This webpage belongs to www.alexandriancomputus.net, which is a website promoting [Jan Zuidhoek (2019) Reconstructing Metonic 19-year Lunar Cycles (on the basis of NASAs Six Millennium Catalog of Phases of the Moon): Zwolle], and concerns the relation between the fundamental concepts Christian Era and Universal Time.
Christian Era and Universal Time
Our era is the Christian Era (see p. 69), 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 (AD 1) was retrospectively and implicitly but nevertheless exactly and definitively laid down by the learned Scythian monk Dionysius Exiguus (see p. 69), by means of his Paschal table (see Appendix I p. 103‑105). Therefore most Christians believe that Jesus was born on 25‑12‑1 = 25 December AD1 or exactly a week before 1-1-1 = 1 January AD1. For example, Charlemagne must have believed that He was born exactly a week before 1‑1‑1, because he let himself crown emperor on 25‑12‑800. However, according to modern historians, Jesus was born some years before the beginning of the Christian Era (and died at 3‑4‑33). So Dionysius Exiguus chronology is only imperfect insofar as its first day is not the day Jesus was born.
By counting the days and measuring the so called Universal Time UT (see p. 23), we measure accurately the total time elapsed since the beginning of our era. Strictly speaking, the beginning of the Christian Era is the Greenwich midnight point in time with which 1‑1‑1 began; therefore, the moment (comprehending date and point in time) of the beginning of our era can be represented by a notation like [1‑1‑1; 00:00:00] or like [1 January AD1; 00:00]. Similarly, each moment of our era can be represented in terms of date and point in time, for instance moment [21 March AD140; 14:17]. Thus we are provided with a somewhat irregular but nevertheless perfect chronological system based on the Christian Era and the Universal Time UT. For example, [21‑3‑140; 14:17] represents a moment, called spring equinox, at which in the northern hemisphere spring began (see p. 41). The same holds for [20‑3‑325; 10:02] (see p. 44) and [20‑3‑415; 05:18] (see p. 45).
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 Universal Time UT that |UT ̶ UTC|, being the absolute value of their (continuously irregularly fluctuating) difference, never exceeds 1 second. Thus,
Keep in mind that it is the local Greenwich time which is exactly equal to UT. This implies, for example, that the local Liverpool time is UT ̶ 12 minutes, the local Rome time is UT + 50 minutes, and the local Alexandria time is UT + 120 minutes. For example, Julius Caesar was murdered on 15 March 44BC probably sometime between 10:30 and 11:50 local Rome time, so round about [15 March 44BC; 10:20].
Keep also in mind that in the framework of our era, Thursday 4‑10‑1582 was the very last Julian calendar day, and that that Thursday was immediately followed by Friday 15‑10‑1582 being the very first Gregorian calendar day. As a result, the year 1582 had only 355 days. Thus that year 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) or 366 (which is the number of days of any leap year). Between the beginning of our era and 2021 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 AD 4 and the years 1700, 1800, and 1900. This implies that 1‑1‑1 was a Sunday, which simple fact can easily be derived from Annianus 532‑year Paschal cycle being part of Beda Venerabilis Easter table (see Appendix II p. 106‑120).
Keep also in mind that our era consists of the years AD 1, 2, 3, and the years 1, 2, 3, BC, on the understanding that:
1) the ones after the year 1582 are considered to be Gregorian calendar years;
2) the ones before the leap year 45 BC and the ones between the leap year AD 8 and the year 1582 are considered to be Julian calendar years;
3) between the leap years 45 BC and 9 BC there was (erroneously) a leap year every three years (instead of every four years) and (therefore) between the leap years 9 BC and AD 8 there was no leap year at all (instead of a leap year every four years).
Keep also in mind that, owing to the prolepticity of the Julian calendar, it is only since somewhere in the twelfth century BC that the spring equinox, which marks the beginning of spring in the northern hemisphere, 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.
Keep also in mind that between 1 BC and AD 1 there was no AD 0 or 0 BC. The first year of our era was AD 1, and its first day 1-1-1. The very first turn of the year must have been [1‑1‑2; 00:00:00], because it came one second after [31‑12‑1; 23:59:59]. Analogously, the very first turn of the decade must have been [1‑1‑11; 00:00:00], because it came one second after [31‑12‑10; 23:59:59]. Analogously, the very first turn of the century must have been [1‑1‑101; 00:00:00], the very first turn of the millenium [1‑1‑1001; 00:00:00], the second turn of the millenium [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 2001 (not 2000).
© Jan Zuidhoek 2019-2021