Florence exhibiion, for the 400 years
of first Galileo's sky observations. 2009 - 2010

The Antikythera Mechanism: model by M.T. Wright

 

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The Antikythera Mechanism: model by M.T. Wright, London

The original fragmentary Hellenistic artefact, recovered from a shipwreck dateable to about 70 B.C. and probably made some decades earlier, is the world’s oldest elaborate astronomical instrument, intended for computation or demonstration. This reconstruction is based on Wright’s examination of the original (Wright, 2007), but incorporates the results of further research by others (Freeth et al., 2006, 2008).

The inner ring of the front dial represents the Zodiac, divided into 360 degrees and with the Zodiacal constellations named. Small letters correspond to a list of annual astronomical events which survives only in part on a detached plate and cannot be restored. The outer ring represents a year of 365 days: twelve named months of 30 days and five extra days. In this, the Egyptian calendar, the dates of the solstices and equinox were reckoned to change by one day every four years, corresponding to a year-length of 365 days; so the calendar ring is moveable.

Hands show the date and the places of the Moon and the Sun; and a small rotating ball within the Moon hand, half black and half white, displays the phase of the Moon. This much is certain. The date hand shows the place of the mean Sun, but since the motion of the Moon hand was modified by a single anomaly, as in the lunar theory of Hipparchus, probably there was a separate Sun hand with a similarly modified motion, as seen here.

Epicyclic mechanism, mostly lost, realized a single-anomaly theory of the place of at least one planet. The model illustrates a conjectural restoration, with hands for the five planets then known, all worked in the same way (Wright, 2002).
 

 


 

On the back two spiral displays, both divided into long sequences of synodic months, offer supplementary information. Sliding indicators on the hands, guided by tongues running in spiral slots, show which turn of each scale must be read.

The upper display represents the Metonic calendrical period; 235 named months, taken to equal 19 years, are laid out in five turns so as to show which months should have 29 days instead of 30, and which years should have 13 months instead of 12. A subsidiary dial to the right shows a four-year cycle of several Panhellenic games. A second subsidiary dial to the left, restored conjecturally, displays the 76-year Callippic period which is cited on a detached fragment.

The lower spiral represents the Saros period of 223 synodic months, after which the pattern of eclipse-possibilities is repeated. Possible lunar and solar eclipses are identified, together with the expected times of day. (The sequence cannot be fully restored.) The whole pattern falls about one-third of a day later in each successive cycle, and the subsidiary dial indicates corrections in hours to be added to the eclipse-times in each cycle.

Separate bronze plates (not shown) covered both dials. Surviving fragments suggest that they were extensively inscribed with information about the displays and perhaps notes on working the instrument.

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The Florence Catalog pages on The Mechanism.

Bibliography :

M.T. Wright, “In the Steps of the Master Mechanic”, Proc. Conf. Ancient Greece and the Modern World, University of Patras 2003, pp. 86 – 97.

T. Freeth et al., “Decoding the ancient Greek astronomical calculator known as the Antikythera Mechanism”, Nature, 444 (30 November 2006), pp. 587 – 591.

M.T. Wright, “The Antikythera Mechanism reconsidered” Interdisciplinary Science Reviews, 2007, vol. 32, no. 1, pp. 27 – 43.

T. Freeth et al., “Calendars with Olympiad display and eclipse prediction on the Antikythera Mechanism”, Nature, 454 (31 July 2008), pp. 614 – 617.

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Pedal actuated Lathe of the type used by M.T. Wright for his works.

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Quickly made cradle for X-ray Axial Tomography used by M. T. Wright and late A. Broomley to obtain plenty of X-ray pictures  of the Antikythera Mechanism fragments at the Athens Museum.

F. S. || 4.08. 2009