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Gregorian calendar
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{{Short description|Internationally accepted civil calendar}}{{About||the calendar of religious holidays and periods|Liturgical year|this year’s Gregorian calendar|{{Current calendar}}}}{{distinguish|Georgian calendar}}{{pp-sock|small=yes}}{{EngvarB|date=May 2014}}{{Use dmy dates|date=April 2024}}{{Year in various calendars|year=2024}}The Gregorian calendar is the calendar used in most parts of the world.{{sfnp|Dershowitz|Reingold|2008|loc=p. 45. “The calendar in use today in most of the world is the Gregorian or new-style calendar designed by a commission assembled by Pope Gregory XIII in the sixteenth century.“}}{{efn|Many countries that use other calendars for religious purposes use the Gregorian calendar as their civil calendar. Iran is a notable exception, in that it uses the solar Hijri calendar.}} It went into effect in October 1582 following the papal bull issued by Pope Gregory XIII, which introduced it as a modification of, and replacement for, the Julian calendar. The principal change was to space leap years differently so as to make the average calendar year 365.2425 days long, more closely approximating the 365.2422-day ’tropical’ or ‘solar’ year that is determined by the Earth’s revolution around the Sun.The rule for leap years is:{{Blockquote|Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400. For example, the years 1700, 1800, and 1900 are not leap years, but the year 2000 is.|source=United States Naval ObservatoryWEB,aa.usno.navy.mil/faq/calendars, Introduction to Calendars, n.d., United States Naval Observatory, 9 May 2022, }}There were two reasons to establish the Gregorian calendar. First, the Julian calendar assumed incorrectly that the average solar year is exactly 365.25 days long, an overestimate of a little under one day per century, and thus has a leap year every four years without exception. The Gregorian reform shortened the average (calendar) year by 0.0075 days to stop the drift of the calendar with respect to the equinoxes.{{sfnp|Gregory XIII|1582}} Second, in the years since the First Council of Nicaea in AD 325,{{efn|Rather than 45 BC when the Roman Empire adopted the Julian calendar.}} the excess leap days introduced by the Julian algorithm had caused the calendar to drift such that the March equinox was occurring well before its nominal 21 March date. This date was important to the Christian churches because it is fundamental to the calculation of the date of Easter. To reinstate the association, the reform advanced the date by 10 days:{{efn|By the time Great Britain and its possessions adopted the reform with effect from 1752, the gap had increased to 11 days; when Russia and Greece did so (for their civil calendars) in the 20th century, the jump was 13 days. For other countries and territories, see List of adoption dates of the Gregorian calendar by country.}} Thursday 4 October 1582 was followed by Friday 15 October 1582.{{sfnp|Gregory XIII|1582}} In addition, the reform also altered the lunar cycle used by the Church to calculate the date for Easter, because astronomical new moons were occurring four days before the calculated dates. Whilst the reform introduced minor changes, the calendar continued to be fundamentally based on the same geocentric theory as its predecessor.BOOK, Applebaum, Wilbur, Encyclopedia of the Scientific Revolution: From Copernicus to Newton, 2000, Garland Publishing, 0-8153-1503-1, Clavius, Christoph (1538-1612), The reform was adopted initially by the Catholic countries of Europe and their overseas possessions. Over the next three centuries, the Protestant and Eastern Orthodox countries also gradually moved to what they called the ”Improved calendar”,{{efn|... to avoid any appearance of recognising the authority of Rome. The British Calendar (New Style) Act 1750 restates the algorithm from first principles without any reference to Gregory.}} with Greece being the last European country to adopt the calendar (for civil use only) in 1923.{{sfnp|Blegen|2013}} However, many Orthodox churches continue to use the Julian calendar for religious rites and the dating of major feasts. To unambiguously specify a date during the transition period (in contemporary documents or in history texts), both notations were given, tagged as ’Old Style’ or ‘New Style’ as appropriate. During the 20th century, most non-Western countries also adopted the calendar, at least for civil purposes.- the content below is remote from Wikipedia
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Description
The Gregorian calendar, like the Julian calendar, is a solar calendar with 12 months of 28â31 days each. The year in both calendars consists of 365 days, with a leap day being added to February in the leap years. The months and length of months in the Gregorian calendar are the same as for the Julian calendar. The only difference is that the Gregorian reform omitted a leap day in three centurial years every 400 years and left the leap day unchanged.A leap year normally occurs every four years: the leap day, historically, was inserted by doubling 24 February{{snd}} there were indeed two days dated 24 February. However, for many years it has been customary to put the extra day at the end of the month of February, adding a 29 February for the leap day. Before the 1969 revision of its General Roman Calendar, the Catholic Church delayed February feasts after the 23rd by one day in leap years; masses celebrated according to the previous calendar still reflect this delay.{{sfnp|Richards|1998|page=101}}{| class=“wikitable“|+A year is divided into twelve months! {{abbr|No.|Number}} !! Name !! Length in days| 31 |
