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Antikythera Mechanism

Evidence of a Lunar Calendar, parts 1 and 2

C. Budiselic, A. T. Thoeni, M. Dubno, A. T. Ramsey
Published: 5 December, 2020
Image used with permission, copyright 2019, David Jones


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New analysis of the Antikythera Mechanism presents evidence that the mechanism’s front-dial ring is a 354-day lunar calendar, not a 365-day calendar as previously supposed.

The importance of the Antikythera Mechanism has been recognised since nearly the moment of its discovery on the Mediterranean Sea floor  in 1901. It is a complex mechanical computer that could be used to predict, amongst other things, solar and lunar motions and their eclipses. It links the craft of the clockmaker all the way back to the origins of mechanical devices 2100 years ago.

Scholars including Derek de Solla Price, Tony Freeth, Alexander Jones, Michael Wright, and Mike Edmunds have expanded our understanding of this device. The authors of this paper based their work on a new statistical analysis of the hole-spacing in the front calendar ring, combined with practical insights gained by experience in construction of traditional clocks and reconstruction of mechanisms from antiquity.

The peer-reviewed Horological Journal is published by the British Horological Institute since 1858, and brings together the diverse disciplines of horology, including practical, historic, aesthetic and market-based studies in clocks, watches and related subjects. This digital edition of ‘The Antikythera Mechanism – Evidence of a Lunar Calendar’ is a pre-press version, published in December 2020. The print edition (with minor revisions) has been published in the March 2021 edition of the Horological Journal.

Among the Mechanism’s many features is a movable calendar ring with three Egyptian month names engraved in ancient Greek. The calendar ring has been universally supposed, without validation, to be an unremarkable example of what is generally referred to as the ‘Egyptian civil calendar’ — a non-lunar calendar of precisely 365-day duration, comprising twelve 30-day months, plus five epagomenal or ‘intercalary’ days.
In this paper we reconsider this feature, and provide new data to show this interpretation to be incorrect, and displace the century-long assumption of a 365-day calendar on the Antikythera Mechanism, proposing instead that it is a 354-day lunar calendar.

The underlying hole-measurement data can be downloaded here:


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