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Dating, and Dating by, the Antikythera Mechanism

Paul Iversen

Case Western Reserve University

The Antikythera Mechanism was salvaged in 1901 from a shipwreck datable to ca. 70-50 BCE (for the date of the ship’s contents, see Vlochogianni et al. 2012 ). In 2005, members of the Antikythera Mechanism Research Project (AMRP) applied both Polynomial Textured Mapping to the study of this ingenious device to better see the outer surface inscriptions, and CT scanning technology to view with enhanced clarity the inner gear work. The CT technology, however, also unexpectedly uncovered finely engraved inscriptions on its inner surfaces that had not been seen in over 2,000 years, including the complete names and order of the months of a Greek luni-solar calendar on what is now known as the “Metonic Spiral” located on the upper back of the device. The lettering of these inscriptions has been variously dated anywhere from the end of the third century to the middle of the first century BCE. In 2006, members of the AMRP, in a seminal article (Freeth, Bitsakis et al., Nature 444.7119: 587-91 + Suppl. ), established that the lower dial (dubbed the “Saros Dial”) on the back face of the device described a series of eclipses using what is known today as the Saros Cycle – a period of 223 lunar months first recognized by the Babylonians in the Neo-Babylonian period (626-539 BCE) as being useful to ascertain recurring solar and lunar eclipse possibilities. The eclipse possibilities are referenced via a series of glyphs inscribed within some of the 223 individual cells, each which represents a lunar month, that are inscribed around the Saros Dial in a spiral pattern. In 2008, members of the AMRP published a second paper (Freeth, Jones, Steele and Bitsakis, Nature 454.7204: 614-7 + Suppl. ) in which they deciphered the meaning of the glyphs, each which references a particular month for a particular eclipse possibility, be it solar or lunar or both, and the time of day. Later, two different groups of researchers ( Carman and Evans 2014 and Freeth 2014 ), using different methods, came to the same conclusion that cell 1 of the Saros Dial best corresponds to the astronomical lunar month beginning April 29, 205 BCE. From this information, it has been argued that the start-up date of the calendar on the “Metonic Spiral” began with the lunar month beginning shortly after the new moon of August 23, 205 BCE ( Iversen 2017 ). In this paper, I will briefly discuss each of the various means of dating the Antikythera Mechanism, from the start-up date of the eclipse cycle, to the date of the science underpinning its functions, to the date of the shipwreck, to the earliest literary references to such devices, to the working shelf-life of such devices, to palaeographical considerations. For this last point, I will introduce a new reading that demonstrates that cursive omega was used as an index letter on what is known as the Back Plate Inscription, thus possibly suggesting a date closer to 50 BCE (although it will be pointed that on the Mechanism this letter-form may have been borrowed from papyrological sources, which employed it by the late third century BCE). In the end, it will be argued that the Mechanism is more likely to date within a generation of the shipwreck. In addition to this, I will discuss how the seasons of the months that belong to this calendar can be identified within reasonable parameters, and thus how the dating events by the Antikythera Mechanism is also possible.

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Inscriptions and Dates

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