Jan Zuidhoek, the author of this new study, 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 steeped himself in the fields of history of mathematics, history of early Christianity, and chronology, he became fascinated by the computus paschalis, i.e. the science developed from the beginning of the third century on behalf of the determination of the date of Paschal Sunday. In 2009 he succeeded in determining the initial year (AD 271) of De ratione paschali, i.e. the medieval Latin text containing the Paschal tract of the famous third century Alexandrian computist Anatolius, founder of the modern way of determining the date of Easter. This was done by reconstructing, on the basis of NASA’s Six Millennium Catalog of Phases of the Moon, the proto-Alexandrian 19-year lunar cycle defined to be the Metonic 19-year lunar cycle Anatolius must have used to construct his legendary 19-year Paschal cycle. The reconstruction in question was the subject of his contribution to the international conference on the science of computus which took place at the university of Galway in 2010. It was published in 2017 as an article in the proceedings of that conference entitled “The initial year of De ratione paschali and the relevance of its paschal dates”.
The present study developed from the presentation the author gave at the university of Galway in June 2018 under the title “Reconstructing the Alexandrian 19-year lunar cycles”. Because the paper in question was accepted outside the theme of the conference, it could not be included as an article in the proceedings of the conference. Therefore the author, convinced of the relevance of his recent discoveries, decided, in view of his old age and in order not to lose time, to publish these new results on his own in the form of this book, in which both the reconstruction of Anatolius’ 19-year lunar cycle and the archetypal Alexandrian 19-year lunar cycle defined to be the ante-Nicene common archetype of the three well-known post-Nicene Metonic 19-year lunar cycles are the main subjects.