Ep´act

(Gr. epaktos , added), in chronology, the exce of the solar month above the lunar synodical month, and of the solar year above the lunar year of twelve synodical months. The epacts then are annual and menstrual or monthly . Suppose the new moon to be on the 1st of January: the month of January containing 31 days, and the lunar month only 29 days, 12 hours, 44 minutes, 3 seconds; the difference, 1 day, 11 hours, 15 minutes, 57 seconds, is the menstrual epact . The annual epact is nearly 11 days; the solar year being 365 days, and the lunar year 354. The epacts were once of some importance in ecclesiastical chronology, being used for finding when Easter would fall.