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Encyclopedia > Leap year

A leap year (or intercalary year) is a year containing one or more extra days (or, in the case of lunisolar calendars, an extra month) in order to keep the calendar year synchronised with the astronomical or seasonal year. For example, in the Gregorian calendar, February would have 29 days in a leap year instead of the usual 28 - and consequently, the whole year would last 366 days instead of the common 365. Because seasons and astronomical events do not repeat at an exact number of full days, a calendar which had the same number of days in each year would, over time, drift with respect to the event it was supposed to track. By occasionally inserting (or intercalating) an additional day or month into the year, the drift can be corrected. A year which is not a leap year is called a common year. Roscoe Conkling Arbuckle (March 24, 1887 – June 29, 1933) was an American silent film comedian. ... Leap Year is a 1921 comedy film directed by and starring Fatty Arbuckle. ... A lunisolar calendar is a calendar whose date indicates both the moon phase and the time of the solar year. ... According to the Gregorian calendar, the calendar year begins on January 1 and ends on December 31. ... A year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... The seasonal year is the time between successive recurrences of a seasonal event such as the flooding of a river, the migration of a species of bird, or the flowering of a species of plant. ... For the calendar of religious holidays and periods, see liturgical year. ... Intercalation is the insertioffn of an extra day, week or month into some calendar years to make the calendar follow the seasons. ... A common year is a year that is common calendar year. ...

Contents

Gregorian calendar

In the Gregorian calendar, the current standard calendar in most of the world, most years whose division by 4 equals an integer are leap years. In one leap year, the month of February has 29 days instead of 28. Adding an extra day to the calendar every four years compensates for the fact that a solar year is almost 6 hours longer than 365 days. For the calendar of religious holidays and periods, see liturgical year. ... Solar year The period of time required for the earth to make one complete revolution around the sun, measured from one vernal equinox to the next. ...


However, some exceptions to this rule are required since the duration of a solar year is slightly less than 365.25 days. Years which are evenly divisible by 100 are not leap years, unless they are also evenly divisible by 400, in which case they are leap years.[1][2] For example, 1600 and 2000 were leap years, but 1700, 1800 and 1900 were not. Similarly, 2100, 2200, 2300, 2500, 2600, 2700, 2900, and 3000 will not be leap years, but 2400 and 2800 will be. By this rule, the average number of days per year will be 365 + 1/4 − 1/100 + 1/400 = 365.2425, which is 365 days, 5 hours, 49 minutes, and 12 seconds.


The Gregorian calendar was designed to keep the vernal equinox on or close to March 21, so that the date of Easter (celebrated on the Sunday after the 14th day of the Moon that falls on or after 21 March) remains correct with respect to the vernal equinox.[3] The vernal equinox year is about 365.242374 days long (and increasing), whereas the average year length of the Gregorian calendar is 365.2425. Illumination of Earth by Sun on the day of equinox The vernal equinox (or spring equinox) marks the beginning of astronomical spring. ... is the 80th day of the year (81st in leap years) in the Gregorian calendar. ... This article is about the Christian festival. ... is the 80th day of the year (81st in leap years) in the Gregorian calendar. ...


The marginal difference of 0.000125 days means that in around 8,000 years, the calendar will be about one day behind where it is now. But in 8,000 years, the length of the vernal equinox year will have changed by an amount which cannot be accurately predicted (see below). Therefore, the current Gregorian calendar suffices for practical purposes, and Herschel's correction (making 4000 AD not a leap year) will probably not be necessary. John Herschel Sir John Frederick William Herschel (7 March 1792 – 11 May 1871) was an English mathematician and astronomer. ...

Image:Gregoriancalendarleap.png
This graph shows the variation between the seasonal year versus the calendar year due to unequally spaced 'leap days' rules. See Iranian calendar to contrast with a calendar based on 8 leap days every 33 years.

