The Gregorian calendar is the most widely used calendar in the world today. The word Calendar consist of two words 1 Cal ( in Pashto means Year in Hindi and Persian is Sal- also means Year It was first proposed by the Calabrian doctor Aloysius Lilius, and decreed by Pope Gregory XIII, after whom it was named, on 24 February 1582 by papal bull Inter gravissimas. Calabria ( Latin: Brutium) is a region in southern Italy, south of Naples, located at the "toe" of Aloysius Lilius (c 1510 &ndash 1576 also Luigi Lilio or Luigi Giglio (or Aluise Lilio or Aloisius Lilius)was an Italian Pope Gregory XIII (January 7 1502 &ndash April 10 1585 born Ugo Boncompagni, was Pope from 1572 to 1585 Events 303 - Galerius, Roman Emperor, publishes his edict that begins the persecution of Christians in his portion of the A Papal bull is a particular type of Letters patent or charter issued by a Pope. Inter gravissimas was a Papal bull issued by Pope Gregory XIII on February 24, 1582. It is a reform of the Julian calendar. The Julian calendar, a reform of the Roman calendar, was introduced by Julius Caesar in 46 BC and came into force in 45 BC (709 Ab urbe condita

Years in the reformed calendar continue the numbering system of the Julian calendar, which are numbered from the traditional Incarnation year of Jesus, which has been labeled the "anno Domini" (AD) era,^[1] and is sometimes labeled the "common era" (CE), otherwise known as the "Christian Era". The Incarnation is the belief in Christianity that Jesus Christ is the God of Israel in the flesh Jesus of Nazareth (7–2 BC / BCE —26–36 AD / CE) ^[2]

The changes made by Gregory corrected the drift in the civil calendar which arose because the mean Julian calendar year was slightly too long, causing the vernal equinox, and consequently the date on which Easter was being celebrated, to drift slowly forward in relation to the civil calendar and the seasons. The civil calendar is any Calendar in use in any country at any point in time which is used for civil official or administrative purposes An equinox is the event of the Sun passing over the Earth's equator in its annual cycle Computus ( Latin for Computation) is the Calculation of the date of Easter in the Christian calendar.

The Gregorian calendar system dropped 10 days to bring the calendar back into synchronization with the seasons and, to keep it there, adopted the following leap year rule:

Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100; the centurial years that are exactly divisible by 400 are still leap years. A leap year (or intercalary year) is a year containing one or more extra days (or in the case of Lunisolar calendars an extra month in order to keep the For example, the year 1900 was not a leap year; the year 2000 was a leap year. ^[3]

In the Julian calendar, all years exactly divisible by 4 are leap years.

Description

The Gregorian solar calendar is an arithmetical calendar. It counts days as the basic unit of time, grouping them into years of 365 or 366 days. The solar calendar repeats completely every 146,097 days, which fill 400 years, and which also happens to be 20,871 seven-day weeks. A week (also called sennight or sevennight) is a unit of Time longer than a Day and shorter than a Month. Of these 400 years, 303 (the "common years") have 365 days, and 97 (the leap years) have 366 days. This gives an average year length of exactly 365. 2425 days, or 365 days, 5 hours, 49 minutes and 12 seconds.

A Gregorian year is divided into twelve months of irregular length:

Detail of the tomb of Pope Gregory XIII celebrating the introduction of the Gregorian Calendar. The month is a unit of Time, used with Calendars which is approximately as long as some natural period related to the motion of the Moon;

A calendar date is fully specified by the year (numbered by some scheme beyond the scope of the calendar itself), the month (identified by name or number), and the day of the month (numbered sequentially starting at 1). Events in January Holidays New Year's Day - January 1 Coptic Christmas - January 7 Overview February was named after the Latin term februum, which means purification, via the purification ritual Februa held on February 15 in the Events in March American Red Cross Month Fire Prevention month ( The Philippines) Women's History Month ( United April holidays and events National Poetry Month - in United States National Sexual Assault Awareness Month - in United MAY ( also known as: Mei メイ 메이 is a Korean singer well known in South Korea for singing the song "Miracle" Events in June Madaraka Day June 1 to commemorate when Kenya gained internal self-rule Events in July The traditional period known as "fence month" (the closed season for deer in England ended July 9 (date varied Other names In Arabic, the month is called أغسطسص ʾUġusṭuṣ or آب ʾĀb; usage varies from place to place and Events in September It is the start of the academic year in many countries in the Northern Hemisphere. October events and holidays Children's Book Week ( England) - First Week of October National Day ( China People's Republic Events in November All Saints' Day (formerly All Hallows Day a Christian holy day is celebrated on November 1, the day after Halloween Events in December Union Day of Romania (1 December World AIDS Day ( December 1) National Day of

Leap years add a 29th day to February, which normally has 28 days. Thus, the essential ongoing differentiating feature of the Gregorian calendar, as opposed to the Julian calendar, is that the Gregorian omits 3 leap days every 400 years. This difference would have been more noticeable in modern memory were it not for the fact that the year 2000 was a leap year in both the Julian and Gregorian calendar systems.

The intercalary day in a leap year is known as a leap day. Intercalation is the insertion of a leap day week or month into some calendar years to make the calendar follow the seasons or moon phases Leap years Although the modern calendar counts a year as 365 days a complete revolution around the sun takes approximately 365 days and 6 hours Since Roman times 24 February (bissextile) was counted as the leap day ^{[4] [5]} , but nowadays 29 February is regarded as the leap day in most countries. Events 303 - Galerius, Roman Emperor, publishes his edict that begins the persecution of Christians in his portion of the A leap year (or intercalary year) is a year containing one or more extra days (or in the case of Lunisolar calendars an extra month in order to keep the Leap years Although the modern calendar counts a year as 365 days a complete revolution around the sun takes approximately 365 days and 6 hours

Although the calendar year runs from 1 January to 31 December, sometimes year numbers were based on a different starting point within the calendar. New Year See also New Year The Ancient Romans began their consular year on January 1st since 153 BC Events 406 – Vandals, Alans and Suebians cross the Rhine, beginning an invasion of Gallia. Confusingly, the term "Anno Domini" is not specific on this point, and actually refers to a family of year numbering systems with different starting points for the years. (See the section below for more on this issue. )

Lunar aspects

Main article: Computus

The Catholic church maintained a tabular lunar calendar, which was primarily to calculate the date of Easter, and the lunar calendar required reform as well. Computus ( Latin for Computation) is the Calculation of the date of Easter in the Christian calendar. Easter ( Greek: Πάσχα Pascha or Pasxa) is the most important religious feast in the Christian Liturgical year. A perpetual lunar calendar was created, in the sense that 30 different arrangements (lines in the expanded table of epacts) for lunar months were created. One of the 30 arrangements applies to a century (for this purpose, the century begins with a year divisible by 100). When the arrangement to be used for a given century is communicated, anyone in possession of the tables can find the age of the moon on any date, and calculate the date of Easter. ^[6]

History

Gregorian reform

The motivation of the Catholic Church in adjusting the calendar was to celebrate Easter at the time it thought the First Council of Nicaea had agreed upon in 325. The First Council of Nicaea, held in Nicaea in Bithynia (present-day İznik in Turkey) convoked by the Roman Emperor Constantine Events By Place Roman Empire Gladiatorial combat is outlawed in the Roman Empire Although a canon of the council implies that all churches used the same Easter, they did not. The Church of Alexandria celebrated Easter on the Sunday after the 14th day of the moon (computed using the Metonic cycle) that falls on or after the vernal equinox, which they placed on 21 March. Metonic cycle or Enneadecaeteris in Astronomy and Calendar studies is a particular approximate common multiple of the Tropical year An equinox is the event of the Sun passing over the Earth's equator in its annual cycle Events 630 - Byzantine emperor Heraclius restores the True Cross to Jerusalem. However, the Church of Rome still regarded 25 March as the equinox (until 342) and used a different cycle to compute the day of the moon. Events 1199 - Richard I is wounded by a crossbow bolt while fighting France which leads to his death on April 6. ^[7] In the Alexandrian system, since the 14th day of the Easter moon could fall at earliest on 21 March its first day could fall no earlier than 8 March and no later than 5 April. Events 630 - Byzantine emperor Heraclius restores the True Cross to Jerusalem. Events 1618 - Johannes Kepler discovers the third law of planetary motion. Events 456 - St Patrick returns to Ireland as a missionary bishop This meant that Easter varied between 22 March and 25 April. Events 238 - Gordian I and his son Gordian II are proclaimed Roman emperor. Events 1607 - Eighty Years' War: The Dutch fleet destroys the anchored Spanish fleet at Gibraltar. At Rome, Easter was not allowed to fall later than 21 April, this being the day of the Parilia or birthday of Rome and a pagan festival. Events 753 BC - Romulus and Remus found Rome ( traditional date) As described in the Fasti (a series of poems by Ovid) the agricultural festival of Parilia, performed annually on April 21, was aimed to cleanse both sheep The first day of the Easter moon could fall no earlier than 5 March and no later than 2 April. Events 363 - Roman Emperor Julian moves from Antioch with an army of 90000 to attack the Sassanid Empire, in a Events 68 - Galba, Governor of Hispania, names himself legatus senatus populique Romani, breaking the line of Easter was the Sunday after the 15th day of this moon, whose 14th day was allowed to precede the equinox. Where the two systems produced different dates there was generally a compromise so that both churches were able to celebrate on the same day. By the tenth century all churches (except some on the eastern border of the Byzantine Empire) had adopted the Alexandrian Easter, which still placed the vernal equinox on 21 March, although Bede had already noted its drift in 725—it had drifted even further by the sixteenth century. Events 630 - Byzantine emperor Heraclius restores the True Cross to Jerusalem. Bede (ˈbiːd (also Saint Bede, the Venerable Bede, or (from Latin Beda (beda (c

