page_title: Antikythera mechanism
section_title: Front face
hierarchical_section_title: Antikythera mechanism / Mechanism / Faces / Front face
caption_attribution_description: Antikythera Machine mechanical model
context_page_description: The Antikythera mechanism is an ancient hand-powered Greek analogue computer which has also been described as the first example of such device used to predict astronomical positions and eclipses for calendar and astrological purposes decades in advance. It could also be used to track the four-year cycle of athletic games which was similar to an Olympiad, the cycle of the ancient Olympic Games.
  This artefact was retrieved from the sea in 1901, and identified on 17 May 1902 as containing a gear by archaeologist Valerios Stais, among wreckage retrieved from a shipwreck off the coast of the Greek island Antikythera. The instrument is believed to have been designed and constructed by Greek scientists and has been variously dated to about 87 BC, or between 150 and 100 BC, or to 205 BC, or to within a generation before the shipwreck, which has been dated to approximately 70–60 BC.
  The device, housed in the remains of a 34 cm × 18 cm × 9 cm wooden box, was found as one lump, later separated into three main fragments which are now divided into 82 separate fragments after conservation efforts. Four of these fragments contain gears, while inscriptions are found on many others.
context_section_description: 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 civil calendar. On the inner ring, a second dial marks the Greek signs of the Zodiac, with division into degrees. The mechanism predates the Julian calendar reform, but the Sothic and Callippic cycles had already pointed to a ​365 ¹⁄₄-day solar year, as seen in Ptolemy III's abortive calendrical reform of 238 BC. The dials are not believed to reflect his proposed leap day (Epag. 6), but 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.
  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:
  ΠΑΧΩΝ (Pachon)
  ΠΑΥΝΙ (Payni)
  ΕΠΙΦΙ (Epiphi)
  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:
  ΚΡΙΟΣ (Krios [Ram], Aries)
  ΤΑΥΡΟΣ (Tauros [Bull], Taurus)
  ΔΙΔΥΜΟΙ (Didymoi [Twins], Gemini)
  ΚΑΡΚΙΝΟΣ (Karkinos [Crab], Cancer)
  ΛΕΩΝ (Leon [Lion], Leo)
  ΠΑΡΘΕΝΟΣ (Parthenos [Maiden], Virgo)
  ΧΗΛΑΙ (Chelai [Scorpio's Claw or Zygos], Libra)
  ΣΚΟΡΠΙΟΣ (Skorpios [Scorpion], Scorpio)
  ΤΟΞΟΤΗΣ (Toxotes [Archer], Sagittarius)
  ΑΙΓΟΚΕΡΩΣ (Aigokeros [Goat-horned], Capricorn)
  ΥΔΡΟΧΟΟΣ (Hydrokhoos [Water carrier], Aquarius)
  ΙΧΘΥΕΣ (Ichthyes [Fishes], Pisces)
  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):
  The parapegma beneath the dials reads:
  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 8.88-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.
  Mechanical engineer Michael Wright 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 angul
caption: Front panel of a 2007 recreation
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