Seasonal error of Gregorian calendar Originally created by Tom Ruen, 2003, using MSExcel graph, labeled with MSPaint Converted from Image:Gregoriancalendarleap. ... The Iranian calendar (Persian: ), also known as Persian calendar or (mistakenly) the Jalāli Calendar is an astronomical solar calendar currently used in Iran and Afghanistan as the main official calendar. ...

Algorithm

This algorithm determines leap years on the proleptic Gregorian calendar, which includes leap years before the official inception in 1582. The proleptic Gregorian calendar is produced by extending the Gregorian Calendar to dates preceding its official introduction in 1582. ... Gregorian Calendar switch: Year 1582 involved conversion to the Gregorian calendar. ...


Pseudocode to determine whether a year is a leap year or not: Pseudocode (derived from pseudo and code) is a compact and informal high-level description of a computer programming algorithm that uses the structural conventions of programming languages, but omits detailed subroutines, variable declarations or language-specific syntax. ...

 if year modulo 400 is 0 then leap else if year modulo 100 is 0 then no_leap else if year modulo 4 is 0 then leap else no_leap 

A more direct algorithm (terms may be grouped either way): In computing, the modulo operation finds the remainder of division of one number by another. ...

 if (year modulo 4 is 0) and (year modulo 100 is not 0) or (year modulo 400 is 0) then leap else no_leap 

Leap day

Main article: February 29

February 29 is a date that usually occurs every four years, and is called leap day. This day is added to the calendar in leap years as a corrective measure, because the earth does not orbit around the sun in precisely 365 days. February 29 is a day added into a leap year of the Gregorian calendar. ...


The Gregorian calendar is a modification of the Julian calendar first used by the Romans. The Roman calendar originated as a lunisolar calendar and named many of its days after the syzygies of the moon: the new moon (Kalendae or calends, hence "calendar") and the full moon (Idus or ides). The Nonae or nones was not the first quarter moon but was exactly one nundinae or Roman market week of nine days before the ides, inclusively counting the ides as the first of those nine days. In 1825, Ideler believed that the lunisolar calendar was abandoned about 450 BC by the decemvirs, who implemented the Roman Republican calendar, used until 46 BC. The days of these calendars were counted down (inclusively) to the next named day, so 24 February was ante diem sextum Kalendas Martii ("the sixth day before the calends of March") often abbreviated a. d. VI Kal. Mar. The Romans counted days inclusively in their calendars, so this was actually the fifth day before March 1 when counted in the modern exclusive manner (not including the starting day).[4] The Julian calendar was a reform of the Roman calendar which was introduced by Julius Caesar in 46 BC and came into force in 45 BC (709 ab urbe condita). ... The Roman calendar changed its form several times in the time between the foundation of Rome and the fall of the Roman Empire. ... A lunisolar calendar is a calendar whose date indicates both the moon phase and the time of the solar year. ... Look up Syzygy in Wiktionary, the free dictionary. ... For other uses, see Full Moon. ... Lunar phase refers to the appearance of the illuminated portion of the Moon as seen by an observer, usually on Earth. ... Christian Ludwig Ideler (September 21, 1766 - August 10, 1846), German chronologist and astronomer, was born near Perleberg on the 21st of September 1766. ... Centuries: 6th century BC - 5th century BC - 4th century BC Decades: 500s BC 490s BC 480s BC 470s BC 460s BC - 450s BC - 440s BC 430s BC 420s BC 410s BC 400s BC Years: 455 BC 454 BC 453 BC 452 BC 451 BC - 450 BC - 449 BC 448 BC... Decemviri (sing. ... The Roman calendar changed its form several times in the time between the foundation of Rome and the fall of the Roman Empire. ... is the 55th day of the year in the Gregorian calendar. ... Ancient Rome was a civilization that grew from a small agricultural community founded on the Italian Peninsula circa the 9th century BC to a massive empire straddling the Mediterranean Sea. ... is the 60th day of the year (61st in leap years) in the Gregorian calendar. ...


