The Astronomical Events of the Parapegma of the Antikythera Mechanism

Abstract

(ProQuest: ... denotes formulae omitted.)1. INTRODUCTIONThe Antikythera Mechanism,1 found in an ancient shipwreck in A.D. 1901, is an extraordinary 2000-year-old astronomical computer that calculated the position of the Sun and the Moon in the sky, was used as a calendrical device, could predict eclipses, and displayed the year when ancient panhellenic games were held. Extended astronomical and technical inscriptions covered its front and back doors and plates.The front side of the Antikythera Mechanism is mainly preserved in Fragment C where small parts of two concentric rings are found: the outer one displays the Egyptian calendar (with month names ???O?, ?????, etc.) and the inner one the signs of the zodiac (???T???S, XHAAI, etc).2 On the zodiac dial, above some of the scale divisions of each zodiac sign, small capital letters (A, B, G,...) are inscribed, that follow the sequence of the letters of the Greek alphabet.3 Attached to Fragment C, there are also two pieces (Cl -a and Cl-b4) of flat plate, inscribed with lines of text describing astronomical phenomena. At the beginning of each line is a separate letter. These 'index letters' almost certainly correspond to the small capital letters found on the zodiac dial, thus forming a 'parapegma'.5 Parapegmata - calendars of astronomical and meteorological events - were widely used in ancient Greece.6 Incomplete lines of parapegma text have been found in four other fragments (Fragments 9, 20, 22 and 28).On the largest of the two pieces of flat plate (Cl -a) attached to Fragment C, the most extensive parapegma inscription, with 9 lines of text (see Figure 1), can be read. From the lines bearing the index letters ?, M and N, only the last words are visible. The rest of the letters were visible duringAlbert Rehm's investigation (early twentieth century) but nowadays they are not, as part of the inscribed plate has broken away since then. These inscriptions were reported by Price,7 who based his reconstruction on unpublished notes of Albert Rehm.The events mentioned on plate Cl -a are typical of events found in parapegmata and are categorized as follows:(a) There are 6 events that refer to the rising and setting of stars. The verb used is either ... (rises) or ... (sets), indicating that the star is in the east or the west, respectively. It is followed by the adjective ...(in the morning) or ... (in the evening) indicating that the Sun is in the east or the west, respectively. The subject is always a star, a star cluster or a constellation. Combining the star and Sun positions, four star events are formed (morning rising (mr), evening rising (er), morning setting (ms) and evening setting (es)). These four events are sometimes called 'star phases' or 'heliacal risings and settings' by modern scholars.(b) There are 2 events that refer to the signs of the zodiac (henceforward called zodiac statements). The subject is always a zodiac constellation/sign, followed by the phrase ... (begins to rise), indicating that the constellation/sign is in the east. The ancients used the same names to indicate the irregularly shaped and sized zodiac constellations and the uniformlysized, 30°-long, zodiac signs. The fact that there is always an index letter at the first scale division of each sign of the zodiac on the zodiac dial (for all three signs with their first scale division preserved ...) indicates that these events most probably mark the crossing of the Sun from one zodiac sign to the next.8 This is somewhat unusual among Greek parapegmata. Parapegmata, not uncommonly, indicate the entry dates in some manner but this is the only parapegma that uses the verb 'rise' to designate the Sun's entry into zodiac signs. More typically we see a notice that a zodiac constellation to on a day that is not necessarily the first day that the Sun is in the zodiac sign of the same name. For example, in the Geminos parapegma, we read that, according to Callippus, the constellation Leo begins to rise on the 30th day that the Sun is in the sign of Cancer; or that, again according to Callippus, the constellation Aries begins to rise on the 3rd day that the Sun is in the sign of Aries. …