Before the introduction of the Metonic cycle, the Olympic year began sometimes with the full moon which followed, at other times with that which preceded the summer solstice, because the year sometimes contained 384 days instead of 354.
METONIC CYCLE, in chronology, a period of 19 years during which there are 235 lunations, so called because discovered by Meton.
The Metonic Cycle, Which May Be Regarded As The Chef D'Oeuvre Of Ancient Astronomy, Is A Period Of Nineteen Solar Years, After Which The New Moons Again Happen On The Same Days Of The Year.
After The Metonic Cycle Had Been In Use About A Century, A Correction Was Proposed By Calippus.
The Period Of Calippus, Therefore, Consisted Of Three Metonic Cycles Of 6940 Days Each, And A Period Of 6939 Days; And Its Error In Respect Of The Moon, Consequently, Amounted Only To Six Hours, Or To One Day In 304 Years.