The Republican calendar's intercalary month was inserted on the first or second day after the Terminalia (a. d. VII Kal. Mar., February 23). The remaining days of Februarius were dropped. This intercalary month, named Intercalaris or Mercedonius, contained 27 days. The religious festivals that were normally celebrated in the last five days of February were moved to the last five days of Intercalaris. Because only 22 or 23 days were effectively added, not a full lunation, the calends and ides of the Roman Republican calendar were no longer associated with the new moon and full moon. In Roman mythology, Terminus was the god of boundaries. ... is the 54th day of the year in the Gregorian calendar. ... Mercedonius was a month in the ancient Roman calendar. ...


The Julian calendar, which was developed in 46 BC by Julius Caesar, and became effective in 45 BC, distributed an extra ten days among the months of the Roman Republican calendar. Caesar also replaced the intercalary month by a single intercalary day, located where the intercalary month used to be. To create the intercalary day, the existing ante diem sextum Kalendas Martii (February 24) was doubled, producing ante diem bis sextum Kalendas Martii. Hence, the year containing the doubled day was a bissextile (bis sextum, "twice sixth") year. For legal purposes, the two days of the bis sextum were considered to be a single day, with the second half being intercalated, but common practice by 238, when Censorinus wrote, was that the intercalary day was followed by the last five days of February, a. d. VI, V, IV, III and pridie Kal. Mar. (which would be those days numbered 24, 25, 26, 27, and 28 from the beginning of February in a common year), i.e. the intercalated day was the first half of the doubled day. All later writers, including Macrobius about 430, Bede in 725, and other medieval computists (calculators of Easter), continued to state that the bissextum (bissextile day) occurred before the last five days of February. The Julian calendar was a reform of the Roman calendar which was introduced by Julius Caesar in 46 BC and came into force in 45 BC (709 ab urbe condita). ... Centuries: 2nd century BC - 1st century BC - 1st century Decades: 90s BC 80s BC 70s BC 60s BC 50s BC - 40s BC - 30s BC 20s BC 10s BC 0s BC 0s Years: 51 BC 50 BC 49 BC 48 BC 47 BC 46 BC 45 BC 44 BC 43 BC... For other uses, see Julius Caesar (disambiguation). ... Centuries: 2nd century BC - 1st century BC - 1st century Decades: 90s BC 80s BC 70s BC 60s BC 50s BC - 40s BC - 30s BC 20s BC 10s BC 0s BC 0s Years: 50 BC 49 BC 48 BC 47 BC 46 BC 45 BC 44 BC 43 BC 42 BC... is the 55th day of the year in the Gregorian calendar. ... Censorinus, Roman grammarian and miscellaneous writer, flourished during the 3rd century AD. He was the author of a lost work De Accentibus and of an extant treatise De Die Natali, written in 238, and dedicated to his patron Quintus Caerellius as a birthday gift. ... Ambrosius Theodosius Macrobius, Roman grammarian and philosopher, flourished during the reigns of Honorius and Arcadius (395-423). ... For other uses, see Bede (disambiguation). ... Computus (Latin for computation) is the calculation of the date of Easter in the Christian calendar. ... This article is about the Christian festival. ...


Until 1970, the Roman Catholic Church always celebrated the feast of Saint Matthias on a. d. VI Kal. Mar., so if the days were numbered from the beginning of the month, it was named February 24 in common years, but the presence of the bissextum in a bissextile year immediately before a. d. VI Kal. Mar. shifted the latter day to February 25 in leap years, with the Vigil of St. Matthias shifting from February 23 to the leap day of February 24. Other feasts normally falling on February 25–28 in common years are also shifted to the following day in a leap year (although they would be on the same day according to the Roman notation). The practice is still observed by those who use the older calendars. Catholic Church redirects here. ... This article is about the New Testament figure. ... is the 55th day of the year in the Gregorian calendar. ... is the 56th day of the year in the Gregorian calendar. ... Vigil, tacuinum sanitatis casanatensis (XIV century) This article is about the period of sleeplessness. ... is the 54th day of the year in the Gregorian calendar. ... is the 55th day of the year in the Gregorian calendar. ...


