Letter

Nature 454, 614-617 (31 July 2008) | doi:10.1038/nature07130; Received 28 March 2008; Accepted 2 June 2008

Calendars with Olympiad display and eclipse prediction on the Antikythera Mechanism
Tony Freeth1,2, Alexander Jones3, John M. Steele4 & Yanis Bitsakis1,5

Antikythera Mechanism Research Project, 3 Tyrwhitt Crescent, Roath Park, Cardiff CF23 5QP, UK
Images First Ltd, 10 Hereford Road, South Ealing, London W5 4SE, UK
Institute for the Study of the Ancient World, 15 East 84th Street, New York, New York 10028, USA
Department of Physics, University of Durham, Rochester Building, South Road, Durham DH1 3LE, UK
Centre for History and Palaeography, 3, P. Skouze str., GR-10560 Athens, Greece
Correspondence to: Tony Freeth1,2 Correspondence and requests for materials should be addressed to T.F. (Email: tony@images-first.com).


Top of pagePrevious research on the Antikythera Mechanism established a highly complex ancient Greek geared mechanism with front and back output dials1, 2, 3, 4, 5, 6, 7. The upper back dial is a 19-year calendar, based on the Metonic cycle, arranged as a five-turn spiral1, 6, 8. The lower back dial is a Saros eclipse-prediction dial, arranged as a four-turn spiral of 223 lunar months, with glyphs indicating eclipse predictions6. Here we add surprising findings concerning these back dials. Though no month names on the Metonic calendar were previously known, we have now identified all 12 months, which are unexpectedly of Corinthian origin. The Corinthian colonies of northwestern Greece or Syracuse in Sicily are leading contenders—the latter suggesting a heritage going back to Archimedes. Calendars with excluded days to regulate month lengths, described in a first century bc source9, have hitherto been dismissed as implausible10, 11. We demonstrate their existence in the Antikythera calendar, and in the process establish why the Metonic dial has five turns. The upper subsidiary dial is not a 76-year Callippic dial as previously thought8, but follows the four-year cycle of the Olympiad and its associated Panhellenic Games. Newly identified index letters in each glyph on the Saros dial show that a previous reconstruction needs modification6. We explore models for generating the unusual glyph distribution, and show how the eclipse times appear to be contradictory. We explain the four turns of the Saros dial in terms of the full moon cycle and the Exeligmos dial as indicating a necessary correction to the predicted eclipse times. The new results on the Metonic calendar, Olympiad dial and eclipse prediction link the cycles of human institutions with the celestial cycles embedded in the Mechanism's gearwork.