed at an academy founded by the ancient Stoic philosopher Posidonius on the island of Rhodes, which was known at the time as a center of astronomy and mechanical engineering, and that perhaps the astronomer Hipparchus was the engineer who designed it, since it contains a lunar mechanism that uses Hipparchus' theory for the motion of the Moon. However, newer findings of The Antikythera Mechanism Research Project published in 2008 suggest that the concept of the mechanism originated in the colonies of Corinth, which might imply a connection with Archimedes.

According to the Antikythera Mechanism Project researchers, 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 scientists have 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. Since the purpose was to position astronomical bodies with respect to the celestial sphere, with reference to the observer's position on the surface of the earth, the device was based on the geocentric model.

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 compensate for the effect of the extra quarter day in the solar year (there are 365.2422 days per year) by turning the scale backwards one day every four years. Worthy of note is that the Julian calendar, the first calendar of the region to contain leap years, was not introduced until about 46 BC, 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 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 for such planetary mechanisms survives, except for one gear otherwise unaccounted for.

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 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 Callipic cycle, as well as the names of other games in ancient Greece, and probably used to track dates of the ancient Olympic Games.

The four sectors of the dial are inscribed with a year number and two Panhellenic Games: the 'crown' games of Isthmia (Isthmian Games), Olympia (Olympic Games), Nemea (Nemean Games) and Pythia (Pythian Games); and two lesser games: Naa (held at Dodona, northwestern Greece, today's Dodoni) and a second game which has not yet been deciphered.

The complexity of the gears found within the Antikythera Mechanism baffled scientists, since this type of technology was not though to have been in existence until around 1575, while many feel that the Mechanism helps to explain how such wonderful phenomena as the ancient pyramids, the Greek Colisseum, and the Parthenon were built with such exquisite detail.

Originally Posted @ Archaeology News

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