Julian, Coptic and Ethiopian calendars

The Julian calendar adds an extra day to February in years evenly divisible by four. The Julian calendar was a reform of the Roman calendar which was introduced by Julius Caesar in 46 BC and came into force in 45 BC (709 ab urbe condita). ...


The Coptic calendar and Ethiopian calendar also add an extra day to the end of the year once every four years before a Julian 29-day February. The Coptic calendar, also called the Alexandrian calendar, is used by the Coptic Orthodox Church. ... The Ethiopian calendar (Amharic: የኢትዮጵያ ዘመን አቆጣጠር ), also called the Geez calendar, is the principal calendar used in Ethiopia and is also the liturgical year of Christians in Eritrea belonging to the Eritrean Orthodox Tewahdo Church, Eastern Catholic Church of Eritrea and Lutheran (Evangelical Church of Eritrea), where it is commonly known...


This rule gives an average year length of 365.25 days. However, it is 11 minutes longer than a real year. This means that the vernal equinox moves a day earlier in the calendar every 131 years.


Revised Julian calendar

The Revised Julian calendar adds an extra day to February in years divisible by four, except for years divisible by 100 that do not leave a remainder of 200 or 600 when divided by 900. This rule agrees with the rule for the Gregorian calendar until 2799. The first year that dates in the Revised Julian calendar will not agree with those in the Gregorian calendar will be 2800, because it will be a leap year in the Gregorian calendar but not in the Revised Julian calendar. The Revised Julian calendar is a calendar that was considered for adoption by the Eastern Orthodox churches at a synod in Istanbul in May 1923. ...


This rule gives an average year length of 365.242222… days. This is a very good approximation to the mean tropical year, but because the vernal equinox year is slightly longer, the Revised Julian calendar does not do as good a job as the Gregorian calendar of keeping the vernal equinox on or close to 21 March. A tropical year is the length of time that the Sun, as viewed from the Earth, takes to return to the same position along the ecliptic (its path among the stars on the celestial sphere). ... is the 80th day of the year (81st in leap years) in the Gregorian calendar. ...


Chinese calendar

The Chinese calendar is lunisolar, so a leap year has an extra month, often called an embolismic month after the Greek word for it. In the Chinese calendar the leap month is added according to a complicated rule, which ensures that month 11 is always the month that contains the northern winter solstice. The intercalary month takes the same number as the preceding month; for example, if it follows the second month (二月) then it is simply called "leap second month" (traditional Chinese: 閏二月; simplified Chinese: 闰二月; pinyin: rùn'èryuè). The Chinese calendar is a lunisolar calendar, incorporating elements of a lunar calendar with those of a solar calendar. ... A lunisolar calendar is a calendar whose date indicates both the moon phase and the time of the solar year. ... Intercalation is the insertion of an extra day or month into some calendar years to make the calendar follow the seasons. ... “Summer solstice” redirects here. ... Traditional Chinese characters refers to one of two standard sets of printed Chinese characters. ... Simplified Chinese character (Simplified Chinese: or ; traditional Chinese: or ; pinyin: or ) is one of two standard sets of Chinese characters of the contemporary Chinese written language. ... Pinyin, more formally called Hanyu Pinyin (Simplified Chinese: ; Traditional Chinese: ; Pinyin: ), is the most common variant of Standard Mandarin romanization system in use. ...


