JULIAN AND GREGORIAN CALENDARS
-----------------------------
John Pazmino
NYSkies Astronomy Inc
www.nyskies.org
nyskies@nyskies.org
2020 August 14
Introduction
----------
Astronomers simulating celestial activity more than a few
centuries ago run into the step between the Gregorian and Julian
calendars. Modern astronomy software automaticly shift gears when the
date rolls thru this step. This standard software feature sounds
simple and carefree.
It isn't.
In the 1580s western Europe was living under the Julian
calendar.This was a continuation of the Roman calendar, as modified by
Julius and Augustus Caesar. The basic year was 365 days, with a
leftover 184 day. This was collected into a full extra day ever y four
years and added to the year as a leapday. The calendar gradually
outpaced the solar year because it was a trifle too long.
Pope Gregory XIII in 1582 modified this calendar to, among other
things, fix up a major glitch in leapdays and to omit a block of
accumulated overrun of ten days. This is the Gregorian calendar. It is
use today as the civil calendar thruout the world.
I give here a short history, full accounts being widely diffused
in chronology litterature. The I show the considerations for handling
the Julian-Gregorian crossover in astronomy software.
Julius Caesar
-----------
The Romans developed a solar calendar with 12 moths of alternating
30-31 days. The first month was either January (Januarius) or March
(Martius), according as the district within the Roman world. March
holds the spring equinox, arguing for it as the more relevant initial
Many. The last month was February (Februarius) with the 29 left over
days to fill out the 365-day year.
Roman astronomers knew that the solar year was 365-1/4 days. The
shortfall was severe, a full da every four years, but there was no
standard way to account for it. Extra days or months were added in a
disorganized way in the various Roman districts. Calendar dates fell
into discord across district frontiers.
Julius Caesar put the calendar in order, based on the March for
the initial month. He in 45 BC put his reform into effect and ruled
that leapdays be added consistently in the empire. The inaugural
leapyear was 41 BC..
His astronomers knew that 1/4 was only a close approximation to
the fractional day closing the year. It was a trifle too long by some
11 minutes per year. Julius thought the error was negligible.
Julius was so thrilled with is work that he renamed the fifth
month Quintillis to himself Julius. This is our July.
There were technical disputes about leapdays insertion, length of
months, start of year. In addition, weak enforcement caused the
calendar to slowly unravel.
August Caesar
-----------
Augustus Caesar put the calendar back in order and made sure that
leapdays were added every fourth year. His astronomers retrofitted the
sequence of leapdays for a smooth pattern from Julius's time. The
initial leapyear under Augustus was 8 AD. Since then the calendar was
rigorously maintained. Deviations here and there in the roman world
fizzled out after a few years and the new Christian faith adopted the
Augustus system for its official calendar.
I couldn't find when the 'multiple of 4' rule started. A common,
and wrong!, explanation is that the first leapday was in 8 AD, a
multiple of 4. 4-year steps then after are multiples of 4.
The initial leapyear was an utter accident. The current count of
years didn't exist.Thweew was no '8 AD' in the time of Augustus.
Our count of years started in the 500s AD and 8 AD just happened
to be the count back into the Augustus period. It could well have been
some other year and we would not have the neat 'multiple of 4' rule.
This revised calendar is the Julian calendar, after the prototype
from Julius Caesar. augustus was proud of his revisions that he
renamed the sixth month, Sextillis, for himself, augustus, our august.
But it had only 30 days by the 30-31 day sequence. He captured a day
from the end of the year, February 29th, tacked it onto August, and
shifted the other months to finish the 30-31 order. February now had
28 days in regular years and 29 in leapyears.
The Julian calendar, while no longer the civil calendar, is in
significant circulation for specific functions. Most relate to the
Eastern Christian faiths, which shows up in the US as a disparity in
the date of Easter between them and the Gregorian calendar.
The most notable example of Julian as the civil calendar in the
20th century is in Russia. When the Bolsheviks overrunned Petrograd
(St Petersburg) on 1917 October 25, Russia was Julian. The
insurrection is still called the Great October Revolution (with a few
variations). It is now celebrated on the Gregorian date of November
7th.
