|
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 CE and Universal Time UT, 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 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
Paschal table. It is therefore that many Christians believe that Jesus was born
on 25 December of the year 1 BC, so no more than seven days before 1-1-1 = 1 January of the year AD 1, or else that Jesus was conceived on 25-3-1 = 25 March of the year AD 1 and was born exactly nine months later,
so on 25-12-1 = 25 December of the year AD 1. For
example, Charlemagne must have believed that Jesus was born on 25 December
of the year 1 BC, because he let himself crown emperor on 25-12-800, exactly
800 years later. 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 virtually
established fact that Jesus was born a few years before the beginning of our
era (in about 5 BC) does neither detract from the perfection of Dionysius Exiguus’ Paschal Table nor from the perfection of the
Christian Era.
§ 2 It is by determining
calendar dates (expressed in terms of calendar year, calendar month, and
calendar day) of our era in combination with points of time (expressed in terms
of hour, minute, and second) of the modern reckoning of time we call the
Universal Time that we measure the time elapsed since the beginning of the
Christian Era: each of the moments in time in question consists of a Julian
(before AD 1582) or Gregorian (after AD 1582) calendar date and a
point of time. In practice, these moments in time are local Greenwich times:
the special moment in time the Christian Era began is by definition the
Greenwich midnight point of time with which the first day of the first month of
the year AD 1 began and can therefore be represented by a notation like
[1 January AD 1; 00:00:00] or ‘1-1-1, 00:00’.
Analogously, any moment in time can be represented, exactly or approximately,
in that way in terms of Julian or Gregorian 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: 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
to CET + 1 hour. Therefore, CEST = UTC + 2 hours. Keep in mind that the
Universal Time 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 that he wanted to gain imperial power; it is estimated that this murder
happened sometime between 10:30 and 11:50 local Rome time. Therefore, the
historic moment in time in question 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), the Gregorian calendar, on the other hand, 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 year 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. These
are the years AD 4,
1700, 1800, and 1900 (see § 6). It is therefore that the first day of the year AD 1 must have been
a Sunday, because of
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 (all this because of § 6): 1 January of the year AD 1
was a Sunday, 1 January of the initial leap year 45 BC 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, until very recently, a much milder climate than the
Pleistocene, its direct predecessor) the spring equinox fell only in June.
§ 9 Despite the existence of the number 0, but
because of the fact that the ancient Romans did not know it, between the years
1 BC and AD 1 there was no year AD 0 or 0 BC, in other words
[31 December 1 BC; 24:00] = [1 January AD 1; 00:00]. This implies
that the first year of the Christian Era was indeed nothing but the year AD 1.
Therefore, the special moment of its first turn of the year was [31-12-1; 24:00] = [1-1-2; 00:00]. This implies that the one of its
first turn of the decade was [1-1-11; 00:00], the one of its
first turn of the century was [1-1-101; 00:00], the one of
its first turn of the millennium was [1-1-1001; 00:00], the
one of its second turn of the millennium was [1-1-2001; 00:00].
We conclude that the first year of the third millennium was 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 great
third Alexandrian scholar Anatolius and the circle of Alexandrian computists around him who invented the special structure of
the Metonic lunar cycle underlying Anatolius’ mysterious 19-year Paschal cycle. It is the Christian
Era and the Universal
Time which together form the backbone of our modern chronological system.
© Jan Zuidhoek 2023‑2026
(updated 11‑11‑2026)