Hebrew calendar

The Hebrew calendar is also lunisolar with an embolismic month. This extra month is called Adar Alef (first Adar) and is added before Adar, which then becomes Adar Bet (second Adar). According to the Metonic cycle, this is done seven times every nineteen years (specifically, in years 3, 6, 8, 11, 14, 17, and 19). The Hebrew calendar (‎) or Jewish calendar is the calendar used by Jews for religious purposes. ... Adar (אֲדָר, Standard Hebrew Adar, Tiberian Hebrew ʾĂḏār: from Akkadian adaru) is the sixth month of the ecclesiastical year and the twelfth month of the civil year on the Hebrew calendar. ... Adar (אֲדָר, Standard Hebrew Adar, Tiberian Hebrew ʾĂḏār: from Akkadian adaru) is the sixth month of the religious year and the twelfth month of the civil year on the Hebrew calendar. ... Adar (אֲדָר, Standard Hebrew Adar, Tiberian Hebrew ʾĂḏār: from Akkadian adaru) is the sixth month of the ecclesiastical year and the twelfth month of the civil year on the Hebrew calendar. ... The Metonic cycle or Enneadecaeteris in astronomy and calendar studies is a particular approximate common multiple of the year (specifically, the seasonal tropical year) and the synodic month. ...


In addition, the Hebrew calendar has postponement rules that postpone the start of the year by one or two days. These postponement rules reduce the number of different combinations of year length and starting days of the week from 28 to 14, and regulate the location of certain religious holidays in relation to the Sabbath. In particular, the first day of the Hebrew year can never be Sunday, Wednesday or Friday. This rule is known in Hebrew as "lo adu rosh", i.e. "Rosh [ha-Shanah, first day of the year] is not Sunday, Wednesday or Friday" (as the Hebrew word adu is written by three Hebrew letters signifying Sunday, Wednesday and Friday). Accordingly, the first day of Pesah (Passover) is never Monday, Wednesday or Friday. This rule is known in Hebrew as "lo badu Pesah", which has a double meaning — "Pesah is not a legend", but also "Pesah is not Monday, Wednesday or Friday" (as the Hebrew word badu is written by three Hebrew letters signifying Monday, Wednesday and Friday). This article is about days of the week. ... For other uses, see Sabbath. ... Note: This article contains special characters. ... Passover, also known as Pesach or Pesah (פסח pesaḥ), is a Jewish holiday (lasting seven days in Israel and among some liberal Diaspora Jews, and eight days among other Diaspora Jews) that commemorates the exodus and freedom of the Israelites from Egypt; it is also observed by some Christians to...


One reason for this rule is that Yom Kippur, the holiest day in the Hebrew calendar, must never be adjacent to the weekly Sabbath (which is Saturday), i.e. it must never fall on Friday or Sunday, in order not to have two adjacent Sabbath days. However, Yom Kippur can be on Saturday. Yom Kippur (Hebrew:יוֹם כִּפּוּר ) is a Jewish holiday, known in English as the Day of Atonement. ... For other uses, see Sabbath. ...


Years consisting of 12 months have between 353 and 355 days. In a k'sidra ("in order") 354-day year, months have alternating 30 and 29 day lengths. In a chaser ("lacking") year, the month of Kislev is reduced to 29 days. In a malei ("filled") year, the month of Cheshvan is increased to 30 days. 13-month years follow the same pattern, with the addition of the 30-day Adar Alef, giving them between 383 and 385 days. Kislev (or Chisleu) (Hebrew: כִּסְלֵו, Standard Kislev Tiberian  ; from Akkadian kislimu) is the third month of the ecclesiastical year and the ninth month of the civil year on the Hebrew calendar. ... Cheshvan (חֶשְׁוָן, Standard Hebrew ḤeÅ¡van, Tiberian Hebrew ḪeÅ¡wān, ḤeÅ¡wān, short for מַרְחֶשְׁוָן, Standard Hebrew MarḥeÅ¡van, Tiberian Hebrew MarḫeÅ¡wān, MarḥeÅ¡wān: from Akkadian waraḫsamnu, literally eighth month) is the second month of the ecclesiastical year and the eighth month of...


Islamic calendar

In the Islamic calendar, leap months are not used. The Qur'an says: The Islamic calendar or Muslim calendar (Arabic: التقويم الهجري; at-taqwīm al-hijrī; Persian: تقویم هجري قمری ‎ taqwīm-e hejri-ye qamari; also called the Hijri calendar) is the calendar used to date events in many predominantly Muslim countries, and used by Muslims everywhere to determine the proper day on which to celebrate... The Qur’ān [1] (Arabic: , literally the recitation; also sometimes transliterated as Quran, Koran, or Al-Quran) is the central religious text of Islam. ...

