Most calendars are based on the solar year. Solar years have
the disadvantage of not being easily observable. Many years of observations
are required to fix them with any significant degree of accuracy. On the
other hand, the phases of the Moon -- and the first visibility after the new
moon in particular -- are very easy and quick to observe. Therefore, the
first calendars defined a lunar year, usually consisting of 12 synodic
months. A synodic month is the interval from one new moon to the next and
lasts 29.530588 days. This is equivalent to 29 days, 12 hours, 44 minutes
and 2.9 seconds. Since for practical reasons a month should contain an
integer number of days, most calendars alternated between months of 29 and
30 days, respectively. A year made out of six months of each type has 354
days and is thus too short by 0.3672 days as compared with a true lunar
year. Therefore lunar calendars have to insert one leap day about every
third year to keep in step with the moon phases. A pure lunar calendar is
not synchronous with the seasons and after 16 years will put the winter in
the summer and vice versa. Over a period of 32 years it will cycle through a
complete year.
The Luni-Solar Year
A luni-solar year is the attempt to combine the phases of the moon and
the seasons into one calendar. This is possible if leap months are inserted.
Several schemes were used in history. The best known solution was found by
the Greek Meton in the year 432 BC but apparently was known to other
cultures before. The Metonic cycle encompasses a total of 235 months of
which 125 are full (i.e. they have 30 days) and 110 are `hollow'
(having 29 days). The months are combined into 12 normal years with 12
months each and 7 leap years with 13 months each. The cycle covers 6940 days
whereas 225 synodic months sum up to 6939.688 days and 19 tropical years to
6939.602 days. The difference in motion between Sun and Moon amounts to only
0.0866 days so that eclipses repeat in the Metonic cycle with high accuracy.
No correction applied
The Hebrew Calendar
The year is divided into 12 lunar months which each start when the new
moon is first visible. This gives a total of approx 354 days. The result of
this is that the entire year moves 11 or 12 days per year. This was
compensated for by adding an additional month seven times in every 19 years.
The names of the Jewish months are - Tishrei (formally Abib), Iyyar
(formally Ziv), Sivan, Tammuz, Av, Elul, Tishri (formally Ethanim),
Marchesvan (Bul), Kislev, Tebet, Shebat and Adar. In a leap year Adar I is
followed by Adar II. The months of Marchesvan and Kislev vary in length to
make the year length correct. The new year starts on the first day of the
first new moon after the vernal equinox. However there are some days of the
week on which the year cannot start as certain holidays cannot precede or
succeed the Sabbath. This means that some years a day is added, or removed,
to ensure that the day/date rules are abided by.
An ordinary year consists of 353, 354 or 355 days. A leap year consists
of 383, 384 or 385 days. These three lengths of each type of year are known
as 'deficient', 'regular' and 'complete' years.
The Hebrew Jubilee Calendar
Very little is known about the Hebrew Jubilee Calendar. The year
consisted of four quarters, each of 91 days. This gave a year of fixed
length of 364 days. No adjustment was made for leap years. There is
disagreement about how the quarters were divided into months.
One theory is that each month consisted of 30 days then one extra day was
added at the end of each quarter to bring the total to 91 days.
Another theory is that each quarter had two months of 28 days and one
month of 35 days. This would mean that the months consisted of four weeks,
four weeks and five weeks respectively. This fits in with the idea that the
calendar may have been based on the number seven, which has great
significance in the Bible. Each month would be a multiple of seven (4 or 5
times 7), the quarters would be 13 times 7 and the year 52 times 7.
No correction applied
ed: Possibly the months were based solely on the Lunar Cycle.
The Julian Calendar
The Julian calendar was introduced by Julius Caesar in 45 BC.
Year of Confusion It was in
common use until the 1500s, when countries started changing to the Gregorian
Calendar. However, some countries (for example, Greece and Russia) used it
into this century, and the Orthodox church in Russia still uses it, as do
some other Orthodox churches.
This does not mean that years were counted the way we do now. They were
counted from the start of the reign of the Emperor or Caesar and reset to
one when the next Emperor took over. Historians sometimes counted
years ab urbe condita, that is since the founding of Rome.