Vernal equinox
-------------
The Christian formal definition of Easter was laid down at the
Council of Nicaea in 325 AD. It fixed the vernal equinox at 21 March,
in place of determining it each year by astronomy procedures. The date
of Easter banks off of this fixed vernal equinox.. It
The Julian calendar was supposed to pace the solar year with its
leapday feature. The 1/4 leftover day was known to be a bit too long,
forcing a drift of calendar dates against the solar year. The equinox
slided earlier on the calendar by 3 days every 400 years.
For a few centuries, specially thru the Dark Ages, the drift
attracted little notice. Easter seemed to work out correctly.
By the 1580s the drift accumulated to 10 days. This came from the
excess leapdays added every four years. The table here was generated
by astronomy software competent with long timespans. The date, in UT,
of the venal equinox is when the Sun crossed the celestial equator. It
may differ by one day from that date listed in a contemporary
calendar.
----------------------
DRFT OF VERNAL EQUINOX
FROM 0 (1 AD) TO 2000 AD
----------------------
year - vernal eq- drift
---- --------- ------
0 - 22 March - -2 day
100 - 21 March - -1 day
200 - 20 March - 0 day
300 - 19 March - 1 day
400 - 19 March - 1 day
500 - 18 March - 2 day
600 - 17 March - 3 day
700 - 16 March - 4 day
800 - 16 March - 4 day
900 - 15 March - 5 day
1000 - 14 March - 6 day
1100 - 13 March - 7 day
1200 - 13 March - 7 day
1300 - 12 March - 8 day
1400 - 11 March - 9 day
1500 - 10 March - 10 day
1600 - 10 March - 10 day
1700 - 9 March - 11 day
1800 - 8 Mar ch- 12 day
1900 - 7 March - 13 day
2000 - 7 March - 13 day
------------------------
When Easter was computed from the equinox of 21 March ON THE
JULIAN CALENDAR Easter could occur deep into spring rather than ne its
start.
Pope Gregory XIII
---------------
By the 1500s the calendar sipped by some 10 days, putting he
vernal equinox on March 10 or 11, far from the established March 21.
Gregory made several changes, banking on his astronomers's studies of
the calendar problem. Two major ones are crucial for us here.
The first was to bring the calendar into synch with the solar
year, putting the vernal equinox back to March 21st. He did this by
making the day after Thursday 4 October 1582 into Friday 15 October
1582. There is no valid date in this transition gap of, say, 8 October
1582.
Nota magis bene that the cycle of weekdays was NOT molested.
Thursday was followed by Friday. The weekdays are ganged to the order
of the seven classical planets (with Moon and Sun). Tinkering with the
names or order of the weekdays would tear out the gears of human
timekeeping beyond all possible repair. In fact, thruout all history
that worked with current weekday system there was never a serious
attempt to mess with it.
The other change by Gregory was to shorten the year to a bit less
than exactly 365.25 day. His astronomers worked out that a year of
365.2425 day is much closer to the solar year. The decrease could be
accomplished by omitting three leapdays in each block of 400 years.
his was done by leaving century years as regular years, except f they
are multiples of 400.
There was no immediate alteration in the series of leapdays. Year
1600 was a leapyear under both Julian and Gregorian systems. The next
three century years (1700,1800, 1900) were regular years missing out
three leapdays. Then 2000 was the second century leapyear.
February
------
The start of the year in March persisted into the Middle Ages,
when gradually countries migrated to a January year start. I do not
explore the history of this shift here. I do note that when a country
made the shift, it generally made the final March-start year a short
year ending in te next December. Then after the year rolled over in
January.
With February now an interior month, I didn't find any country
shuffling days to give February a full 30-day length. December, the
new last month, would be the short month.
February remains the short month and also the month taking on
the lwapday.
Accuracy
------
For the simplicity of the alterations to the Julian calendar, the
Gregorian is amazingly accurate for the long term. The mean solar year
in the 20th century was 365.2422 mean solar days. The Gregorian year
is 365.2425 days versus the solar year of 365.2422 days. The excess is
0.003 day/year, or one day in some 3.300 years. With only 400or so
years of the Gregorian calendar past so far. we got over 2.500 more
years before thinking about an adjustment. The simplest is to skip the
leapday, February stays at 28 days, in a designatrd year.
