|
This webpage is part of www.alexandriancomputus.net,
which supports the new book on early Alexandrian Paschal reckoning [Jan
Zuidhoek (2023) Reconstructing Alexandrian Lunar Cycles (on the basis of Espenak’s Six Millennium Catalog
of Phases of the Moon): Zwolle], and concerns the complementary chronological
concepts Christian Era and Universal Time, which both play a fundamental role
in this new book, which is available via this website. |
Christian
Era and Universal Time
§ 1 Our era, in the sense of an
infinite sequence of consecutive calendar years, is the common era, which is
nothing but the Christian Era. However,
nobody knows exactly when Jesus was born. Nevertheless, in about AD 525,
more than five centuries after Jesus’ birth, the very first year of the
Christian Era, referred to as the year AD 1, was retrospectively and
implicitly, but nevertheless exactly and definitively, laid down by the
Scythian monk and scholar Dionysius Exiguus, by means of his famous Paschal
table. It is therefore that many Christians believe that Jesus was born on
25 December of the year 1 BC, so exactly seven days before 1‑1‑1 =
1 January of the year AD 1, or else that He was conceived on 25‑3‑1 = 25 March of the year AD 1 and born nine months later, on
25‑12‑1 = 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
25‑12‑800. However, according to modern
historians, Jesus was born not in 1 BC or in AD 1 but a few years
before AD 1, and died on Friday 3 April of the year AD 33 (the
latter in accordance with the vision of the great thirteenth century English
scholar Roger Bacon, by the way). But the fact that Jesus was born a few years
before the beginning of the Christian Era does neither detract from the
perfection of Dionysius Exiguus’ Paschal Table nor from the perfection of our era.
§ 2 It is by determining (Julian or Gregorian) calendar dates (expressed in terms
of calendar year, calendar month, and calendar day whether or not in reverse
order) of the Christian Era and points in time (expressed in terms of hour,
minute, and second) of the reckoning of
time we call the Universal Time UT that we as accurately as possible measure the time elapsed since the
beginning of our era. Since Universal Times, being moments of time, each
consisting of a calendar date and a point in time, are by definition nothing
but local Greenwich times, the extraordinarily special moment of time the
Christian Era began is nothing but the Greenwich midnight point in time with
which the first day of the first month of the year AD 1 began. Therefore,
that special moment of the beginning of the common 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 special moment, any particular moment can be represented, exactly
or approximately, in that way in terms of calendar date and point in time. Just
to give an example: the spring equinox of the year AD 140 can
approximately be represented by [21‑3‑140; 14:17] =
[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 (as will be shown): 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 (but never exactly known) Universal Time
UT that |UT ‑ UTC|, i.e. the absolute value of the
(continuously irregularly fluctuating) difference between them, never exceeds
1 second. The thus atomic clock generated Coordinated Universal Time UTC
is continuously a sharp approximation of the
(real) Universal Time UT.
§ 4 By definition, the Central
European Time CET is equal to UTC + 1 hour, the Central European
Summer Time CEST is equal to 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 about UT ‑ 36 minutes, the
local Rome time about UT + 50 minutes, the local Alexandria time
about UT + 120 minutes, the local Jerusalem time about
UT + 141 minutes. For example, Julius Caesar was assassinated in
Rome on 15 March of the year 44 BC by a group of senators who feared
he wanted to gain imperial power; it is estimated that this murder happened
sometime between 10:30 and 11:50 local Rome time. Therefore, that historic
moment can approximately be represented by
[15 March 44 BC; 10:20].
