A group of Greek researchers announced that they were able to determine the “zero day” of the famous Antikythera mechanism, based on the so-called saros cycle – the time interval after which the sequence of lunar and solar eclipses is approximately repeated. Knowing this “eclipse trigger” moment is critical to ensuring the accuracy of the device. Preprint of new work published on arXiv.org
The device in question was found on April 4, 1900 near the Greek island of Antikythera, after which it got its name. It was found that it was assembled in the 2nd century BC, and now this mechanism is considered the most complex device of the ancient world that has come down to our days.
“Any measuring system, from a thermometer to the Antikythera Mechanism, needs to be calibrated to make its calculations correctly,” lead author Aristeidis Voulgaris of Thessaloniki Culture and Tourism Authority in Greece told New Scientist. “Of course, the mechanism does not work perfectly – it’s gears, not a digital computer – but it was very good at predicting solar and lunar eclipses.”
Voulgaris and co-authors based their new analysis on the 223-month saros cycle, which is shown on the back of the device. This cycle covers the time it takes for the Sun, Moon and Earth to return to their previous positions and includes the corresponding solar and lunar eclipses. Based on current knowledge of the device’s operation, as well as the inscriptions on it, the team hypothesized that “zero day” coincided with an annular solar eclipse, during which the Sun and Moon are exactly aligned with the Earth, but the Moon’s disk appears smaller than the Sun. and covers only its central part, leaving the outer edges of the Sun visible. At this moment, the Moon is at the most distant point of its near-Earth orbit – at apogee. Voulgaris and his colleagues searched the NASA database to find all examples of such events dating back to the time period when the Antikythera Mechanism was supposedly built.
It turned out that the most suitable saros cycle, including an annular solar eclipse, began on December 23, 178 BC. “Usually, to perform time calculations, a date is chosen from the recent past, and not from the future, this is especially true in relation to ancient times, when predictions for long periods of time were much more doubtful than at present,” the authors say. “This fact could also have influenced the creation of the Antikythera Mechanism in that era.”
As additional evidence, Greek scientists also cite several other significant astronomical events that occurred around the same time and were reflected on the outer case of the ancient mechanism. At the same time, the alternative date for the “launch of the mechanism”, previously proposed by other researchers, falls on the summer of 204 BC.