This is a naive solution because it assumes the revolution and
rotation of Earth are constant thruout such long spans of time. They
aren't.
They vary in ways still not thoroly known. As example the length
of the solar year, from one vernal equinox to the next, is illustrated
here from 1950 to 2040. The fractional day is expressed in clock
notation for easier appreciation.
--------------------------------------
Year, vern eq-vern eq d h m s
---------------------- --- - -- --
March 1950- March 1951 365 5 50 33
March 1960 - March 1961 365 5 49 16
March 1970- March 1971 365 5 41 50
March 1980 - March 1981 365 5 53 20
March 1990 - March 1991 365 5 42 48
March 2000- March 2001 365 5 55 22
March 2010- March 2011 365 5 48 23
March 2020 - March 2021 365 5 47 55
March 2030- March 2031 365 5 49 6
March 2040 - March 2041 365 5 55 7
--------------------------------------
No astronomy software I know or heard of include a Gregorian
adjustment for far future times. None offer a choice of plausible
methods to jigger the far off Gregorian date. It's straight gregorian
until the program's end of time.
Precession
--------
Discussion of calendars inevitably bring in the role of
precession. By gyration of Earth's axis the equatorial coordinate grid
rotate against the ecliptic grid. One effect is the westward migration
of the vernal equinox point along the ecliptic. 2,000 years ago it was
in Aries. Now it's in Pisces. The drift is roughly one sign every two
millennia, to complete a cycle in some 25/000 years.
In the mid north latitudes, where the bulk of early cultures
lived, calendars were ganged to the seasons. The lifes of the people
were impelled by the changes in weather, temperature, river flow,
yield from hunting and fishing, snow & ice, farming & gathering.he
society needed a calendar hat alerted it to the arrival of these favor
and disfavors of nature.
The seasons are produced by the axis inclination of Earth, causing
a wide range of daylight , shorter in winter, longer in summer, and
the solar altitude, lower in winter, higher in summer.
Precession as a distinct astronomy phaenomenon wasn't recognized
until Hipparchus in the 100s BC, but the consequences in the seasonal
mutations was long appreciated. A calendar that maintains, or tries to
maintain, the dates in synch with the seasons is a solar calendar and
embeds the effect of precession.
In places with no strong seasons the need for a solar calendar is
weaker. Two examples are the Nile River society in Egypt and the
Islamic society in the Middle East.The Egyptian civil calendar had 365
days with no consideration for the left over 1/4 day. When the 365
days run out, a new year began. The Islamic calendar is a lunar
calendar tied to the synodic, phase, cycle of the Moon. When twelve
phase cycles, 354 days, run out, the new year begins.
The Julian and Gregorian calendars tries to make the calendar
dates line up with the seasons. The slipping of dates in the Julian
calendar came from the inexact adjustments to account for the 1/4 day
after 365. The Gregorian is a far better fit with its leapday rules.
Before Julius
-----------
Historians, and astronomers, must hang human events onto a stable
calendar spanning all cultures. Else they can not confidently link
native chronologies or investigate celestial events.
The Julian calendar is extended backward to the beginning of time
on Earth as a global chronological framework. The years step down with
every fourth being a leapyear.
That's why an eclipse is said to occur on 1500 BC August 1 in New
York (it was a deep partial event in mid morning). There were no
months of our modern names back then, or the multiple-of-4 rule for
leapdays. This prolonged Julian calendar is the Julian Proleptic
system.
Years before the AD, or CE, era are numbered two ways. The
historical way, marked BC or BCE, omits the year number '0' in the
year count. The year immediately prior to 1 AD is 1 BC. This method
throws off calendar maths and forces a second look at the leapyears.
Was 29 BC a leapyear?
The other, algebraic, method includes zero as the year prior to 1
AD. Then before the years are negative numbers, compliant with
calendar maths. The leapyear rule works. 29 BC is -28, a multiple of
4, and a leapyear. For emphasis or clarity, sometimes the AD years are
written with the plus signum, 2020 AD is +2020.