The old Roman calendar was very complicated and required a group of men,
known as the pontiffs, to decide when days should be added or removed to
keep the calendar in track with the seasons. This made planning ahead
difficult and the pontiffs were open to bribery in order to prolong the term
of elected officials or hasten elections. In order to avoid these problems
Julius Caesar abolished the use of the lunar year and the intercalary month,
and regulated the civil year entirely by the sun. With the advice and
assistance of Sosigenes, he fixed the mean length of the year at 365 1/4
days, and decreed that every fourth year should have 366 days, the other
years having each 365. In order to restore the vernal equinox to the 25th of
March, the place it occupied in the time of Numa, he ordered two
extraordinary months to be inserted between November and December in the
current year, the first to consist of thirty three, and the second of
thirty-four days. The intercalary month of twenty-three days fell into the
year of course, so that the ancient year of 355 days received an
augmentation of ninety days; and the year on that occasion contained in all
445 days. This was called the last year of confusion. The first Julian year
commenced with the 1st of January of the 46th before the birth of Christ,
and the 708th from the foundation of the city.
In the distribution of the days through the several months, Caesar
adopted a simpler arrangement than that which we have now. He had ordered
that the first, third, fifth, seventh, ninth, and eleventh months, that is
January, March, May, July, September and November, should each have
thirty-one days, and the other months thirty, except February, which in
common years should have only twenty-nine day, but every fourth year thirty
days. This order was interrupted in 8 BC to gratify the vanity of Augustus,
by giving the month bearing his name as many days as July, which had been
re-named after the first Caesar during 44BC. A day was accordingly taken
from February and given to August; and in order that three months of
thirty-one days might not come together, September and November were reduced
to thirty days, and thirty-one given to October and December.
The additional day which occurred every fourth year was given to
February, being the shortest month, and was inserted in the calendar between
the 24th and 25th day. February having then twenty-nine days, the 25th was
the 6th of the calends of March, sexto calendas; the preceding, which was
the additional or intercalary day, was called bis-sexto calendas,--hence the
term bissextile, which is still employed to distinguish the year of 366
days. The English denomination of leap year would have been more appropriate
if that year had differed from common years in defect, and contained only
364 days. In the modern calendar the intercalary day is still added to
February, not, however, between the 24th and 25th, but as the 29th.
In the Julian calendar, the tropical year is approximated as 365 1/4 days
= 365.25 days. This gives an error of 1 day in approximately 128 years.
The approximation 365 1/4 is achieved by having 1 leap year every 4 years
(as explained above) and the rule for calculation is that every year
divisible by 4 is a leap year.
However, this rule was not followed in the first years after the
introduction of the Julian calendar in 45 BC. Due to a counting error, every
3rd year was a leap year in the first years of this calendar's existence.
The leap years were:
45 BC, 42 BC, 39 BC, 36 BC, 33 BC, 30 BC,
27 BC, 24 BC, 21 BC, 18 BC, 15 BC, 12 BC, 9 BC,
AD 8, AD 12, and every 4th year from then on.
There were no leap years between 9 BC and AD 8. This period without leap
years was decreed by emperor Augustus as part of his reform.
It is a curious fact that although the method of reckoning years after
the (official) birth year of Christ was not introduced until the 6th
century, by some stroke of luck the Julian leap years coincide with years of
our Lord that are divisible by 4.
The seven day week was introduced by the Emperor Constantine I in the 4th
century AD.
Problems with the Julian Calendar.
The Julian calendar introduces an error of 1 day every 128 years. So
every 128 years the tropical year shifts one day backwards with respect to
the calendar. Furthermore, the method for calculating the dates for Easter
was inaccurate and needed to be refined.
In order to remedy this, two steps were necessary: 1) The Julian calendar
had to be replaced by something more adequate. 2) The extra days that the
Julian calendar had inserted had to be dropped.
The solution to problem 1) was the Gregorian Calendar.
The solution to problem 2) depended on the fact that it was felt that 21
March was the proper day for vernal equinox (because 21 March was the date
for vernal equinox during the Council of Nicaea in AD 325). The Gregorian
calendar was therefore calibrated to make that day vernal equinox. By 1582
vernal equinox had moved (1582-325)/128 days = approximately 10 days
backwards. So 10 days had to be dropped.
What is a Julian date and a modified Julian date?
It's the number of days since noon 4713 BC January 1. What's so special
about this date?
