about

the metonic cycle is a period of 19 years corresponding to almost exactly 235 synodic lunar months or full cycles of moon phases. named after meton of athens, a greek mathematician and astronomer from the 5^th century bc, the cycle provides a framework for building lunisolar calendars by synchronizing the solar with the lunar year.

a mechanical lunisolar calculator based on the metonic cycle is integrated into the antikythera mechanism, a hand-powered model of the solar system built in the 2^nd century bc. this virtual model is inspired by the ancient mechanism and features a gearing system simulating the synodic cycle of the moon following the ratio ⁶²⁄₂₃ × ³⁹⁄₁₇ × 2 ≈ 12.37. the draconic lunar month is the period between the moon’s passage through the same lunar node, calculated using the ratio ⁸²⁄₂₃ × ⁶⁴⁄₁₇ ≈ 13.42.

the orange triangle marks the date, while the white dot tracks the draconic moon position. the orange dots at the top and bottom indicate the lunar nodes, while the orange angle markers show the ecliptic limits, opaque for the moon and transparent for the sun. total eclipse limits are denoted by solid lines; partial eclipse limits by dots.

controls on the right allow for toggling between animation and the current moon phase as well as jumping to the next or previous new or full moon. the calculated date is indicated at the bottom. the small orange dot on the right marks equinox on march 21^st, the reference date used for easter date calculations. the animation speed is set to one solar year per minute. the mechanism will deviate by one day every 1678 years (synodic cycle) and every 12,879 years (draconic cycle) respectively.

prof. em. thomas weibel
basel, switzerland

(ȼ) twb