**This webpage belongs to www.janzuidhoek.com****, which is a website promoting [Jan Zuidhoek
(2021) 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 groundbreaking book, which is available via this website****.**

**Summary**

**It is the development the
Alexandrian computus underwent which forms the
mainstream of the history of the computus paschalis that had risen in third century Alexandria
(Egypt) to ultimately flow into the modern method of determining Gregorian
calendar dates of Easter. Between the construction of the very first Metonic 19‑year lunar cycle by the Alexandrian computist Anatolius (in about AD
260) and the replacement of the Julian calendar with the Gregorian calendar (in
AD 1582, ****turning point in the history of
chronology)**** it
was only once, namely shortly before the first council of Nicaea
(in AD 325, ****turning point in the history of
Christianity), ****that in Alexandria a completely new Metonic 19‑year
lunar cycle was constructed, like its predecessor directly or indirectly on the
basis of at the time recent lunar tables, but according to a different set of computistical principles. After having reconstructed both
of these lost ante‑Nicene Metonic 19‑year
lunar cycles, we establish that:**

**1) the first of them (referred
to as ‘Anatolius’ 19-year lunar cycle’) is equal to
the proto-Alexandrian cycle reconstructed in 2009;**

**2) the second of them
(referred to as ‘the archetypal Alexandrian 19‑year lunar cycle’) is
nothing but the 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 either by adopting the very same Metonic structure of the archetypal Alexandrian cycle or by
moving its saltus 1 year afterward or 2 years
forward (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 Paschal dates generated by it according
to the old Alexandrian Paschal rule have de facto lower limit date
23 March;**

**5) the archetypal Alexandrian
19‑year lunar cycle has de facto lower limit date 21 March but the
sequence of Paschal dates generated by it according to the new Alexandrian
Paschal rule has de facto lower limit date 22 March (the same applies to
the well-known three post‑Nicene Alexandrian Metonic
19-year lunar cycles).**

**We conclude that Anatolius can be considered to be the founder of the
efficient Alexandrian Metonic 19-year lunar cycle
method of determining Julian calendar dates of Paschal Sunday from which after**** the Gregorian calendar reform in AD 1582, after preparatory work
by the Italian astronomer Luigi Lilio, the German
mathematician Christoph Clavius
would develop a modern system for determining Gregorian calendar dates of
Easter.**

**© Jan Zuidhoek
2019-2022**