Worse, the reckoned Moon that was used to compute Easter was fixed to the Julian year by a 19 year cycle. Computus ( Latin for Computation) is the Calculation of the date of Easter in the Christian calendar. Metonic cycle or Enneadecaeteris in Astronomy and Calendar studies is a particular approximate common multiple of the Tropical year However, that approximation built up an error of one day every 310 years, so by the sixteenth century the lunar calendar was out of phase with the real Moon by four days.

The Council of Trent approved a plan in 1563 for correcting the calendrical errors, requiring that the date of the vernal equinox be restored to that which it held at the time of the First Council of Nicaea in 325 and that an alteration to the calendar be designed to prevent future drift. The Council of Trent was the 19th Ecumenical Council of the Roman Catholic Church. An equinox is the event of the Sun passing over the Earth's equator in its annual cycle This would allow for a more consistent and accurate scheduling of the feast of Easter. Easter ( Greek: Πάσχα Pascha or Pasxa) is the most important religious feast in the Christian Liturgical year.

The fix was to come in two stages. First, it was necessary to approximate the correct length of a solar year. The value chosen was 365. 2425 days in decimal notation. ^[8] Although close to the mean tropical year of 365. A tropical year (also known as a solar year) is the length of time that the Sun takes to return to the same position in the cycle of seasons as seen from Earth 24219 days, it is even closer to the vernal equinox year of 365. A tropical year (also known as a solar year) is the length of time that the Sun takes to return to the same position in the cycle of seasons as seen from Earth 2424 days; this fact made the choice of approximation particularly appropriate as the purpose of creating the calendar was to ensure that the vernal equinox would be near a specific date (21 March). Events 630 - Byzantine emperor Heraclius restores the True Cross to Jerusalem. (See Accuracy).

The second stage was to devise a model based on the approximation which would provide an accurate yet simple, rule-based calendar. The formula designed by Aloysius Lilius was ultimately successful. Aloysius Lilius (c 1510 &ndash 1576 also Luigi Lilio or Luigi Giglio (or Aluise Lilio or Aloisius Lilius)was an Italian It proposed a 10-day correction to revert the drift since Nicaea, and the imposition of a leap day in only 97 years in 400 rather than in 1 year in 4. To implement the model, it was provided that years divisible by 100 would be leap years only if they were divisible by 400 as well. A leap year (or intercalary year) is a year containing one or more extra days (or in the case of Lunisolar calendars an extra month in order to keep the So, in the last millennium, 1600 and 2000 were leap years, but 1700, 1800 and 1900 were not. In this millennium, 2100, 2200, 2300 and 2500 will not be leap years, but 2400 will be. This theory was expanded upon by Christopher Clavius in a closely argued, 800 page volume. Christopher Clavius, ( March 25, 1538 &ndash February 12, 1612) was a German Jesuit Mathematician and He would later defend his and Lilius's work against detractors.

The 19-year cycle used for the lunar calendar was also to be corrected by one day every 300 or 400 years (8 times in 2500 years) along with corrections for the years (1700, 1800, 1900, 2100 et cetera) that are no longer leap years. In fact, a new method for computing the date of Easter was introduced.

In 1577 a Compendium was sent to expert mathematicians outside the reform commission for comments. Some of these experts, including Giambattista Benedetti and Giuseppe Moleto, believed Easter should be computed from the true motions of the sun and moon, rather than using a tabular method, but these recommendations were not adopted. Giambattista (Gianbattista Benedetti ( August 14 1530 &ndash January 20 1590) was an Italian mathematician from Venice ^[9]

Lilius originally proposed that the 10-day correction should be implemented by deleting the Julian leap day on each of its ten occurrences during a period of 40 years, thereby providing for a gradual return of the equinox to 21 March. Events 630 - Byzantine emperor Heraclius restores the True Cross to Jerusalem. However, Clavius's opinion was that the correction should take place in one move and it was this advice which prevailed with Gregory. Accordingly, when the new calendar was put in use, the error accumulated in the 13 centuries since the Council of Nicaea was corrected by a deletion of ten days. The last day of the Julian calendar was Thursday, 4 October 1582 and this was followed by the first day of the Gregorian calendar, Friday, 15 October 1582 (the cycle of weekdays was not affected). Events 610 - Heraclius arrives by ship from Africa at Constantinople, overthrows Byzantine Emperor Phocas Events 533 - Byzantine General Belisarius makes his formal entry into Carthage, having conquered it from the

Adoption

William Hogarth (c. William Hogarth (10 November 1697 &ndash 26 October 1764 was a major English painter, printmaker, pictorial satirist, social critic 1755) painting which is the main source for "Give us our Eleven Days"

Though Gregory's reform was "enacted" in the most solemn of forms available to the Church, in fact the bull had no authority beyond the Catholic Church and the Papal States. Year 1755 ( MDCCLV) was a Common year starting on Wednesday (link will display the full calendar of the Gregorian calendar (or A Papal bull is a particular type of Letters patent or charter issued by a Pope. The Papal States, State(s of the Church or Pontifical States (in Italian Stato Ecclesiastico, Stato della Chiesa, Stati della Chiesa The changes which he was "proposing" were changes to the civil calendar over which he had no authority. The civil calendar is any Calendar in use in any country at any point in time which is used for civil official or administrative purposes The changes required "adoption" by the civil authorities in each country to have legal effect.

The Nicene Council of 325 sought to devise rules whereby all Christians would celebrate Easter on the same day. The First Council of Nicaea, held in Nicaea in Bithynia (present-day İznik in Turkey) convoked by the Roman Emperor Constantine Easter ( Greek: Πάσχα Pascha or Pasxa) is the most important religious feast in the Christian Liturgical year. In fact it took a very long time before Christians achieved that objective (see Easter for the issues which arose). Easter ( Greek: Πάσχα Pascha or Pasxa) is the most important religious feast in the Christian Liturgical year. However, the bull Inter gravissimas became the law of the Catholic Church. Inter gravissimas was a Papal bull issued by Pope Gregory XIII on February 24, 1582. It was not recognised, however, by Protestant Churches nor by Orthodox Churches and others. Protestantism refers to the forms of Christian faith and practice that originated in the 16th century Protestant Reformation. Families of churches Eastern Christians have a shared tradition but they became divided ( Schism) during the early centuries of Christianity in disputes about Consequently, the days on which Easter and related holidays were celebrated by different Christian Churches again diverged.

Adoption in Europe

Only four (Catholic) countries adopted the new calendar on the date specified by the bull. Other Catholic countries experienced some delay before adopting the reform; and non-Catholic countries, not being subject to the decrees of the Pope, initially rejected or simply ignored the reform altogether, although they all eventually adopted it. Hence, the dates 5 October 1582 to 14 October 1582 (inclusive) are valid dates in many countries. Events 869 - The Fourth Council of Constantinople is convened to decide about what to do about Patriarch Photius of Constantinople Events 1066 - Norman Conquest: Battle of Hastings - In England on Senlac Hill seven miles from Hastings, the forces

Spain, Portugal, the Polish-Lithuanian Commonwealth, and most of Italy implemented the new calendar on Friday, 15 October 1582, following Julian Thursday, 4 October 1582. Spain () or the Kingdom of Spain (Reino de España is a country located mostly in southwestern Europe on the Iberian Peninsula. Portugal, officially the Portuguese Republic (República Portuguesa is a country on the Iberian Peninsula. The Polish–Lithuanian Commonwealth, officially the Commonwealth of the Crown of the Polish Kingdom and the Grand Duchy of Lithuania also known as the Most Serene Republic Italy (Italia officially the Italian Republic, (Repubblica Italiana is located on the Italian Peninsula in Southern Europe, and on the two largest Events 533 - Byzantine General Belisarius makes his formal entry into Carthage, having conquered it from the Events 610 - Heraclius arrives by ship from Africa at Constantinople, overthrows Byzantine Emperor Phocas The Spanish and Portuguese colonies adopted the calendar later due to the slowness of communication. France adopted the new calendar on Monday, 20 December 1582, following Sunday, 9 December 1582. This article is about the country For a topic outline on this subject see List of basic France topics. Events 69 - Vespasian, formerly a general under Nero, enters Rome to claim the title of Emperor. Events 536 - Byzantine General Belisarius enters Rome while the Ostrogothic garrison peacefully leaves the city ^[10] The Protestant Dutch provinces of Holland and Zeeland also adopted it in December of that year. "United Netherlands" redirects here For the "Kingdom of the United Netherlands" see United Kingdom of the Netherlands.

