A 28-year period applicable to the Julian calendar, in which the first day of the year is restored to the same day of the week. Since the days of the week are 7, and the number of years in an intercalary period are 4, their product (4 x 7 = 28) must include all possible combinations. At the end of each cycle, the Dominical letters return again in the same order on the same days of the month. v. Calendar.
ASTROLABE ENCYCLOPEDIA
