This artefact was retrieved from the sea in , and identified on 17 May as containing a gear by archaeologist Valerios Stais ,  among wreckage retrieved from a shipwreck off the coast of the Greek island Antikythera. Four of these fragments contain gears, while inscriptions are found on many others. It is a complex clockwork mechanism composed of at least 30 meshing bronze gears. A team led by Mike Edmunds and Tony Freeth at Cardiff University used modern computer x-ray tomography and high resolution surface scanning to image inside fragments of the crust-encased mechanism and read the faintest inscriptions that once covered the outer casing of the machine. Detailed imaging of the mechanism suggests that it had 37 gear wheels enabling it to follow the movements of the Moon and the Sun through the zodiac, to predict eclipses and even to model the irregular orbit of the Moon , where the Moon's velocity is higher in its perigee than in its apogee.
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This artefact was retrieved from the sea in , and identified on 17 May as containing a gear by archaeologist Valerios Stais ,  among wreckage retrieved from a shipwreck off the coast of the Greek island Antikythera. Four of these fragments contain gears, while inscriptions are found on many others. It is a complex clockwork mechanism composed of at least 30 meshing bronze gears. A team led by Mike Edmunds and Tony Freeth at Cardiff University used modern computer x-ray tomography and high resolution surface scanning to image inside fragments of the crust-encased mechanism and read the faintest inscriptions that once covered the outer casing of the machine.
Detailed imaging of the mechanism suggests that it had 37 gear wheels enabling it to follow the movements of the Moon and the Sun through the zodiac, to predict eclipses and even to model the irregular orbit of the Moon , where the Moon's velocity is higher in its perigee than in its apogee. This motion was studied in the 2nd century BC by astronomer Hipparchus of Rhodes , and it is speculated that he may have been consulted in the machine's construction.
The knowledge of this technology was lost at some point in antiquity. Similar technological works later appeared in the medieval Byzantine and Islamic worlds , but works with similar complexity did not appear again until the development of mechanical astronomical clocks in Europe in the fourteenth century. The team retrieved numerous large artefacts, including bronze and marble statues, pottery, unique glassware, jewellery, coins, and the mechanism.
The mechanism was retrieved from the wreckage in , most probably in July of that year. All of the items retrieved from the wreckage were transferred to the National Museum of Archaeology in Athens for storage and analysis. The mechanism appeared at the time to be little more than a lump of corroded bronze and wood; it went unnoticed for two years, while museum staff worked on piecing together more obvious treasures, such as the statues. On 17 May , archaeologist Valerios Stais found that one of the pieces of rock had a gear wheel embedded in it.
He initially believed that it was an astronomical clock, but most scholars considered the device to be prochronistic , too complex to have been constructed during the same period as the other pieces that had been discovered.
Investigations into the object were dropped until British science historian and Yale University professor Derek J. Price published an extensive page paper on their findings in Two other searches for items at the Antikythera wreck site in and have yielded a number of fascinating art objects and a second ship which may or may not be connected with the treasure ship on which the Mechanism was found. The disk has four "ears" which have holes in them, and it was thought by some that it may have been part of the Antikythera Mechanism itself, as a " cog wheel ".
However, there appears to be little evidence that it was part of the Mechanism; it is more likely that the disk was a bronze decoration on a piece of furniture. The Antikythera mechanism is generally referred to as the first known analogue computer. In , 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.
In , continued research by the Antikythera Mechanism Research Project suggested that the concept for the mechanism may have originated in the colonies of Corinth , since they identified the calendar on the Metonic Spiral as coming from Corinth or one of its colonies in Northwest Greece or Sicily. 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 that it was constructed at an academy founded by Stoic philosopher Posidonius on that Greek island.
The mechanism uses Hipparchus's theory for the motion of the Moon, which suggests the possibility that he may have designed it or at least worked on it. In , a study by Carman and Evans argued for a new dating of approximately BC based on identifying the start-up date on the Saros Dial as the astronomical lunar month that began shortly after the new moon of 28 April BC. Further dives were undertaken in , with plans to continue in , in the hope of discovering more of the mechanism.
The original mechanism apparently came out of the Mediterranean as a single encrusted piece. Soon afterward it fractured into three major pieces. Other small pieces have broken off in the interim from cleaning and handling,  and still others were found on the sea floor by the Cousteau expedition. Other fragments may still be in storage, undiscovered since their initial recovery; Fragment F came to light in that way in Of the 82 known fragments, seven are mechanically significant and contain the majority of the mechanism and inscriptions.
There are also 16 smaller parts that contain fractional and incomplete inscriptions. Fragment A also contains divisions of the upper left quarter of the Saros spiral and 14 inscriptions from said spiral.
The fragment also contains inscriptions for the Exeligmos dial and visible on the back surface the remnants of the dial face. Finally, this fragment contains some back door inscriptions.