Most non-Catholic countries initially objected to adopting a Catholic invention, especially during the Counter-Reformation (of which Gregory was a leading proponent); some Protestants feared the new calendar was part of a plot to return them to the Catholic fold. The Counter-Reformation (also Catholic Reformation denotes the period of Catholic revival from the pontificate of Pope Pius IV in 1560 to the close of the Protestantism refers to the forms of Christian faith and practice that originated in the 16th century Protestant Reformation. In the Czech lands, Protestants resisted the calendar imposed by the Hapsburg Monarchy. Habsburg Monarchy (alternatively Habsburg Empire) refers to the territories ruled by the Austrian branch of the House of Habsburg, and then by the successor 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. Ireland (pronounced /ˈaɾlənd/ Éire) is the third largest island in Europe, and the twentieth-largest island in the world The Nine Years War (Cogadh na Naoi mBliana in Ireland took place from 1594 to 1603 and is also known as Tyrone's Rebellion. The Kingdom of Ireland (Ríocht na hÉireann was the name given to the Irish state from 1541 by the Crown of Ireland Act 1542 of the Parliament of Ireland. The Congregation for the Evangelization of Peoples ( Congregatio pro Gentium Evangelisatione) is the congregation of the Roman Curia responsible for In the Canon Law of the Roman Catholic Church, a dispensation is the suspension by competent authority of general rules of law in particular cases ^[11]

Denmark, Norway and the Protestant states of Germany adopted the solar portion of the new calendar on Monday, 1 March 1700, ^[12] following Sunday, 18 February 1700, due to the influence of Ole Rømer, but did not adopt the lunar portion. The Kingdom of Denmark ( ˈd̥ænmɑɡ̊ (archaic ˈd̥anmɑːɡ̊ commonly known as Denmark, is a country in the Scandinavian region of northern Europe Norway ( Norwegian: Norge ( Bokmål) or Noreg ( Nynorsk) officially the Kingdom of Norway, is a Constitutional Germany, officially the Federal Republic of Germany ( ˈbʊndəsʁepuˌbliːk ˈdɔʏtʃlant is a Country in Central Europe. Events 86 BC - Lucius Cornelius Sulla, at the head of a Roman Republic army enters in Athens, removing the Tyrant Events 3102 BC - Epoch (origin of the Kali Yuga. 1229 - The Sixth Crusade: Frederick II Holy Ole Christensen Rømer (o(ːlə ˈʁœːˀmɐ in Danish 25 September 1644, Århus – 19 September 1710, Copenhagen) Instead, they decided to calculate the date of Easter astronomically using the instant of the vernal equinox and the full moon according to Kepler's Rudolphine Tables of 1627. Johannes Kepler (ˈkɛplɚ ( December 27 1571 &ndash November 15 1630) was a German Mathematician, Astronomer The Rudolphine Tables ( Latin: Tabulae Rudolphinae) consist of a Star catalog and planetary tables published by Johannes Kepler in 1627 They finally adopted the lunar portion of the Gregorian calendar in 1776. The remaining provinces of the Dutch Republic also adopted the Gregorian calendar in 1700. "United Netherlands" redirects here For the "Kingdom of the United Netherlands" see United Kingdom of the Netherlands.

Sweden's relationship with the Gregorian Calendar was a difficult one. "Sverige" redirects here For other uses see Sweden (disambiguation and Sverige (disambiguation. 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. Leap years Although the modern calendar counts a year as 365 days a complete revolution around the sun takes approximately 365 days and 6 hours In the meantime, not only would the Swedish calendar be out of step with both the Julian calendar and the Gregorian calendar for 40 years, but the difference would not be constant but would change every 4 years. This strange system clearly had great potential for endless confusion when working out the dates of Swedish events in this 40 year period. To make matters worse, the system was poorly administered and the leap days that should have been excluded from 1704 and 1708 were not excluded. The Swedish calendar (according to the transition plan) should have been 8 days behind the Gregorian, but was still in fact 10 days behind. King Charles XII wisely recognised that the gradual change to the new system was not working and abandoned it.

However, 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 the year 1712, adjusting the discrepancy in the calendars from 10 back to 11 days. occurs in some calendars unlike the Gregorian calendar Sweden finally adopted the Gregorian calendar in 1753, when Wednesday, 17 February was followed by Thursday, 1 March. Events 1500 - Battle of Hemmingstedt. 1600 - Philosopher Giordano Bruno is burned alive at Campo de' Fiori Events 86 BC - Lucius Cornelius Sulla, at the head of a Roman Republic army enters in Athens, removing the Tyrant Since Finland was under Swedish rule at that time, it did the same. ^[13]

Britain and the British Empire (including the eastern part of what is now the United States) adopted the Gregorian calendar in 1752 (see the Calendar (New Style) Act 1750) by which time it was necessary to correct by 11 days. The Kingdom of Great Britain, also known as the United Kingdom of Great Britain, was a State in northwest Europe, in existence from 1707 to 1800 The British Empire was the largest empire in history and for over a century was the foremost global power. The United States of America —commonly referred to as the See also Old Style and New Style dates See also Gregorian calendar, Julian calendar The Calendar (New Style Act 1750 (also known as Wednesday, 2 September 1752 was followed by Thursday, 14 September 1752 to account for 29 February 1700 (Julian). Events 44 BC - Pharaoh Cleopatra VII of Egypt declares her son co-ruler as Ptolemy XV Caesarion. Year 1752 ( MDCCLII) was a Leap year starting on Saturday (link will display the full calendar for European countries but not Great Britain) of Events 81 - Domitian becomes Emperor of the Roman Empire upon the death of his brother Titus. Year 1752 ( MDCCLII) was a Leap year starting on Saturday (link will display the full calendar for European countries but not Great Britain) of Leap years Although the modern calendar counts a year as 365 days a complete revolution around the sun takes approximately 365 days and 6 hours After 1753, the British tax year in Britain continued to operate on the Julian calendar and began on 5 April, which was the "Old Style" new tax year of 25 March. Events 456 - St Patrick returns to Ireland as a missionary bishop Old Style (or OS) and New Style (or NS) are used in English language historical studies either to indicate that the start of the Julian year Events 1199 - Richard I is wounded by a crossbow bolt while fighting France which leads to his death on April 6. A 12th skipped Julian leap day in 1800 changed its start to 6 April. Events 46 BC - Julius Caesar defeats Caecilius Metellus Scipio and Marcus Porcius Cato in the Battle of Thapsus 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. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located Events 46 BC - Julius Caesar defeats Caecilius Metellus Scipio and Marcus Porcius Cato in the Battle of Thapsus

In Alaska, the change took place when Friday, 6 October 1867 was followed again by Friday, 18 October after the US purchase of Alaska from Russia, which was still on the Julian calendar. Alaska ( Аляска Alyaska) is a state in the United States of America, in the northwest of the North American continent Events 105 BC - Battle of Arausio: The Cimbri inflict the heaviest defeat on the Roman army of Gnaeus Mallius Maximus Year 1867 ( MDCCCLXVII) was a Common year starting on Tuesday (link will display the full calendar of the Gregorian calendar (or a Common year starting Events 1009 - The Church of the Holy Sepulchre, a Christian church in Jerusalem, is completely destroyed by the Fatimid Instead of 12 days, only 11 were skipped, and the day of the week was repeated on successive days, because the International Date Line was shifted from Alaska's eastern to western boundary along with the change to the Gregorian calendar.

In Russia the Gregorian calendar was accepted after the October Revolution (so named because it took place in October 1917 in the Julian calendar). Russia (Россия Rossiya) or the Russian Federation ( Rossiyskaya Federatsiya) is a transcontinental Country extending The October Revolution (Октябрьская революция Oktyabrskaya revolyutsiya) also known as the Soviet Revolution 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. Events 41 - Gaius Caesar (Caligula, known for his eccentricity and cruel Despotism, is Assassinated by his disgruntled Year 1918 ( MCMXVIII) was a Common year starting on Tuesday (link will display the full calendar of the Gregorian calendar (or a Common Council of Ministers of the USSR (Совет Министров СССР tr Decrees (декреты were legislative acts of the highest Soviet institutions primarily of the Council of People's Commissars (the highest executive body and Events 1504 - France cedes Naples to Aragon. 1606 - Gunpowder Plot: Guy Fawkes Year 1918 ( MCMXVIII) was a Common year starting on Tuesday (link will display the full calendar of the Gregorian calendar (or a Common Events 842 - Charles the Bald and Louis the German swear the Oaths of Strasbourg in the French and German Year 1918 ( MCMXVIII) was a Common year starting on Tuesday (link will display the full calendar of the Gregorian calendar (or a Common

The last country of Eastern Orthodox Europe to adopt the Gregorian calendar was Greece on Thursday, 1 March 1923, following Wednesday, 15 February 1923. Greece (Ελλάδα transliterated: Elláda, historically, Ellás,) officially the Hellenic Republic (Ελληνική Δημοκρατία Events 86 BC - Lucius Cornelius Sulla, at the head of a Roman Republic army enters in Athens, removing the Tyrant Year 1923 ( MCMXXIII) was a Common year starting on Monday (link will display the full calendar of the Gregorian calendar. Events 590 - Khosrau II is crowned as king of Persia 1637 - Ferdinand III becomes Holy Roman Emperor Year 1923 ( MCMXXIII) was a Common year starting on Monday (link will display the full calendar of the Gregorian calendar.