| 28 (29 in leap years) |
| 31 |
| 30 |
| 31 |
| 30 |
| 31 |
| 31 |
| 30 |
| 31 |
| 30 |
| 31 |
Gregorian reform
{{gallery | height=140 | width=200Background
Because the date of Easter is a function{{snd}}the computus{{snd}}of the date of the spring equinox in the northern hemisphere, the Catholic Church considered unacceptable the increasing divergence between the canonical date of the equinox and observed reality. Easter is celebrated on the Sunday after the ecclesiastical full moon on or after 21 March, which was adopted as an approximation to the March equinox.{{sfnp|Richards|2013|page=599}} European scholars had been well aware of the calendar drift since the early medieval period.Bede, writing in the 8th century, showed that the accumulated error in his time was more than three days. Roger Bacon in {{Circa|1200}} estimated the error at seven or eight days. Dante, writing {{Circa|1300}}, was aware of the need for calendar reform. An attempt to go forward with such a reform was undertaken by Pope Sixtus IV, who in 1475 invited Regiomontanus to the Vatican for this purpose. However, the project was interrupted by the death of Regiomontanus shortly after his arrival in Rome.BOOK, Ari, Ben-Menahem, Historical Encyclopedia of Natural and Mathematical Sciences, 1, 2009,books.google.com/books?id=9tUrarQYhKMC&pg=PA863, 863, Springer, 9783540688310, The increase of astronomical knowledge and the precision of observations towards the end of the 15th century made the question more pressing. Numerous publications over the following decades called for a calendar reform, among them two papers sent to the Vatican by the University of Salamanca in 1515 and 1578,{{sfnp|Carabias Torres|2012|page=241}} but the project was not taken up again until the 1540s, and implemented only under Pope Gregory XIII (r. 1572â1585).Preparation
In 1545, the Council of Trent authorised Pope Paul III to reform the calendar, 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. This would allow for more consistent and accurate scheduling of the feast of Easter.In 1577, a 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.{{sfnp|Ziggelaar|1983|pages=211, 214}} The reform adopted was a modification of a proposal made by the Calabrian doctor Aloysius Lilius (or Lilio).{{sfnp|Moyer|1983}}Lilius’s proposal included reducing the number of leap years in four centuries from 100 to 97, by making three out of four centurial years common instead of leap years. He also produced an original and practical scheme for adjusting the epacts of the Moon when calculating the annual date of Easter, solving a long-standing obstacle to calendar reform.Ancient tables provided the Sun’s mean longitude.{{efn|See, for example, (Prague 1401â4). A full set of Alphonsine Tables (including tables for mean motions, conjunctions of Sun and Moon, equation of time, spherical astronomy, longitudes and latitudes of cities, star tables, eclipse tables).BOOK, Tabule illustrissimi principis regis alfonsii, The tablet of the most illustrious prince King Alphonsus, John of Saxony,archive.org/details/ljs174/page/n3/mode/2up, 1401, la, For an example of the information provided see Jacques Cassini, , Table III.BOOK, Tables astronomiques du soleil, de la lune, des planètes, des étoiles fixes, et des satellites de Jupiter et de Saturne, fr, Astronomical tables of the sun, the moon, the planets, the fixed stars, and the satellites of Jupiter and Saturn, Jacques, Cassini, 1740, Paris, Imprimerie Royale, T10,archive.org/details/s2id11854200/page/10/mode/1up, }} The German mathematician Christopher Clavius, the architect of the Gregorian calendar, noted that the tables agreed neither on the time when the Sun passed through the vernal equinox nor on the length of the mean tropical year. Tycho Brahe also noticed discrepancies.BOOK, Dreyer, J L E,books.google.com/books?id=CdzSAgAAQBAJ&pg=PA52, Tycho Brahe, 2014, Cambridge University Press, 978-1-108-06871-0, Cambridge, 52, He remarks that both the Alphonsine and the Prutenic Tables are several hours wrong with regard to the time of the equinoxes and solstices., BOOK,books.google.com/books?id=q2xxatst4OQC&pg=PA29, North, J, The Universal frame: historical essays in astronomy, natural philosophy and scientific method, London, 1989, 29, 978-0-907628-95-8, He noted on one occasion that the Alphonsine tables differed from the Prutenic by nineteen hours as to the time of the vernal equinox of 1588., The Gregorian leap year rule (97 leap years in 400 years) was put forward by Petrus Pitatus of Verona in 1560. He noted that it is consistent with the tropical year of the Alfonsine tables and with the mean tropical year of Copernicus (De revolutionibus) and Erasmus Reinhold (Prutenic tables). The three mean tropical years in Babylonian sexagesimals as the excess over 365 days (the way they would have been extracted from the tables of mean longitude) were 0;14,33,9,57 (Alfonsine), 0;14,33,11,12 (Copernicus) and 0;14,33,9,24 (Reinhold).