This webpage is part of, which is a website promoting [Jan Zuidhoek (2021) Reconstructing Metonic 19-year Lunar Cycles (on the basis of NASA’s Six Millennium Catalog of Phases of the Moon): Zwolle], which groundbreaking book is available via this website, and concerns the relationship between the complementary fundamental concepts Christian Era and Universal Time.





Christian Era and Universal Time

§ 1        Our era is the Christian Era, but nobody knows precisely when Jesus was born. Nevertheless, in AD 525, more than five centuries after Jesus’ birth, the first year of our era, referred to as the year AD 1, was retrospectively and implicitly but nevertheless exactly and definitively laid down by the learned Scythian monk Dionysius Exiguus, by means of his Paschal table. Therefore most Christians believe that Jesus was born on 25 December of the year 1 BC, which is exactly a week before 1-1-1 = 1 January of the year AD 1, or that He was conceived on 25‑3‑1 = 25 March of the year AD 1 and born on 25121 = 25 December of the year AD 1. For example, Charlemagne must have believed that He was born on 25 December of the year 1 BC, because he let himself crown emperor on 2512800. However, according to modern historians, Jesus was born some years before the beginning of the Christian Era (and died on Friday 3‑4‑33, as already established by the great thirteenth century English scholar Roger Bacon). Although Dionysius Exiguus’ Paschal table was perfect in its kind, his chronology fell a little short because Jesus was born some years before the year AD 1.

§ 2        By determining (calendar) dates (expressed in terms of calendar day, calendar month, and calendar year) of the Christian Era and points in time (expressed in terms of hour, minute, and second) of the Universal Time we measure accurately the total time elapsed since the beginning of our era. Since Universal Times, i.e. moments (comprehending date and point in time) of the Universal Time, are by definition nothing but local Greenwich times, the moment the Christian Era began is simply the special moment being the Greenwich midnight point in time with which the first day of the first month of the year AD 1 began. Therefore, the moment of the beginning of our era can be represented by a notation like ‘1‑1‑1, 00:00:00’ or, preferably, like [1‑1‑1; 00:00:00] or [1 January AD 1; 00:00]. Besides that very moment, any moment of our era can be represented, exactly or approximately, in that way in terms of date and point in time. Just to give an example: the moment of the spring equinox of the year AD 140 can be approximately represented by [21 March AD 140; 14:17], which means that in AD 140 in the northern hemisphere spring began on 21 March at about 14:17. Thus we are provided with an admittedly somewhat irregular but nevertheless perfect chronological system: it is the complementary fundamental concepts Christian Era and Universal Time which together form its backbone.

§ 3        Nowadays, for practical scientific and economic reasons, extremely accurate atomic clocks are used to generate the so called Coordinated Universal Time UTC, which is continuously such a close approximation of the (real) Universal Time UT that |UT  ̶  UTC|, being the absolute value of the (continuously irregularly fluctuating) difference between them, never exceeds 1 second. Shortly:

the atomic clock generated Coordinated Universal Time UTC

is continuously a sharp approximation of the Universal Time UT.

§ 4        By definition, the Central European Time CET is UTC + 1 hour, the Central European Summer Time CEST is CET + 1 hour. This implies that CEST = UTC + 2 hours. Keep in mind that the universal time UT is in fact nothing but the local Greenwich time. To give some examples, the local Galway time is UT  ̶  36 minutes, the local Rome time is UT + 50 minutes, the local Alexandria time is UT + 120 minutes, the local Jerusalem time is UT + 141 minutes. For instance, Julius Caesar was assassinated in Rome on 15 March of the year 44 BC (two years after the year he decreed the establishment of the Julian calendar); it is estimated that this murder happened sometime between 10:30 and 11:50 local Rome time. Therefore, that historic moment can be approximately represented by [15 March 44 BC; 10:20].

§ 5        The Julian calendar was established by Julius Caesar in 46 BC (first great calendar reform); in AD 1582 pope Gregory XIII of Rome replaced the Julian calendar with the Gregorian calendar (second great calendar reform). Modern historians (and not only they) consider the Julian calendar to be proleptic, the Gregorian calendar to be not proleptic. Julian calendar years are the calendar years of our era before the year AD 1582, Gregorian calendar years are the ones after the year AD 1582. Thursday 4‑10‑1582 being the very last Julian calendar day was immediately followed by Friday 15‑10‑1582 being the very first Gregorian calendar day. As a result, the year AD 1582, that turning point in the history of chronology, had only 355 days. This implies that the year AD 1582 is the only calendar year of our era which had a number of days which is not 365 (which is the number of days of any normal calendar year of our era) or 366 (which is the number of days of any leap year of our era). Between the beginning of our era (AD 1) and the present day there were only four calendar years of our era whose year number was divisible by 4 but whose number of days was nevertheless 365, namely the years AD 4, 1700, 1800, 1900. This implies that 1‑1‑1 was a Sunday because as a matter of fact 1‑1‑8 was a Sunday, which can easily be derived from Annianus’ (sixteen centuries old) 532‑year Paschal cycle being part of Beda Venerabilis’ (thirteen centuries old) Easter table being the perfect extension of Dionysius Exiguus’ (fifteen centuries old) Paschal table. Keep in mind that our familiar weekly cycle, being from Jewish origin, dates continuously from centuries before the beginning of the Christian Era.

