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The Antikythera Mechanism

It's an ancient analog computer designed to predict astronomical positions and eclipses for calendrical and astrological purposes,as well as the Olympiads, the cycles of the ancient Olympic Games

The mechanism was discovered in a shipwreck off Point Glyphadia on the Greek island of Antikythera. The wreck was found in April 1900 by a group of Greek sponge divers.

The Antikythera mechanism (/ˌæntɨkɨˈθɪərə/ ANT-i-ki-THEER-ə or /ˌæntɨˈkɪθərə/ ANT-i-KITH-ə-rə) is an ancient analog computer designed to predict astronomical positions and eclipses, as well as the cycles of Olympic Games.

Found housed in a 340 mm × 180 mm × 90 mm wooden box, the device is a complex clockwork mechanism composed of at least 30 meshing bronze gears. Its remains were found as 82 separate fragments, of which only seven contain any gears or significant inscriptions. The largest gear (clearly visible in Fragment A at right) is approximately 140 mm in diameter and originally had 223 teeth.

The artifact was recovered in 1900–1901 from the Antikythera shipwreck off the Greek island of Antikythera.Believed to have been designed and constructed by Greek scientists, the instrument has been dated either between 150 and 100 BC, or, according to a more recent view, at 205 BC.

After the knowledge of this technology was lost at some point in Antiquity, technological artifacts approaching its complexity and workmanship did not appear again until the development of mechanical astronomical clocks in Europe in the fourteenth century.

All known fragments of the Antikythera mechanism are kept at the National Archaeological Museum of Athens.

Generally referred to as the first known analog computer the quality and complexity of the mechanism's manufacture suggests it has undiscovered predecessors made during the Hellenistic period. Its construction relied upon theories of astronomy and mathematics developed by Greek astronomers, and is estimated to have been created around the late second century BC.

In 1974, British science historian and Yale University professor Derek de Solla Price concluded from gear settings and inscriptions on the mechanism's faces that it was made about 87 BC and lost only a few years later.Jacques Cousteau and associates visited the wreck in 1976 and recovered coins dated to between 76 and 67 BC.Though its advanced state of corrosion has made it impossible to perform an accurate compositional analysis, it is believed the device was made of a low-tin bronze alloy (of approximately 95% copper, 5% tin). All its instructions are written in Koine Greek, and the consensus among scholars is that the mechanism was made in the Greek-speaking world.

In the late 2000s, findings of The Antikythera Mechanism Research Project suggest the concept for the mechanism originated in the colonies of Corinth, since some of the astronomical calculations seem to indicate observations that can be made only in the Corinth area of ancient Greece. Syracuse was a colony of Corinth and the home of Archimedes, which might imply a connection with the school of Archimedes.Another theory suggests that coins found by Jacques Cousteau in the 1970s at the wreck site date to the time of the device's construction, and posits its origin may have been from the ancient Greek city of Pergamon, home of the famous Library of Pergamum. With its many scrolls of art and science, it was second in importance only to the Library of Alexandria during the Hellenistic period

The ship carrying the device also contained vases in the Rhodian style, leading to a hypothesis the device was constructed at an academy founded by the Stoic philosopher Posidonius on that Greek island. A busy trading port in antiquity, Rhodes was also a center of astronomy and mechanical engineering, home to the astronomer Hipparchus, active from about 140 BC to 120 BC. That the mechanism uses Hipparchus's theory for the motion of the moon suggests the possibility he may have designed, or at least worked on it.

Cardiff University professor Michael Edmunds, who led a 2006 study of the mechanism, described the device as "just extraordinary, the only thing of its kind", and said that its astronomy was "exactly right". He regarded the Antikythera mechanism as "more valuable than the Mona Lisa

In 2014, a study by Carman and Evans argued for a new dating of approximately 200 BC.Moreover, according to Carman and Evans, the Babylonian arithmetic style of prediction fits much better with the device's predictive models than the traditional Greek trigonometric style.

In mid-2014, a diving expedition to the shipwreck initiated by the Hellenic Ministry of Culture and Sports hoped to discover further parts of the Antikythera Mechanism but was cut short due to bad weather. Another expedition was planned for spring 2015.

The front dial has two concentric, circular scales that represent the path of the ecliptic through the heavens. The outer ring is marked off with the days of the 365-day Egyptian calendar, or the Sothic year, based on the Sothic cycle. On the inner ring, there is a second dial marked with the Greek signs of the Zodiac and it is divided into degrees. The outer calendar dial may be moved against the inner dial to compensate for the effect of the extra quarter day in the solar year by turning the scale backward one day every four years. A 3651⁄4-day year was used in the Callippic cycle circa 330 BCE and in the Decree of Canopus during 238 BCE, but that is not reflected in the dials.

