Metonic cycle

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The Metonic cycle is a period of 19 solar years that is very close to 235 synodic months. After this interval, lunar phases recur on nearly the same dates of the solar year.

Nineteen tropical years equal about 6,939.6 days, while 235 synodic months equal about 6,939.7 days. The small difference means the correspondence is close but not exact.

The cycle was known in ancient Babylonian astronomy and is associated with the Greek astronomer Meton, who introduced it into the Athenian calendar in the fifth century BCE.

Metonic cycles are used in lunisolar calendars to coordinate lunar months with the seasons. They also contribute to calculations of religious dates, including the traditional determination of Easter.

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• Source / publisher: Wikipedia
• URL type: WWW
• Credits: Wikipedia
• URL: https://en.wikipedia.org/wiki/Metonic_cycle