The #MetonicCycle or enneadecaeteris (from #AncientGreek: ἐννεακαιδεκαετηρίς, from ἐννεακαίδεκα, "nineteen") is a period of almost exactly 19 years after which the #lunarPhases recur at the same time of the year. The recurrence is not perfect, and by precise observation the Metonic cycle defined as 235 #synodicMonths is just 2 hours, 4 minutes and 58 seconds longer than 19 #tropicalYears. #MetonOfAthens.