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85-546: Unlike the Gregorian calendar , the Coptic calendar does not skip leap years three times every 400 years, and therefore it stays synchronised with the Julian calendar over a four-year leap year cycle. The Coptic year is the extension of the ancient Egyptian civil year, retaining its subdivision into the three seasons, four months each. The three seasons are commemorated by special prayers in

170-584: 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 – there were indeed two days dated 24 February . However, for many years it has been customary to put

255-583: 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 −0001 , 0000, 0001, and 0002. The Gregorian calendar continued to employ the Julian months, which have Latinate names and irregular numbers of days : Northern Hemisphere The Northern Hemisphere

340-631: A civil holiday on 25 December (the " Festival of the Birth of the Unconquered Sun ") to celebrate the deity Sol Invictus . Finally, joyous festivals are needed at that time of year to fight the natural gloom of the season (in the Northern Hemisphere ). Until the 16th century, 25 December coincided with 29 Koiak of the Coptic calendar. However, upon the introduction of the Gregorian calendar in 1582, 25 December shifted 10 days earlier in comparison with

425-407: 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

510-605: A computation for the date of Easter that achieved the same result as Gregory's rules, without actually referring to him. 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

595-611: A counterclockwise pattern. Hurricanes and tropical storms (massive low-pressure systems) spin counterclockwise in the Northern Hemisphere. The shadow of a sundial moves clockwise on latitudes north of the subsolar point and anticlockwise to the south. During the day at these latitudes, the Sun tends to rise to its maximum at a southerly position. Between the Tropic of Cancer and the Equator,

680-433: A date that currently corresponds with 7 January on the more widely used Gregorian Calendar (which is also when Christmas is observed in many Eastern Orthodox countries such as Russia). The 25 December Nativity of Christ was alleged very early by Hippolytus of Rome (170–236) in his Commentary on Daniel 4:23: "The first coming of our Lord, that in the flesh, in which he was born at Bethlehem, took place eight days before

765-548: A small part of South America . During the 2.5 million years of the Pleistocene , numerous cold phases called glacials ( Quaternary ice age ), or significant advances of continental ice sheets, in Europe and North America , occurred at intervals of approximately 40,000 to 100,000 years. The long glacial periods were separated by more temperate and shorter interglacials which lasted about 10,000–15,000 years. The last cold episode of

850-425: Is ⁠365 + 97 / 400 ⁠ days = 365.2425 days, or 365 days, 5 hours, 49 minutes and 12 seconds. The Gregorian calendar was a reform of the Julian calendar. It was instituted by papal bull Inter gravissimas dated 24 February 1582 by Pope Gregory XIII, after whom the calendar is named. The motivation for the adjustment was to bring the date for the celebration of Easter to the time of year in which it

935-468: Is 365.2425463 days. 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

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1020-453: Is the calendar used in most parts of the world. It went into effect in October 1582 following the papal bull Inter gravissimas 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

1105-415: Is the change from the Julian calendar to the Gregorian calendar as enacted in various European countries between 1582 and the early 20th century. In England , Wales , Ireland , and Britain's American colonies , there were two calendar changes, both in 1752. The first adjusted the start of a new year from Lady Day (25 March) to 1 January (which Scotland had done from 1600), while the second discarded

1190-482: Is the first Sunday after a full moon occurring after the northern vernal equinox , which falls on or after 21 March in Alexandria. When Julius Caesar reformed the calendar, the northern vernal equinox was nominally on 25 March which was abandoned shortly after Nicaea. The reason for the observed discrepancy was all but ignored (the actual tropical year is not quite equal to the Julian year of 365 1 ⁄ 4 days, so

1275-572: Is the half of Earth that is north of the Equator . For other planets in the Solar System , north is defined as being in the same celestial hemisphere relative to the invariable plane of the Solar System as Earth's North Pole . Due to Earth's axial tilt of 23.439281°, there is a seasonal variation in the lengths of the day and night. There is also a seasonal variation in temperatures, which lags