§ 6        The Christian Era consists of the years AD 1, 2, 3, …… and the years 1, 2, 3, …… BC, of which the ones after the year AD 1582 satisfy the leap year rule of the Gregorian calendar, that is, satisfy the principle that a year AD x is a leap year only if the number x is an integer divisible by 4 but not by 100 unless by 400, but the ones before the year AD 1582 satisfy the leap year rule of the Julian calendar, that is, satisfy the principle ‘there is a leap year every four successive calendar years’ albeit on the understanding that:

1) before the initial leap year 45 BC there was, simply by retroactive definition (principle of prolepticity), a leap year every four successive calendar years;

2) between the leap years 45 BC and 9 BC there was, erroneously (as an unfortunate consequence of Julius Caesar’s premature death), a leap year every three (instead of four) successive calendar years;

3) between the leap years 9 BC and AD 8 there was, in order to adequately compensate for the error, no leap year at all;

4) between the leap year AD 8 and the year AD 1582 there was, indeed, a leap year every four successive calendar years.

This implies, just to give some examples, that 1 January of the initial leap year 45 BC must have been a Friday, 15 March of the year 44 BC, which was the day on which Julius Caesar was assassinated, a Wednesday, and 16 January of the year 27 BC, which was the day on which Octavian became emperor Augustus, a Tuesday (not a Sunday). Keep in mind that since 45 BC there are twelve months in a calendar year, namely January (consisting of 31 days), February (28 or 29 days), March (31 days), April (30 days), May (31 days), June (30 days), Quinctilis (in 44 BC renamed July, 31 days), Sextilis (in 8 BC renamed August, 31 days), September (30 days), October (31 days, with the exception of October 1582, which consisted of 21 days), November (30 days), and December (31 days).

§ 7        Since the second great calendar reform (in AD 1582) the spring equinox, which marks the beginning of spring in the northern hemisphere, falls either on 20 March (mostly) or on 19 or 21 March. Owing to the prolepticity of the Julian calendar it is only since somewhere in the twelfth century BC that the spring equinox falls in March. As a matter of fact, at the (relatively very abrupt) beginning of the Holocene (around 9700 BC) the spring equinox fell only in June. From somewhere in the ninetieth to somewhere in the fiftieth century BC it fell in May, from somewhere in the fiftieth to somewhere in the twelfth century BC in April.

§ 8        Keep in mind that between the years 1 BC and AD 1 there was no year AD 0 or 0 BC. Therefore the first year of our era was the year AD 1, its first day was 1‑1‑1. One second after [31‑12‑1; 23:59:59] came [1‑1‑2; 00:00:00], which was therefore the first turn of the year. One second after [31‑12‑10; 23:59:59] came [1‑1‑11; 00:00:00], which was therefore the first turn of the decade. Analogously, the first turn of the century was [1‑1‑101; 00:00:00], the first turn of the millennium was [1‑1‑1001; 00:00:00], the second turn of the millennium was [1‑1‑2001; 00:00:00]. As a consequence, the first day of the third millennium was 1‑1‑2001 (not 1‑1‑2000), its first year was the year 2001 (not 2000).

§ 9        The Universal Time can be considered to be the microstructure, the Christian Era to be the macrostructure of our modern chronological system. The former we owe to the ancient Egyptians (its day is reckoned from midnight to midnight and is divided into 24 hours) and the ancient Babylonians (its hour is divided in 60 minutes and its minute in 60 seconds), the latter to Dionysius Exiguus, who on his turn owed the perfection of his Paschal table to Anatolius, the legendary third century Alexandrian computist who, some years before he became bishop of Laodicea (Syria) in AD 268, invented the Metonic structure (based on the famous Metonic cycle named after the fifth century BC Athenian astronomer Meton) according to which the 19‑year periodic sequence of dates of the Paschal full moon underlying the sequence of Paschal dates of Dionysius Exiguus’ Paschal table would be framed.





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