The number of months with Allah has been twelve months by Allah's ordinance since the day He created the heavens and the earth. Of these four are known as sacred; That is the straight usage, so do not wrong yourselves therein, and fight those who go astray collectively as they fight against you collectively. But know that Allah is with those who are pious.
Verily the transposing (of a prohibited month) is an addition to Unbelief: The Unbelievers are led to wrong thereby: for they make it lawful one year, and forbidden another year, of months forbidden by Allah and make such forbidden ones lawful. The evil of their course seems pleasing to them. But Allah guideth not those who reject Faith. (Qur'an 9:36-37)

Calendars with Leap Years synchronized with Gregorian

The Indian National Calendar and the Revised Bangla Calendar of Bangladesh organise their leap years so that the leap day is always close to February 29 in the Gregorian calendar. This makes it easy to convert dates to or from Gregorian. The Indian national calendar (sometimes called Saka calendar) is the official civil calendar in use in India. ... The Bangla calendar also known as Bônggabdo in the Bengali language, is the traditional calendar used in Bangladesh and Bangla-speaking regions of India. ... February 29 is a day added into a leap year of the Gregorian calendar. ... For the calendar of religious holidays and periods, see liturgical year. ...


The Bahá'í calendar is structured such that the leap day always falls within Ayyám-i-Há, a period of four or five days corresponding to Gregorian February 26March 1. Because of this, Baha'i dates consistently line up with exactly one Gregorian date. The Baháí calendar, also called the Badí‘ calendar, used by the Baháí Faith, is a solar calendar with regular years of 365 days, and leap years of 366 days. ... Ayyám-i-Há refers to a period of four or five intercalary days in the Baháí calendar, where Baháís celebrate the Festival of Ayyám-i-Há.[1] The four or five days occur in between the 18th and 19th months of the calender from February 26 to... is the 57th day of the year in the Gregorian calendar. ... is the 60th day of the year (61st in leap years) in the Gregorian calendar. ...


The Thai solar calendar uses the Buddhist Era (BE), but has been synchronized with the Gregorian since AD 1941. The Thai solar, or Suriyakati (สุริยคติ), calendar is used in traditional and official contexts in Thailand, although the Western calendar is sometimes used in business. ... The Thai solar, or Suriyakati (สุริยคติ), calendar is used in traditional and official contexts in Thailand, although the Western calendar is sometimes used in business. ... Look up AD, ad-, and ad in Wiktionary, the free dictionary. ... For other uses, see 1941 (disambiguation). ...


Hindu calendar

In the Hindu calendar, which is a lunisolar calendar, the embolismic month is called adhika maas (extra month). It is the month in which the sun is in the same sign of the stellar zodiac on two consecutive dark moons. Adhika Maas typically occurs once every 3 years, or 4 times over 11 years. So the yearly lag of a lunar year (which tends to have ten fewer days (355-356 days) per year than solar calendar) is adjusted every 3 years. Thus, Hindu festivals tend to occur within a given span. For example: the No Moon during Diwali festival tends to occur between October 22 and November 15. A page from the Hindu calendar 1871-72. ... A lunisolar calendar is a calendar whose date indicates both the moon phase and the time of the solar year. ...


Iranian calendar

The Iranian calendar also has a single intercalated day once in every four years, but every 33 years or so the leap years will be five years apart instead of four years apart. The system used is more accurate and more complicated, and is based on the time of the March equinox as observed from Tehran. The 33-year period is not completely regular; every so often the 33-year cycle will be broken by a cycle of 29 or 37 years. The Iranian calendar (Persian: ), also known as Persian calendar or (mistakenly) the Jalāli Calendar is an astronomical solar calendar currently used in Iran and Afghanistan as the main official calendar. ... For other uses, see Tehran (disambiguation). ...


