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The Gregorian calendar, used by most of the world, also doesn't match up exactly with a solar year. Because of this, there are leap days about 24 times a century, according to the Atlantic.
Eventually the Greeks adopted a more accurate period known as the Metonic cycle, which equates 19 solar years with 235 lunar months.
He observed that 235 lunar months correspond very closely to 19 solar years -- so closely, in fact, that it takes over 200 years for the two periodicities to get out of sync by one day.

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