section_path: Tabular Byzantine calendar
section_name: Tabular Byzantine calendar
paragraph_text: Tabular Byzantine calendar
  
  The tabular Byzantine calendar is used to calculate the date of Easter. It dates back to AD 284, when the new moon fell on the fifth epagemonal day of the Alexandrian calendar (28 August). Eusebius (vii.32) recounts that Anatolius of Laodicea was the first to arrange the 19-years cycle (when the new moon returns to the same Julian date) for ecclesiastical purposes. Anatolius says that he places the new moon of the first year of his cycle on the Alexandrian equivalent of 22 March, the day of the vernal equinox. In the Julian calendar, the equinox recedes at the rate of 1 day in 128 years; by the time of the First Council of Nicaea in AD 325 it was falling on 21 March. 22 March is 26 Phamenoth in the Alexandrian calendar.
  
  The lunar new year was not allowed to begin before 15 Thoth (12 September, or 13 September if the following February has 29 days), and the month in which Easter fell was not allowed to begin before 12 Phamenoth (8 March). As the paschal full moon (the full moon before Easter), like all full moons is assigned to the 14th day of the lunar month, its earliest date was thus 25 Phamenoth (21 March), and Easter fell at earliest on 26 Phamenoth (22 March) and at latest on 30 Pharmouthi (25 April). The month in which Easter fell could thus begin no later than 10 Pharmouthi (5 April) and the Easter full moon could fall no later than 18 April (23 Pharmouthi).
  
  If, at the end of the twelfth lunar month, the next lunar month would begin before 15 Thoth, an additional 30-day month was inserted. This caused Easter to jump forward in years 3, 6, 9, 11, 14, 17 and 19 of the cycle. The lunar date of the sixth epagemonal day (considered the first day of a leap year) was the same as that of the previous day. The Alexandrian months, all of thirty days, are:
  
  The first lunar month had 29 days, and following lunar months had 30 and 29 days alternately. Thus the sixth lunar month, preceding the one in which Easter fell, had 30 days, minimising the chance of Easter clashing with Passover. This calendar uses the Callippic cycle of 76 years, under which the lunar year averages 365.25 days. But with this arrangement the lunar year averages 366.25 days. Therefore, in cycle 19, when the eleventh lunar month began on 7 Mesore and had 29 days, the next month (beginning on 1 Thoth) also had 29 days (saltus lunae) and the first month of the new lunar year began on 30 Thoth. In the sixth century, after it accepted that it no longer mattered if the birthday of Rome (23 April) fell within Lent, the Roman church abandoned its own calculation (the Supputatio Romana) for the Alexandrian one. This involved recasting the lunar months so that their first days were given in terms of the Julian calendar. While Easter continued to jump forward in years 3, 6, 8, 11, 14, 17 and 19 of the cycle the extra months were more equitably spaced, generally being hidden within those Julian months which contained two new moons. Their starting dates were: