Adoption of the Gregorian calendar
The Gregorian calendar was decreed in 1582 by the papal bull Inter gravissimas by Gregory XIII. Although Gregory's reform was enacted in the most solemn of forms available to the Church, the bull had no authority beyond the Catholic Church and the Papal States. The changes that he was proposing were changes to the civil calendar, over which he had no authority. They required adoption by the civil authorities in each country to have legal effect.
The bull became the law of the Catholic Church in 1582, but it was not recognised by Protestant churches, Orthodox churches, and a few others. Consequently, the days on which Easter and related holidays were celebrated by different Christian churches again diverged.
A month after having decreed the reform, the pope (with a brief of 3 April 1582) granted to one Antoni Lilio the exclusive right to publish the calendar for a period of ten years. The Lunario Novo secondo la nuova riforma was printed by Vincenzo Accolti, one of the first calendars printed in Rome after the reform, notes at the bottom that it was signed with papal authorization and by Lilio (Con licentia delli Superiori... et permissu Ant(onii) Lilij). The papal brief was revoked on 20 September 1582, because Antonio Lilio proved unable to keep up with the demand for copies.
Differences between Julian and Gregorian dates
Adoption in Catholic countries
Catholic states such as France, the Italian principalities, Poland, Spain (along with her European and overseas possessions), Portugal and the Catholic states of the Holy Roman Empire were first to change to the Gregorian calendar. Thursday, 4 October 1582 was followed by Friday, 15 October 1582, with ten days "missing". Countries that did not change until the 18th century had by then observed an additional leap year, necessitating eleven "missing days". Some countries did not change until the 19th or 20th century, necessitating one or two more "missing days".
Philip II of Spain decreed the change from the Julian to the Gregorian calendar, which affected much of Roman Catholic Europe, as Philip was at the time ruler over Spain and Portugal as well as much of Italy. In these territories, as well as in the Polish–Lithuanian Commonwealth (ruled by Anna Jagiellon) and in the Papal States, the new calendar was implemented on the date specified by the bull, with Julian Thursday, 4 October 1582, being followed by Gregorian Friday, 15 October 1582; the Spanish and Portuguese colonies followed somewhat later de facto because of delay in communication.
Other Catholic countries soon followed. France adopted the new calendar with Sunday, 9 December 1582, being followed by Monday, 20 December 1582. The Dutch provinces of Brabant and Zeeland, and the Staten-Generaal adopted it on 25 December of that year; the provinces forming the Southern Netherlands (modern Belgium) except the Duchy of Brabant adopted it on 1 January 1583; the province of Holland adopted it on 12 January 1583.The seven Catholic Swiss cantons adopted the new calendar in January 1684 while Geneva and several Protestant cantons adopted it in January 1701 or at other dates throughout the 18th century. The two Swiss communes of Schiers and Grüsch there the last areas of Western and Central Europe to switch to the Gregorian calendar in 1812.
Adoption in Protestant countries
Many Protestant countries initially objected to adopting a Catholic innovation; some Protestants feared the new calendar was part of a plot to return them to the Catholic fold. In the Czech lands, Protestants resisted the calendar imposed by the Habsburg Monarchy. In parts of Ireland, Catholic rebels until their defeat in the Nine Years' War kept the "new" Easter in defiance of the English-loyal authorities; later, Catholics practising in secret petitioned the Propaganda Fide for dispensation from observing the new calendar, as it signalled their disloyalty.
Through Ole Rømer's influence, Denmark, which then included Norway, adopted the solar portion of the Gregorian calendar with Sunday, 18 February 1700, being followed by Monday, 1 March 1700, simultaneously with Prussia and the Protestant states of Germany. None of these states adopted the lunar portion, instead calculating the date of Easter astronomically using the instant of the vernal equinox and the full moon according to Kepler's Rudolphine Tables of 1627; this combination was referred to by the German states as the "improved calendar" (Verbesserte Kalender) and considered to be distinct from the Gregorian. They finally adopted the Gregorian calculation of Easter in 1774. The remaining provinces of the Dutch Republic adopted the Gregorian calendar on 12 July 1700 (Gelderland), 12 December 1700 (Overijssel and Utrecht), 12 January 1701 (Friesland and Groningen) and 12 May 1701 (Drenthe).
