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92-448: The days of the 3, 5, 6, and 7 day weeks are arranged in simple recurring cycles - much like the seven days of the week in the Gregorian calendar . Because 210 is not divisible by 4, 8, or 9, extra days must be added to the 4-, 8-, and 9-day weeks. For both the 4- and 8-day weeks, the penultimate day of the week is repeated twice in the week that would have otherwise ended on the 72nd day. For

184-633: 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

276-566: 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 : Equinox A solar equinox

368-407: 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

460-605: 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

552-399: A correspondence is arbitrary. Dershowitz and Reingold chose the first Pawukon that began on a positive Julian Day Number, which was specifically JDN 146 (May 26, 4713 BCE in the proleptic Julian calendar ; April 18 of that year in the proleptic Gregorian ). The most recent Pawukon as of this writing began on Gregorian date July 5, 2020, making the date of this edit (Tuesday, January 5, 2021)

644-415: A day of the one-day week. The day in the ten-day week is the one for which the calculated value matches its urip. For example the first day of the year has a value of 9 in the five-day-week, 5 in the seven-day-week: 9+5+1-10=5, which is equivalent to the urip value of the first day of the ten-day-week, so the day is a Sri in the ten-day week. The sixth day of the year has 9 urip in the five-day-week and 6 in

736-541: A few days around the equinox when the Sun goes directly behind the satellite relative to Earth (i.e. within the beam-width of the ground-station antenna) for a short period each day. The Sun's immense power and broad radiation spectrum overload the Earth station's reception circuits with noise and, depending on antenna size and other factors, temporarily disrupt or degrade the circuit. The duration of those effects varies but can range from

828-400: A few days towards the winter side of each equinox. One result of this is that, at latitudes below ±2.0 degrees, all the days of the year are longer than the nights. The times of sunset and sunrise vary with the observer's location ( longitude and latitude ), so the dates when day and night are equal also depend upon the observer's location. A third correction for the visual observation of

920-403: A few minutes to an hour. (For a given frequency band, a larger antenna has a narrower beam-width and hence experiences shorter duration "Sun outage" windows.) Satellites in geostationary orbit also experience difficulties maintaining power during the equinox because they have to travel through Earth's shadow and rely only on battery power. Usually, a satellite travels either north or south of

1012-476: A few more details, the Pawukon is complete. The saptawara (seven-day week) is special in that each of its thirty weeks is named. When certain days of the pancawara and saptawara coincide, it is a special day. These days of conjunction are Buda-Keliwon, Saniscara-Keliwon, Buda-Wage, Anggara-Keliwon, and Redite-Keliwon. Pawukon cycles are unnumbered, so the calendar has no epoch, and the choice of date on which to base

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1104-437: A mountain peak turning gold in the sunlight long before the lower slopes are illuminated. The date on which the day and night are exactly the same is known as an equilux ; the neologism , believed to have been coined in the 1980s, achieved more widespread recognition in the 21st century. At the most precise measurements, a true equilux is rare, because the lengths of day and night change more rapidly than any other time of

1196-416: A sunrise (or sunset) is the angle between the apparent horizon as seen by an observer and the geometric (or sensible) horizon. This is known as the dip of the horizon and varies from 3 arcminutes for a viewer standing on the sea shore to 160 arcminutes for a mountaineer on Everest. The effect of a larger dip on taller objects (reaching over 2½° of arc on Everest) accounts for the phenomenon of snow on

1288-425: 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

1380-468: 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

1472-460: Is 50 arcminutes below the geometric horizon, which is the intersection with the celestial sphere of a horizontal plane through the eye of the observer. These effects make the day about 14 minutes longer than the night at the equator and longer still towards the poles. The real equality of day and night only happens in places far enough from the equator to have a seasonal difference in day length of at least 7 minutes, actually occurring

1564-479: Is a moment in time when the Sun crosses the Earth's equator , which is to say, appears directly above the equator, rather than north or south of the equator. On the day of the equinox, the Sun appears to rise "due east" and set "due west". This occurs twice each year, around 20 March and 23 September . More precisely, an equinox is traditionally defined as the time when the plane of Earth 's equator passes through

1656-453: 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

1748-415: 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

1840-423: 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

1932-905: 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

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2024-507: 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

2116-543: 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

2208-573: 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

2300-495: The March equinox , indicating that at that moment the solar declination is crossing the celestial equator in a northward direction, and southward equinox for the September equinox , indicating that at that moment the solar declination is crossing the celestial equator in a southward direction. Daytime is increasing at the fastest at the vernal equinox and decreasing at the fastest at the autumnal equinox. Systematically observing

2392-524: 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

2484-519: The atmospheric refraction is assumed to be 34 arcminutes, and the assumed semidiameter (apparent radius ) of the Sun is 16  arcminutes . (The apparent radius varies slightly depending on time of year, slightly larger at perihelion in January than aphelion in July , but the difference is comparatively small.) Their combination means that when the upper limb of the Sun is on the visible horizon, its centre