Astronomy softwares work with one of the methods or offer the
choice. For uncertain situations, test the program by entering '0' for
the year. The response tells which year system is in force.
J-G step in software
------------------
Modern astronomy software embeds the step and jumps thru it
automaticly without operator intervention. The calendar mode is
indicated somehow in readouts with a symbol or char.
A few programs offer the choice to do all work in the one or other
calendar. This ignores the J-G step and leaves it to the operator to
manually interpret the results.
However the step is handled in the program, one and all assume
that the step occurred simultaneously worldwide. And that's when
trouble comes along.
A special situation applies to compilations of events spanning the
J-G step, like a list of Jupiter oppositions for the Middle Ages. The
software almost certainly run Gregorian after the official step and
Julian, projected to the indefinite past, before the step. The caution
is that these lists and tables are produced without operator
intervention. The dates are internally generated by the software.
Some softwares do not clearly describe the handling of the J-G
step. In such cases, while exercising the program, do test runs. Run a
planet ephemeris between 1582 Sep 20 and 1582 October 20 at one-day
intervals. Does the step appear at Oct 4 with the very next day Oct
15? Do calendar math on 1582 Sep 30 and 1582 Oct 20. is the interval
20 days or 10 days? Simulate planet motion from 1582 Sep 20 to 1582
Oct 30, while watching the date readout. Did the date jump from Oct 4
to Oct 15? Look at the Julian Day Number, the continuous count of days
since 4713 BC. This is a common way to get around clumsy calendar
maths in astronomy. Does the JDN show one day interval across the J-G.
Do these runs in reverse! A dew softwares work properly for time
running forward but break down for backwards time.t
Once this is all figured out for the software, make a written note
about the J-G step and keep it with the program's instructions.
Dates of J-G step
---------------
Countries allied with the Pope switched to Gregorian in October
1582, or a few months later due to slow mail travel. But even in
Europe some countries did the step decades or centuries later. Before
the switch dates were recorded in Julian, almost always without
caution of comment. A country may do the step in its homeland but its
colonies may be switched over in stages later.
Outside of Europe there could be no prior use of the Julian
calendar. The Gregorian calendar supplanted a native calendar. or,
commonly, the native one continued in use along side Gregorian for
cultural purposes. In these countries any dates before the Greorian
inauguration are retrojected and must be somehow linked to the
cultural calendar.
A nasty situation, particularly in Europe, was a REVERSAL of
calendar! Julian was restored after a period of Gregorian. This
happened when a Gregorian country was conquered by a Julian country.
The victor imposes Julian on the land. In this situation the initial
Julian date under the new ruler are EARLIER than the final dates in
the previous Gregorian. There is a foldover of dates and I have no
idea how this was handled in the change of society.
These cases must be considered when working astronomy software
with observer in the affected countries. This could mean investigation
the history of the country and perhaps reading material from it
written in the native language. Such mental gyrations are et an other
example how astronomy interacts with humankind.
Typical example
-------------
Probably the most common whacks in the neck for astronomers in the
US are celestial events during the colonial era. The present United
States was built from regions ruled by England, Holland, France,
spain, Russia (Russia?). All converted from Julian to Gregorian at
different times. Travelling thru the US was somewhat like travelling
thru the crazy-quilt system of Daylight Savings Time before the 1960s.
An instance I inquired after, sparking me to compose this piece,
was the solar eclipse in New York on 4 October 1717. This was well
well after the official J-G step. The planetarium software I played
this eclipse on calculated in Gregorian. Contemporary accounts, taken
from webs, assert this eclipse took place on 23 September 1717. 11
days too early.
When I simulated the eclipse with the contemporary date, there was
no eclipse. The Moon was a waning gibbous, far west from the Sun.
New York was then a British colony. Altho the official Julian-
Gregorian step was about 140 years earlier, the British regions stayed
with Julian until 1752. The account was in the prevailing Julian
calendar.
