Cycle metonic
In Astronomy and in the establishment of the Calendar S, the cycle of Méton or cycle metonic is a common approximate multiple of the orbital periods of the Ground and the Moon. It is by definition the synodical duration of 235 lunar Mois S. Indeed, nineteen tropical years and 235 synodical Mois S differ only from two hours; thus at the end of nineteen years, the same dates of the year correspond with same the phases of the Moon.
The one year old row in this cycle is called Golden section , because it was engraved each year on the pillars of a Temple with Athens. Thereafter about the year 800 it will be used for the calculation of the date of Easter.
The name cycle of Méton comes from the Greek Astronome Méton which had already noticed this coincidence around -432, as the astronomer chaldéen Kidinnu did it towards -380. But of the writings Cunéiforme S seem to indicate that this cycle was already known in Mésopotamie as of sixth century BC and was used to predict the eclipse S.
The cycle of Méton is employed in the lunisolar calendars. Indeed, in a typical lunisolar calendar, the majority of the years are twelve months lunar years, but seven the nineteen years have one month additional, known under the name of intercalated Mois or embolismic.
In the Babylonian calendars and Hebrew ancient, the years: 3,6,8,11,14,17 and 19, are the thirteen months years of the cycle metonic.
There exist also two other similar cycles: the octaeteris (8 years ≈ 99 lunations, cf Calendar attic) and the tritos (11 years ≈ 136 lunations).
The cycle of Méton is also close (except for a half-light) to 255 draconitic Mois S. It is thus also a cycle of eclipse (weak), which lasts only four or five eclipses. The tritos, near 146,5 months draconitic, is a better cycle of eclipse. But they do not have anything comparable with the Saros.
External bonds
- did Méton invent the cycle which bears its name?
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