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 5th 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 aligns with the principles of ancient greek astronomy and features a gearing system simulating the synodic cycle of the moon following the ratio ²³⁵⁄₁₉ = ⁴⁷⁄₁₄ × ⁷⁰⁄₁₉ ≈ 12.37. the draconic lunar month is the period between the moon’s passage through the same lunar node, calculated using the ratio ⁴⁷²⁵⁄₃₅₂ = ⁷⁵⁄₁₆ × ⁶³⁄₂₂ ≈ 13.42. the mechanism will deviate by one day every 220 years (synodic) and every 28 years (draconic) respectively.

the orange triangle marks the date while the white dot tracks the draconic moon positionc, the small white dot marks the march equinox for easter date calculation. 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 animation speed is set to one solar year per minute.

prof. thomas weibel
university of applied sciences of the grisons
berne university of the arts
switzerland

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