This webpage belongs to, 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 concerns this pioneering book, which is available via this website, and its author Jan Zuidhoek.



Book and Author

This book explains, by following the mainstream of the history of the computus paschalis developed from early in the third century for the purpose of determining (Alexandrian or Julian calendar) dates of Paschal Sunday which rised shortly after AD 250 in Alexandria (Egypt) to ultimately (in AD 1582) flow into the modern way of determining (Gregorian calendar) dates of Easter, how of old dates of Paschal Sunday depend on phases of the moon and, on the basis of NASA’s Six Millennium Catalog of Phases of the Moon, how both lost Metonic 19‑year lunar cycles constructed in Alexandria before the first council of Nicaea (in AD 325) can be reconstructed.

The author of this pioneering book was born in 1938, studied mathematics, physics, and astronomy at the university of Utrecht from 1960 to 1969, and was a teacher of mathematics from 1970 to 2001 at the Gymnasium Celeanum in Zwolle. After having gone deeply into the fields of history of mathematics, of chronology, and of early Christianity, ultimately resulting in his lucid webpage “Christian Era and Universal Time”, he became fascinated by the Alexandrian computus. In 2009 he determined the initial year (AD 271) of De ratione paschali, i.e. the medieval Latin text containing the legendary 19‑year Paschal cycle of the famous third century Alexandrian computist Anatolius who invented the first Metonic 19‑year lunar cycle. The presentations he gave at the international conferences on the science of computus at the university of Galway in 2010 and 2018 resulted in 2017 in an article entitled “The initial year of De ratione paschali and the relevance of its paschal dates” and in 2019 in the first edition of this book reducing that article to a preparatory study.



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© Jan Zuidhoek 2019-2021