The position of the sun on the ecliptic is synonymous with the current date in the year. The moon and the five planets known to the Greeks travel along the ecliptic fairly closely, close enough that it made sense defining their position on the ecliptic.

The following Egyptian months are inscribed, in Greek letters on the outer ring:

ΘΟΘ (Thoth)
ΦΑΩΦΙ (Phaophi)
ΑΟΤΡ (Athyr, Hathor)
ΧΟΙΑΚ (Choiak)
ΤΥΒΙ (Tybi)
ΜΕΧΕΙΡ (Mecheir)
ΦΑΜΕΝΩΘ (Phamenoth)
ΦΑΡΜΟΥΘΙ (Pharmouthi)
ΠΑΧΩΝ (Pachon)
ΠΑΥΝΙ (Payni)
ΕΠΙΦΙ (Epiphi)
ΜΕΣΟΡΗ (Mesore)
ΕΠ (Ep[agomene])
The Zodiac dial contains Greek inscriptions of the members of the zodiac, which is believed to be adapted to the tropical month version rather than the sidereal

ΚΡIOΣ (Krios [Ram], Aries)
ΤΑΥΡΟΣ (Tauros [Bull], Taurus)
ΔIΔΥΜΟΙ (Didymoi [Twins], Gemini)
ΚΑΡΚIΝΟΣ (Karkinos [Crab], Cancer)
ΛEΩΝ (Leon [Lion], Leo)
ΠΑΡΘEΝΟΣ (Parthenos [Maiden], Virgo)
ΧΗΛΑΙ (Chelai [Scorpio's Claw or Zygos], Libra)
ΣΚΟΡΠΙΟΣ (Skorpios [Scorpion], Scorpio)
ΤΟΞΟΤΗΣ (Toxotes [Archer], Sagittarius)
ΑIΓOΚΕΡΩΣ (Aigokeros [Sea goat], Capricorn)
YΔΡΟΧΟΟΣ (Hydrokhoos [Water carrier], Aquarius)
IΧΘΥΕΣ (Ichthyes [Fish], Pisces)
Also on the zodiac dial are a number of single characters at specific points (see reconstruction here. They are keyed to aparapegma, a precursor of the modern day almanac inscribed on the front face beyond the dials. They mark the locations of longitudes on the ecliptic for specific stars. Some of the parapegma reads (brackets

indicate inferred text):
{Κ} Evening
{Λ} The Hyades set in the evening
{Μ} Taurus begins to rise
{N} Vega rises in the evening
{Θ} The Pleiades rise in the morning
{Ο} The Hyades rise in the morning
{Π} Gemini begins to rise
{Ρ} Altair rises in the evening
{Σ} Arcturus sets in the morning

At least two pointers indicated positions of bodies upon the ecliptic. A lunar pointer indicated the position of the moon, and a mean sun pointer also was shown, perhaps doubling as the current date pointer. The moon position was not a simple mean moon indicator that would indicate movement uniformly around a circular orbit; it allowed for the acceleration and deceleration typical of what is known today is an elliptical orbit, through the earliest extant use of epicyclic gearing.
It also tracked the precession of the elliptical orbit around the ecliptic in a 8.88 year cycle. The mean sun position is, by definition, the current date. It is speculated that since such pains were taken to get the position of the moon correct, then there also was likely to have been a "true sun" pointer in addition to the mean sun pointer likewise, to track the elliptical anomaly of the sun (the orbit of Earth around the sun), but there is no evidence of it among the ruins of the mechanism found to date. Similarly, neither is there the evidence of planetary orbit pointers for the five planets known to the Greeks among the ruins. See Proposed planet indication gearing schemes below.

Finally, mechanical engineer Michael Wright has demonstrated that there was a mechanism to supply the lunar phase in addition to the position.The indicator was a small ball embedded in the lunar pointer, half-white and half-black, which rotated to show the phase (new, first quarter, half, third quarter, full, and back) graphically. The data to support this function is available given the sun and moon positions as angular rotations; essentially, it is the angle between the two, translated into the rotation of the ball. It requires a differential gear, a gearing arrangement that sums or differences two angular inputs. Among its other first-known aspects, the Antikythera Mechanism is the earliest extant construction of a deliberate differential gear scheme in history.

In July 2008, scientists reported new findings in the journal Nature showing that the mechanism not only tracked the Metonic calendar and predicted solar eclipses, but also calculated the timing of the Ancient Olympic Games.Inscriptions on the instrument closely match the names of the months that are used on calendars from Illyria and Epirus in northwestern Greece and with the island of Corfu.

