The 28-year cycle of the Sun, on which is based the Dominical Letter, brings the Sun back to the same day of the week. The 19-year Metonic Cycle restores the new moon to the same day of the month. Therefore 28 X 19 = 532 years - the period on which Lunations recur on the same day of the month and the same day of the week. This is the Dionysian Period, so called after Dionysius Exiguus; also called the Victorian period, after Victorius of Aquitain. Its use in determining Easter Sunday was discontinued with the Gregorian reformation of the Julian calendar.
ASTROLABE ENCYCLOPEDIA