I manually had to make the date adjustment. That particular
program had no way to alter the J-G step. I played the eclipse on an
other program that allowed the choice of Julian or Gragorian. I threw
the switch to 'Juluinan'. On 23 September 1717 the Moon covered the
Sun in a deep partial event in mid morning.
As asides, when England went Gregorian it neffa-effa mentioned the
Pope. The new calendar was the New Style calendar.
Table of J-G step
---------------
The table here is based on the one from Wikipeedia. It gives the
present name of the country, section or area at the time of the step,
final Julian date, initial Gregorian date.
In a few countries there are no definite dates for the step.
Likely there are too scanty documents to stating the dates but there
later there were enough to fix the year. In these instances the dates
are replaced with '?'.
When there was no prior Julian calendar in force the Julian date
is replaced by 'NJC' for 'no Julian calendar'. The country used a
native or cultural calendar. The native calendar still may be used
for special functions.
Some countries returned to Julian. The dates are the final
Gregorian and initial Julian and a flag 'RTJ' is added. This is
'return to Julian'.
This table was produced thru rearl strong effort! It is thot, with
emphasis on European countries. Plausibly records on the J-G step are
denser there than else where and are easier to acquire.
Until the 20th century most of the rest of the world was under an
empire of a European country. When the home country went Gregorian,
the entire empire did also. There could be a lag of weeks or months
due to slow comms among parts of the empire. This is why in, for
example, Africa has few entries. The whole continent was included in a
one or other empire. Similar situation applies in Middle East, the
Americas, much of Asia and Pacific.
I noticed two omissions for the United States. Altho Alaska is
mentioned, Hawaii is not. Hawaii probably ran on a native system
before Gregorian was adopted.
The table misses the Dutch colonies,.The Dutch ruled in present
New York City, parts of Hudson River, parts of Long Island. I can
accept that with Holland, the Netherlands, having such a fractured J-G
history in this table, the author may have let Dutch America a;one.
If this table doesn't help for peculiar instance, a concerted
research into the history of the observer's location is needed. This
may be a difficult task if documents or other evidence is spotty or
not recoverable.
There is no obvious order to this table. To locate a country or
area do a 'find on this page' in the browser or wordproc.
---------------------
Netherlands - Zeeland
1582 14 Dec - 25 Dec
Montenegro - Yugoslavia
1919 14 Jan - 28 Jan
North Macedonia - Yugoslavia
1919 14 Jan - 28 Jan [18]
Serbia - Yugoslavia
1919 14 Jan - 28 Jan
Germany - Wrzburg
1583 4 Nov - 15 Nov
Germany - Westphalia
1584 1 Jul - 12 Jul
Italy - various
1582 4 Oct - 15 Oct
Switzerland - Valais
1655 28 Feb - 11 Mar
Netherlands - Utrecht
1700 30 Nov - 12 Dec
Ukraine - Ukrainian People's Republic
1918 5 Feb - 1 Mar [24]
Italy - Tyrol
1583 5 Oct - 16 Oct
Germany - Trier
1583 4 Oct - 15 Oct
Romania - Transylvania
1590 14 Dec - 25 Dec
Armenia - Transcaucasian Democratic Federative Republic
1918 17 Apr - 1 May
Azerbaijan - Transcaucasian Democratic Federative Republic
1918 17 Apr - 1 May
Georgia - Transcaucasian Democratic Federative Republic
1918 17 Apr - 1 May
Switzerland - Thurgau, Appenzell-Innerrhoden, Appenzell-Ausserrhoden
1584 ? - ?