1360-423: Is the year using astronomical year numbering , that is, use 1 − (year BC) for BC years. ⌊ x ⌋ {\displaystyle \left\lfloor {x}\right\rfloor } means that if the result of the division is not an integer it is rounded down to the nearest integer. The general rule, in years which are leap years in the Julian calendar but not the Gregorian, is: Up to 28 February in

1445-905: 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

1530-507: 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 ", with Greece being the last European country to adopt the calendar (for civil use only) in 1923. However, many Orthodox churches continue to use the Julian calendar for religious rites and

1615-543: 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 Compendium was sent to expert mathematicians outside

1700-573: The First Council of Nicaea in AD 325, 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: Thursday 4 October 1582

1785-460: The Northern temperate zone . The changes in these regions between summer and winter are generally mild, rather than extreme hot or cold. However, a temperate climate can have very unpredictable weather. Tropical regions (between the Tropic of Cancer and the Equator, 0° latitude) are generally hot all year round and tend to experience a rainy season during the summer months, and a dry season during

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1870-524: The Roman Republic and the Roman Empire was the consular year, which began on the day when consuls first entered 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, continued to use 1 January as the first day of the new year . Even though the year used for dates changed, the civil year always displayed its months in

1955-478: The calendar year and the astronomical year . Within the Northern Hemisphere, oceanic currents can change the weather patterns that affect many factors within the north coast. Such events include El Niño–Southern Oscillation . Trade winds blow from east to west just above the equator. The winds pull surface water with them, creating currents, which flow westward due to the Coriolis effect . The currents then bend to

2040-566: The last glacial period ended about 10,000 years ago. Earth is currently in an interglacial period of the Quaternary , called the Holocene . The glaciations that occurred during the glacial period covered many areas of the Northern Hemisphere. The Arctic is a region around the North Pole (90° latitude ). Its climate is characterized by cold winters and cool summers. Precipitation mostly comes in

2125-501: 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: 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. There were two reasons to establish

2210-538: The Coptic Liturgy. This calendar is still in use all over Egypt by farmers to keep track of the various agricultural seasons. The Coptic calendar has 13 months, 12 of 30 days each and one at the end of the year of five days (six days in leap years). The Coptic Leap Year follows the same rules as the Julian Calendar so that the extra month always has six days in the year before a Julian Leap Year. The year starts on

2295-452: The Coptic pope, and Pope Francis , the Catholic pope, agreed to the proposal to celebrate Easter on the same day. Pope Tawadros's suggested to celebrate Easter on the second Sunday of April. The following table refers to dates for Coptic years not containing 29 February . Such years are preceded by a Coptic leap day at the end of the preceding year. This causes dates to move one day later in

2380-460: 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). A month after having decreed the reform, the pope (with a brief of 3 April 1582) granted to one Antoni Lilio the exclusive right to publish the calendar for a period of ten years. The Lunario Novo secondo la nuova riforma

2465-401: 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. It

2550-571: The Feast of Neyrouz , the first day of the month of Thout , the first month of the Egyptian year. For 1900 to 2099 it coincides with the Gregorian Calendar's 11 September, or 12 September before a leap year, but for any year, it coincides with the Julian Calendar's 29 August, or 30 August before a leap year. Coptic years are counted from 284 AD, the year Diocletian became Roman Emperor, whose reign

2635-490: 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

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2720-409: The Gregorian calendar. D = ⌊ Y / 100 ⌋ − ⌊ Y / 400 ⌋ − 2 , {\displaystyle D=\left\lfloor {Y/100}\right\rfloor -\left\lfloor {Y/400}\right\rfloor -2,} where D {\displaystyle D} is the secular difference and Y {\displaystyle Y}

2805-412: 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 . Second, in the years since

2890-595: 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

2975-482: The Julian and Coptic calendars. Furthermore, the Gregorian calendar drops 3 leap days every 400 years to closely approximate the length of a solar year. As a result, the Coptic Christmas advances a day each time the Gregorian calendar drops a leap day (years AD 1700, 1800, and 1900). This is the reason why Old-Calendarists (using the Julian and Coptic calendars) presently celebrate Christmas on 7 January, 13 days after

3060-631: The Julian and Gregorian Calendars from the Coptic New Year's Day until the leap day of the Julian or Gregorian Calendar respectively. Sahidic: Greek ἐπαγόμεναι < ἐπαγωγή < ἐπαγειν < ἐπι + ἄγειν : to bring in Giustino de Jacobis (Roman Catholic), Nine Saints  • Armenian Apostolic liturgical calendar , Coptic calendar , Eastern Orthodox liturgical calendar  • [REDACTED] Category:Ethiopian saints Gregorian calendar The Gregorian calendar

3145-515: The Julian calendar in favour of the Gregorian calendar, removing 11 days from the September 1752 calendar to do so. To accommodate the two calendar changes, writers used dual dating to identify a given day by giving its date according to both styles of dating. For countries such as Russia where no start of year adjustment took place, O.S. and N.S. simply indicate the Julian and Gregorian dating systems. Many Eastern Orthodox countries continue to use

3230-574: The Nativity under the name "Epiphany." John Chrysostom, in a sermon preached in Antioch in 387, relates how the correct date of the Nativity was brought to the East ten years earlier. Dionysius of Alexandria emphatically quoted mystical justifications for this very choice. 25 March was considered to be the anniversary of Creation itself. It was the first day of the year in the medieval Julian, or Old Style, calendar and

3315-555: The New-Calendarists (using the Gregorian calendar), who celebrate Christmas on 25 December. From AD 2101, the Coptic Christmas will be on the Gregorian date of 8 January. The First Council of Nicaea (325) sent a letter to the Church of Alexandria stating "all our brethren in the East who formerly followed the custom of the Jews are henceforth to celebrate the said most sacred feast of Easter at

3400-704: The Sun can be seen to the north, directly overhead, or to the south at noon, depending on the time of year. In the Southern Hemisphere, the midday Sun is predominantly in the north. When viewed from the Northern Hemisphere, the Moon appears inverted compared to a view from the Southern Hemisphere. The North Pole faces away from the Galactic Center of the Milky Way . This results in the Milky Way being sparser and dimmer in

3485-478: 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. 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

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3570-504: The birth of Christ, Christmas , on 25 December. There may have been more practical considerations for choosing 25 December. The choice would help substitute a major Christian holiday for the popular Pagan celebrations surrounding the Winter Solstice (Roman Sol Sticia, the three-day stasis when the sun would rise consecutively in its southernmost point before heading north, 21, 22 and 23 December. In AD 274, Emperor Aurelian had declared

3655-430: The calendar being converted from , add one day less or subtract one day more than the calculated value. Give February the appropriate number of days for the calendar being converted into . When subtracting days to calculate the Gregorian equivalent of 29 February (Julian), 29 February is discounted. Thus if the calculated value is −4 the Gregorian equivalent of this date is 24 February. The year used in dates during

3740-473: The calends of January, a Wednesday, in the forty-second year of the reign of Augustus, 5500 years from Adam." "Another early source is Theophilus Bishop of Caesarea (115–181): "We ought to celebrate the birth-day of our Lord on what day soever the 25th of December shall happen." However, it was not until 367 that 25 December began to be universally accepted. Before that, the Eastern Church had kept 6 January as

3825-458: The change a few months later: 9 December was followed by 20 December. 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

3910-516: The date of the equinox keeps creeping back in the Julian calendar). Between the Catholic Church and the Orthodox Church, there are different dates for holidays. In recent years there have been multiple attempts to unify these dates. Some people are skeptical about the success of these attempts. Eastern Orthodox use the Julian calendar while Catholics use the Gregorian calendar. Pope Tawadros ,

3995-498: 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 Gregorian calendar, like the Julian calendar , is a solar calendar with 12 months of 28–31 days each. The year in both calendars consists of 365 days, with

4080-417: 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. Gregorian years are identified by consecutive year numbers. A calendar date is fully specified by

4165-419: 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

4250-630: The form of snow. Areas inside the Arctic Circle (66°34′ latitude) experience some days in summer when the Sun never sets, and some days during the winter when it never rises. The duration of these phases varies from one day for locations right on the Arctic Circle to several months near the Pole, which is the middle of the Northern Hemisphere. Between the Arctic Circle and the Tropic of Cancer (23°26′ latitude) lies

4335-520: 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. 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

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4420-455: 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. This affected much of Roman Catholic Europe, as Philip

4505-518: 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). In decimal notation, these are equal to 0.24254606, 0.24255185, and 0.24254352, respectively. All values are

4590-456: 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, which required adoption by the civil authorities in each country to have legal effect. The bull Inter gravissimas became

4675-468: The new year was moved to 1 September. In common usage, 1 January was regarded as New Year's Day and celebrated as such, but from the 12th century until 1751 the legal year in England began on 25 March ( Lady Day ). So, for example, the Parliamentary record lists the execution of Charles I on 30 January as occurring in 1648 (as the year did not end until 24 March), although later histories adjust

4760-573: The nominal vernal equinox (it had been the actual equinox at the time of the Decree of Canopus in terms of the Julian calendar which adopted it without correction when originally designed). Considering that Jesus was thought to have been conceived on New Year's Day of the Old Style calendar, 25 March was recognised as the Feast of the Annunciation which had to be followed, nine months later, by the celebration of

4845-514: The norm, can be identified. In other countries, the customs varied, and the start of the year moved back and forth as fashion and influence from other countries dictated various customs. Neither the papal bull nor its attached canons explicitly fix such a date, though the latter states that the " Golden number " of 1752 ends in December and a new year (and new Golden number) begins in January 1753. During

4930-466: 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. The German mathematician Christopher Clavius ,

5015-451: The older Julian calendar for religious purposes. 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,

5100-599: The order January to December from the Roman Republican period until the present. During the Middle Ages, under the influence of the Catholic Church, many Western European countries moved the start of the year to one of several important Christian festivals—25 December ( Christmas ), 25 March ( Annunciation ), or Easter, while the Byzantine Empire began its year on 1 September and Russia did so on 1 March until 1492 when

5185-454: 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,

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5270-501: 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, but the project was not taken up again until the 1540s, and implemented only under Pope Gregory XIII (r. 1572–1585). In 1545,

5355-406: The putative creation of the world; it then stands for Anno Mundi . Easter is reckoned by the Julian Calendar in combination with the uncorrected repetition of the 19-year Metonic cycle . To obtain the Coptic year number, subtract from the Julian year number either 283 (before the Julian new year) or 284 (after it). Coptic Christmas is observed on what the Julian Calendar labels 25 December,

5440-480: 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. The reform adopted was a modification of a proposal made by the Calabrian doctor Aloysius Lilius (or Lilio). Lilius's proposal included reducing

5525-529: The right, heading north. At about 30 degrees north latitude, a different set of winds, the westerlies , push the currents back to the east, producing a closed clockwise loop. Its surface is 60.7% water, compared with 80.9% water in the case of the Southern Hemisphere , and it contains 67.3% of Earth's land. The continents of North America and mainland Eurasia are located entirely in the Northern Hemisphere, together with about two-thirds of Africa and

5610-410: The same basis, for years before 1582), and the difference between Gregorian and Julian calendar dates increases by three days every four centuries (all date ranges are inclusive). The following equation gives the number of days that the Gregorian calendar is ahead of the Julian calendar, called the "secular difference" between the two calendars. A negative difference means the Julian calendar is ahead of

5695-456: The same day, it took almost five centuries before virtually all Christians achieved that objective by adopting the rules of the Church of Alexandria (see Easter for the issues which arose). Because the date of Easter is a function – the computus  – of the date of the spring equinox in the northern hemisphere, the Catholic Church considered unacceptable

5780-523: The same time with the Romans and yourselves and all those who have observed Easter from the beginning." At the Council of Nicaea, it became one of the duties of the patriarch of Alexandria to determine the dates of the Easter and to announce it to the other Christian churches. This duty fell on this officiate because of the erudition at Alexandria he could draw on. The rules to determine this are complex, but Easter

5865-516: 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. 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. A commonly used value in Lilius's time, from the Alfonsine tables,

5950-437: The start of the year to 1 January and record the execution as occurring in 1649. Most Western European countries changed the start of the year to 1 January before they adopted the Gregorian calendar. For example, Scotland changed the start of the Scottish New Year to 1 January in 1600 (this means that 1599 was a short year). England, Ireland and the British colonies changed the start of the year to 1 January in 1752 (so 1751

6035-400: The variation in day and night. Conventionally, winter in the Northern Hemisphere is taken as the period from the December solstice (typically December 21 UTC ) to the March equinox (typically March 20 UTC), while summer is taken as the period from the June solstice through to the September equinox (typically on 23 September UTC). The dates vary each year due to the difference between

6120-427: 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

6205-448: The weather patterns that affect many factors within the north coast. For the same reason, flows of air down toward the northern surface of the Earth tend to spread across the surface in a clockwise pattern. Thus, clockwise air circulation is characteristic of high pressure weather cells in the Northern Hemisphere. Conversely, air rising from the northern surface of the Earth (creating a region of low pressure) tends to draw air toward it in

6290-482: The winter months. In the Northern Hemisphere, objects moving across or above the surface of the Earth tend to turn to the right because of the Coriolis effect . As a result, large-scale horizontal flows of air or water tend to form clockwise-turning gyres . These are best seen in ocean circulation patterns in the North Atlantic and North Pacific oceans. Within the Northern Hemisphere, oceanic currents can change

6375-612: The year (numbered according to a calendar era , in this case Anno Domini or Common Era ), the month (identified by name or number), and the day of the month (numbered sequentially starting from 1). Although the calendar year currently runs from 1 January to 31 December, at previous times year numbers were based on a different starting point within the calendar (see the "beginning of the year" section below). Calendar cycles repeat completely every 400 years, which equals 146,097 days. Of these 400 years, 303 are regular years of 365 days and 97 are leap years of 366 days. A mean calendar year

6460-432: 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. "Old Style" (O.S.) and "New Style" (N.S.) indicate dating systems before and after a calendar change, respectively. Usually, this

6545-474: Was a short year with only 282 days). Later in 1752 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 . In some countries, an official decree or law specified that the start of the year should be 1 January. For such countries, a specific date when a "1 January year" became

6630-636: Was at the time ruler over Spain and Portugal as well as much of Italy . In these territories, as well as in the Polish–Lithuanian Commonwealth 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 de facto because of delay in communication. The other major Catholic power of Western Europe, France, adopted

6715-457: Was celebrated when it was introduced by the early Church. The error in the Julian calendar (its assumption that there are exactly 365.25 days in a year) had led to the date of the equinox according to the calendar drifting from the observed reality, and thus an error had been introduced into the calculation of the date of Easter . Although a recommendation of the First Council of Nicaea in 325 specified that all Christians should celebrate Easter on

6800-404: Was extended to include use for general purposes and the number of the year became the same as in most other countries. This section always places the intercalary day on 29 February even though it was always obtained by doubling 24 February (the bissextum (twice sixth) or bissextile day) until the late Middle Ages . The Gregorian calendar is proleptic before 1582 (calculated backwards on

6885-415: Was followed by Friday 15 October 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. The reform was adopted initially by

6970-621: Was marked by tortures and mass executions of Christians, especially in Egypt. Hence, the Coptic year is identified by the abbreviation A.M. (for Anno Martyrum or "in the Year of the Martyrs"). The first day of year I of the Coptic era was 29 August 284 in the Julian calendar. Note that the abbreviation A.M. is also used for unrelated calendar eras (such as the Freemasonic and Jewish calendar epochs) which start at

7055-529: Was more than three days. Roger Bacon in c.  1200 estimated the error at seven or eight days. Dante , writing c.  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. The increase of astronomical knowledge and

7140-404: 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. Although Gregory's reform was enacted in

7225-412: 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. When the new calendar was put in use, the error accumulated in the 13 centuries since

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