Reconstructing the Antikythera Mechanism lost eclipse events applying the Draconic gearing - the impact of gear error

Abstract

We present new observations concerning the procedure for the reconstruction of the lost eclipse events engraved in the Saros spiral cells of the Antikythera Mechanism. For the reconstructed eclipse events we applied the necessary, albeit missing, Draconic gearing of the Antikythera Mechanism [using the Fragment D(raconic) – gear r1], which was probably a part of the Mechanism’s gearing, representing the fourth lunar motion, the Draconic cycle. The Draconic gearing is very critical for the eclipse prediction and defines whether an eclipse will occur. For our research we created a program which presents the phase of the four lunar cycles - including the position of the Draconic pointer relative to the ecliptic limits. After calibrating the program according to the preserved eclipse events, the lost eclipse events of the Saros spiral were calculated and discussed. The procedure for the calculation of the events’ times by using solely the Mechanism based on the pin&slot configuration, is also presented. The eccentricity error of a gear which is preserved on the ancient prototype is analyzed. An experimental setup facilitated the analysis of the mechanical errors of the gears and the study of the motion transmission between gears with triangular teeth. The experimental study of the gears errors revealed the strong impact the Antikythera Mechanism pointers’ position has on the results.

Keywords

• antikythera mechanism saros spiral
• draconic gearing
• nodes
• ecliptic limits
• gear errors
• gear eccentricity
• eclipse events