{{efn|For an explanation of this notation, see Sexagesimal#Notations.}} In decimal notation, these are equal to 0.24254606, 0.24255185, and 0.24254352, respectively. All values are the same to two sexagesimal places (0;14,33, equal to decimal 0.2425) and this is also the mean length of the Gregorian year. Thus Pitatus’s solution would have commended itself to the astronomers.{{sfnp|Swerdlow|1986}}Lilius’s proposals had two components. First, he proposed a correction to the length of the year. The mean tropical year is 365.24219 days long.{{sfnp|Meeus|Savoie|1992}} A commonly used value in Lilius’s time, from the Alfonsine tables, is 365.2425463 days.{{sfnp|Moyer|1983}} As the average length of a Julian year is 365.25 days, the Julian year is almost 11 minutes longer than the mean tropical year. The discrepancy results in a drift of about three days every 400 years. Lilius’s proposal resulted in an average year of 365.2425 days (see Accuracy). At the time of Gregory’s reform there had already been a drift of 10 days since the Council of Nicaea, resulting in the vernal equinox falling on 10 or 11 March instead of the ecclesiastically fixed date of 21 March, and if unreformed it would have drifted further. Lilius proposed that the 10-day drift should be corrected by deleting the Julian leap day on each of its ten occurrences over a period of forty years, thereby providing for a gradual return of the equinox to 21 March.Lilius’s work was expanded upon by Christopher Clavius in a closely argued, 800-page volume. He would later defend his and Lilius’s work against detractors. Clavius’s opinion was that the correction should take place in one move, and it was this advice that prevailed with Gregory.The second component consisted of an approximation that would provide an accurate yet simple, rule-based calendar. Lilius’s formula was a 10-day correction to revert the drift since the Council of Nicaea, and the imposition of a leap day in only 97 years in 400 rather than in 1 year in 4. The proposed rule was that “years divisible by 100 would be leap years only if they were divisible by 400 as well”.The 19-year cycle used for the lunar calendar required revision because the astronomical new moon was, at the time of the reform, four days before the calculated new moon.{{sfnp|Richards|2013|page=599}} It was to be corrected by one day every 300 or 400 years (8 times in 2500 years) along with corrections for the years that are no longer leap years (i.e. 1700, 1800, 1900, 2100, etc.) In fact, a new method for computing the date of Easter was introduced. The method proposed by Lilius was revised somewhat in the final reform.{{sfnp|Ziggelaar|1983|page = 220}}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 10 days. The Julian calendar day Thursday, 4 October 1582 was followed by the first day of the Gregorian calendar, Friday, 15 October 1582 (the cycle of weekdays was not affected).{{clear}}First printed Gregorian calendar
File:Reforma Gregoriana del Calendario Juliano.jpg|thumb|Lunario Novo, Secondo la Nuova Riforma della Correttione del l’Anno Riformato da N.S. Gregorio XIII,{{efn|name=Lunario|“New Almanac according to the new reform for the correction of the year, [as] reformed by His Holiness Gregory XIII”.}} printed in RomeRomeA 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 {{efn|name=Lunario}} 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.BOOK, Mezzi, E., Vizza, F., Luigi Lilio Medico Astronomo e Matematico di Cirò, Laruffa Editore, Reggio Calabria, 2010, 14, 52, 9788872214817, citing as primary references: , Magl. 5.10.5/a, Vatican Apostolic Archive A.A., Arm. IâXVIII, 5506, f. 362r.Adoption
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 (of which he was the supreme religious authority) and the Papal States (which he personally ruled). 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, Eastern Orthodox Churches, Oriental Orthodox Churches, and a few others. Consequently, the days on which Easter and related holidays were celebrated by different Christian Churches again diverged.On 29 September 1582, Philip II of Spain decreed the change from the Julian to the Gregorian calendar.BOOK, Kamen, Henry, 1998, Philip of Spain,books.google.com/books?id=wyWourPR5S8C&q=gregorian%20calendar, Yale University Press, 248, 978-0300078008, This 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 PolishâLithuanian CommonwealthWEB, Cohen, Jennie, 6 Things You May Not Know About the Gregorian Calendar,www.history.com/news/6-things-you-may-not-know-about-the-gregorian-calendar, 23 July 2021, HISTORY, 23 August 2018, en, (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. The Spanish and Portuguese colonies followed somewhat later because of delay in communication.WEB,hdl.loc.gov/loc.wdl/wdl.2837, “Pragmatica” on the Ten Days of the Year, 1584, World Digital Library, : the first known South American imprint, produced in 1584 by Antonio Ricardo, of a four-page edict issued by King Philip II of Spain in 1582, decreeing the change from the Julian to the Gregorian calendar. {{Dead link|date=May 2022}} The other major Catholic power of Western Europe, France, adopted the change a few months later: 9 December was followed by 20 December.WEB,www.tondering.dk/claus/cal/gregorian.php, Tondering.dk, The Calendar FAQ: The Gregorian Calendar, 3 May 2022, 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. For example, the British could not bring themselves to adopt the Catholic system explicitly: the Annexe to their Calendar (New Style) Act 1750 established a computation for the date of Easter that achieved the same result as Gregory’s rules, without actually referring to him.WEB,www.legislation.gov.uk/apgb/Geo2/24/23/section/3, Calendar (New Style) Act 1750, Section 3, Parliament of Great Britain, National Archives, Britain and the British Empire (including the eastern part of what is now the United States) adopted the Gregorian calendar in 1752. Sweden followed in 1753.Prior to 1917, Turkey used the lunar Islamic calendar with the Hijri era for general purposes and the Julian calendar for fiscal purposes. The start of the fiscal year was eventually fixed at 1 March and the year number was roughly equivalent to the Hijri year (see Rumi calendar). As the solar year is longer than the lunar year this originally entailed the use of “escape years” every so often when the number of the fiscal year would jump. From 1 March 1917 the fiscal year became Gregorian, rather than Julian. On 1 January 1926, the use of the Gregorian calendar was extended to include use for general purposes and the number of the year became the same as in most other countries.Adoption by country
{{hatnote|This is a brief summary. For a comprehensive table, see List of adoption dates of the Gregorian calendar by country}}{| class=“wikitable“! Year! Country/-ies/AreasKingdom of Bohemia, some Catholic Swiss cantons{{efn>name=“CH“|In the Old Swiss Confederacy, Helvetic Republic, or Switzerland, adoptions were made between 1584 and 1811. Some Catholic cantons switched in 1584, some Protestant in 1700/1701. For a complete list see List of adoption dates of the Gregorian calendar per country.}} |
Low Countries, Norway, Denmark, some Protestant Swiss cantons{{efn> name=“CH“}} |
Kingdom of Great Britain>Great Britain, Kingdom of Ireland | , and the British Empire#“First” British Empire (1707â1783)>“First” British Empire (1707â1783) |
Romania, Yugoslavia{{efn>1919 in the regions comprising the former Kingdoms of Serbia and Montenegro (present-day Kosovo, Montenegro, Serbia and North Macedonia). The western and northern regions of what became Yugoslavia were already using the Gregorian calendar. For example, most of Slovenia adopted the Gregorian calendar at the same time as Austria in 1583. Coastal Croatia, which was at the time ruled by Venice, adopted the Gregorian calendar in 1582. Inland Croatia, ruled by the House of Habsburg | , adopted it in 1587 along with Hungary. The Gregorian calendar was used in Bosnia and Herzegovina since the 16th century by the Catholic Church>Catholic population and was formally adopted for government use in 1878 following occupation by Austria-Hungary.}} |
Difference between Gregorian and Julian calendar dates{| class“wikitable floatright“|+Conversion from Julian to Gregorian dates.A more extensive list is available at Conversion between Julian and Gregorian calendars
! Gregorian range || Julian range || Difference10 days |
11 days |
12 days |
13 days |
14 days |
Roman Republic,Roman Empire > | | |
Kronologi (2nd ed., Dansk Historisk Fællesforening, Copenhagen 1967), pp. 48â50. >| 1700 |
Papal States > | | 1582 |
Holy Roman Empire(Catholic states) > | | 1583 |
Bond | p=99{{ndash}}100}} | 1582 |
Holy Roman Empire(Protestant states) > | Protestant states in Germany used an astronomical Easter from 1700 to 1774, based on Kepler’s Rudolphine Tables, differing from the Gregorian Easter twice, one week early in 1724 and 1744.{{citation | first=Roscoe | title=The reform of the Julian calendar | journal=Popular Astronomy | pages=18â32|bibcode=1920PA.....28...18L }}}} |
Bond | p=98}} | 1753 |
WEBSITE=WWW.HENK-REINTS.NL, | 1582{{efn|In 1793 France abandoned the Gregorian calendar in favour of the French Republican Calendar. This change was reverted in 1805.}} |
Southern Netherlands > | Osteranfang {{Webarchive>url=https://web.archive.org/web/20160713092953www.manuscripta-mediaevalia.de/gaeste/Grotefend/g_o.htm#Osteranfang | Zeitrechnung de Deutschen Mittelalters und der Neuzeit {{Webarchive>url=https://web.archive.org/web/20160628120344www.manuscripta-mediaevalia.de/gaeste/grotefend/grotefend.htm | | 1582 |
Lorraine (province)>Lorraine | 1579{{sfnp | 1875 | Lorraine reverted to Julian in 1735 and adopted Gregorian again in 1760.}} |
Dutch Republic > | Bond | p=94{{ndash}}95}} | 1582 |
Bond | p=92}} | 1752 |
The reform of the Julian calendar {{Webarchive>url=https://web.archive.org/web/20151230150923articles.adsabs.harvard.edu/full/1920PA.....28...18L | Popular Astronomy 28 (1920) 18â32. Decree of Peter the Great is on pp. 23â24.>|1918 |
Tuscany >| 1750*Alexandre Dumas, Storia del governo della Toscana: sotto La casa de’Medici.
|
Kingdom of Great Britain>Great Britain andthe British Empireexcept Scotland | 1752 | 1752 |
Republic of Venice > | | 1582 |
Dual dating
File:Memorial to John Etty (18373251064).jpg|thumb|Memorial plaque to John Etty in 170|8|9}}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. 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 (1527â1608/9), notes that immediately after 1582 English letter writers “customarily” used “two dates” on their letters, one OS and one NS.BOOK, Benjamin, Woolley, The Queen’s Conjurer: The science and magic of Dr. John Dee, adviser to Queen Elizabeth I, New York, Henry Holt, 2001, 173,Old Style and New Style dates
Proleptic Gregorian calendar
{{unreferenced section|date=October 2020}}Extending the Gregorian calendar backwards to dates preceding its official introduction produces a proleptic calendar, which should be used with some 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. For example, the Battle of Agincourt is universally considered to have been fought on 25 October 1415 which is Saint Crispin’s Day.Usually, the mapping of new dates onto old dates with a start of year adjustment works well with little confusion for events that 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 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. Confusion occurs when an event affects both. For example, William III of England set sail from the Netherlands on 11 November 1688 (Gregorian calendar) and arrived at Brixham in England on 5 November 1688 (Julian calendar).Shakespeare and Cervantes seemingly died on exactly the same date (23 April 1616), but Cervantes predeceased Shakespeare by ten days in real time (as Spain used the Gregorian calendar, but Britain used the Julian calendar). This coincidence encouraged UNESCO to make 23 April the World Book and Copyright Day.Astronomers avoid this ambiguity by the use of the Julian day number.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 older Julian calendar) does not have a year 0 and instead uses the ordinal numbers 1, 2, ... both for years AD and BC. Thus the traditional time line 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. Thus the ISO 8601 time line is {{nowrap|â0001}}, 0000, 0001, and 0002.{{anchor|Month|Months of the year}}Months
The Gregorian calendar continued to employ the Julian months, which have Latinate names and irregular numbers of days:- January (31 days), from Latin , “Month of Janus”,{{citation |contribution=January, n. |contribution-url=http://www.oed.com/view/Entry/100755 |title=Oxford English Dictionary |url=http://www.oed.com/ |location=Oxford |publisher=Oxford University Press }}. the Roman god of gates, doorways, beginnings and endings
- February (28 days in common and 29 in leap years), from Latin , “Month of the Februa”, the Roman festival of purgation and purification,{{citation |contribution=February, n. |contribution-url=http://www.oed.com/view/Entry/68878 |title=Oxford English Dictionary }}.{{citation |last=Liberman |first=Anatoly |date=7 March 2007 |contribution=On a Self-Congratulatory Note |contribution-url=http://blog.oup.com/2007/03/on_a_self_congr |title=Oxford Etymologist Archives |url=https://blog.oup.com/category/series-columns/oxford_etymologist/ |publisher=Oxford University Press |location=Oxford }}. cognate with fever, the Etruscan death god Februus (“Purifier“),{{citation needed|date=February 2017}} and the Proto-Indo-European word for sulfur
- March (31 days), from Latin , “Month of Mars”,{{citation |contribution=March, n. |contribution-url=http://www.oed.com/view/Entry/113951 |title=Oxford English Dictionary }}. the Roman war god
- April (30 days), from Latin ’, of uncertain meaning{{citation |contribution=April, n. |contribution-url=http://www.oed.com/view/Entry/9939 |title=Oxford English Dictionary }}. but usually derived from some form of the verb ’ (“to open“){{efn|It is not unusual for month names to be based on natural descriptions but this etymology is sometimes doubted since no other Roman months have such names.}} or the name of the goddess Aphrodite{{efn|This derivation was apparently a popular one in ancient Rome, given by Plutarch{{citation |author=Plutarch |url=https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Plutarch/Lives/Numa.htmlRomulan_year |title=Life of Numa |at=Ch. xix }}. but rejected by Varro and Cincius.{{where|date=February 2017}}BOOK, Scullard, H H, Festivals and Ceremonies of the Roman Republic, Aspects of Greek and Roman Life, Cornell University Press, Ithaca, 1990, 96, 9780801414022,
- May (31 days), from Latin ’, “Month of Maia”,{{citation |contribution=May, n. |contribution-url=http://www.oed.com/view/Entry/115285 |title=Oxford English Dictionary }}. a Roman vegetation goddess whose name is cognate with Latin ’ (“great“) and English major
- June (30 days), from Latin , “Month of Juno”,{{citation |contribution=June, n. |contribution-url=http://www.oed.com/view/Entry/102068 |title=Oxford English Dictionary }}. the Roman goddess of marriage, childbirth, and rule
- July (31 days), from Latin , “Month of Julius Caesar”, the month of Caesar’s birth, instituted in 44{{nbsp}}BC{{citation |contribution=July, n. |contribution-url=http://www.oed.com/view/Entry/102005 |title=Oxford English Dictionary }}. as part of his calendrical reforms
- August (31 days), from Latin , “Month of Augustus”, instituted by Augustus in 8{{nbsp}}BC in agreement with July and from the occurrence during the month of several important events during his rise to power{{citation |contribution=August, n. |contribution-url=http://www.oed.com/view/Entry/13110 |title=Oxford English Dictionary }}.
- September (30 days), from Latin , “seventh month”, of the ten-month Roman year of Romulus {{circa|750}}{{nbsp}}BC{{citation |contribution=September, n. |contribution-url=http://www.oed.com/view/Entry/176171 |title=Oxford English Dictionary }}.
- October (31 days), from Latin , “eighth month”, of the ten-month Roman year of Romulus {{circa|750}}{{nbsp}}BC{{citation |contribution=October, n. |contribution-url=http://www.oed.com/view/Entry/130330 |title=Oxford English Dictionary }}.
- November (30 days), from Latin , “ninth month”, of the ten-month Roman year of Romulus {{circa|750}}{{nbsp}}BC{{citation |contribution=November, n. |contribution-url=http://www.oed.com/view/Entry/130330 |title=Oxford English Dictionary }}.
- December (31 days), from Latin , “tenth month”, of the ten-month Roman year of Romulus {{circa|750}}{{nbsp}}BC{{citation |contribution=December, n. |contribution-url=http://www.oed.com/view/Entry/48106 |title=Oxford English Dictionary }}.
Weeks
In conjunction with the system of months, there is a system of weeks. A physical or electronic calendar provides conversion from a given date to the weekday and shows multiple dates for a given weekday and month. Calculating the day of the week is not very simple, because of the irregularities in the Gregorian system. When the Gregorian calendar was adopted by each country, the weekly cycle continued uninterrupted. For example, in the case of the few countries that adopted the reformed calendar on the date proposed by Gregory XIII for the calendar’s adoption, Friday, 15 October 1582, the preceding date was Thursday, 4 October 1582 (Julian calendar).Opinions vary about the numbering of the days of the week. ISO 8601, in common use worldwide, starts with Monday=1; printed monthly calendar grids often list Mondays in the first (left) column of dates and Sundays in the last. In North America, the week typically begins on Sunday and ends on Saturday.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 365.2425 mean solar days long.{{sfnp|Seidelmann|1992|pages=580â581}} This approximation has an error of about one day per 3,030 years{{efn|Using value from Richards (2013, p. 587) for tropical year in mean solar days, the calculation is {{nowrap|1/(365.2425-365.24217).}}}} with respect to the current value of the mean tropical year. However, because of the precession of the equinoxes, which is not constant, and the movement of the perihelion (which affects the Earth’s orbital speed) the error with respect to the astronomical vernal equinox is variable; using the average interval between vernal equinoxes near 2000 of 365.24237 days{{sfnp|Meeus|Savoie|1992|page=42}} implies an error closer to 1 day every 7,700 years. By any criterion, the Gregorian calendar is substantially more accurate than the 1 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 every 4,000 years, instead of 970 leap days that the Gregorian calendar would insert over the same period.BOOK, John, Herschel,visualiseur.bnf.fr/Visualiseur?Destination=Gallica&O=NUMM-94926, Outlines of Astronomy, 1849, 629, This would reduce the average year to 365.24225 days. Herschel’s proposal would make the year 4000, and multiples thereof, common instead of leap. While this modification has often been proposed since, it has never been officially adopted.BOOK, Steel, Duncan, Marking Time: The Epic Quest to Invent the Perfect Calendar, 2000, John Wiley & Sons, 978-0-471-29827-4, 185,books.google.com/books?id=rxvVdXyr_hMC&pg=PA185, On time scales of thousands of years, the Gregorian calendar falls behind the astronomical seasons. This is because the Earth’s speed of rotation is gradually slowing down, which makes each day slightly longer over time (see tidal acceleration and leap second) while the year maintains a more uniform duration.Calendar seasonal error
(File:Gregoriancalendarleap solstice.svg|frameless|upright=3.65|Gregorian calendar seasons difference)This image shows the difference between the Gregorian calendar and the astronomical seasons.The y-axis is the date in June and the x-axis is Gregorian calendar years.Each point is the date and time of the June solstice in that particular 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 in the 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 solsticeâabout 2.35 days of variation compared with the astronomical event.Proposed reforms
The following are proposed reforms of the Gregorian calendar:- Holocene calendar
- International Fixed Calendar (also called the International Perpetual calendar)
- World Calendar
- World Season Calendar
- Leap week calendars
See also
- Calendar (New Style) Act 1750
- Calendar reform
- Conversion between Julian and Gregorian calendars
- Doomsday rule
- French revolutionary calendar
- Hebrew calendar
- Dionysius Exiguus
- s:Translat â Wikisource
- Julian day
- History of calendars
- ISO 8601, an international standard for the representation of dates and times, which uses the Gregorian calendar (see Section 3.2.1).
- List of adoption dates of the Gregorian calendar by country
- List of calendars
- Old Calendarists
- Revised Julian calendar (MilankoviÄ) â used in Eastern Orthodoxy
- Johannes de Sacrobosco, De Anni Ratione (“On reckoning the years“), {{Circa|1235}}
- Roger Bacon, (“Greater Work“), {{Circa|1267}}
Notes
{{notelist}}Citations
{{Reflist}}References
- BOOK, Blackburn, Bonnie, Holford-Strevens, Leofranc, 1999, The Oxford Companion to the Year, Oxford University Press, 9780192142313,archive.org/details/oxfordcompaniont00blac, .
- WEB, Blegen, Carl W.,nataliavogeikoff.com/2013/12/25/an-odd-christmas-or-the-christmasless-year-of-1923-in-greece/, An Odd Christmas, Natalia, Vogeikoff-Brogan, 25 December 2013, From the Archivist’s Notebook, 1 April 2018,
- BOOK, Bond, John James, Handy Book of Rules and Tables for Verifying Dates With the Christian Era Giving an Account of the Chief Eras and Systems Used by Various Nations..., George Bell & Sons, 1875, London, John James Bond, Commencement of the Year, on the 1st of January or otherwise, and adoption of the Gregorian Calendar,archive.org/details/handybookofrules00inbond/page/91/mode/2up,
- BOOK, Carabias Torres, A. M, 2012, Salamanca y la medida del tiempo, es, Salamanca, Ediciones Universidad de Salamanca,
- BOOK, Nachum Dershowitz, Dershowitz, D., Edward Reingold, Reingold, E. M, 2008, Calendrical Calculations, 3rd, Cambridge University Press, Cambridge,
- BOOK, Gregory XIII, Gregory XIII, 1582,en.wikisource.org/wiki/Translation:Inter_gravissimas, Inter Gravissimas, Wikisource, Amongst the most serious tasks of our pastoral office,
- JOURNAL, Jean Meeus, Meeus, J., Savoie, D., 1992,adsabs.harvard.edu/abs/1992JBAA..102...40M, The history of the tropical year, Journal of the British Astronomical Association, 102, 1, 40â42, 1992JBAA..102...40M,
- CONFERENCE, Moyer, Gordon,articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?journal=grc..&year=1983&volume=book&page_ind=181, Aloisius Lilius and the Compendium Novae Rationis Restituendi Kalendarium, Coyne, G. V., Hoskin, M. A., Pedersen, O., 1983, Gregorian Reform of the Calendar: Proceedings of the Vatican Conference to Commemorate its 400th Anniversary, Vatican City, Pontifical Academy of Sciences, Specolo Vaticano, 171â188,
- JOURNAL, 1995, ‘Give us our eleven days!’: calendar reform in eighteenth-century England,insight.cumbria.ac.uk/id/eprint/684/1/Poole_GiveUsOurEleven.pdf, Past & Present, Oxford Academic, 95â139, 10.1093/past/149.1.95, 651100, 4 December 2020, Poole, Robert, Robert Poole (historian), 149,
- BOOK, Richards, E. G., 1998, Mapping Time: The Calendar and its History, Oxford University Press,
- BOOK, Richards, E. G., 2013, Calendars, S. E., Urban, P. K., Seidelmann, Explanatory Supplement to the Astronomical Almanac, 3rd, 585â624, Mill Valley CA, University Science Books, 978-1-891389-85-6,
- BOOK, Seidelmann, P. K., 1992, Explanatory Supplement to the Astronomical Almanac, 2nd, Sausalito, CA, University Science Books,
- JOURNAL, Swerdlow, N. M., 1986,adsabs.harvard.edu/abs/1986JHA....17..109S, The Length of the Year in the Original Proposal for the Gregorian Calendar, Journal for the History of Astronomy, 17, 49, 109â118, 10.1177/002182868601700204, 1986JHA....17..109S, 118491152,
- MAGAZINE, Walker, G. W.,adsabs.harvard.edu/full/1945PA.....53..218W, Easter Intervals, Popular Astronomy, 6, June 1945, 53, 162â178, 218â232, 1945PA.....53..218W,
- CONFERENCE, Ziggelaar, A., 1983,articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?journal=grc..&year=1983&volume=book&page_ind=209, The Papal Bull of 1582 Promulgating a Reform of the Calendar, Coyne, G. V., Hoskin, M. A., Pedersen, O., Gregorian Reform of the Calendar: Proceedings of the Vatican Conference to Commemorate its 400th Anniversary, Vatican City, Pontifical Academy of Sciences, Specolo Vaticano, 201â239,
Further reading
- BOOK, Barsoum, Ignatius A., 2003, The Scattered Pearls: A History Of Syriac Literature And Sciences, Piscataway, Georgias Press,archive.org/details/EphremBarsoumMattiMoosaTheScatteredPearlsAHistoryOfSyriacLiteratureAndSciences/page/n13/mode/2up?q=Gregorian,
- BOOK, Blackburn, Bonnie, Holford-Strevens, Leofranc, 2003, The Oxford Companion to the Year: An exploration of calendar customs and time-reckoning, Oxford University Press, 9780192142313, corrected reprinting of 1999,
- JOURNAL, Borkowski, K. M., 1991,articles.adsabs.harvard.edu//full/1991JRASC..85..121B/0000125.000.html, The tropical calendar and solar year, Journal of the Royal Astronomical Society of Canada, 85, 3, 21â130, 1991JRASC..85..121B,
- CONFERENCE, Coyne, G. V., Hoskin, M. A., Pedersen, O., 1983,archive.org/details/GregorianReformOfTheCalendar, Gregorian Reform of the Calendar, Vatican Conference to Commemorate its 400th Anniversary, 1582â1982, Vatican City, Pontifical Academy of Sciences, Vatican Observatory (),
- BOOK, Duncan, D. E, 1999, Calendar: Humanity’s Epic Struggle To Determine A True And Accurate Year, HarperCollins, 9780380793242,
- JOURNAL, Morrison, L. V., Stephenson, F. R., 2004,adsabs.harvard.edu/abs/2004JHA....35..327M, Historical values of the Earth’s clock error ÎT and the calculation of eclipses, Journal for the History of Astronomy, 35, part 3, 120, 327â336, 10.1177/002182860403500305, 2004JHA....35..327M, 119021116,
- MAGAZINE, Moyer, Gordon, 5, 246, May 1982, The Gregorian Calendar, Scientific American, 144â152,
- CONFERENCE, Pedersen, O, 1983,articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?journal=grc..&year=1983&volume=book&page_ind=34, The Ecclesiastical Calendar and the Life of the Church, Coyne, G. V., Hoskin, M. A., Pedersen, O., Gregorian Reform of the Calendar: Proceedings of the Vatican Conference to Commemorate its 400th Anniversary, Vatican City, Pontifical Academy of Sciences, Specolo Vaticano, 17â74,
External links
{{Wikisource|Translation:Inter gravissimas|Inter gravissimas in English}}- {{In Our Time|Gregorian calendar|p00548m9|Gregorian_calendar}}
- Calendar Converter
- Inter Gravissimas {{in lang|la|fr|en}}
- History of Gregorian Calendar {{Webarchive|url=https://web.archive.org/web/20140106001448www.webexhibits.org/calendars/year-history.html |date=6 January 2014 }}
- The Perpetual Calendar Gregorian Calendar adoption dates for many countries.
- World records for mentally calculating the day of the week in the Gregorian Calendar
- www.tondering.dk/claus/calendar.html" title="web.archive.org/web/20051228123115www.tondering.dk/claus/calendar.html">The Calendar FAQ â Frequently Asked Questions about Calendars
- Today’s date (Gregorian) in over 800 more-or-less obscure foreign languages {{Webarchive|url=https://web.archive.org/web/20230308031826curiousnotions.com/todays-date/ |date=8 March 2023 }}
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