Sweden's relationship with the Gregorian calendar was a difficult one. Sweden started to make the change from the Julian calendar and towards the Gregorian calendar in 1700, but it was decided to make the (then 11-day) adjustment gradually by excluding the leap days (29 February) from each of 11 successive leap years, 1700 to 1740. Meanwhile, the Swedish calendar would be out of step with both the Julian calendar and the Gregorian calendar for 40 years; also, the difference would not be constant but would change every four years. This system had potential for confusion when working out the dates of Swedish events in this 40-year period. To add to the confusion, the system was poorly administered, and the leap days that should have been excluded in 1704 and 1708 were not excluded. The Swedish calendar (according to the transition plan) should have been 8 days behind the Gregorian but was 10 days behind. King Charles XII recognised that the gradual change to the new system was not working, and he abandoned it. Rather than proceeding directly to the Gregorian calendar, it was decided to revert to the Julian calendar. This was achieved by introducing the unique date 30 February in 1712, adjusting the discrepancy in the calendars from 10 back to 11 days. Sweden finally adopted the solar portion of the Gregorian calendar in 1753, when Wednesday, 17 February, was followed by Thursday, 1 March. Since Finland was under Swedish rule at that time, it did the same. Finland's annexation to the Russian Empire did not revert this, since autonomy was granted, but government documents in Finland were dated in both the Julian and Gregorian styles. This practice ended when independence was gained in 1917.
Great Britain and its colonies
Through enactment of the Calendar (New Style) Act 1750, Great Britain and the British Empire (including the eastern part of what is now the United States) adopted the Gregorian calendar in 1752, by which time it was necessary to correct by 11 days. Wednesday, 2 September 1752, was followed by Thursday, 14 September 1752. Claims that rioters demanded "Give us our eleven days" grew out of a misinterpretation of a painting by William Hogarth.
With the same Act, the Empire (except Scotland, which had already done so from 1600) changed the start of the civil year to the 1st of January (from 5th April). Consequently, the custom of dual dating (giving a date in both old and new styles) can refer to the Julian/Gregorian calendar change, or to the start of year change, or to both.
The British tax year traditionally began on Lady Day (25 March) on the Julian calendar and thus became 5 April, which was the "Old Style" equivalent. A 12th skipped Julian leap day in 1800 changed its start to 6 April. It was not changed when a 13th Julian leap day was skipped in 1900, so the tax year in the United Kingdom still begins on 6 April.
Adoption in the Americas
The European colonies of the Americas adopted the change when their mother countries did. In Alaska, the change took place after the United States purchased Alaska from Russia. Friday, 6 October 1867 was followed by Friday, 18 October. Instead of 12 days, only 11 were skipped, and the day of the week was repeated on successive days, because at the same time the International Date Line was moved, from following Alaska's eastern border with Canada to following its new western border, now with Russia.
Adoption in Eastern Europe
The switch to the Gregorian calendar for secular use occurred in Eastern Orthodox countries as late as the 20th century, and some religious groups in some of these countries still use the Julian calendar for ecclesiastical purposes. Many of the countries of Eastern Europe were officially Eastern Orthodox or Islamic and adopted the Gregorian calendar much later than Western Christian countries.
The Ottoman Empire's Rumi calendar, used for civil purposes, was realigned from a Julian to a Gregorian starting on 1 March 1917. The Islamic calendar remained the official calendar until 1927, when it was replaced by the Gregorian calendar. The beginning of the year was reset to 1 January starting in 1918. Year numbering, however, remained uniquely Turkish until the Gregorian calendar was introduced for general purposes in 1926.
In Russia the Gregorian calendar was accepted after the October Revolution (so named because it took place in October 1917 in the Julian calendar). On 24 January 1918 the Council of People's Commissars issued a Decree that Wednesday, 31 January 1918, was to be followed by Thursday, 14 February 1918, thus dropping 13 days from the calendar. Articles about the October Revolution which mention this date difference tend to do a full conversion to the dates from Julian to the Gregorian calendar. For example, in the article "The October (November) Revolution" the Encyclopædia Britannica uses the format of "25 October (7 November, New Style)" to describe the date of the start of the revolution.
Other countries of Eastern Europe, most notably Eastern Orthodox countries, adopted the Gregorian calendar in the 1910s or early 1920s. The last country of Eastern Orthodox Europe to adopt the Gregorian calendar for civil purposes was Greece, at the time under military administration following the 11 September 1922 Revolution, with Wednesday 15 February 1923 being followed by Thursday 1 March 1923. The Soviet decree expressly limited the reform to lay (i.e. non-religious) matters, as did the Greek decree. None of these reforms affected the dates of religious holidays. (See below.)
