This webpage is part of www.janzuidhoek.net and represents section Summary of [J. Zuidhoek (2019) Reconstructing Metonic 19-year Lunar Cycles (on the basis of NASA’s Six Millennium Catalog of Phases of the Moon): Zwolle].
The development of the Metonic 19-year lunar cycle formed the mainstream of the history of the computus paschalis which had risen in third century Alexandria (Egypt) and would in 1582 flow out into the modern method which since then is used in order to determine the Gregorian calendar date of Easter. Between the active construction of the first version of this lunar cycle by Anatolius (somewhere between AD 250 and 270) and the replacement of the Julian with the Gregorian calendar (in 1582) it happened only one time, namely somewhere between AD 300 and 325, hence still before the first council of Nicaea, that a new version of it was actively constructed. After having reconstructed (on the basis of NASA’s Six Millennium Catalog) the two lost ante-Nicene versions in question, we establish that:
1) the first of them (referred to as ‘Anatolius’ 19-year lunar cycle’) is nothing but the proto-Alexandrian 19-year lunar cycle (reconstructed ten years ago);
2) the second (referred to as ‘the archetypal 19-year lunar cycle’) must considered to be the archetype from which after AD 325 one after another the three well-known post-Nicene Metonic 19-year lunar cycles were obtained simply by one or two times moving only 1 of its 19 different dates one day forward or back;
3) the cause of the 2-day gap between them (referred to as ‘the ante-Nicene Alexandrian 2-day gap’) must be sought in the transition from the more Jewish Christian world of the third century to the more Gentile one of the fourth, as a result of which Alexandrian computists went to use the more familiar Egyptian lunar calendar instead of the Alexandrian version of the Jewish lunar calendar.