The ancient greek astronomer Meton observed that the lunar phases are repeated on the same weekday once every 19th year. therefore this period is referred to as the

Meton Cycle.  Theses days were carved in a stone at Forum Romanum in ancinet rome and they also play an importatnt part in the Baha’i calender as well as other calendars based on the lunar-phases.

He also observed that one tropical year consists of 365 days 6 hours and 19 minutes.

Thus one Meton cycle equals 6 940 days.

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