2576-448: The date of Easter , which means he wanted to move the vernal equinox to the date on which it fell at that time (21 March is the day allocated to it in the Easter table of the Julian calendar), and to maintain it at around that date in the future, which he achieved by reducing the number of leap years from 100 to 97 every 400 years. However, there remained a small residual variation in

2668-435: The sunrise , people discovered that it occurs between two extreme locations at the horizon and eventually noted the midpoint between the two. Later it was realized that this happens on a day when the duration of the day and the night are practically equal and the word "equinox" comes from Latin aequus , meaning "equal", and nox , meaning "night". In the northern hemisphere, the vernal equinox (March) conventionally marks

2760-421: The 185th day of the current cycle. Consulting the table below, we find that it is Menga, Beteng, Jaya, Umanis, Was, Anggara, Kala, Jangur, Dewa. The Saptawara maps to the Gregorian weekday cycle one-to-one, with Redite as Sunday, which provides a simple double-check mechanism: since we have Anggara on Tuesday, we have not made an obvious error in the counting. Gregorian calendar The Gregorian calendar

2852-453: 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

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2944-409: The 9-day week, the first day of the week is repeated 3 times in the first week of the 210-day Pawukon. The complexity of the calendar is increased by the calculations required to determine the arrangement of the days of the 1-, 2-, and 10-day weeks, which are not ordered in simple recurring 1, 2 and 10-day cycles. Each of the days of the five, seven, and ten day weeks has a urip, or ritual value. For

3036-460: 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

3128-401: 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

3220-474: The Earth's shadow because Earth's axis is not directly perpendicular to a line from the Earth to the Sun at other times. During the equinox, since geostationary satellites are situated above the Equator, they are in Earth's shadow for the longest duration all year. Equinoxes are defined on any planet with a tilted rotational axis. A dramatic example is Saturn, where the equinox places its ring system edge-on facing

3312-490: 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

3404-409: 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}

3496-412: 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

3588-595: 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

3680-515: 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

3772-521: The North Pole is 18 March 07:09 UTC, and sunset on the South Pole is 22 March 13:08 UTC. Also in 2021, sunrise on the South Pole is 20 September 16:08 UTC, and sunset on the North Pole is 24 September 22:30 UTC. In other words, the equinoxes are the only times when the subsolar point is on the equator, meaning that the Sun is exactly overhead at a point on the equatorial line. The subsolar point crosses

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3864-421: The Sun, atmospheric refraction , and the rapidly changing duration of the length of day that occurs at most latitudes around the equinoxes. Long before conceiving this equality, equatorial cultures noted the day when the Sun rises due east and sets due west , and indeed this happens on the day closest to the astronomically defined event. As a consequence, according to a properly constructed and aligned sundial ,

3956-450: The Sun. As a result, they are visible only as a thin line when seen from Earth. When seen from above – a view seen during an equinox for the first time from the Cassini space probe in 2009 – they receive very little sunshine ; indeed, they receive more planetshine than light from the Sun. This phenomenon occurs once every 14.7 years on average, and can last a few weeks before and after

4048-403: The Sun. It is only after a complete Gregorian leap-year cycle of 400 years that the seasons commence at approximately the same time. In the 21st century the earliest March equinox will be 19 March 2096, while the latest was 21 March 2003. The earliest September equinox will be 21 September 2096 while the latest was 23 September 2003 ( Universal Time ). On the date of

4140-478: 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

4232-595: The beginning of spring in most cultures and is considered the start of the New Year in the Assyrian calendar , Hindu, and the Persian or Iranian calendars , while the autumnal equinox (September) marks the beginning of autumn. Ancient Greek calendars too had the beginning of the year either at the autumnal or vernal equinox and some at solstices. The Antikythera mechanism predicts the equinoxes and solstices. The equinoxes are

4324-399: The calendar "drifted" with respect to the two equinoxes – so that in 300 AD the spring equinox occurred on about 21 March, and by the 1580s AD it had drifted backwards to 11 March. This drift induced Pope Gregory XIII to establish the modern Gregorian calendar . The Pope wanted to continue to conform with the edicts of the Council of Nicaea in 325 AD concerning

4416-430: 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

4508-509: 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

4600-405: The date and time of the vernal equinox of about ±27 hours from its mean position, virtually all because the distribution of 24 hour centurial leap-days causes large jumps (see Gregorian calendar leap solstice ). The dates of the equinoxes change progressively during the leap-year cycle, because the Gregorian calendar year is not commensurate with the period of the Earth's revolution about

