THE ANTIKYTHERA MECHANISM 2. Is it Posidonius' Orrery?

Abstract

The structure and functions of the ancient Greek astroomical calculator, known as the Antikythera Mechanism, are still hotly debated. A remarkable quote from Cicero,exactly contemporary with the mechanism, describes an orrery made by Posidonius, which shows the "…motios of the sun, the moon and the five planets…". In Edmunds and Morgan 2000,it is persuasively argued that the device might have been primarily astrological and therefore likely to have included planetary mechanisms - possible designs are also described.Building on this work a Theory of Planetary Mechanisms is developed which links their gear ratios with the‘period relations' in the Babylonian Astronomical Diaries. Several possible designs for these mechanisms are also explored.It is often argued that there is insufficient space for all five planets in the Antikythera Mechanism,but it is shown here that they can fit in the case, using the same basic design and technology -it could in fact be Posidonius' Orrery.