Adoption in Eastern Asia

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. REPUBLIC OF CHINA ARTICLE GUIDELINES New Year See also New Year The Ancient Romans began their consular year on January 1st since 153 BC Year 1912 ( MCMXII) was a Leap year starting on Monday (link will display the full calendar of the Gregorian calendar (or a Leap year starting A warlord is a person with power who has military control over a subnational area due to Armed forces loyal to the warlord and not to a central authority 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. Chinese reunification (1928, better known in Chinese history as the Northeast Flag Replacement ( is a historical term that refers to Zhang Xueliang This article discusses history of the state which currently governs Taiwan Area. New Year See also New Year The Ancient Romans began their consular year on January 1st since 153 BC Year 1929 ( MCMXXIX) was a Common year starting on Tuesday (link will display the full calendar of the Gregorian calendar. However, 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 this ROC government retains control. A Chinese era name ( is the Era name, reign period or regnal title used when traditionally numbering years in an emperor's reign and naming certain Chinese Taiwan ( Taiwanese: Tâi-oân/Tāi-oân (historically 大灣/台員/大員/台圓/大圓/台窩灣 is an Island in East Asia. 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. Talk People's Republic of China) PEOPLE'S REPUBLIC OF CHINA ARTICLE GUIDELINES

Japan replaced the traditional lunisolar calendar with the Gregorian calendar on 1 January 1873, but, like China, continued to number the months, and used reign names instead of the Common Era: Meiji 1=1868, Taisho 1=1912, Showa 1=1926, Heisei 1=1989, and so on. For a topic outline on this subject see List of basic Japan topics. New Year See also New Year The Ancient Romans began their consular year on January 1st since 153 BC Year 1873 ( MDCCCLXXIII) was a Common year starting on Wednesday (link will display the full calendar of the Gregorian calendar (or a Common The "Western calendar" (西暦, seireki) using western year numbers, is also widely accepted by civilians and to a lesser extent by government agencies.

Korea started using the Gregorian calendar on 1 January 1896 due to Japanese influence. Korea is a geographic area composed of two sovereign countries a civilization and a former state situated on the Korean Peninsula in East Asia. New Year See also New Year The Ancient Romans began their consular year on January 1st since 153 BC Year 1896 ( MDCCCXCVI) was a Leap year starting on Wednesday (link will display the full calendar of the Gregorian Calendar (or a Leap year The lunisolar Korean calendar used immediately before that day was based on the lunisolar Chinese calendar. The traditional Korean calendar is a Lunisolar calendar which like the traditional calendars of other East Asian countries was based on the Chinese calendar The Chinese calendar is lunisolar, incorporating elements of a Lunar calendar with those of a Solar calendar. ^[14]

Adoption by Orthodox Churches

Despite all the civil adoptions, none of the national Orthodox Churches recognized it. Instead, a Revised Julian calendar was proposed in May 1923 which dropped 13 days in 1923 and adopted a different leap year rule. The Revised Julian calendar or less formally New Calendar, is a Calendar scheme originated in 1923 which effectively discontinued the 340 years of divergence between There will be no difference between the two calendars until 2800. The Orthodox churches of Constantinople, Alexandria, Antioch, Greece, Cyprus, Romania, and Bulgaria adopted the Revised Julian calendar, so these New calendarists would celebrate the Nativity along with the Western churches on 25 December in the Gregorian calendar until 2800. History Early history Christianity in Byzantium existed from the time of the Twelve Apostles, but it was in the year 330 that the Roman Emperor The Greek Orthodox Church of Alexandria, also known as the Greek Orthodox Patriarchate of Alexandria and All Africa ( Greek:) is one of the autocephalous The Greek Orthodox Church of Antioch, also known as the Eastern Orthodox Church of Antioch and All the East, the Antiochian Orthodox Church, the Orthodox Patriarchate The Church of Greece ( Greek: Ekklēsía tês Helládos, ekliˈsia tis eˈlaðos is one of the fifteen Autocephalous Eastern Orthodox churches The ancient Greek Orthodox Church of Cyprus ( Greek: Ekklēsía tês Kýprou) is one of the fourteen or fifteen independent (' autocephalous The Romanian Orthodox Church ( Biserica Ortodoxă Română in Romanian) is a Autocephalous Eastern Orthodox church The Bulgarian Orthodox Church (Българска православна църква Bălgarska pravoslavna cărkva) is an Autocephalous Eastern Orthodox Church The New calendarists are those Eastern Orthodox Churches that adopted the Revised Julian calendar, namely the Orthodox churches of Constantinople Alexandria Antioch For depictions in painting and sculpture see Nativity of Jesus in art. Events 274 - Roman Emperor Aurelian

The Orthodox churches of Jerusalem, Russia, Serbia, Georgia, Poland and the Greek Old Calendarists did not accept the Revised Julian calendar. The Greek Orthodox Church of Jerusalem ( Greek: Patriarcheîon Hierosolýmōn, Arabic كنيسة الروم الأرثوذكس في القدس See also Eastern Orthodox Church Structure and organization The Slavic Orthodox Church is organized in a hierarchical structure The Serbian Orthodox Church ( Serbian: Српска Православна Црква / Srpska Pravoslavna Crkva; СПЦ / SPC) or the Christianity in ancient and feudal Georgia According to tradition when the Apostles were sent out to preach the Gospel to the nations of the world the Apostle History The establishment of the church was undertaken after the Treaty of Riga left large amount of territory previously under the Russian Empire, as part Greek Old Calendarists ( Greek: Παλαιοημερολογίτες Paleoimerologites) are groups that separated from the Orthodox Church of Greece All these Old Calendarists continue to celebrate the Nativity on 25 December in the Julian calendar, which is 7 January in the Gregorian calendar until 2100. The term Old Calendarist refers to any Orthodox Christian or any Orthodox Church body which uses the historic Julian calendar (called " Old Style Calendar Events 274 - Roman Emperor Aurelian Events 1325 - Alfonso IV becomes King of Portugal. 1558 - France takes Calais, the last continental

All of the other Eastern churches, the Oriental Orthodox churches (Coptic, Ethiopian, Eritrean, Syrian, Armenian) and the Assyrian Church, continue to use their own calendars, which usually result in fixed dates being celebrated in accordance with the Julian calendar. Oriental Orthodoxy is the communion of Eastern Christian Churches that recognize only three Ecumenical councils — the First Council of Nicaea, the History of the Coptic Orthodox Church of Alexandria Apostolic foundation Egypt is identified in the Bible as the place of refuge that the The Ethiopian Orthodox Tewahedo Church (in transliterated Amharic: Yäityop'ya ortodoks täwahedo bétäkrestyan) is an Oriental The Eritrean Orthodox Tewahedo Church is an Oriental Orthodox church. The Syriac Orthodox Church is an autocephalous Oriental Orthodox church based in the Middle East with members spread throughout the world The Armenian Apostolic Church (Հայաստանեայց Առաքելական Եկեղեցի Hayasdaneaytz Arakelagan The Holy Apostolic Catholic Assyrian Church of the East (ܥܕܬܐ ܩܕܝܫܬܐ ܘܫܠܝܚܝܬܐ ܩܬܘܠܝܩܝ ܕܡܕܢܚܐ ܕܐܬܘܪ̈ܝܐ ‘Ittā Qaddishtā wa-Shlikhāitā Qattoliqi

All Eastern churches continue to use the Julian Easter with the sole exception of the Finnish Orthodox Church, which has adopted the Gregorian Easter. Structure and organization Along with the Evangelical Lutheran Church of Finland the Orthodox Church of Finland has a special position in Finnish law

Timeline

Difference between Gregorian and Julian calendar dates

Since the introduction of the Gregorian calendar, the difference between Gregorian and Julian calendar dates has increased by three days every four centuries:

Beginning of the year

Ancient Romans began their years on 1 January since 153 BC. Events 533 - Byzantine General Belisarius makes his formal entry into Carthage, having conquered it from the Events 202 BC - coronation ceremony of Liu Bang as Emperor Gaozu of Han takes place initiating four centuries of the Han Dynasty 's rule Events 869 - The Fourth Council of Constantinople is convened to decide about what to do about Patriarch Photius of Constantinople Events 3102 BC - Epoch (origin of the Kali Yuga. 1229 - The Sixth Crusade: Frederick II Holy Events 86 BC - Lucius Cornelius Sulla, at the head of a Roman Republic army enters in Athens, removing the Tyrant Events 202 BC - coronation ceremony of Liu Bang as Emperor Gaozu of Han takes place initiating four centuries of the Han Dynasty 's rule Year -of the Julian calendar. The Gregorian calendar was 11 days ahead of the Julian calendar until Friday, but 12 days ahead since Saturday. Events 197 - Roman Emperor Septimius Severus defeats usurper Clodius Albinus in the Battle of Lugdunum Events 1500 - Battle of Hemmingstedt. 1600 - Philosopher Giordano Bruno is burned alive at Campo de' Fiori Year -of the Julian calendar. The Gregorian calendar was 11 days ahead of the Julian calendar until Friday, but 12 days ahead since Saturday. Events 86 BC - Lucius Cornelius Sulla, at the head of a Roman Republic army enters in Athens, removing the Tyrant Year -of the Julian calendar. The Gregorian calendar was 11 days ahead of the Julian calendar until Friday, but 12 days ahead since Saturday. Events 202 BC - coronation ceremony of Liu Bang as Emperor Gaozu of Han takes place initiating four centuries of the Han Dynasty 's rule Year 1900 ( MCM) was an exceptional Common year starting on Monday (link will display the full calendar of the Gregorian calendar Events 3102 BC - Epoch (origin of the Kali Yuga. 1229 - The Sixth Crusade: Frederick II Holy Year -of the Julian calendar. The Gregorian calendar was 11 days ahead of the Julian calendar until Friday, but 12 days ahead since Saturday. Events 1249 - Andrew of Longjumeau is dispatched by Louis IX of France as his ambassador to meet with the Khan of the Mongols Year 1900 ( MCM) was an exceptional Common year starting on Monday (link will display the full calendar of the Gregorian calendar Events 86 BC - Lucius Cornelius Sulla, at the head of a Roman Republic army enters in Athens, removing the Tyrant Year 1900 ( MCM) was an exceptional Common year starting on Monday (link will display the full calendar of the Gregorian calendar Events 202 BC - coronation ceremony of Liu Bang as Emperor Gaozu of Han takes place initiating four centuries of the Han Dynasty 's rule Events 1500 - Battle of Hemmingstedt. 1600 - Philosopher Giordano Bruno is burned alive at Campo de' Fiori Year 1900 ( MCM) was an exceptional Common year starting on Monday (link will display the full calendar of the Gregorian calendar Events 590 - Khosrau II is crowned as king of Persia 1637 - Ferdinand III becomes Holy Roman Emperor Events 86 BC - Lucius Cornelius Sulla, at the head of a Roman Republic army enters in Athens, removing the Tyrant Events 202 BC - coronation ceremony of Liu Bang as Emperor Gaozu of Han takes place initiating four centuries of the Han Dynasty 's rule The 22nd century of the Common Era will span the years 2101&ndash2200 of the Gregorian calendar. Events 1249 - Andrew of Longjumeau is dispatched by Louis IX of France as his ambassador to meet with the Khan of the Mongols Events 842 - Charles the Bald and Louis the German swear the Oaths of Strasbourg in the French and German The 22nd century of the Common Era will span the years 2101&ndash2200 of the Gregorian calendar. New Year See also New Year The Ancient Romans began their consular year on January 1st since 153 BC During the Middle Ages, under the influence of the Christian Church, many countries moved the start of the year to one of several important Christian festivals — 25 December (the Nativity of Jesus), 1 March, 25 March (Annunciation), or Easter. Events 274 - Roman Emperor Aurelian For depictions in painting and sculpture see Nativity of Jesus in art. Events 86 BC - Lucius Cornelius Sulla, at the head of a Roman Republic army enters in Athens, removing the Tyrant Events 1199 - Richard I is wounded by a crossbow bolt while fighting France which leads to his death on April 6. In Christianity the Annunciation ( grc Ευαγγελισμός της Θεοτόκου, Evangelismós tēs Theotókou in Greek) is the revelation Easter ( Greek: Πάσχα Pascha or Pasxa) is the most important religious feast in the Christian Liturgical year. ^[13] Eastern European countries (most of them with populations showing allegiance to the Orthodox Church) began their numbered year on 1 September from about 988. The word orthodox, from Greek orthodoxos "having the right opinion" from orthos ("right true straight" + doxa ("opinion Events 462 - Possible start of first Byzantine indiction cycle. Events By Place Africa Al-Azhar University is founded in Cairo, Egypt (the second oldest university in the world

In common usage, 1 January was regarded as New Year's Day and celebrated as such^[15], but from the 12^th century until 1751 the legal year in England began on 25 March (Lady Day). New Year See also New Year The Ancient Romans began their consular year on January 1st since 153 BC Events 1199 - Richard I is wounded by a crossbow bolt while fighting France which leads to his death on April 6. In the Christian calendar, Lady Day is the Feast of the Annunciation ( 25 March) and the first of the four traditional Irish and ^[16] So, for example, the Parliamentary record records the execution of Charles I occurring in 1648, (as the year did not end until 24 March,) ^[17] although modern histories adjust the start of the year to 1 January and record the execution as occurring in 1649. Charles I, (19 November 1600 &ndash 30 January 1649 was King of England, Scotland and Ireland from 27 March 1625 until his execution. ^[18]

Most Western European countries changed the start of the year to 1 January before they adopted the Gregorian calendar. New Year See also New Year The Ancient Romans began their consular year on January 1st since 153 BC For example Scotland changed the start of the Scottish New Year to 1 January in 1600 (this means that 1599 was a short year). New Year See also New Year The Ancient Romans began their consular year on January 1st since 153 BC England, Ireland and the British colonies changed the start of the year to 1 January in 1752, (so 1751 was a short year with only 282 days). New Year See also New Year The Ancient Romans began their consular year on January 1st since 153 BC Later that year in September the Gregorian calendar was introduced throughout Britain and the British colonies (See the section Adoption). These two reforms were implemented by the Calendar (New Style) Act 1750. See also Old Style and New Style dates See also Gregorian calendar, Julian calendar The Calendar (New Style Act 1750 (also known as ^[16]

Neither the papal bull nor its attached canons explicitly fix such a date, though it is implied by two tables of saint's days, one labeled 1582 which ends on 31 December, and another for any full year that begins on 1 January. New Year See also New Year The Ancient Romans began their consular year on January 1st since 153 BC Venice ( Italian: Venezia, Venetian: Venesia or Venexia) is a city in Northern Italy, the capital of the The Holy Roman Empire ( HRE; German Heiliges Römisches Reich (HRR, Latin Sacrum Romanum Imperium (SRI was a union of territories in Spain () or the Kingdom of Spain (Reino de España is a country located mostly in southwestern Europe on the Iberian Peninsula. Portugal, officially the Portuguese Republic (República Portuguesa is a country on the Iberian Peninsula. The Southern Netherlands (Zuidelijke Nederlanden Países Bajos del Sur Pays-Bas du sud were a part of the Low Countries controlled by Spain ( Spanish Prussia ( Latin: Borussia, Prutenia; Prūsija Prūsija Prusy Old Prussian: Prūsa) was most recently a historic state The Kingdom of Denmark ( ˈd̥ænmɑɡ̊ (archaic ˈd̥anmɑːɡ̊ commonly known as Denmark, is a country in the Scandinavian region of northern Europe "Sverige" redirects here For other uses see Sweden (disambiguation and Sverige (disambiguation. This article is about the country For a topic outline on this subject see List of basic France topics. Lorraine (Lorraine Lothringen is a historical area in present-day northeast France. "United Netherlands" redirects here For the "Kingdom of the United Netherlands" see United Kingdom of the Netherlands. Scotland ( Gaelic: Alba) is a Country in northwest Europethat occupies the northern third of the island of Great Britain. Russia (Россия Rossiya) or the Russian Federation ( Rossiyskaya Federatsiya) is a transcontinental Country extending Tuscany (Toscana is a region in Italy. It has an area of 22990 km² and a population of about 3 The Kingdom of Great Britain, also known as the United Kingdom of Great Britain, was a State in northwest Europe, in existence from 1707 to 1800 The British Empire was the largest empire in history and for over a century was the foremost global power. A saint (from the Latin sanctus) is a human being to whom has been attributed (and who has generally demonstrated a high level of Holiness and Sanctity Events 406 – Vandals, Alans and Suebians cross the Rhine, beginning an invasion of Gallia. New Year See also New Year The Ancient Romans began their consular year on January 1st since 153 BC It also specifies its epact relative to 1 January, in contrast with the Julian calendar, which specified it relative to 22 March. The epact (from Greek epaktai hèmerai = added days is a quantification of the difference between the solar and lunar calendars New Year See also New Year The Ancient Romans began their consular year on January 1st since 153 BC Events 238 - Gordian I and his son Gordian II are proclaimed Roman emperor. These would have been the inevitable result of the above shift in the beginning of the Julian year.