Joseph Justus Scaliger (1540--1609) was a noted Italian-French
philologist and historian who was interested in chronology and reconciling
the dates in historical documents. As many calendars were in use around the
world this created the problem of which one to use. To solve this Scaliger
invented his own era and reckoned dates by counting days. He started with
4713 BC January 1 because that was when solar cycle of 28 years (when the
days of the week and the days of the month in the Julian calendar coincide
again), the Metonic cycle of 19 years (because 19 solar years are roughly
equal to 235 lunar months) and the Roman indiction of 15 years (decreed by
the Emperor Constantine) all coincide. There was no recorded history as old
as 4713 BC known in Scaliger's day, so it had the advantage of avoiding
negative dates. Joseph Justus's father was Julius Caesar Scaliger, which
might be why he called it the Julian Cycle. Astronomers adopted the Julian
cycle to avoid having to remember "30 days hath September ...." and to avoid
the 10/11 day hiatus in the Gregorian calendar.
For reference, Julian day 2450000 began at noon on 1995 October 9.
Because Julian dates are so large, astronomers often make use of a "modified
Julian date"; MJD = JD - 2400000.5. (Though, sometimes they're sloppy and
subtract 2400000 instead.)
The Gregorian Calendar
The Gregorian calendar is the one commonly used today. It was proposed by
Aloysius Lilius, a physician from Naples, and adopted by Pope Gregory XIII
in accordance with instructions from the Council of Trent (1545-1563) to
correct for errors in the older Julian Calendar. It was decreed by Pope
Gregory XIII in a papal bull in February 1582.
In the Gregorian calendar, the tropical year is approximated as 365
97/400 days = 365.2425 days. Thus it takes approximately 3300 years for the
tropical year to shift one day with respect to the Gregorian calendar.
The approximation 365 97/400 is achieved by having 97 leap years every
400 years.
These are calculated as follows : Every year divisible by 4 is a leap
year. However, every year divisible by 100 is not a leap year. However,
every year divisible by 400 is a leap year after all.
So, 1700, 1800, 1900, 2100, and 2200 are not leap years. But 1600, 2000,
and 2400 are leap years.
(Destruction of a myth: There are no double leap years, i.e. no years
with 367 days. See, however, the note on Sweden lower down this page.)
The 4000-year rule.
It has been suggested (by the astronomer John Herschel (1792-1871) among
others) that a better approximation to the length of the tropical year would
be 365 969/4000 days = 365.24225 days. This would dictate 969 leap years
every 4000 years, rather than the 970 leap years mandated by the Gregorian
calendar. This could be achieved by dropping one leap year from the
Gregorian calendar every 4000 years, which would make years divisible by
4000 non-leap years.
This rule has, however, not been officially adopted.
The change-over from the Julian to the Gregorian calendar.
The papal bull of February 1582 decreed that 10 days should be dropped
from October 1582 so that 15 October should follow immediately after 4
October, and from then on the reformed calendar should be used.
This was observed in Italy, Poland, Portugal, and Spain. Other Catholic
countries followed shortly after, but Protestant countries were reluctant to
change, and the Greek orthodox countries didn't change until the start of
this century.
The following list contains the dates for changes in a number of
countries.
Albania: December 1912
Austria: Different regions on different dates
5 Oct 1583 was followed by 16 Oct 1583
14 Dec 1583 was followed by 25 Dec 1583
Belgium: Different authorities say
14 Dec 1582 was followed by 25 Dec 1582
21 Dec 1582 was followed by 1 Jan 1583
Bulgaria: Different authorities say
Sometime in 1912
Sometime in 1915
18 Mar 1916 was followed by 1 Apr 1916
China: Different authorities say
18 Dec 1911 was followed by 1 Jan 1912
18 Dec 1928 was followed by 1 Jan 1929
Czechoslovakia (i.e. Bohemia and Moravia):
6 Jan 1584 was followed by 17 Jan 1584
Denmark (including Norway):
18 Feb 1700 was followed by 1 Mar 1700
Egypt: 1875
Estonia: January 1918
Finland: Then part of Sweden. (Note, however, that Finland later
became part of Russia, which then still used the
Julian calendar. The Gregorian calendar remained
official in Finland, but some use of the Julian
calendar was made.)