Long term leap year rules

The accumulated difference between the Gregorian calendar and the vernal equinoctial year amounts to 1 day in about 8,000 years. This suggests that the calendar needs to be improved by another refinement to the leap year rule: perhaps by avoiding leap days in years evenly divisible by 8,000.


(The most common such proposal is to avoid leap years in years evenly divisible by 4,000.[5] This is based on the difference between the Gregorian calendar and the mean tropical year. Others claim, erroneously, that the Gregorian calendar itself already contains a refinement of this kind.[6])


A system of 128-year-based leap years has been proposed,[7] and it can be adopted directly without any modification to current leap year calculations until the year 2048 because no year between now and 2048 is divisable by 128. This rule gives a mean year of 365 + 1/4 − 1/128 = 365.2578125 days, which is 365 days, 6 hours, 11 minutes, and 15 seconds.


However, there is little point in planning a calendar so far ahead because over a timescale of tens of thousands of years the number of days in a year will change for a number of reasons, most notably:

  1. Precession of the equinoxes moves the position of the vernal equinox with respect to perihelion and so changes the length of the vernal equinoctial year.
  2. Tidal acceleration from the sun and moon slows the rotation of the earth, making the day longer.

In particular, the second component of change depends on such things as post-glacial rebound and sea level rise due to climate change. We can't predict these changes accurately enough to be able to make a calendar that will be accurate to a day in tens of thousands of years. Precession of the equinoxes refers to the precession of the Earths axis of rotation. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... It has been suggested that Tidal friction be merged into this article or section. ... Changes in the elevation of Lake Superior due to glaciation and post-glacial rebound Post-glacial rebound (sometimes called continental rebound, isostatic rebound or isostatic adjustment) is the rise of land masses that were depressed by the huge weight of ice sheets during the last ice age, through a process... Sea level measurements from 23 long tide gauge records in geologically stable environments show a rise of around 20 centimeters per century (2 mm/year). ... Variations in CO2, temperature and dust from the Vostok ice core over the last 450,000 years For current global climate change, see Global warming. ...


Folk traditions

In the English speaking world, it is a tradition that women may propose marriage only on leap years. While it has been argued that the tradition was initiated by Saint Patrick or Brigid of Kildare in 5th century Ireland, it is dubious as the tradition has not been attested before the 19th century.[8] Supposedly, a 1288 law by Queen Margaret of Scotland (then age five and living in Norway), required that fines be levied if a marriage proposal was refused by the man; compensation ranged from a kiss to £1 to a silk gown, in order to soften the blow.[9] Because men felt that put them at too great a risk, the tradition was in some places tightened to restricting female proposals to the modern leap day, 29 February, or to the medieval leap day, 24 February. According to Felten: "A play from the turn of the 17th century, 'The Maydes Metamorphosis,' has it that 'this is leape year/women wear breeches.' A few hundred years later, breeches wouldn't do at all: Women looking to take advantage of their opportunity to pitch woo were expected to wear a scarlet petticoat -- fair warning, if you will."[10] For other uses, see Tradition (disambiguation). ... St Patrick redirects here, for other uses, see St. ... Saint Brigid redirects here. ... Europe in 450 The 5th century is the period from 401 to 500 in accordance with the Julian calendar in the Christian Era. ... Alternative meaning: Nineteenth Century (periodical) (18th century — 19th century — 20th century — more centuries) As a means of recording the passage of time, the 19th century was that century which lasted from 1801-1900 in the sense of the Gregorian calendar. ... Events February 22 - Nicholas IV becomes Pope. ... Margaret (9 April 1283– 26 September 1290), usually known as the Maid of Norway (Norwegian: , literally The Virgin of Norway), sometimes known as Margaret of Scotland (Margrete av Skottland), was a Norwegian–Scottish princess who is widely considered to have been Queen of Scots from 1286 until her death, although... February 29 is a day added into a leap year of the Gregorian calendar. ... is the 55th day of the year in the Gregorian calendar. ...


