Gregorian calendar

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Gregorian Calendar is the most widely used civil calendar in the world. It was named after Pope Gregory XIII, who introduced it in October 1582. Calendar spaces leaped for years to make a 365,2425-day average year, closer to 365,2422 tropical years of the day as determined by the Earth's rotation around the Sun. The rules for leap year are as follows:

Each precise year divided by four is a leap year, except for the years actually divided by 100, but these centurial years are leap years if they are actually divided by 400. For example, in 1700, 1800, and 1900 is not a leap year, but the year 2000 is.

The calendar was developed as a refinement of the Julian calendar, shortening the year's average by 0.0075 days to stop calendar deviations with respect to the equinox. To deal with 10 days of accumulated savings, the date was advanced so that October 4, 1582 was followed by 15 October 1582. There was no discontinuity in the weekday cycle or the calendar era Anno Domini . The Reformation also changed the moon cycle used by the Church to calculate the date of the Passover, returning it to the time of year as originally celebrated by the early Church.

The Reformation was adopted initially by European Catholic countries. Over the next three centuries, the Protestant and Eastern Orthodox countries also moved to what they called the Improvement calendar, with Greece becoming the last European country to adopt the calendar in 1923. To determine exactly a date during times transition, double dating is sometimes used to define the date of Old Style and New Style. Due to globalization in the 20th century, the calendar has also been adopted by most non-European countries for civilian purposes. The calendar era carries the secular name of the General Era.

Video Gregorian calendar

Deskripsi

Gregorian calendar is a sun calendar with 12 months each 28-31 days. The regular Gregorian year consists of 365 days, but in certain years known as leap years, leap days are added to February. The Gregorian years are identified by successive years. The full calendar date is determined by year (numbered by calendar era), month (identified by name or number), and day of the month (numbered starting from 1). Although the current calendar year runs from 1 January to 31 December, in previous years the number of years is based on different starting points in the calendar (see section "earlier this year" below).

In the Julian calendar, a leap year occurs every 4 years, and a leap day is inserted by doubling February 24. The Gregorian Reform eliminates leap days in three of every 400 years and leaves a leap day unchanged. However, it has become a habit in the modern period to count the days sequentially without a gap, and February 29 is usually regarded as a leap day. Prior to 1969 the revision of the Roman Calendar, the Roman Catholic Church postponed the celebration of February after the 23rd by one day in a leap year; Mass celebrated in accordance with the previous calendar still reflects this delay.

The calendar cycle repeats completely every 400 years, which is equivalent to 146,097 days. Of these 400 years, 303 are regular 365 days and 97 leap years are 366 days. The average calendar year is 365 97 / 400 days = 365.2425 days, or 365 days, 5 hours, 49 minutes, and 12 seconds.

Maps Gregorian calendar

Gregorian Reform

The Gregorian calendar is the Julian calendar reform. It was instituted in 1582 by Pope Gregory XIII, after whom the calendar was named, by the papal bull Inter gravissimas of 24 February 1582. The motivation for the adjustment was to bring the date for the Passover to the time of the year in which it celebrated when introduced by the early Church. The error in the Julian calendar (assuming that there is exactly 365.25 days a year) has caused the equinox date corresponding to the calendar drifting from the observed reality, and thus the error has been incorporated into the calculation of the date of the Passover. Although the recommendation of the First Council of Nicea in 325 stipulates that all Christians should celebrate Easter on the same day, it took almost five centuries before almost all Christians achieved that goal by adopting the rules of the Alexandrian Church (see Easter on this issue that arose).

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Since the date of Easter was tied to the Spring Equinox, the Roman Catholic Church considers the seasonal shift in the Easter date undesirable. The Church of Alexandria celebrates Easter on Sunday after the 14th day of the month (calculated using the Metonic cycle) that falls on or after the spring turning point, which they place on 21 March. However, the Church of Rome still considers March 25 (Lady Day) as an equinox (up to 342), and uses different cycles to count the day of the moon. In the Alexandrian system, from the 14th day of the month Easter may fall as early as March 21, its first day may fall no earlier than March 8 and not later than 5 April. This means that Easter varies between March 22 and April 25. In Rome, Easter is not allowed to fall over April 21, which is the day of Parilia or the anniversary of Rome and the festival of idolaters. The first day of Easter month should not be earlier than March 5 and not later than April 2nd.

Easter is Sunday after the 15th day of this month, which day 14 is allowed to precede a turning point. Where two systems produce different dates, there is generally a compromise so both churches can celebrate on the same day. In the 10th century all the churches (except a few on the eastern border of the Byzantine Empire) had adopted the Pasch of Alexandria, which still put a spring turning point on March 21, even though Bede had recorded drift in 725 - it had drifted further. in the 16th century.

Even worse, the calculated Moon used to calculate the Passover is set in the Julian year with a 19-year cycle. This estimate builds one day's errors every 310 years, so in the 16th century the lunar calendar has come out of phase with the real Moon by four days.

European intellectuals are well aware of the calendar that has floated since the early Middle Ages. Bede, writing in the 8th century, points out that the accumulation of errors in his day was more than three days. Roger Bacon at c. 1200 estimates error on seven or eight days. Dante, writes c. 1300, aware of the need for calendar reform. The first attempt to move forward with such reform was done by Pope Sixtus IV, who in 1475 invited Regiomontanus to the Vatican for this purpose. However, the project was troubled by the death of Regiomontanus shortly after his arrival in Rome. The increase of astronomical knowledge and the accuracy of observation towards the end of the 15th century made the question even more urgent. Many publications during the next decade called for calendar reform, among them paper sent to the Vatican by the University of Salamanca in 1515, but the project was not retrieved until the 1540s, and implemented only under Pope Gregory XIII (r.1572-1585).

Get started

In 1545, the Council of Trent authorized Pope Paul III to reform the calendar, requiring that the spring's turning point be restored to what he held at the First Council of Nicea in 325 and that a change to the calendar became designed to prevent future shifts. This will enable more consistent and accurate Easter scheduling.

In 1577, a Compendium was sent to a mathematician outside the reform commission for comment. Some of these experts, including Giambattista Benedetti and Giuseppe Moleto, believe Easter should be counted from actual sun and moon movements, rather than using tabular methods, but these recommendations are not adopted. The reforms adopted were modifications of a proposal made by Calabria physician Aloysius Lilius (or Lilio).

Lilius's proposal includes reducing the number of leap years in the four centuries from 100 to 97, making three of the four centurial years general, not leap years. He also produced a genuine and practical scheme to match the episode of the moon when calculating Easter's annual date, breaking enduring obstacles to calendar reform.

The ancient table provides the longitude of the sun. Christopher Clavius, the architect of the Gregorian calendar, notes that the tables disagree as the sun passes through the spring turning point or the length of the tropical year on average. Tycho Brahe also found a discrepancy. The Gregorian leap year rule (97 leap years in 400 years) was put forward by Peter Pitatus of Verona in 1560. He noted that it is consistent with the tropical years of the Alfonsine table and with Copernicus tropical average year ( De revolutionibus ) and Reinhold ( Prutenic tables ). The three average tropical years in Babylonian sexagesimals as excess for 365 days (the way they will be extracted from the average longitude table) are 14,33,9,57 (Alphonsine), 14,33,11,12 (Copernicus). ) and 14,33,9,24 (Reinhold). All values ​​are the same for two places (14:33) and this is also the average length of the Gregorian year. So Pitatus's solution will praise astronomers.

The Lilius proposal has two components. First, he proposes corrections for the whole year. The average tropical year is 365.24219 days. Since the average length of one year of Julian is 365.25 days, Julian's is almost 11 minutes longer than the average tropical year. The result difference in deviation is about three days every 400 years. The Lilius Proposal yields an average of 365,245 days a day (see Accuracy). At the time of Gregory's reform there had been a 10-day deviation since the Council of Nicea, which caused the falling falls to fall on 10 or 11 March, instead of an ecclesiastically determined date of 21 March, and if not reformed it would drift further. Lilius proposes that a 10-day deviation should be corrected by removing Julian's leap day on each of his ten events over a period of forty years, thereby giving the equinox's return gradually to 21 March.

Lilius's work was expanded by Christopher Clavius ​​in a volume of about 800 pages. He then defends and works his Lilius against the critics. Clavius's opinion is that the correction must be done in one fell swoop, and this is the counsel that applies with Gregory.

The second component consists of an approach that will provide an accurate but simple rule-based calendar. The Lilius formula is a 10-day correction to restore the current since the Nicene Council, and the imposition of a leap day in 97 years at 400 rather than in 1 year in 4. The proposed rule is that the years divisible by 100 will be a leap year only if they are discharged divided by 400 as well.

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

When the new calendar came into use, errors accumulated in the 13th century since the Council of Nicaea were corrected by the abolition of 10 days. The Julian calendar day of Thursday, October 4, 1582 was followed by the first day of the Gregorian calendar, Friday, October 15, 1582 (weekday cycles were not affected).

Adoption

Although Gregory's reform is enacted in the greatest forms available to the Church, it has no authority outside the Catholic Church and the Pontifical State. The changes he proposed were changes to the civil calendar, where he had no authority. They require adoption by civil authorities in each country to have a legal effect.

Bull Inter gravissimas became the law of the Catholic Church in 1582, but it was not recognized by the Protestant Church, the Eastern Orthodox Church, the Oriental Orthodox Church, and several others. Consequently, the days on which Easter and related holidays are celebrated by different Christian Churches are again distorted.

A month after the declaration of reform, the pope briefly 3 April 1582 was awarded to Antonio Lilio, brother of Luigi Lilio, the exclusive right to publish the calendar for a period of ten years. The Lunario Novo secondo la nuova riforma was printed by Vincenzo Accolti, one of the first calendars printed in Rome after the reformation, recorded at the bottom signed with the authorization of the pope and by Lilio ( Con licentia delli Superiori... et permissu Ant (onii) Lilij ). The papal brief was subsequently lifted, on September 20, 1582, as Antonio Lilio proved unable to comply with requests for copies.

On September 29, 1582, Philip II of Spain decided a change from Julian to the Gregorian calendar. It affected most of the Roman Catholic Europe, as Philip at that time ruled over Spain and Portugal as well as most of Italy. In this region, as well as in the Polish-Lithuanian Commonwealth (ruled by Anna Jagiellon) and in the Papal States, a new calendar was held on a date determined by the bull, with Julian Thursday, October 4, 1582, followed by Gregorian Friday, 15 October 1582. Spanish Colony and the Portuguese followed a little later de facto due to delays in communication.

Many Protestant countries initially objected to adopting Catholic innovations; some Protestants fear the new calendar is part of a plan to return them to Catholic groups. For example, the British could not adopt the Catholic system explicitly: The Appendix for Their Calendars (New Style) of the 1750 Act set the calculations for the date of Easter that achieved the same results as Gregory's rule, without actually referring to it.

Britain and the United Kingdom (including the eastern part of what is now the United States) adopted the Gregorian calendar in 1752. Sweden followed the year 1753.

Prior to 1917, Turkey used the lunar Islamic calendar with the Hegira era for public purposes and the Julian calendar for fiscal purposes. The beginning of the fiscal year is finally set on 1 March and the number of years is roughly equivalent to the year of Hegira (see Rumi's calendar). Since the sun's year is longer than the lunar year, this initially involves the use of "escape years" so often when the number of fiscal years will jump. From 1 March 1917 the fiscal year became Gregorian, not Julian. On January 1, 1926, the use of the Gregorian calendar was extended to include general-purpose use and the number of years to be the same as in most other countries.

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Difference between Gregorian and Julian calendar dates

Since the introduction of the Gregorian calendar, the difference between the Gregorian and Julian calendars has increased three days every four centuries (all date ranges are inclusive):

This section always puts the turkey on February 29 even though it is always obtained by doubling February 24 ( bissextum (twice sixth) or bissextile days) until The late Middle Ages. The Gregorian calendar is proleptic before 1582 (assumed to exist before 1582).

Persamaan berikut memberikan jumlah hari (sebenarnya, tanggal) bahwa kalender Gregorian berada di depan kalender Julian, yang disebut perbedaan sekuler di antara dua kalender. Perbedaan negatif berarti kalender Julian berada di depan kalender Gregorian.

${\ displaystyle D = \ kiri \ lfloor {Y/100} \ right \ rfloor - \ left \ lfloor {Y/400} \ right \ rfloor -2}  ÂÂ$

di mana ${\ displaystyle D}  ÂÂ$ adalah perbedaan sekuler dan ${\ displaystyle Y}  ÂÂ$ adalah tahun menggunakan penomoran tahun astronomi, yaitu, gunakan (tahun SM) - 1 untuk tahun SM. ${\ displaystyle \ left \ lfloor {x} \ right \ rfloor}  ÂÂ$ berarti bahwa jika hasil pembagian bukan merupakan bilangan bulat, maka dibulatkan ke bawah ke bilangan bulat terdekat. Jadi selama 1900-an, 1900/400 = 4, sementara selama -500, -500/400 = -2.

The general rule, in those years which are leap years in the Julian calendar but not Gregorian, is as follows:

Up to February 28th on your calendar convert from add one day less or less a day more than the calculated value. Remember to give February the exact number of days for the calendar you converted to . As you reduce the days to move from Julian to Gregorian, be careful, when calculating the 29 February Gregorian equivalent (Julian), to keep in mind that February 29 was discounted. So if the calculated value is -4, the Gregorian equivalent of this date is February 24.

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Beginning

The year used in the date during the Roman Republic and the Roman Empire was the consular year, which began on the day when the first consul entered the office - probably 1 May before 222 BC, 15 March from 222 BC and 1 January from 153 BC. The Julian calendar, which began in 45 BC, continues to use January 1 as the first day of the new year. Although the year used for the date changed, the civilian year always displays its months in January to December sequence from the period of the Roman Republic to the present.

During the Middle Ages, under the influence of the Catholic Church, many Western European countries moved earlier this year to one of several important Christian festivals - 25 December (Nativity of Jesus), 25 March (Annunciation), or Easter (France), while the Byzantine Empire started the year on September 1 and Russia did it from March 1 to 1492 when the new year was moved to September 1.

In general usage, January 1 is considered a New Year's Day and is celebrated as such, but from the 12th century to 1751 years the law in England begins on March 25 (Lady Day). Thus, for example, the Parliamentary record records the execution of Charles I on January 30 as it did in 1648 (since the year does not end until 24 March), although later history adjusts the beginning of the year to January 1 and records the execution as occurring in 1649.

Most Western European countries changed the beginning of the year to January 1 before they adopted the Gregorian calendar. For example, Scotland changed the start of the Scottish New Year to January 1 in 1600 (this means 1599 is a short year). The British, Irish and British colonies changed the beginning of the year to January 1 in 1752 (so 1751 was a short year with only 282 days) although in England the start of the fixed tax year on March 25 (OS), 5 April (NS) until 1800, when moved to 6 April. Then in 1752 in September, the Gregorian calendar was introduced throughout England and the British colonies (see Adoption section). Both of these reforms are implemented by Calendar (New Style) Act 1750.

In some countries, official decisions or laws stipulate that the beginning of the year should be January 1. For countries such as a certain year when the January 1-year become the norm can be identified. In other countries customs vary, and the beginning of the year moves back and forth as fashion and influence from other countries dictate the various customs.

Both the papal bull and the explicitly bound canons establish such dates, although they are implied by two holy day tables, one labeled 1582 that ends on December 31, and the other for each full year beginning on 1 January. It also specifies its epist relative to January 1, in contrast to the Julian calendar, which is determined relative to 22 March. The old date comes from the Greek system: formerly Supposatio Romana mentions it relatively January 1st.

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Double dating

During the period between 1582, when the first countries adopted the Gregorian calendar, and 1923, when the last European country adopted it, it is often necessary to show the dates of several events on the Julian calendar and the Gregorian calendar, for example, "10/21 February 1750/51" where multiple year accounts for some countries have started numbered on January 1 while others still use some other dates. Even before 1582, the year should sometimes have double dates because of the beginning of different years in different countries. Woolley, writing in the 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.

Old Style and New Style Date

The "Old Style" (OS) and "New Style" (NS) are sometimes added to the date to identify which calendar reference system was used for the given date. In England and its Colonies, where the 1750's Calendar Act changed the beginning of the year, and also aligned the English calendar with the Gregorian calendar, there was some confusion about the meaning of these terms. They can show that the beginning of the Julian year has been adjusted to start on January 1 (NS) although contemporary documents use a different beginning of the year (OS); or to indicate that the date corresponds to the Julian calendar (OS), previously used in many countries, rather than the Gregorian calendar (NS).

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Gregorian Proleptic Calendar

Extending the Gregorian calendar back to date before the official introduction generates a proleptic calendar, which should be used with caution. For ordinary purposes, the date of events occurring before 15 October 1582 is generally displayed when it appears in the Julian calendar, with the year beginning January 1, and no conversion to their Gregorian equivalents. For example, the Battle of Agincourt is universally considered to have fought on October 25, 1415 which is the Day of Saint Crispin.

Typically, mapping a new date to an old date with an initial year adjustment works well with a bit of confusion for events that occurred 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 England on September 14, 1752, there can be great confusion between events in continental western Europe and in the English domain in English history.

Events in continental western Europe are usually reported in English history as it occurs under the Gregorian calendar. For example, the Battle of Blenheim was always given on August 13, 1704. Confusion occurs when an event affects both. For example, William III of England arrived at Brixham in England on 5 November 1688 (Julian calendar), after sailing from the Netherlands on November 11, 1688 (Gregorian calendar).

Shakespeare and Cervantes seem to die on exactly the same date (April 23, 1616), but Cervantes precedes Shakespeare for ten days in real time (since Spain uses the Gregorian calendar, but the English uses the Julian calendar). This coincidence prompted UNESCO to make April 23 as World Book Day and Copyright.

Astronomers avoid this ambiguity by using Julian's day number.

For dates prior to year 1, unlike the Gregorian proleptic calendar used in the international standard of ISO 8601, traditional proleptic Gregorian calendars (such as the Julian calendar) do not have the year 0 and instead use the ordinal number 1, 2,... both for AD and BC. Thus the traditional timeline is 2 BC, 1 BC, AD 1, and AD 2. ISO 8601 uses astronomical year numbering which includes year 0 and previous negative numbers. Thus the ISO 8601 time line is -0001 , 0000, 0001, and 0002.

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Bulan

The Gregorian calendar continues to use the month of Julian, which has a Latent name and an irregular number of days:

• January (31 days), from Latin m? nsis I? nu? rius , "Moon of Janus", the god of the Roman gate, door, beginning and end
• February (28 same days and 29 leap years), from Latin m? nsis Februari? rius , "The Moon of Februa", Roman purgatory and purification, allied with fever, Etruscan death god Februus ("Purifier"), and PIE word for sulfur
• March (31 days), from Latin m? nsis M? rtius , "Moon of Mars", the Roman god of war
• April (30 days), from Latin m? nsis Apr? lis , from an uncertain meaning but usually derived from some form of verb aperire ("open") or the name of the goddess Aphrodite
• May (31 days), from Latin m? nsis M? ius , "Moon of Maia", the Roman goddess whose name is the same as Latin magnus ("great") and major English
• June (30 days), from Latin m? nsis I? nius , "Moon Juno", the Roman goddess of marriage, childbirth, and rules
• July (31 days), from Latin m? nsis I? lius , "Julius Caesar" month, Caesar's birth month, was instituted in 44 BC as part of his calendar reform
• August (31 days), from Latin m. Augustus' nsis, "Augustus", instituted by Augustus in BC BC in the July agreement and from the events during the month of some important events during its ascent to power
• September (30 days), from Latin m? nsis september , "seventh month", from its position in the Roman calendar before 153 BC
• October (31 days), from Latin m? ok ok? ber , "eighth month", from his position on the Roman calendar before 153 BC
• November (30 days), from Latin m? nsis november , "the ninth month", from its position in the Roman calendar before 153 BC
• December (31 days), from Latin m. nsis december , "tenth month", from its position in the Roman calendar before 153 BC

Europeans sometimes try to remember the number of days in each month by memorizing some form of the traditional "Thirty Day Hath September" verse. It appears in Latin, Italian, and French, and belongs to a vast oral tradition but the fastest form of poetry proved today is the English marginalia incorporated into the saints' calendar c. 1425 :

Variations appear in Mother Goose and continue to be taught in schools. The inconvenience of the involved mnemonics has been parodied as "Thirty days have been September /But all the rest I do not remember" but it has also been called "probably the only ordinary sixteenth-century poem to know with heart". The common nonverbal alternative is the mnemonic knuckle, remembering the knuckles of one's hands as the moon with 31 days and the lower space between them as the moon with fewer days. Using two hands, one can start from the little finger as January and count, eliminating the space between the index knuckles (July and August). The same procedure can be done by using one-handed knuckles, returning from the last (July) to the first (August) and continuing. A similar Mnemonic is moving a piano keyboard in a semitone of the F key, taking the white button as a longer moon and black buttons as shorter buttons.

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Sunday

In connection with the system for months there are systems for weeks. Physical or electronic calendars provide conversions from a specific date to a business day, and show some dates for specific weekdays and months. Counting days of the week is not too simple, because of the irregularities in the Gregorian system. When the Gregorian calendar is adopted by each country, the weekly cycle continues uninterrupted. For example, in the case of some countries adopting a reformed calendar on the date proposed by Gregory XIII for the adoption of the calendar, Friday, October 15, 1582, the previous date is Thursday, October 4, 1582 (Julian calendar).

Opinions vary about numbering days of the week. ISO 8601, commonly used worldwide, starts with Monday = 1; printed monthly calendar letters often include Monday in the first (left) date and last Sunday. The software often starts with Sunday = 0, which puts the Sunday in the left column of the monthly calendar page.

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Accuracy

The Gregorian calendar enhances the approach made by the Julian calendar by spending three days on Julian's leap in every 400 years, giving an average of 365.2425 years means long sun days. This estimate has errors of about one day per 3030 years with respect to the current value of the average tropical year. However, due to unqualified equinoxes precession, and perihelion movement (affecting the Earth's orbital velocity) errors related to astronomical vernal equinox are variables; using the average interval between vernal equinoxes near 2000 from 365.24237 days implies an error approaching 1 day every 7,700 years. With any criteria, the Gregorian calendar is substantially more accurate than 1 day in 128 years of Julian calendar errors (average year 365.25 days).

In the nineteenth century, Sir John Herschel proposed modifications to the Gregorian calendar with 969 leap days every 4000 years, instead of 970 leap days to be inserted by the Gregorian calendar during the same period. This will reduce the average year to 365.24225 days. Herschel's proposal would make the year 4000, and its multiples, generally not jumps. Although this modification has been frequently filed since then, it has never been formally adopted.

On a time scale of thousands of years, the Gregorian calendar falls behind the astronomical seasons as the Earth's rotational slowdown makes each day a little longer over time (see tidal acceleration and the second jump) while the year maintains a more uniform duration.

Calendar of seasonal errors

This picture shows the difference between the Gregorian calendar and the astronomical season.

The y -axis is the date in June and x -axis is the Gregorian calendar year.

Each point is the date and time of the June solstice in a given year. Mistakes shifted by about a quarter day per year. Centurial years are ordinary years, unless they are divisible by 400, in which case they are leap years. This caused a correction in 1700, 1800, 1900, 2100, 2200, and 2300.

For example, this correction caused December 23, 1903 to be the last turning point of December, and December 20, 2096 to be the earliest turning point - about 2.35 days of variation compared to seasonal events.

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Proposed reform

The following proposed Gregorian calendar reform:

• Holocene calendar
• International Fixed Calendar (also called International Perpetual Calendar )
• The World Calendar
• Seasonal Calendar
• leap week calendar
  • Pax Calendar
  • Symmetry454
  • Hanke-Henry Permanent Calendar

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See also

• Calendar (New Style) Act 1750
• Calendar Reform
• Conversion between Julian and Gregorian calendars
• Doomsday Rule
• French revolutionary calendar
• the Hebrew calendar
• Islamic Calendar
• Inter gravissimas in English - Wikisource
• Julian day count
• Calendar history
• List of Gregorian calendar adoption dates per country
• Calendar list
• Old Calendar
  • Old Greek Calendar
• The revised Julian calendar (Milankovi?) - used in Eastern Orthodox

Gregorian reform precursors Johannes de Sacrobosco, De Anni Ratione ("Over the years"), c. 1235

Roger Bacon, Opus Majus ("Work Greater"), c. 1267

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Note

Quote

References

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• Blackburn, B. & amp; Holford-Strevens, L. (1999). The Oxford Companion to the Year . Oxford University Press. ISBN: 0-19-214231-3.
• Blackburn, B. & amp; Holford-Strevens, L. (2003). The Oxford Companion to the Year: Exploration of calendar habits and timing , Oxford University Press.
• Blegen, Carl W. (n.d.). "An Odd Christmas". Posted by introduction by Natalia Vogeikoff-Brogan on December 25, 2013. From Archive Archive taken April 1, 2018.
• Borkowski, K. M., (1991). "Tropical calendar and solar year", J. Royal Astronomical Soc. Canada 85 (3): 121-130.
• Coyne, G.V, Hoskin, M. A., Pedersen, O. (Eds.) (1983). Gregorian Calendar Reform: Proceeding of the Vatican Conference to Commemorate 400th Anniversary, 1582-1982 . Vatican City: Pontifical Academy of Sciences, Vatican Observatory (Pontificia Academia Scientarum, Specola Vaticana).
• Duncan, D. E. (1999). Calendar: The Human Epic Struggle To Determine The Correct And Accurate Year . HarperCollins. ISBN: 9780380793242.
• Gregory XIII. (2002 [1582]). Inter Gravissimas (subscription required) (W. Spenser & R. T. Crowley, Trans.). International Organization for Standardization.
• Meeus, J & amp; Savoie, D. (1992). History of tropical years. Journal of the Astronomical Association of England , 102 (1): 40-42.
• Morrison, L. V. & amp; Stephenson, F. R. (2004). Historical values ​​of Earth clock error? T and eclipse calculations. Journal for Astronomy History Vol. 35, Part 3, No. 120, p. 327-336.
• Moyer, Gordon (May 1982). "Gregorian Calendar". Scientific American , p. 144-152.
• Moyer, Gordon (1983). "Aloisius Lilius and Compendium of Novae Rationis Restituendi Calendary ". In Coyne, Hoskin, Pedersen (1983), pp.Ã, 171-188.
• Pattie, T.S. (1976) "Unexpected effects of calendar changes in 1752". British Library Journal .
• Pedersen, O. (1983). "Ecclesiastical Calendar and Church Life". In Coyne, Hoskin, Pedersen (eds), Gregorian Calendar Reform: Proceedings of the Vatican Conference to Commemorate its 400th Anniversary . Vatican City: Pontifical Academy for Science, Specolo Vaticano, pp.Ã, 17-74.
• Richards, E. G. (1998). Mapping Time: Calendar and History . Oxford U. Press.
• Richards, E. G. (2013). "Calendar". In S. E. Urban and P. K. Seidelmann (eds.), Supplementary Explanation for Almanac Astronomy (pp.Ã, 585-624). Mill Valley CA: University Science Book. ISBN 978-1-891389-85-6
• Seidelmann, P. K. (Ed.) (1992). Supplementary Explanation to Almanac Astronomy. Sausalito, CA: University Science Book.
• Swerdlow, N. M. (1986). Length of Year in Original Proposal for Gregorian Calendar. Journal for Astronomy History Vol. 17, No. 49, pp.Ã, 109-118.
• Walker, G. W. "Easter Interval". Popular Astronomy June 1945, Vol. 53, pp 162-178, 218-232.
• Ziggelaar, A. (1983). "The Papal Bull of 1582 Announces Calendar Reform". In Coyne, Hoskin, Pedersen (eds), Gregorian Calendar Reform: Proceedings of the Vatican Conference to Commemorate its 400th Anniversary . Vatican City: Pontifical Academy for Science, Specolo Vaticano, pp.Ã, 201-239.

External links

• The Gregorian Calendar at In Our Time on the BBC.
• Calendar Converter
• Inter Gravissimas (Latin and French plus English)
• Gregorian Calendar History
• Calendar Calendar The Gregorian calendar dates adoption for many countries.
• A world record to calculate mentally Sunday in the Gregorian Calendar
• Calendar FAQ - Frequently Asked Questions about Calendars
• Today's date (Gregorian) in more than 400 less obvious foreign languages ​​

Source of the article : Wikipedia