France: 9 Dec 1582 was followed by 20 Dec 1582
Germany: Different states on different dates:
Catholic states on various dates in 1583-1585
Prussia: 22 Aug 1610 was followed by 2 Sep 1610
Protestant states: 18 Feb 1700 was followed by 1 Mar 1700
Great Britain and Dominions (including what is now the USA):
2 Sep 1752 was followed by 14 Sep 1752
The Calendar(new style) Act,1750
Year of Confusion
September 1752
To make the weeks work out, eleven days were
subtracted and three real days were eliminated to make this adjustment,
which puts our calendar out of sync with time measured prior to this
change. Count the days. |
| Su |
M |
Tu |
W |
Th |
F |
Sa |
| &; |
&; |
1 |
2 |
14 |
3 |
15 |
4 |
16 |
5 |
| 17 |
6 |
18 |
7 |
19 |
8 |
20 |
9 |
21 |
10 |
22 |
11 |
23 |
12 |
| 24 |
13 |
25 |
26 |
27 |
28 |
29 |
30 |
link article: How Britain got the Calendar Wrong
Greece: 9 Mar 1924 was followed by 23 Mar 1924
Hungary: 21 Oct 1587 was followed by 1 Nov 1587
Italy: 4 Oct 1582 was followed by 15 Oct 1582
Japan: Different authorities say:
19 Dec 1872 was followed by 1 Jan 1873
18 Dec 1918 was followed by 1 Jan 1919
Latvia: During German occupation 1915 to 1918
Lithuania: 1915
Luxembourg: 14 Dec 1582 was followed by 25 Dec 1582
Netherlands:
Brabant, Flanders, Holland, Artois, Hennegau:
14 Dec 1582 was followed by 25 Dec 1582
Geldern, Friesland, Zeuthen, Groningen, Overysel:
30 Nov 1700 was followed by 12 Dec 1700
Norway: Then part of Denmark.
Poland: 4 Oct 1582 was followed by 15 Oct 1582
Portugal: 4 Oct 1582 was followed by 15 Oct 1582
Prussia : 22 Aug 1610 was followed by 2 Sept 1610
Romania: 31 Mar 1919 was followed by 14 Apr 1919
Russia: 31 Jan 1918 was followed by 14 Feb 1918
Spain: 4 Oct 1582 was followed by 15 Oct 1582
Sweden (including Finland):
17 Feb 1753 was followed by 1 Mar 1753 (see note below)
Switzerland:
Catholic cantons: 1583 or 1584
Zurich, Bern, Basel, Schafhausen, Neuchatel, Geneva:
31 Dec 1700 was followed by 12 Jan 1701
St Gallen: 1724
Transylvania : 14 Dec 1590 was followed by 25 Dec 1590
Turkey: 18 Dec 1926 was followed by 1 Jan 1927
Tyrol : 5 Oct 1583 was followed by 16 Oct 1583
USA: See Great Britain, of which it was then a colony.
Yugoslavia: 14 January 1919 was followed by 28 January 1919
but parts of the country had changed over earlier.
Sweden has a curious history. Sweden decided to make a gradual change
from the Julian to the Gregorian calendar. By dropping every leap year from
1700 through 1740 the eleven superfluous days would be omitted and from 1
Mar 1740 they would be in sync with the Gregorian calendar. (But in the
meantime they would be in sync with nobody!)
So 1700 (which should have been a leap year in the Julian calendar) was
not a leap year in Sweden. However, by mistake 1704 and 1708 became leap
years. This left Sweden out of synchronisation with both the Julian and the
Gregorian world, so they decided to go ‘back’ to the Julian calendar. In
order to do this, they inserted an extra day in 1712, making that year a
double leap year! So in 1712, February had 30 days in Sweden.
Later, in 1753, Sweden changed to the Gregorian calendar by dropping 11
days like everyone else.
It should be noted that the Gregorian Calendar is useless for astronomy
because it has a ten-day hiatus in it. For the purpose of calculating
positions backward in time, astronomers use the Julian Date Calendar.
-- source:Calendopaedia
Calendar changes over time...
The Julian calendar, introduced by Julius Caesar in 45 BC, began on 1st
January, with the length of months alternating between 31 and 30 days -
except for February, which had 30 days in a leap year and 29 days otherwise.
