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Calendars with Olympiad display and eclipse prediction on the Antikythera Mechanism


Previous 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.

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Figure 1: The ‘instruction manual’.
Figure 2: The back dials.
Figure 3: Deciphering the Metonic and Olympiad dials.
Figure 4: The glyphs.

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This research was carried out under the aegis of the Antikythera Mechanism Research Project with the collaboration of M. G. Edmunds, J. Seiradakis, X. Moussas, A. Tselikas and the National Archaeological Museum in Athens. We acknowledge the essential collaboration of the Museum Director, N. Kaltsas, H. Mangou, M. Zafeiropoulou (who catalogued the fragments, revealing fragment F and several smaller fragments), G. Makris and many other contributing staff. The X-ray data were gathered by a team from X-Tek Systems (UK)/Metris (NL), led by R. Hadland, and we particularly thank A. Ramsey and A. Ray. We appreciate the support of C. Reinhart of Volume Graphics. We thank the team from Hewlett-Packard (US), led by T. Malzbender, who carried out the surface imaging. We are indebted to N. Economou (deceased), H. Kritzas, E. Georgoudakis and M. Anastasiou. We thank F. Espenak of NASA/GSFC for all the modern eclipse data and predictions. The J. F. Costopoulos Foundation partly funded T.F. and the National Bank of Greece partly funded Y.B. J.M.S. was supported by a Royal Society University Research Fellowship.

Author Contributions T.F. and A.J. carried out the CT analysis of the inscriptions and A.J. provided most of the interpretation and historical analysis, with input from Y.B. A.J. identified the excluded days on the Metonic dial, the Olympiad dial and the index letters in the glyphs. T.F. proposed how the Olympiad dial was turned. J.S., T.F. and A.J. contributed ideas about the glyphs and T.F. carried out the analysis of glyph sequence generation and glyph times and explained why the Saros dial has four turns. J.S. identified the role of the Exeligmos dial. All the authors contributed to the written manuscript. T.F collated and condensed the text and designed the illustrations.

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Correspondence to Tony Freeth.

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The file contains Supplementary Notes, including Supplementary Figures 1-25 with Legends and additional references. Supplementary Figs 20 and 25 were amended on 02 June 2011. (PDF 3076 kb)

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Freeth, T., Jones, A., Steele, J. et al. Calendars with Olympiad display and eclipse prediction on the Antikythera Mechanism. Nature 454, 614–617 (2008).

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