4692-498: 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

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4784-404: The day of the seven-day week and then add one - if the sum is more than ten, then ten must be subtracted from it. This calculated value determines which day of the week it is in the 1-, 2-, and 10-day weeks. If the calculated value is even, then the day is Pepet in the two-day week and Luang in the one-day week. But, if the calculated value is odd then the day is Menga in the two-day week and is not

4876-558: The daytime duration is 12 hours. In the Northern Hemisphere , the March equinox is called the vernal or spring equinox while the September equinox is called the autumnal or fall equinox. In the Southern Hemisphere , the reverse is true. During the year, equinoxes alternate with solstices . Leap years and other factors cause the dates of both events to vary slightly. Hemisphere-neutral names are northward equinox for

4968-481: The equator moving northward at the March equinox and southward at the September equinox. When Julius Caesar established the Julian calendar in 45 BC, he set 25 March as the date of the spring equinox; this was already the starting day of the year in the Persian and Indian calendars. Because the Julian year is longer than the tropical year by about 11.3 minutes on average (or 1 day in 128 years),

5060-428: The equinox, the center of the Sun spends a roughly equal amount of time above and below the horizon at every location on the Earth, so night and day are about the same length. Sunrise and sunset can be defined in several ways, but a widespread definition is the time that the top limb of the Sun is level with the horizon. With this definition, the day is longer than the night at the equinoxes: In sunrise/sunset tables,

5152-556: The equinox; the Angkor Wat Equinox during which the sun rises in a perfect alignment over Angkor Wat in Cambodia is one such example. Catholic churches , since the recommendations of Charles Borromeo , have often chosen the equinox as their reference point for the orientation of churches . One effect of equinoctial periods is the temporary disruption of communications satellites . For all geostationary satellites, there are

5244-461: The equinoxes are currently defined to be when the apparent geocentric longitude of the Sun is 0° and 180°. The word is derived from the Latin aequinoctium , from aequus (equal) and nox (night). On the day of an equinox, daytime and nighttime are of approximately equal duration all over the planet. Contrary to popular belief, they are not exactly equal because of the angular size of

5336-466: The equinoxes. The equinoxes are sometimes regarded as the start of spring and autumn. A number of traditional harvest festivals are celebrated on the date of the equinoxes. People in countries including Iran, Afghanistan, Tajikistan celebrate Nowruz which is spring equinox in northern hemisphere. This day marks the new year in Solar Hijri calendar . Religious architecture is often determined by

5428-475: 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

5520-419: 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

5612-568: The geometric center of the Sun 's disk. Equivalently, this is the moment when Earth's rotation axis is directly perpendicular to the Sun-Earth line, tilting neither toward nor away from the Sun. In modern times , since the Moon (and to a lesser extent the planets) causes Earth's orbit to vary slightly from a perfect ellipse , the equinox is officially defined by the Sun's more regular ecliptic longitude rather than by its declination . The instants of

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5704-472: 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

5796-455: 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

5888-518: 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

5980-505: 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

6072-468: 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

6164-464: 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

6256-419: 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 ,

6348-451: 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,

6440-455: The only times when the solar terminator (the "edge" between night and day) is perpendicular to the equator. As a result, the northern and southern hemispheres are equally illuminated. For the same reason, this is also the time when the Sun rises for an observer at one of Earth's rotational poles and sets at the other. For a brief period lasting approximately four days, both North and South Poles are in daylight. For example, in 2021 sunrise on

6532-599: 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

6624-454: 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,

6716-501: 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,

6808-480: 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

6900-410: 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

6992-456: 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

7084-516: 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,

7176-399: The seven-day-week: 9+6+1-10=6, which is equivalent to the urip value of the fourth day of the ten-day-week, so the day is Manuh. Using the rules given above, the table of the days of Pawukon was constructed below. Since the days of the Pawukon, as given in the table below, do not change from one Pawukon to the next, a durable representation of the Pawukon can be used over and over again. With

7268-497: 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

7360-411: The ten-day week, the urip of the days are - from the first day to the tenth day - 5, 2, 8, 6, 4, 7, 10, 3, 9, 1. For the seven-day week, the urip of the days are - from first day to seventh day - 5, 4, 3, 7, 8, 6, and 9. For the five-day week, the urip of the days are - from the first day to the fifth day - 9, 7, 4, 8, 5. For any particular day of the Pawukon, add the urip of the day of the 5-day week to

7452-427: 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

7544-612: 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

7636-482: The year around the equinoxes. In the mid-latitudes, daylight increases or decreases by about three minutes per day at the equinoxes, and thus adjacent days and nights only reach within one minute of each other. The date of the closest approximation of the equilux varies slightly by latitude; in the mid-latitudes, it occurs a few days before the spring equinox and after the fall equinox in each respective hemisphere. Mirror-image conjugate auroras have been observed during

7728-432: 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

7820-474: 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

7912-636: 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

8004-457: 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

8096-404: 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

8188-415: 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

8280-529: 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

8372-404: 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

8464-412: 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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