The civil year consisted in general of twelve months or lunations, but occasionally a thirteenth was added in order to preserve its correspondence with the solar year.
From the same period also they have employed, in the adjustment of their solar and lunar years, a period of nineteen years, twelve of which are common, containing twelve lunations each, and the remaining seven intercalary, containing thirteen lunations.
The moons of the civil year are also distinguished by their place in the cycle of sixty; and as the intercalary moons are not reckoned, for the reason before stated, namely, that during one of these lunations the sun enters into no new sign, there are only twelve regular moons in a year, so that the cycle is renewed every five years.
METONIC CYCLE, in chronology, a period of 19 years during which there are 235 lunations, so called because discovered by Meton.
Computation from modern data shows that 235 lunations are 6939 days, 16.5 hours; and 19 solar years, 6939 days, 14.5 hours.