Many of the smaller fragments that have been found contain nothing of apparent value; however, a few have some inscriptions on them. Fragment 19 contains significant back door inscriptions including one reading " Other inscriptions seem to describe the function of the back dials.
In addition to this important minor fragment, 15 further minor fragments have remnants of inscriptions on them. Information on the specific data gleaned from the ruins by the latest inquiries is detailed in the supplement to Freeth's Nature article.
On the front face of the mechanism there is a fixed ring dial representing the ecliptic , the twelve zodiacal signs marked off with equal degree sectors. This matched with the Babylonian custom of assigning one twelfth of the ecliptic to each zodiac sign equally, even though the constellation boundaries were variable. Outside of that dial is another ring which is rotatable, marked off with the months and days of the Sothic Egyptian calendar , twelve months of 30 days plus five intercalary days.
The months are marked with the Egyptian names for the months transcribed into the Greek alphabet. The first task, then, is to rotate the Egyptian calendar ring to match the current zodiac points. The Egyptian calendar ignored leap days, so it advanced through a full zodiac sign in about years.
The mechanism was operated by turning a small hand crank now lost which was linked via a crown gear to the largest gear, the four-spoked gear visible on the front of fragment A, the gear named b1.
This moved the date pointer on the front dial, which would be set to the correct Egyptian calendar day. The year is not selectable, so it is necessary to know the year currently set, or by looking up the cycles indicated by the various calendar cycle indicators on the back in the Babylonian ephemeris tables for the day of the year currently set, since most of the calendar cycles are not synchronous with the year.
The crank moves the date pointer about 78 days per full rotation, so hitting a particular day on the dial would be easily possible if the mechanism were in good working condition. The action of turning the hand crank would also cause all interlocked gears within the mechanism to rotate, resulting in the simultaneous calculation of the position of the Sun and Moon , the moon phase , eclipse , and calendar cycles, and perhaps the locations of planets.
The operator also had to be aware of the position of the spiral dial pointers on the two large dials on the back.
The pointer had a "follower" that tracked the spiral incisions in the metal as the dials incorporated four and five full rotations of the pointers. When a pointer reached the terminal month location at either end of the spiral, the pointer's follower had to be manually moved to the other end of the spiral before proceeding further. 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 day Egyptian civil calendar.
On the inner ring, a second dial marks the Greek signs of the Zodiac , with division into degrees. The dials are not believed to reflect his proposed leap day Epag. The position of the Sun on the ecliptic corresponds to the current date in the year.
The orbits of the Moon and the five planets known to the Greeks are close enough to the ecliptic to make it a convenient reference for defining their positions as well. The following three Egyptian months are inscribed in Greek letters on the surviving pieces of the outer ring: . The other months have been reconstructed, although some reconstructions of the mechanism omit the five days of the Egyptian intercalary month.
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 :  : 8 [ failed verification ]. Also on the zodiac dial are a number of single characters at specific points see reconstruction here: .
They are keyed to a parapegma , a precursor of the modern day almanac inscribed on the front face above and beneath the dials. They mark the locations of longitudes on the ecliptic for specific stars. The parapegma above the dials reads square brackets indicate inferred text :. 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 approximated the acceleration and deceleration of the Moon's elliptical orbit, through the earliest extant use of epicyclic gearing. It also tracked the precession of the elliptical orbit around the ecliptic in an 8. 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,  : 20, 24 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.
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 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.
In July , 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 several panhellenic athletic games, including the Ancient Olympic Games. On the back of the mechanism, there are five dials: the two large displays, the Metonic and the Saros , and three smaller indicators, the so-called Olympiad Dial,  which has recently been renamed the Games dial as it did not track Olympiad years the four-year cycle it tracks most closely is the Halieiad ,  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 synodic 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 months in five 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. 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.
Based on the fact that the calendar month names are consistent with all the evidence of the Epirote calendar and that the Games dial mentions the very minor Naa games of Dodona in Epirus , it has recently been argued that the calendar on the Antikythera Mechanism is likely to be the Epirote calendar, and that this calendar was probably adopted from a Corinthian colony in Epirus, possibly Ambracia.
The Callippic dial is the left secondary upper dial, which follows a year cycle. The Callippic cycle is four Metonic cycles, and so this dial indicates the current Metonic cycle in the overall Callippic cycle.
The Games 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 the sixth and final set of Games recently deciphered as the Halieia of Rhodes.
The Saros dial is the main lower spiral dial on the rear of the mechanism. 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 one-third of a rotation farther to the west.
Glyphs in 51 of the synodic month cells of the dial specify the occurrence of 38 lunar and 27 solar eclipses. Some of the abbreviations in the glyphs read: [ citation needed ]. The glyphs show whether the designated eclipse is solar or lunar, and give the day of the month and hour.
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.
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