§ 5 In 46 BC,
Julius Caesar decreed (on the advice of the Alexandrian astronomer Sosigenes)
the establishment of the Julian calendar: henceforth, to begin with the initial
leap year 45 BC (consisting of 366 days), calendar years should begin with
January instead of with March and should normally consist of 365 days but once
every four years of 365 days plus a leap day in February. This was the first
great calendar reform. In AD 1582 pope Gregory XIII of Rome replaced
the Julian calendar with the Gregorian calendar (see § 6). This was
the second great calendar reform. Modern astronomers and modern historians
consider (not without reason because the old Roman calendar was a mess) the
Julian calendar to be proleptic (see § 6),
but 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 the ones after that very calendar year. Thursday 4‑10‑1582, being the last Julian calendar day,
was immediately followed by Friday 15‑10‑1582, being the
first Gregorian calendar day. As a result, the year AD 1582, that unique
turning point in the history of chronology, had only 355 days. This
implies that the year AD 1582 is the only calendar year of the common 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). Furthermore, between the first day of our era and the
present day there were only four calendar years of the Christian Era whose year
number was divisible by 4 but whose number of days was nevertheless 365. These
are the years AD 4, 1700, 1800, and 1900 (see § 6). This
implies that 1-1‑1 was a Sunday, which can easily be derived
from Annianus’ 532‑year Paschal cycle (constructed in about AD 412 on the basis of
Annianus’ lunar cycle) being part of Beda Venerabilis’
Easter table (published in AD 725). The latter is a perfect extension of
Dionysius Exiguus’ Paschal table, which was constructed shortly before AD 526,
also on the basis of Annianus’ lunar cycle. Keep in mind that our familiar
weekly cycle originates from the Babylonians but that our familiar original
(Jewish) weekday numbering (which means that Sunday is the first day of the
week because Saturday is the last) has continuously remained unchanged from
centuries before the beginning of the Christian Era until now.
§
6 The Christian Era consists of
the years 1, 2, 3, …… BC and the years
AD 1, 2, 3, ……, 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, a leap year every four successive
calendar years (principle of prolepticity);
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 once every three (instead of once every four)
successive calendar years;
3) between the leap years 9 BC and AD 8,
in order to adequately compensate for that error, there were no leap years 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.
§ 7 Just to give some
interesting examples: 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. Keep in mind that
all Julian and all Gregorian calendar years consist of twelve calendar months:
January (31 days), February (28 or 29 days, but had originally 29 or 30
days), March (31 days), April (30 days), May (31 days), June (30 days), July
(originally called Quinctilis, 31 days), August (originally called Sextilis, 31 days, but had originally 30 days),
September (30 days, but had originally 31 days), October (31 days, but had
originally 30 days and in AD 1582 only 21 days), November (30 days, but had
originally 31 days), and December (31 days, but had originally 30 days).
§ 8 Since the introduction of the
Gregorian calendar 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 (in AD 1582 it still fell on 10 March). It is mainly owing to the prolepticity of the Julian calendar that the spring equinox
falls in March since somewhere in the twelfth century BC, fell in April from
about the fiftieth to about the twelfth century BC, fell in May from about the
ninetieth to about the fiftieth century BC. At the time of the (rather abrupt)
beginning (around 9700 BC) of the Holocene (which had a milder climate than the
Pleistocene, its direct predecessor) the spring equinox fell only in June.
§ 9 Despite the existence of the number 0, between the years 1 BC and AD 1
there is no year AD 0 or 0 BC. This mplies that [31
December 1 BC; 24:00] = [1 January AD 1;
00:00]. Therefore the first year of the common era was the year AD 1,
its first turn of the year [31-12-1; 24:00:00] = [1-1-2; 00:00:00], its first turn of the decade [1-1-11; 00:00:00], its first turn of the century [1-1-101; 00:00:00], its first turn of the millennium [1-1-1001; 00:00:00]. Consequently, no doubt, its second
turn of the millennium must have been [1-1-2001; 00:00:00]. We conclude that the first day of
the third millennium was nothing but 1-1-2001, its first year the year AD 2001.
§ 10 Ultimately, we owe the modern fundamental concept
Universal Time, which can be regarded as the microstructure of our modern chronological system, to the ancient
Egyptians (their day, reckoned from
sunrise to sunrise, consisted of 24 hours) and the
ancient Babylonians (not only their
day, reckoned from sunset to
sunset, consisted of 24 hours, but also their hour consisted
of 60 minutes and their
minute of 60 seconds), but we owe
the fifteen centuries old fundamental
concept Christian Era, which can
be regarded as the macrostructure of our modern chronological system, to Dionysius Exiguus, who on his turn owed the perfection of his Paschal table to
the circle of third century Alexandrian
computists around the great Alexandrian
scholar Anatolius which invented the Metonic structure
of the 19-year lunar cycle underlying Anatolius’ sequence of Paschal dates. Thus the Christian Era and the Universal Time form together the backbone of our modern chronological system.
© Jan Zuidhoek 2023‑2025