On the back of the mechanism, there are five dials: the two large displays, the Metonic and the Saros, and three smaller indicators, the Olympiad, the Callippic, and the Exeligmos.The Metonic Dial is the main upper dial on the rear of the mechanism. The Metonic cycle, defined in several physical units, is 235synodic months, which is very close (to within less than 13 one-millionths) to 19 tropical years. It is therefore a convenient interval over which to convert between lunar and solar calendars. The Metonic dial covers 235 months in 5 rotations of the dial, following a spiral track with a follower on the pointer that keeps track of the layer of the spiral. The pointer points to the synodic month, counted from new moon to new moon, and the cell contains the Corinthian month names:

ΦΟΙΝΙΚΑΙΟΣ (Phoinikaios)
ΚΡΑΝΕΙΟΣ (Kraneios)
ΛΑΝΟΤΡΟΠΙΟΣ (Lanotropios)
ΜΑΧΑΝΕΥΣ (Machaneus)
ΔΩΔΕΚΑΤΕΥΣ (Dodekateus)
ΕΥΚΛΕΙΟΣ (Eukleios)
ΑΡΤΕΜΙΣΙΟΣ (Artemisios)
ΨΥΔΡΕΥΣ (Psydreus)
ΓΑΜΕΙΛΙΟΣ (Gameilios)
ΑΓΡΙΑΝΙΟΣ (Agrianios)
ΠΑΝΑΜΟΣ (Panamos)
ΑΠΕΛΛΑΙΟΣ (Apellaios)

Thus, setting the correct solar time (in days) on the front panel indicates the current lunar month on the back panel, with resolution to within a week or so.

The Callippic dial is the left secondary upper dial, which follows a 76-year cycle. The Callippic cycle is four Metonic cycles, and this dial indicates which of the four Metonic cycles is the current one in the Callippic cycle.

The Olympiad dial is the right secondary upper dial; it is the only pointer on the instrument that travels in a counter-clockwise direction as time advances. The dial is divided into four sectors, each of which is inscribed with a year indicator and the name of two Panhellenic Games: the "crown" games of Isthmia, Olympia, Nemea, and Pythia; and two lesser games: Naa (held at Dodona) and another Olympiad location that to date, has not been deciphered.The inscriptions on each one of the four divisions are
Year of the cycleInside the dial inscriptionOutside the dial inscription
1LAΙΣΘΜΙΑ (Isthmia)
ΟΛΥΜΠΙΑ (Olympia)
2LBNEMEA (Nemea)
NAA (Naa)
3ΙΣΘΜΙΑ (Isthmia)
ΠΥΘΙΑ (Pythia)
4L∆ΝΕΜΕΑ (Nemea)

The Saros dial is the main lower spiral dial on the rear of the mechanism.The Saros cycle is 18 years and 11-1/3 days long (6585.333... days), which is very close to 223 synodic months (6585.3211 days). It is defined as the cycle of repetition of the positions required to cause solar and lunar eclipses, and therefore, it could be used to predict them — not only the month, but the day and time of day. Note that the cycle is approximately 8 hours longer than an integer number of days. Translated into global spin, that means an eclipse occurs not only eight hours later, but 1/3 of a rotation farther to the west. Glyphs in 51 of the 223 synodic month cells of the dial specify the occurrence of 38 lunar and 27 solar eclipses. Some of the abbreviations in the glyphs read:

Σ = ΣΕΛΗΝΗ (Moon)
Η = ΗΛΙΟΣ (Sun)
H\M = ΗΜΕΡΑΣ (of the day)
ω\ρ = ωρα (hour)
N\Y = ΝΥΚΤΟΣ (of the night)

The glyphs show whether the designated eclipse is solar or lunar, and give the day of the month and hour; obviously, solar eclipses may not be visible at any given point, and lunar eclipses are visible only if the moon is above the horizon at the appointed hour.

The Exeligmos Dial is the secondary lower dial on the rear of the mechanism. The Exeligmos cycle is a 54-year triple Saros cycle, that is 19,756 days long. Since the length of the Saros cycle is to a third of a day (eight hours), so a full Exeligmos cycle returns counting to integer days, hence the inscriptions. The labels on its three divisions are:
Blank (representing the number zero)
H (number 8)
Iϛ (number 16)

Thus the dial pointer indicates how many hours must be added to the glyph times of the Saros dial in order to calculate the exact eclipse times.

The mechanism has a wooden casing with a front and a back door, both containing inscriptions.The back door appears to be the "Instruction Manual". On one of its fragments is written "76 years, 19 years" representing the Callippic and Metonic cycles. Also written is "223" for the Saros cycle. On another one of its fragments is written on the spiral subdivisions "235" for the Metonic dial.