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, i.e. the science developed from the early third century on behalf of the determination of the (Alexandrian or Julian calendar) date of Paschal Sunday, which rised shortly after AD 250 in Alexandria (Egypt) to finally (in the year 1582) flow into the modern way of determining the (Gregorian calendar) date of Easter, how of old the date of Paschal Sunday depends on the phases of the moon, and provides, on the basis of NASA’s Six Millennium Catalog of Phases of the Moon, the reconstruction of both lost Metonic 19‑year lunar cycles which were actively constructed in Alexandria already before the first council of Nicaea (AD 325), turning point in the history of Christianity.

The author of this 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, chronology, and history of early Christianity, he became fascinated by the Alexandrian computus. In 2009 he succeeded, by using the Six Millennium Catalog, in determining the initial year (AD 271) of De ratione paschali, i.e. the medieval Latin text containing the legendary 19-year Paschal cycle of Anatolius, the famous third century Alexandrian computist who invented the very 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 this pioneering book reducing that article to a preparatory study.



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© Jan Zuidhoek 2019-2021