Switzerland - Switzerland, Protestant parts
1700 31 Dec - 1701 12 Jan
Sweden - Swedish Empire, including Finland
1700 28 Feb - 1 Mar - conversion mistake
Sweden - Swedish Empire, including Finland
1712 30 Feb - 1 Mar - RTJ with mistake in conversion
Sweden - Sweden, Including Finland
1753 17 Feb - 1 Mar
Netherlands - States Genera
1582 14 Dec - 25 Dec
Spain - Spanish Empire
1582 4 Oct - 15 Oct
Belgium - Southern Netherlands, except Spanish-hrlf areas
1582 20 Dec - 31 Dec
Czech Republic - Silesia
1584 12 Jan - 23 Jan
Germany - Silesia
1584 12 Jan - 23 Jan
Poland - Silesia
1584 12 Jan - 23 Jan
Thailand - Siam 1
1889 NJC - 1 Apr
France - Sedan
1582 9 Dec - 20 Dec
Saudi Arabia - Saudi Arabia
2016 NJC - 1 Oct
United States of America - Russian Empilre, Alaska
1867 6 Oct - 18 Oct
Belarus - Russia
1918 31 Jan - 14 Feb
Russia - Russia
1918 31 Jan - 14 Feb
Romania - Romania
1919 31 Mar - 14 Apr
Switzerland - Roman Catholic Diocese of Basel
1583 20 Oct - 31 Oct
France - Roman Catholic Archdiocese of Strasbourg
1583 16 Nov - 27 Nov
Germany - Prince-Bishopric of Hildesheim
1631 15 Mar - 26 Mar
Portugal - Portuguese Empire
1582 4 Oct - 15 Oct [7][8]
Poland - Poland
1582 4 Oct - 15 Oct
Germany - Pfalz-Neuburg
1585 13 Dec - 24 Dec
Germany - Paderborn
1585 16 Jun - 27 Jun
Netherlands - Overijssel
1700 30 Nov - 12 Dec [7][19]
Turkey - Ottoman Empire
1917 15 Feb - 1 Mar
Germany - Osnabrck
1624 ? - ?
Switzerland - Obwalden, Nidwalden
1584 11 Feb - 22 Feb
Canada - Nova Scotia
1710 13 Oct - 3 Oct - RTJ
Faroe Islands - Norway
1700 16 Nov - 28 Nov 11
Iceland - Norway
1700 16 Nov - 28 Nov
Germany - Mnster, Duchy of Cleves
1583 17 Nov - 28 Nov
ÑFrance - ÑMulhouse
1700 31 Dec - 12 Jan
Czech Republic - Moravia
15843 Oct - 14 Oct
Germany - Mainz
1583 11 Nov - 22 Nov
Switzerland - Luzern, Uri, Schwyz, Zug, Freiburg, Solothurn, LeLanderon
1584 11 Jan - 22 Jan
Switzerland - Lower Valais
1623 ? - ?
France - Lorraine
1582 9 Dec - 20 Dec
France - Lorraine
1735 ? - ? - RTJ
France - Lorraine
1760 16 Feb - 28 Feb 11
Latvia - Livland
1915 22 Aug - 5 Sep
Lithuania - Lithuania Governorate
1800 11 Jan - 1 Jan - RTJ
Belgium - LiŠge
1583 10 Feb - 21 Feb
ÑLithuania - Kovno and Vilna Governorates
1915 11 May - 25 May [17]
North Korea - Korea
1896 NJC - 1 Jan
South Korea - Korea
1896 NJC - 1 Jan
Ireland - Kingdom of Ireland
1752 2 Sep - 14 Sep
United Kingdom - Kingdom of Great Britain andKingdom of Ireland
1752 2 Sep - 14 Sep
Germany - Jlich-Berg
1583 2 Nov -13 Nov
Japan - Japan
1873 NJC - 1 Jan
Netherlands - Holland
1583 1 Jan -12 Jan
Netherlands - Groningen (province), Stad and Ommelanden]
1700 31 Dec - 1701 12 Jan
Netherlands - Groningen (city)
1583 1 Mar - 12 Mar
Netherlands - Groningen (city)
1594 19 Nov - 10 Nov RTJ
Greece - Greece, excluding Mount Athos
1923 15 Feb - 1 Mar 13
Switzerland - Oberengadin and Bergel
1783 ? - ?