Non-adoption by Orthodox Churches
While the civil administrations of Eastern European countries adopted the Gregorian calendar in the 1910s or early 1920s, none of the national Orthodox Churches have recognised the Gregorian calendar for church or religious purposes. Instead, a Revised Julian calendar was proposed in May 1923 at the Pan-Orthodox Congress of Constantinople which dropped 13 days in 1923 (though no churches adopted it until 1924) and adopted a different leap year rule. There will be no difference between the two calendars until 2800.
The Greek Orthodox Church of Jerusalem, Russian Orthodox Church, Serbian Orthodox Church, Georgian Orthodox and Apostolic Church, Polish Orthodox Church, Macedonian Orthodox Church and the Greek Old Calendarists did not accept the Revised Julian calendar, and continue to celebrate Christmas on 25 December in the Julian calendar, which is 7 January in the Gregorian calendar until 2100.
All of the other Eastern churches, the Oriental Orthodox churches (Coptic Orthodox Church of Alexandria, Ethiopian Orthodox Tewahedo Church, Eritrean Orthodox Tewahdo Church, and Syriac Orthodox Church) continue to use their own calendars, which usually result in fixed dates being celebrated in accordance with the Julian calendar. This is most interesting in the case of the Syriac Orthodox Church, as one of its Patriarchs Ignatius Nemet Allah I was one of the nine scholars who devised the Gregorian calendar. The Indian Orthodox Church uses the Gregorian calendar along with their autonomous Syriac Orthodox counterparts in India, the Jacobite Syriac Orthodox Church.
Adoption in East Asia
Japan decided to officially replace its traditional lunisolar calendar with the Gregorian calendar in 1872, so the day following the second day of the twelfth month of the fifth year of the Meiji emperor's rule, became 1 January 1873. (The Japanese rendering of the Western months is simply ichi-gatsu or "One-month" for January, ni-gatsu or "Two-month" for February, etc.) This brought Japan's calendar in alignment with that of the major Western powers (excluding Russia). To this day, however, it is common to use Nengo, reign names instead of the Common Era or Anno Domini system, especially for official documents; for instance, Meiji 1 for 1868, Taisho 1 for 1912, Showa 1 for 1926, Heisei 1 or 1989, and so on. Still, this system has increasingly been replaced in popular usage by the "Western calendar" (西暦, seireki) over the course of the twentieth century.
Korea adopted the Gregorian calendar on 1 January 1895 with the active participation of Yu Kil-chun. Although the new calendar continued to number its months, there were multiple systems used to refer to its years: during the Joseon Dynasty, in 1895–97, its years were numbered from the founding of that dynasty, regarding 1392 as year one; then between 1897 and 1910, and again from 1948 to 1962, Korean era names were used for its years; and between 1910 and 1945, when Korea was under Japanese rule, Japanese era names were used to count the years of the Gregorian calendar used in Korea.
In South Korea, from 1945 until 1961, Gregorian calendar years were also counted from the foundation of Gojoseon in 2333 BC (regarded as year one), the date of the legendary founding of Korea by Dangun, hence these Dangi (단기) years were 4278 to 4294. This numbering was informally used with the Korean lunar calendar before 1945 but is only occasionally used today. North Korea from 1997 officially counts years based on the Juche era, the first year of which is 1912.
The Republic of China (ROC) formally adopted the Gregorian calendar at its founding on 1 January 1912, but China soon descended into a period of warlordism with different warlords using different calendars. With the unification of China under the Kuomintang in October 1928, the Nationalist government decreed that effective 1 January 1929 the Gregorian calendar would be used. China retained the Chinese traditions of numbering the months and a modified Era System, backdating the first year of the ROC to 1912; this system is still in use in Taiwan where the ROC government retains control. Upon its foundation in 1949, the People's Republic of China continued to use the Gregorian calendar with numbered months, but abolished the ROC Era System and adopted Western numbered years.
Countries that used lunisolar calendars
Japan, Korea, and China started using the Gregorian calendar on 1 January 1873, 1896, and 1912, respectively. They had used lunisolar calendars previously. None of them used the Julian calendar; the Old Style and New Style dates in these countries usually mean the older lunisolar dates and the newer Gregorian calendar dates respectively. In these countries, the old style calendars were similar but not all the same. The Arabic numerals may be used for both calendar dates in modern Japanese and Korean languages, but not for Chinese old-style dates.
Japan started using the Gregorian calendar on 1 January 1873, locally known as "the first day of the first month of Meiji 6" (明治6年1月1日 Meiji rokunen ichigatsu tsuitachi). The preceding day, 31 December 1872, was "the second day of the twelfth month of Meiji 5" (明治5年12月2日 Meiji gonen jūnigatsu futsuka).