Dual Dating

Main article: Dual Dating

During the period between 1582, when the first countries adopted the Gregorian calendar, and 1923, when the last European country adopted it, it was often necessary to indicate the date of some event in both the Julian calendar and in the Gregorian calendar, for example, "10/21 February 1750/51", where the dual year accounts for some countries already beginning their numbered year on 1 January while others were still using some other date. In historical materials dates will often be indicated with what appears to be duplicate or excessive digits sometimes separated by a hyphen or a slash New Year See also New Year The Ancient Romans began their consular year on January 1st since 153 BC Even before 1582, the year sometimes had to be double dated because of the different beginnings of the year in various countries. Woolley, writing in his biography of John Dee (1527–1608/9), notes that immediately after 1582 English letter writers "customarily" used "two dates" on their letters, one OS and one NS. John Dee (13 July 1527 – 1608 or 1609 was a noted English mathematician, astronomer, astrologer, geographer, occultist ^[21]

Old Style and New Style dates

Main article: Old Style and New Style dates

"Old Style" (OS) and "New Style" (NS) are sometimes added to dates to identify which system is used in the British Empire and other countries that did not immediately change. Old Style (or OS) and New Style (or NS) are used in English language historical studies either to indicate that the start of the Julian year The British Empire was the largest empire in history and for over a century was the foremost global power. Because the Calendar Act of 1750 altered the start of the year,^[22] and also aligned the British calendar with the Gregorian calendar, there is some confusion as to what these terms mean. See also Old Style and New Style dates See also Gregorian calendar, Julian calendar The Calendar (New Style Act 1750 (also known as They can indicate that the start of the Julian year has been adjusted to start on 1 January (NS) even though contemporary documents use a different start of year (OS); or to indicate that a date conforms to the Julian calendar (OS), formerly in use in many countries, rather than the Gregorian calendar (NS). The Julian calendar, a reform of the Roman calendar, was introduced by Julius Caesar in 46 BC and came into force in 45 BC (709 Ab urbe condita New Year See also New Year The Ancient Romans began their consular year on January 1st since 153 BC ^{[18][23][24][13]}

Use of dates from historical documents in present-day documents

There was a great deal of confusion when the calendar changed, and the confusion continues today. Other months were 'affected' by the change, for instance, although the calendar 'moved' March to January, and every person automatically became 11 days older by fiat, the change actually often occurred at another time of year, for instance, in September of 1752 in the British Empire, including the American colonies. Consequently, the actual date of the change over created confusion regarding the months other than January through March, and can be seen in quite a few months, but not in the American Colonies in December and August, for reasons that are not yet known. In some cases, historians did not differentiate between the years - leading some researchers to guess between two years when interpreting the information.

When 'translating' dates from historical documents to current documents for dates that have been incorrectly double dated by historians, both years should be entered into present-day documents until a copy of the original primary source verifying which year was written in the 'official record'. Often errors have been perpetuated from the early 19th century and still exist today. When 'translating' dates from historical documents to current documents for dates that have been correctly double dated by historians, the standard practice is to enter the earlier year first, and the later year second.

Proleptic Gregorian calendar

The Gregorian calendar can, for certain purposes, be extended backwards to dates preceding its official introduction, producing the proleptic Gregorian calendar. The proleptic Gregorian calendar is produced by extending the Gregorian calendar backward to dates preceding its official introduction in 1582. However, this proleptic calendar should be used with great caution.

For ordinary purposes, the dates of events occurring prior to 15 October 1582 are generally shown as they appeared in the Julian calendar, with the year starting on 1 January, and no conversion to their Gregorian equivalents. Events 533 - Byzantine General Belisarius makes his formal entry into Carthage, having conquered it from the New Year See also New Year The Ancient Romans began their consular year on January 1st since 153 BC The Battle of Agincourt is universally known to have been fought on 25 October 1415 which is Saint Crispin's Day. The Battle of Agincourt was an English victory against a larger French army in the Hundred Years' War. Events 1147 - The Portuguese, under Afonso I, and Crusaders from England and Flanders conquer Lisbon after a See also Crispin of Viterbo, Capuchin Franciscan Blessed Crispin and Crispinian are the Christian Patron saints of cobblers

Usually, the mapping of new dates onto old dates with a start of year adjustment works well with little confusion for events which happened before the introduction of the Gregorian Calendar. But for the period between the first introduction of the Gregorian calendar on 15 October 1582 and its introduction in Britain on 14 September 1752, there can be considerable confusion between events in continental western Europe and in British domains in English language histories. Events 533 - Byzantine General Belisarius makes his formal entry into Carthage, having conquered it from the Events 81 - Domitian becomes Emperor of the Roman Empire upon the death of his brother Titus. Year 1752 ( MDCCLII) was a Leap year starting on Saturday (link will display the full calendar for European countries but not Great Britain) of Events in continental western Europe are usually reported in English language histories as happening under the Gregorian calendar. For example the Battle of Blenheim is always given as 13 August 1704. The Battle of Blenheim (referred to in some countries as the Second Battle of Höchstädt) fought on 13 August 1704 was a major battle of the War of the Spanish Succession Events 3114 BC - According to the Lounsbury correlation the start of the Maya calendar. Year 1704 ( MDCCIV) was a Leap year starting on Tuesday (link will display the full calendar of the Gregorian calendar (or a However confusion occurs when an event affects both. For example William III of England arrived at Brixham in England on 5 November (Julian calendar), after setting sail from the Netherlands on 11 November (Gregorian calendar). William III or William of Orange (14 November 1650 &ndash 8 March 1702 He is informally known in Northern Ireland and Scotland as "King Billy" Brixham (ˈbrɪksəm is a small town in the county of Devon, in the south-west of England. Events 1499 - Publication of the Catholicon in Treguier ( Brittany) The Netherlands ( Dutch:, ˈnedərlɑnt is the European part of the Kingdom of the Netherlands, which consists of the Netherlands the Netherlands Events 308 - The Congress of Carnuntum: Attempting to keep peace within the Roman Empire, the leaders of the Tetrarchy declare

Shakespeare and Cervantes apparently died on exactly the same date (23 April 1616), but in fact Cervantes predeceased Shakespeare by ten days in real time (for dating these events, Spain used the Gregorian calendar, but Britain used the Julian calendar). William Shakespeare ( baptised Miguel de Cervantes Saavedra ( in modern Spanish; September 29, 1547 &ndash April 22, 1616) was a Spanish Novelist Events 215 BC - A temple is built on the Capitoline Hill dedicated to Venus Erycina to commemorate the Roman defeat at This coincidence however has allowed UNESCO to make 23 April the World Book and Copyright Day. United Nations Educational Scientific and Cultural Organization ( UNESCO) is a specialized agency of the United Nations established on November 16 Events 215 BC - A temple is built on the Capitoline Hill dedicated to Venus Erycina to commemorate the Roman defeat at World Book and Copyright Day (also known as International Day of the Book or World Book Days) is a yearly event on 23 April, organized by UNESCO

Astronomers avoid this ambiguity by the use of the Julian day number. The Julian date (JD is the interval of time in days and fractions of a day since 4713 B

For dates before the year 1, unlike the proleptic Gregorian calendar used in the international standard ISO 8601, the traditional proleptic Gregorian calendar (like the Julian calendar) does not have a year 0 and instead uses the ordinal numbers 1, 2, … both for years AD and BC. International standards are Standards developed by international Standards organisations International standards are available for consideration and use worldwide ISO 8601 is an International standard for date and Time representations issued by the International Organization for Standardization (ISO There is no year zero in the widely used Gregorian calendar, nor in its predecessor the Julian calendar. Thus the traditional timeline is 2 BC, 1 BC, AD 1, and AD 2. ISO 8601 uses astronomical year numbering which includes a year 0 and negative numbers before it. Astronomical year numbering is based on AD ( Anno Domini)/CE ( Common Era) year numbering but follows normal Decimal Integer numbering more strictly Thus the ISO 8601 timeline is -0001, 0000, 0001, and 0002.

Months of the year

English speakers sometimes remember the number of days in each month by the use of the traditional mnemonic verse:

Thirty days hath September,

April, June, and November. A mnemonic device (nəˈmɒnɪk is a Memory aid Commonly met mnemonics are often verbal something such as a very short poem or a special word used to help a person remember

All the rest have thirty-one,

excepting February alone,

which hath twenty-eight.

Leap year cometh one year in four,

in which February hath one day more.

