出典:Wiktionary
Metonic cycle (複数形 Metonic cycles)
出典:Wikipedia
出典:『Wikipedia』 (2011/07/04 16:32 UTC 版)
In astronomy and calendar studies, the Metonic cycle or Enneadecaeteris (from Greek words for nineteen years) is a period of very close to 19 years which is remarkable for being very nearly a common multiple of the tropical year and the synodic (lunar) month. The Greek astronomer Meton of Athens observed that a period of 19 tropical years is almost exactly equal to 235 synodic months, and rounded to full days counts 6940 days. The difference between the two periods (of 19 tropical years and 235 synodic months) is only 2 hours.