This webpage belongs to www.janzuidhoek.net, which is a website promoting [Jan Zuidhoek
(2019) Reconstructing Metonic 19-year Lunar Cycles (on the basis of NASA’s Six
Millennium Catalog of Phases of the Moon): Zwolle], and shows section Summary
of this book (ISBN 9789090324678).
Summary
It is the development of the Alexandrian Metonic 19-year lunar cycle that
formed the mainstream of the history of the computus paschalis which had risen
in third century Alexandria (Egypt) and would in the year 1582 flow into the
modern method which since then is used in order to determine the Gregorian
calendar date of Easter Sunday. Between the active construction of the first
version of the Metonic 19‑year lunar cycle by the Alexandrian computist
Anatolius, somewhere between AD 250 and 270, and the replacement of the
Julian calendar with the Gregorian calendar (in the year 1582) it happened only
one time, namely somewhere between AD 300 and 324, in any case still
before the first council of Nicaea, that a radically new Alexandrian version of
this lunar cycle was actively constructed. After having reconstructed (on the
basis of NASA’s Six Millennium Catalog) both these ante-Nicene versions of the
Metonic 19-year lunar cycle, we establish that:
1) the first of them (referred to as ‘Anatolius’ 19-year lunar cycle’) is
nothing but the lost proto-Alexandrian 19-year lunar cycle (reconstructed in 2009);
2) the second (referred to as ‘the archetypal Alexandrian 19-year lunar
cycle’) is nothing but the lost ante-Nicene archetype from which after AD 325
one after another each of the three well-known post-Nicene Alexandrian Metonic
19‑year lunar cycles was obtained simply by moving only 1 of the 19
different dates of its immediate predecessor one day forward or back (see
Table 8);
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 Christian
world of the fourth, as a result of which Alexandrian computists began to use
the Egyptian lunar calendar more familiar to them instead of the Alexandrian
version of the Jewish lunar calendar;
4) both Anatolius’ 19-year lunar cycle and the sequence of dates of
Paschal Sunday generated by it have a de facto lower limit 23 March;
5) the archetypal Alexandrian 19-year lunar cycle has a de facto lower
limit 21 March but the sequence of dates of Paschal Sunday generated by it
has a de facto lower limit 22 March (the same applies to the well-known
three post-Nicene Alexandrian Metonic 19-year lunar cycles).
We conclude that Anatolius may be considered to be the founder of the
efficient Metonic 19-year lunar cycle method of determining the Julian calendar
date of Paschal Sunday from which thirteen centuries later the Italian
astronomer Luigi Lilio and subsequently the German mathematician Christoph
Clavius could depart to develop a modern, astronomically more correct, system
for determining the Gregorian calendar date of Easter.
© Jan Zuidhoek 2019-2020