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 dials. The upper back dial is a 19-year calendar, based on the Metonic cycle, arranged as a five-turn spiral. The lower back dial is a Saros eclipse-prediction dial, arranged as a four-turn spiral of 223 lunar months, with glyphs indicating eclipse predictions. 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 source, have hitherto been dismissed as implausible. 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 thought, 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 modification. 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.
Observations and Predictions of Eclipse Times by Early Astronomers
Preface. I: Introductory Orientations. 1. Introduction. II: The Western Heritage. 2. Mesopotamia. 3. The Greco-Roman World. 4. The Islamic Near East. 5. Late Medieval and Renaissance Europe. III: The Eastern Heritage. 6. China. 7. Japan. IV: Conclusions. 8. Discussion. V: Appendices. References. Subject Index. Index of Texts.
Solar Eclipse Times Predicted by the Babylonians
In the preceding paper, I F.R. Stephenson and I investigated the times of lunar eclipses predicted by the Late Babylonian astronomers. In this paper I shall investigate the predictions of solar eclipse times recorded in the Late Babylonian astronomical texts. Solar eclipses are visible only upon a small part of the Earth's surface. As a result their accurate prediction is much more difficult than in the case of lunar eclipses, and requires a knowledge of the size and shape of the Earth, information which was not available to the Babylonian astronomers. It appears that the eclipses were predicted purely by use of a cyclical procedure, in the same fashion as for lunar eclipses.