(This replaced an earlier Roman calendar which had 10 months of alternating
30 and 31 days, followed by a "winter gap", the length of which varied from
year to year. The last year of this old calendar actually had 445 days.)
Complications to the Julian system began when the Senate wanted to name a
month after the then Emperor Augustus. To avoid slighting the Emperor, the
month named for Augustus must be as long as the month named for Julius, and
should follow it directly. And so July and August became 31 days each, and
February surrendered an extra day. (To avoid 3 successive 31 day months,
September was shortened to 30 days, October lengthened to 31, and so on.)
The Romans initially introduced leap years every 3 years, but by about 9
BC it was seen that the calendar was getting out of step with the solstices,
so leap years were abandoned altogether, until about AD 4 or 8, when leap
years were re-introduced as every 4 years. Even this was not completely
accurate, giving an error of 45 minutes in 4 years, or 3 days in 400 years.
In time, this miscalculation became quite noticeable.
Around 150 AD Christian churches decided to take over the pagan festival
of Saturnalia (the winter solstice) and celebrate 25th December as Christ's
birthday. Later, when the cult of the Virgin Mary became popular, it was
thought that the Christian era should start on the day of Christ's
conception, that is, 9 months earlier on 25th March, which they named
Ladyday. The year began on 25th March and ended on the following 24th March.
All moveable feasts in the church calendar relate to Easter. In turn,
gospel tradition related Easter to the Jewish festival of Passover, which in
turn was related to the spring equinox, the phase of the moon and the
celebration of the Sabbath. Over the centuries, by following the Julian
calendar, the Easter festival was slowly but surely moving away from the
spring equinox towards the summer solstice. The new system adopted by Pope
Gregory in the 16th century, specified a calendar with a year length of 365
days, 5 hours, 40 minutes, 20 seconds. Therefore 3 days had to be dropped
every 400 years. So those years which were divisible by 100 would only be
leap years if they were divisible by 400. To correct errors which had built
up over centuries, Pope Gregory declared that Thursday 4th October 1582 in
the Julian Calendar should be immediately followed by Friday 15th October in
the Gregorian Calendar.
Scotland and most Roman Catholic countries of Europe adopted the
Gregorian Calendar in 1582 or soon after. Most Protestant countries however
ignored this Papal decision for another 200 years. In England, they still
followed the old Julian Calendar (year ending 24th March) until 1751. Lord
Chesterfield's Act of 1751/2 stated that the year 1752 would begin on 1st
January and end on the following 31 December. In addition, in 1752 only, the
calendar was adjusted to omit 11 days (2nd September was followed by 14th
September) to bring their "new" (Gregorian) calendar back in line with most
of the rest of Europe.
Orthodox countries (those following allegiance to the Patriarch of
Constantinople) were even slower to change. Russia, for example, did not
convert to the new calendar until after the Russian Revolution. An
interesting consequence of this was that when London hosted the 1908 Olympic
Games, the Russian team arrived 12 days late because of it! Turkey was the
last major European country to adopt the Gregorian Calendar - on 1st January
1927.
In England, the "quarter days" (for quarterly events like the Quarter
Court sessions) were Lady Day (March 25) when the legal year started, St
John the Baptist Day (Midsummer Day, June 24), Michaelmas (September 29) and
Christmas (December 25). These were close to the equinoxes and solstices and
were regarded as the beginning of the dates of the seasons. In the City of
London, when the calendar changed, bankers refused to pay their taxes 11
days early, and so would not pay before 5th April, which still remains the
date of the end of the fiscal year.
When reading English dates prior to 1752, regard the years with care. Was
the date written by someone from that time? - in which case remember the
year ran from March to March. However if the date was written by a modern
researcher, did they understand the calendar in place at the time - and what
system were they using when they described a date such as 2nd January 1701?
To avoid confusion the convention is to write that date as 2nd January
1701/2 which uniquely identifies the year. (1701 in this case being the year
according to the old Julian Calendar, and 1702 according to the "new"
Gregorian Calendar.)
an article by Kerry Farmer
Link:
A History of the
International Date Line
 |
will save)
would
affirm today; it's the same truth He
attested to as he walked this earth
some 2000 years ago - an exclusive way to the Father
(John 14:6) and that man,
as a sinful creature, is in need of a
Saviour.(John
3:16-21).