Switzerland - Schiers and Grsch
1811 25 Dec - 1812 7 Jan
Switzerland - Graubnden (Catholic parts)
1623 25 Dec - 1624 7 Jan
Lithuania - Grand Duchy of Lithuania
1585 21 Dec - 1586 1 Jan
Switzerland - Glarus (Protestant part)
1798 22 Jun - 4 Jul
Switzerland - Glarus (Catholic part)
1700 31 Dec - 1701 12 Jan
Germany - Germany, Protestant parts
1700 18 Feb - 1 Mar
Netherlands - Gelderland
1700 30 Jun - 12 Jul
Netherlands - Frisia
1700 31 Dec - 1701 12 Jan
[7][19]
United States - French colonial empire and Spanish Empire
1582 9 Dec - 20 Dec
Cambodia - French colonial empire
1863 NJC - ?
Canada - French colonial empire
1582 9 Dec - 20 Dec
Laos - French colonial empire
1889 NJC - ?
France - France, excluding Alsace and Lorraine
1582 9 Dec - 20 Dec 0
Belgium - Flanders
1582 14 Dec - 2 Dec
Estonia - Estonia
1918 15 Feb - 1 Mar
Egypt - Egypt
1875 NJC - 11 Sep
Austria - Duchy of Styria
1583 14 Dec - 25 Dec
Slovenia - Duchy of Styria
1583 14 Dec - 25 Dec
Lithuania - Duchy of Prussia
1612 22 Aug - 2 Sep
Poland - Duchy of Prussia
1612 22 Aug - 2 Sep
Russia - Duchy of Prussia
1612 22 Aug - 2 Sep
Luxembourg - Duchy of Luxemburg
1582 20 Dec - 31 Dec
Netherlands - Drenthe
1701 30 Apr - 12 May
Denmark - Denmark-Norway
1700 18 Feb - 1 Mar
Norway - Denmark-Norway
1700 18 Feb - 1 Mar
Latvia - Courland
1617 ? - ? - ?
Latvia - ÑCourland
1796 7 Feb - 28 Jan - RTJ
Latvia - Courland
1915 11 May - 25 May
Germany - Cologne (archdiocese)
1583 3 Nov - 14 Nov
Switzerland - City of St. Gallen
1724 ? - ?
China - China
1912 NJJC - 1Jan
Austria - Carinthia
1584 6 Jan - 17 Jan
Myanmar - Burma (British Empire)
1885 NJC - ?
Bulgaria - Bulgaria
1916 31 Mar - 14 Apr
Austria - Brixen, Salzburg, Tyrol
1583 5 Oct - 16 Oct 10
Canada - British Empire
1752 2 Sep - 14 Sep
United States of America - British Empire
1752 2 Sep - 14 Sep 11
Germany - Breisgau-Hochschwarzwald
1583 13 Oct - 24 Oct
Netherlands - Brabant
1582 14 Dec - 25 Dec
Czech Republic - Bohemia
1584 6 Jan - 17 Jan
Germany - Bishopric of Minden
1668 1 Feb - 12 Feb
Germany - Bavaria, Regensburg, Freising
1583 5 Oct - 16 Oct
Germany - Baden-Baden
1583 16 Nov - 27 Nov
rance - Austrian Upper Alsace and Breisgau
1583 13 Oct - 24 Oct 10 [11]
Germany - Augsburg
1583 13 Feb - 24 Feb
Switzerland - Appenzell-Ausserrhoden
1597 ? - ? - RTJ
Switzerland - Appenzell-Ausserrhoden
1798 3 Dec - 25 Dec
France - Alsace, Strasbourg
1682 5 Feb - 16 Feb
Albania - Albania
1912 14 Nov - 28 Nov
Albamia - Albanua Cathlic area
1583 NJC - 5 Oct
Germany - Aachen
1582 31 Dec - 1583 11 Jan
-----------------------
Conclusion
--------
Home astronomers know something about the calendar step in the
15800s and may recite the textbook story. When astronomy softwares
matured, astronomers saw that the programs built in the Julian-
Gregorian step. Missed out from most astronomy tuition was the
irregular an slow adoption of the J-G step among countries. It wasn't
clocked in at once worldwide.
When exploring early celestial events, it is crucial to inquire
after the observer's calendar regime. The example I used is a typical
one for events in colonial New York. The City was still in Julian,
over a hundred years after the official J-G step. Astronomy software
can not easily handle the many cases of delayed adoption -- and
reversals -- of the Gregorian calendar.
Investigations into the calendar status of the observer leads into
fascinating history and culture, which previously passed you by.