User:Jan Zu

Jan Zuidhoek 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”. Jan Zuidhoek is also the author of "Reconstructing Metonic 19-year Lunar Cycles". This new book is a study developed from the presentation he 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 a book, in which the reconstruction of Anatolius’ 19-year lunar cycle and the one of 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. It is the development of the Metonic 19-year lunar cycle that formed the mainstream of the history of the computus paschalis which had risen in third century Alexandria (Egypt) and would in 1582 flow out into the modern method which since then is used in order to determine the Gregorian calendar date of Easter Sunday. Between the active construction of the first version of this lunar cycle by Anatolius (somewhere between AD 250 and 275) and the replacement of the Julian calendar with the Gregorian one (in 1582) it happened only one time, namely somewhere between AD 300 and 325, hence still before the first council of Nicaea, that a new version of it was actively constructed. After having reconstructed (on the basis of NASA’s Six Millennium Catalog) the two lost ante-Nicene versions of the Metonic 19-year lunar cycle in question, we establish that: 1) the first of them (referred to as ‘Anatolius’ 19-year lunar cycle’) is nothing but the proto-Alexandrian 19-year lunar cycle (reconstructed ten years ago); 2) the second (referred to as ‘the archetypal 19-year lunar cycle’) must considered to be the archetype from which after AD 325 one after another each of the three well-known post-Nicene Metonic 19-year lunar cycles was obtained simply by moving only 1 of the 19 different dates of its predecessor one day forward or back; 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 one 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.