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This
webpage is part of www.alexandriancomputus.net, which
supports the new book
on early Alexandrian Paschal reckoning [Jan Zuidhoek (2023) Reconstructing
Alexandrian Lunar Cycles (on the basis of Espenak’s
Six Millennium Catalog of Phases of the Moon):
Zwolle]. This webpage shows section Summary of this new book, which is available via this website. |
The development the Alexandrian
method for determining Alexandrian or Julian calendar dates of Paschal Sunday
underwent is nothing less than the mainstream of the history of computus (i.e. Paschal reckoning) which rose in third
century Alexandria (Egypt) to ultimately (in sixteenth century Rome) flow into
an astronomically more realistic method for determining Gregorian calendar
dates of Easter. In this mainstream there were only two real rapids:
1) the construction (on the basis of
at the time quite recent tables of lunar phases) of the proto-Alexandrian
lunar cycle (around AD 260) and Anatolius’ lunar cycle (around AD 270),
the former being the (lost) Metonic lunar cycle from which the great third
century Alexandrian computist Anatolius originally
started to determine his Paschal dates, the latter being the one from which he
ultimately started in order to construct his famous and mysterious Paschal
table of 19 years;
2) the construction (idem) of the
archetypal Alexandrian lunar cycle (around AD 320), supposed to be the
(lost) ante-Nicene Alexandrian Metonically structured common archetype of the three
(well-known) post-Nicene Alexandrian Metonic lunar cycles.
The proto-Alexandrian lunar cycle and
Anatolius’ lunar cycle were constructed in the third quarter of the third
century, the archetypal Alexandrian lunar cycle was constructed half a century later,
relatively shortly before the first council of Nicaea in AD 325, turning point
in the history of Christianity. And so it must have been not so much because of
different moments of construction as because of different sets of computistical principles according to which they were
constructed that the latter lunar cycle differs so much from both the former
ones. After having reconstructed them, we establish that:
1) there exists a 2-day gap (actually
a systematic difference of on average just over 2 days) between Anatolius’
lunar cycle and the archetypal Alexandrian lunar cycle, the cause of which must
be sought exclusively in the transition in Alexandria and beyond 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
went to use the more familiar Egyptian lunar calendar instead of the
Alexandrian version of the Jewish lunar calendar);
2) both the proto Alexandrian lunar
cycle and Anatolius’ lunar cycle have de facto limit dates 23 March and 20
April, both sequences of Paschal dates generated by them have, according to the
old Alexandrian Paschal rule, de facto limit dates 23 March and 26 April;
3) the archetypal Alexandrian lunar
cycle is the archetype from which in the end one by one each of the three
(well-known) post-Nicene Alexandrian Metonic lunar cycles was obtained either by
accepting the archetype without any modification or by moving its saltus one
year afterward or two years forward;
4) the three (well-known) post-Nicene
Alexandrian Metonic lunar cycles, as well as the archetypal Alexandrian lunar
cycle, have de facto limit dates 21 March and 18 April, the four sequences of
Paschal dates generated by them have, according to the new Alexandrian Paschal
rule, de facto limit dates 22 March and 25 April.
We conclude that the Alexandrian computists who constructed the three (lost) ante-Nicene
Alexandrian Metonic lunar cycles, most famous the great scholar Anatolius (he
died in about AD 282), can be regarded as the founders, their post-Nicene
followers Annianus (around AD 400), Dionysius Exiguus
(around AD 500), and Beda Venerabilis (around AD 700)
as the great developers of the efficient Alexandrian method for determining
Julian calendar dates of Paschal Sunday from (and thanks to) which eventually, thirteen
centuries after Anatolius’ death, an astronomically more realistic method for
determining Gregorian calendar dates of Easter would be developed.
© Jan Zuidhoek 2023‑2026
(updated 12-10-2026)