For variations and alternate endings, see Thirty days hath September. Thirty days hath September is a traditional English Mnemonic rhyme of which many variants are commonly used in English-speaking countries to remember the lengths

A language-independent alternative used in many countries is to hold up your two fists with the index knuckle of your left hand against the index knuckle of your right hand. Then, starting with January from the little knuckle of your left hand, count knuckle, space, knuckle, space through the months. A knuckle represents a month of 31 days, and a space represents a short month (a 28- or 29-day February or any 30-day month). The junction between the hands is not counted, so the two index knuckles represent July and August. This method also works by starting the sequence on the right hand's little knuckle, and continue toward to the left. You can also use just one hand; after counting the fourth knuckle as July, start again counting the first knuckle as August. A similar mnemonic can be found on a piano keyboard: starting on the key F for January, moving up the keyboard in semitones, the black notes give the short months, the white notes the long ones. A musical keyboard is the set of adjacent depressible levers or keys on a Musical instrument, particularly the piano A semitone, also called a half step or a half tone, is the smallest Musical interval commonly used in Western tonal music and it is considered the

The Origins of English naming used by the Gregorian calendar:

• January: Janus (Roman god of gates, doorways, beginnings and endings)
• February: Februus (Etruscan god of death) Februarius (mensis) (Latin for "month of purification (rituals)" it is said to be a Sabine word, the last month of ancient pre-450 BC Roman calendar). In Roman mythology, Janus (or Ianus was the god of Gates Doors doorways beginnings and endings This article is about the Etruscan god For the Edinburgh -based band see their website The Etruscans were a people of unknown origin living in Northern Italy, who were eventually integrated into Roman culture and politically became part of the Roman Republic The Roman calendar changed its form several times in the time between the foundation of Rome and the fall of the Roman Empire. It is related to fever. Fever (also known as pyrexia, from the Greek pyretos meaning fire or a febrile response, from the Latin word Febris ^[25][26][27]
• March: Mars (Roman god of war)
• April: Aprilis (mensis) (Latin for "month of Venus," second month of ancient Roman calendar)
• May: Maia Maiestas (Roman goddess)
• June: Juno (Roman goddess, wife of Jupiter)
• July: Julius Caesar (Roman dictator) (month was formerly named Quintilis, the fifth month of the calendar of Romulus)
• August: Augustus (first Roman emperor) (month was formerly named Sextilis, the sixth month of Romulus)
• September: septem (Latin for seven, the seventh month of Romulus)
• October: octo (Latin for eight, the eighth month of Romulus)
• November: novem (Latin for nine, the ninth month of Romulus)
• December: decem (Latin for ten, the tenth month of Romulus)

Week

Main article: Days of the week

In conjunction with the system of months there is a system of weeks. Mars was the Roman Warrior god, the son of Juno and Jupiter, husband of Bellona, and the lover of Venus. Venus was a major Roman Goddess principally associated with Love, Beauty and fertility, the equivalent of the Greek goddess Maia (/ˈmeɪə/ in Greek mythology, was the eldest of the Pleiades, the seven daughters of Atlas and Pleione. Juno was the protector and special counselor of the Roman state Romulus (c 771 BC– c 717 BC and Remus (c 771 BC–c 753 BC are the traditional founders of Rome, appearing in Roman mythology Augustus ( Latin: IMPERATOR·CAESAR·DIVI·FILIVS·AVGVSTVS September 23 63 BC – August 19 AD 14) born Gaius Octavius Thurinus, was The names of the days of the week in various world languages can be classified as either numerical or planetary; however in either case the names of one or more days A week (also called sennight or sevennight) is a unit of Time longer than a Day and shorter than a Month. A physical or electronic calendar provides conversion from a given date to the weekday, and shows multiple dates for a given weekday and month. A week (also called sennight or sevennight) is a unit of Time longer than a Day and shorter than a Month. Calculating the day of the week is not very simple, because of the irregularities in the Gregorian system. This article details various mathematical Algorithms to calculate the Day of the Week for any particular date in the past or future When the Gregorian calendar was adopted by each country, the weekly cycle continued uninterrupted. So, using the original proposed adoption date, Thursday, 4 October 1582 would be followed by Friday 15 October. Events 610 - Heraclius arrives by ship from Africa at Constantinople, overthrows Byzantine Emperor Phocas Events 533 - Byzantine General Belisarius makes his formal entry into Carthage, having conquered it from the

Distribution of dates by day of the week

Since the 400-year cycle of the Gregorian calendar consists of a whole number of weeks, each cycle has a fixed distribution of weekdays among calendar dates. It then becomes possible that this distribution is not even.

Indeed, because there are 97 leap years in every 400 years in the Gregorian Calendar, there are on average 13⁶⁄₇ for each starting weekday in each cycle. This already shows that the frequency is not the same for each weekday, which is due to the effects of the "common" centennial years (1700, 1800, 1900, 2100, 2200 etc. ).

The absence of an extra day in such years causes the following leap year (1704, 1804, 1904, 2104 etc. ) to start on the same day of the week as the leap year twelve years before (1692, 1792, 1892, 2092 etc. ). Similarly, the leap year eight years after a "common" centennial year (1708, 1808, 1908, 2108 etc. ) starts on the same day of the week as the leap year immediately prior to the "common" centennial year (1696, 1796, 1896, 2096 etc. ). Thus, those days of the week on which such leap years begin gain an extra year or two in each cycle. In each cycle there are:

• 13 leap years starting on Monday
• 14 leap years starting on Tuesday
• 14 leap years starting on Wednesday
• 13 leap years starting on Thursday
• 15 leap years starting on Friday
• 13 leap years starting on Saturday
• 15 leap years starting on Sunday

Note that as a cycle, this pattern is symmetric with respect to the low Saturday value. This is the Calendar for any Leap year starting on Monday ( Dominical letter GF) such as 1996. This is the Calendar for any Leap year starting on Tuesday ( Dominical letter FE) such as 2008. This is the Calendar for any Leap year starting on Wednesday ( Dominical letter ED) such as 1992. This is the Calendar for any Leap year starting on Thursday ( Dominical letter DC) such as 2004. This is the Calendar for any Leap year starting on Friday ( Dominical letter CB) such as 1988. This is the Calendar for any Leap year starting on Saturday ( Dominical letter BA) such as 2000. This is the Calendar for any Leap year starting on Sunday ( Dominical letter AG) such as 2012.

A leap year starting on Sunday means the next year does not start on Monday, so more leap years starting on Sunday means fewer years starting on Monday, etc. Thus the pattern of number of years starting on each day is inverted and shifted by one weekday: 56, 58, 57, 57, 58, 56, 58 (symmetric with respect to the high Sunday value).

The number of common years starting on each day is found by subtraction: 43, 44, 43, 44, 43, 43, 43.

The frequency of a particular date being on a particular weekday can easily be derived from the above (for dates in March and later, relate them to the next New Year).

See also the cycle of Doomsdays. The Doomsday rule or Doomsday algorithm is a way of Calculating the day of the week of a given date

Accuracy

The Gregorian calendar improves the approximation made by the Julian calendar by skipping three Julian leap days in every 400 years, giving an average year of 365. The Julian calendar, a reform of the Roman calendar, was introduced by Julius Caesar in 46 BC and came into force in 45 BC (709 Ab urbe condita 2425 mean solar days long,^[28] which has an error of about one day per 3300 years with respect to the mean tropical year, which in 2000 had a length of 365. Solar times are measures of the apparent position of the Sun on the Celestial sphere. A day (symbol d is a unit of Time equivalent to 24 Hours and the duration of a single Rotation of planet Earth with respect to the A year (from Old English gēr) is the time between two recurrences of an event related to the Orbit of the Earth around the Sun A tropical year (also known as a solar year) is the length of time that the Sun takes to return to the same position in the cycle of seasons as seen from Earth 24219 days (each day consisting of 86,400 SI seconds)^[29] but less than half this error with respect to the vernal equinox year of 365. A tropical year (also known as a solar year) is the length of time that the Sun takes to return to the same position in the cycle of seasons as seen from Earth 24237 days. By either criterion, the Gregorian calendar is substantially more accurate than the one day in 128 years error of the Julian calendar (average year 365. 25 days).

In the 19th century, Sir John Herschel proposed a modification to the Gregorian calendar with 969 leap days per 4000 years, instead of 970 leap days that the Gregorian calendar would insert over the same period. Sir John Frederick William Herschel 1st Baronet KH, FRS ( March 7, 1792 &ndash May 11, 1871)was an ^[30] This would reduce the average year to 365. 24225 days. Herschel's proposal would make the year 4000 common instead of leap. While this modification has often been proposed since, it has never been officially adopted.