Japan currently uses two eras: the western era and a modified traditional Japanese era name (nengō). The months and days are those of the Gregorian calendar, but the year is either the western year number or a year of the nengō of the emperor on the throne. Since 1873, an era and the first year of that era has begun on the day of the year that the emperor ascended the throne. The second year of that era began on the next 1 January even if the first year contained only a few days. All subsequent years of that era began on 1 January until that emperor died. For example, the first year of the Showa Era, that of Emperor Hirohito, contained only the last six days of 1926, while Showa 64, his last year, contained only the first seven days of 1989. The current Gregorian year 2016 corresponds to Heisei 28.
Korea started using the Gregorian calendar on 1 January 1896, which was the 17th day of the 11th lunar month not only in Korea but also in China, which still used the lunisolar calendar. The lunisolar Korean calendar is now used for very limited unofficial purposes only. The North Korean calendar uses Gregorian months and days, but with Kim Il-Sung's year of birth (1912) used as year 1.
China and Taiwan
The Republic of China government under Provisional President Sun Yat-sen abolished the lunisolar Chinese calendar and adopted the Gregorian calendar on 1 January 1912. The public, however, resisted the change and continued to observe traditional holidays. President Yuan Shikai switched to a dual-calendar policy, under which the Gregorian calendar was to be used for most purposes except traditional holidays, which were to be timed according to the Chinese calendar. When the communists took over China in the late 1940s they kept this two-calendar system for the People's Republic of China. Today China, Hong Kong, Macau, Malaysia, Indonesia, Singapore and Taiwan all observe traditional holidays based on the traditional calendar, such as Lunar New Year, while timing other holidays, especially national anniversaries, according to the Gregorian calendar.
In China national guidelines (GB/T 15835-1995, General rules for writing numerals in publications) require writing new style dates with Arabic numerals but old-style dates with Chinese characters. The use of Arabic numerals is considered overly casual for old-style dates.
In Taiwan it is common to see Arabic numerals in new-style dates, though Chinese characters sometimes appear in these. Chinese characters are normally used for old style dates. The calendar year in Taiwan is determined according to the traditional custom of era names, but using the founding of the Republic of China government in 1912 as the start rather than the regnal year of an emperor.
Today, the vast majority of countries use the Gregorian calendar as their sole civil calendar. Countries which have not adopted the Gregorian calendar include Saudi Arabia (Islamic calendar), Ethiopia (Ethiopian calendar), Nepal (Vikram Samvat), and Iran and Afghanistan (Persian calendar). Some countries use other calendars alongside the Gregorian calendar, including India (Indian national calendar), Bangladesh (Bengali calendar), Pakistan (Islamic calendar), Israel (Hebrew calendar) and Burma (Burmese calendar); and other countries use a modified version of the Gregorian calendar, including Thailand (Thai solar calendar), Japan (Japanese calendar), North Korea (North Korean calendar) and Taiwan (Minguo calendar).
While many religious organizations reckon their liturgical year by the Gregorian civil calendar, others have retained their own calendars. Alternative calendars are used in many regions of the world today to mark cycles of religious and astrological events.
Possible date conflicts
Occasionally using different calendars has caused confusion between contemporaries. For example, it is related that one of the contributory factors for Napoleon's victory at the Battle of Austerlitz was the confusion between the Russians, who were using the Julian calendar, and the Austrians, who were using the Gregorian calendar, over the date that their forces should combine. However, this tale is not supported in a contemporary account from a major-general of the Austrian Imperial and Royal Army, who tells of a joint advance of the Russian and Austrian forces (in which he himself took part) five days before the battle, and it is explicitly rejected in Goetz's 2005 book-length study of the battle.
The date when each country adopted the Gregorian calendar, or an equivalent, is marked against a horizontal time line. The vertical axis is used for expansion to show separate national names for ease in charting, but otherwise has no significance.
- 'New Almanac according to the new reform'.
- For purposes of the table, the year always begins on January 1. A Julian leap year is every year divisible by 4. A Gregorian leap year is a year exactly divisible by 4 but not by 100 unless it is exactly divisible by 400. So 1600 and 2000 were leap years under both calendars, but the other centuries (e.g., 1700, 1800, 1900) were leap years under the Julian calendar but not the Gregorian calendar. The Gregorian calendar did not exist until 1582. The extension of the Gregorian calendar before 1582 is called the proleptic Gregorian calendar, in which the years 400, 800, and 1200 are leap years but other century years are not.
- See discussion and references at Rumi calendar.
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