On timescales of thousands of years, the Gregorian calendar falls behind the seasons because the slowing down of the Earth's rotation makes each day slightly longer over time (see tidal acceleration, leap second, and precession) while the year maintains a more uniform duration. A rotation is a movement of an object in a circular motion A two- Dimensional object rotates around a center (or point) of rotation Tidal acceleration is an effect of the Tidal forces between an orbiting Natural satellite ( i A leap second is a one- Second adjustment that keeps broadcast standards for time of day close to mean solar time. Precession refers to a change in the direction of the axis of a rotating object Borkowski reviewed mathematical models in the literature, and found the results generally fall between a model by McCarthy and Babcock, and another by Stephenson and Morrison. If so, in the year 4000, the calendar will fall behind by at least 0. 8, but less than 1. 1 days. In the year 12,000 the calendar would fall behind at least 8, but less than 12 days. ^[31]

Calendar seasonal error

This image shows the difference between the Gregorian calendar and the seasons.

The y-axis is "days error" and the x-axis is Gregorian calendar years.

Each point represents a single date on a given year. The error shifts by about a quarter of a day per year. Centurial years are ordinary years, unless they are divisible by 400, in which case they are leap years. This causes a correction on years 1700, 1800, 1900, 2100, 2200, and 2300.

For instance, these corrections cause 23 December 1903 to be the latest December solstice, and 20 December 2096 to be the earliest solstice—2. Events 962 - Byzantine-Arab Wars: Under the future Emperor Nicephorus Phocas, Byzantine troops stormed the city Year 1903 ( MCMIII) was a Common year starting on Thursday (link will display calendar of the Gregorian calendar or a Common year starting Events 69 - Vespasian, formerly a general under Nero, enters Rome to claim the title of Emperor. The 2090s is a Decade that will start in the year 2090 and end in the year 2099. 25 days of variation compared with the seasonal event.

Numerical facts

When leap years and common years are taken into account, there are a total of 14 possible Gregorian calendars.

When different dates of Easter are also taken into account, there are a total of 70 possible Gregorian calendars.

An average year is 365. 2425 days = 52. 1775 weeks = 8,765. 82 hours = 525,949. 2 minutes = 31,556,952 seconds. All these numbers are exact, apart from leap seconds.

A common year is 365 days = 8,760 hours = 525,600 minutes = 31,536,000 seconds.

A leap year is 366 days = 8,784 hours = 527,040 minutes = 31,622,400 seconds.

Since 1971, some years may also contain one or more leap seconds, to account for cumulative irregularities in the Earth's rotation. A leap second is a one- Second adjustment that keeps broadcast standards for time of day close to mean solar time. So far, these have always been positive and have occurred on average once every 18 months.

The day of the year is somewhat inconvenient to compute, partly because the leap day does not fall at the end of the year. But the calendar exhibits a repeating pattern for the number of days in the months March through July and August through December: 31, 30, 31, 30, 31, for a total of 153 days each. In fact, any five consecutive months not containing February contain exactly 153 days.

See also common year starting on Sunday and dominical letter. This is the calendar for any Common year starting on Sunday ( Dominical letter A) or for any year in which “ Doomsday ” is Tuesday Dominical letters are letters A B C D E F and G assigned to days in a cycle of seven with the letter A always set against 1 January as an aid for finding the day of the Week

The 400-year cycle of the Gregorian calendar has 146,097 days and hence exactly 20,871 weeks. So, for example, the days of the week in Gregorian 1603 were exactly the same as for 2003. The years that are divisible by 400 begin on a Saturday. In the 400-year cycle, more months begin on a Sunday (and hence have Friday 13) than any other day of the week (see above under #Week for a more detailed explanation of how this happens). Friday the 13th is superstitiously considered a day of bad Luck in English - French - and German -speaking countries as well as in other 688 out of every 4800 months (or 172/1200) begin on a Sunday, while only 684 out of every 4800 months (171/1200) begin on each of Saturday and Monday, the least common cases.

A smaller cycle is 28 years (1,461 weeks), provided that there is no dropped leap year in between. Days of the week in years may also repeat after 6, 11, 12, 28 or 40 years. Intervals of 6 and 11 are only possible with common years, while intervals of 28 and 40 are only possible with leap years. An interval of 12 years only occurs with common years when there is a dropped leap year in between.

The Doomsday algorithm is a method by which you can discern which of the 14 calendar variations should be used in any given year (after the Gregorian reformation). The Doomsday rule or Doomsday algorithm is a way of Calculating the day of the week of a given date It is based on the last day in February, referred to as the Doomsday.

The Rata Die is the number of days from January 1, 1 A.D. (counting that day as day 1) in the proleptic Gregorian calendar. Rata Die ( RD) is a system for assigning numbers to calendar days (optionally with time of day independent of any calendar for the purposes of Calendrical calculations New Year See also New Year The Ancient Romans began their consular year on January 1st since 153 BC Year 1 ( I) was a Common year starting on Saturday of the Julian calendar. For June 9, 2008, it is 733202. It is 678,576 more than the Modified Julian date, and 1,721,425 less than the Julian date 2454627. The Julian date (JD is the interval of time in days and fractions of a day since 4713 B

Day of week

Common years always begin and end on the same day of the week, since 364 (365 - 1) is a multiple of 7, the number of days in a week. For example, 2003 began on a Wednesday and ended on a Wednesday. Leap years end on the next day of the week from which they begin. For example, 2004 began on a Thursday and ended on a Friday.

Not counting leap years, any calendar date will move to the next day of the week the following year. For example, if your birthday fell on a Tuesday in 2002, it fell on a Wednesday in 2003. Leap years make things a little more complicated. 2004 was a leap year, so calendar days of March 1 or later in the year, moved two days of the week from 2003. Events 86 BC - Lucius Cornelius Sulla, at the head of a Roman Republic army enters in Athens, removing the Tyrant However, calendar days occurring before March 1 do not make the extra day of the week jump until the year following a leap year. Events 86 BC - Lucius Cornelius Sulla, at the head of a Roman Republic army enters in Athens, removing the Tyrant So, if your birthday is June 15, then it must have fallen on a Sunday in 2003 and a Tuesday in 2004. Events 763 BC - Assyrians record a Solar eclipse that will be used to fix the Chronology of Mesopotamian history If, however, your birthday is February 15, then it must have fallen on a Saturday in 2003, a Sunday in 2004 and a Tuesday in 2005. Events 590 - Khosrau II is crowned as king of Persia 1637 - Ferdinand III becomes Holy Roman Emperor

In any year (even a leap year), July always begins on the same day of the week that April does. Therefore, the only difference between a July calendar page and an April calendar page in the same year is the extra day July has. The same relationship exists between September and December as well as between March and November. Add an extra day to the September page and you've got December. Take a day away from the March page and you've got November. In common years only, there are additional matches: October duplicates January, and March and November duplicate February in their first 28 days. In leap years only, there is a different set of additional matches: July is a duplicate of January while February is duplicated in the first 29 days of August.

See also

References

• Blackburn, B. The World Calendar is a proposed reform of the Gregorian calendar created by Elisabeth Achelis of Brooklyn New York in 1930 The Julian date (JD is the interval of time in days and fractions of a day since 4713 B A calendar reform is any significant revision of a Calendar system Computus ( Latin for Computation) is the Calculation of the date of Easter in the Christian calendar. Greek Old Calendarists ( Greek: Παλαιοημερολογίτες Paleoimerologites) are groups that separated from the Orthodox Church of Greece In current use Assyrian calendar Astronomical year numbering Bahá'í calendar Bengali calendar In historical materials dates will often be indicated with what appears to be duplicate or excessive digits sometimes separated by a hyphen or a slash & Holford-Strevens, L. (1999). The Oxford Companion to the Year. Oxford University Press ISBN 0-19-214231-3. Pages 98-99.
• Coyne, G. V. , Hoskin, M. A. , and Pedersen, O. (Eds. ) (1983). Gregorian reform of the calendar: Proceedings of the Vatican conference to commemorate its 400th anniversary, 1582-1982. Vatican City: Pontifical Academy of Sciences, Specolo Vaticano
• Duncan, D. E. (1999). Calendar: Humanity's Epic Struggle To Determine A True And Accurate Year. Harper Perennial. HarperCollins is a Publishing company owned by News Corporation. ISBN 0-380-79324-5.
• Gregory XIII. Pope Gregory XIII (January 7 1502 &ndash April 10 1585 born Ugo Boncompagni, was Pope from 1572 to 1585 (2002). Inter Gravissimas (W. Spenser & R. T. Crowley, Trans. ). International Organization for Standardization. (Original work published 1582)
• Online Etymology Dictionary retrieved August 23, 2006
• Seidelmann, P. Events 79 - Mount Vesuvius begins stirring on the feast day of Vulcan the Roman god of fire Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. K. (Ed. ). (1992). Explanatory Supplement to the Astronomical Almanac. Sausalito, CA: University Science Books.

Footnotes

External links

• Calendar Converter
• Inter Gravissimas (Latin and French plus English)
• Frequently Asked Questions about Calendars
• The Perpetual Calendar Gregorian Calendar adoption dates for many countries.
• Synoptical Julian - Gregorian calendar Compare Old and New Style dates 1582–2100.
• Gregorian Calendar Printer
• Gregorian Calendar in Norwegian, with some Norwegian information
• History of Gregorian Calendar