In Denmark, the tradition is that women may propose on leap day 24 February and that refusal must be compensated with 12 pairs of gloves. is the 55th day of the year in the Gregorian calendar. ...


In Greece, it is believed that getting married in a leap year is bad luck for the couple[citation needed]. Thus, mainly in the middle of the past century, couples avoided setting a marriage date in a leap year. This article is about fortune. ...

Birthdays

A person born on February 29 may be called a "leapling" or a "leaper" [11]. In common years they usually celebrate their birthdays on 28 February or 1 March. February 29 is a day added into a leap year of the Gregorian calendar. ... For other uses, see Birthday (disambiguation). ... is the 59th day of the year in the Gregorian calendar. ... is the 60th day of the year (61st in leap years) in the Gregorian calendar. ...


For legal purposes, their legal birthdays depend on how different laws count time intervals. In Taiwan, for example, the legal birthday of a leapling is 28 February in common years, so a Taiwanese leapling born on February 29, 1980 would have legally reached 18 years old on February 28, 1998. is the 59th day of the year in the Gregorian calendar. ... February 29 is a day added into a leap year of the Gregorian calendar. ... Year 1980 (MCMLXXX) was a leap year starting on Tuesday (link displays the 1980 Gregorian calendar). ... is the 59th day of the year in the Gregorian calendar. ... Year 1998 (MCMXCVIII) was a common year starting on Thursday (link will display full 1998 Gregorian calendar). ...

If a period fixed by weeks, months, and years does not commence from the beginning of a week, month, or year, it ends with the ending of the day which proceeds the day of the last week, month, or year which corresponds to that on which it began to commence. But if there is no corresponding day in the last month, the period ends with the ending of the last day of the last month.[12]

In some situations, March 1 is used as the birthday in a non-leap year since it then is the day just after February 28.


There are many instances in children's literature where a person's claim to be only a quarter of their actual age turns out to be based on counting their leap-year birthdays. A similar device is used in the plot of Gilbert and Sullivan's 1879 comic opera The Pirates of Penzance: As a child, Frederic was apprenticed to a band of pirates until the age of 21. Now, having passed his 21st year, he leaves the pirate band and falls in love. However, it turns out that the pirate indenture says that his apprenticeship does not end until his 21st birthday, and since he was born on February 29, that day will not arrive until he is in his eighties, and so he must leave his fiancée and return to the pirates. Of course, it all turns out happily in the end. W. S. Gilbert Arthur Sullivan Gilbert and Sullivan refers to the Victorian era partnership of librettist W. S. Gilbert (1836–1911) and composer Arthur Sullivan (1842–1900). ... Comic opera, or light opera, denotes a sung dramatic work of a light or comic nature, usually with a happy ending. ... Drawing of the Act I finale The Pirates of Penzance, or The Slave of Duty, is a comic opera in two acts, with music by Arthur Sullivan and libretto by W. S. Gilbert. ... If youre looking for the TV show, see The Apprentice. ... Look up pirate and piracy in Wiktionary, the free dictionary. ... An Indentured servant is an unfree labourer under contract to work (for a specified amount of time) for another person, often without any pay, but in exchange for accommodation, food, other essentials and/or free passage to a new country. ...


According to DC Comics editor Julius Schwartz, the birth date of Superman is February 29th. This was chosen both as a way to keep the character young as well as account for the differences between Earth years and Kryptonian years. DC Comics is an American comic book and related media company. ... Julius Julie Schwartz (June 19, 1915 – February 8, 2004) was a comic book and pulp magazine editor, and a science fiction agent and prominent fan. ... Superman is a fictional character and comic book superhero , originally created by American writer Jerry Siegel and Canadian artist Joe Shuster and published by DC Comics. ...


See also

The leap week calendar is a reformed calendar system with a whole number of weeks every year, and with every year starting on the same weekday. ... A leap second is a one-second adjustment to civil time in order to keep it close to the mean solar time. ... Zellers congruence is an algorithm devised by Christian Zeller to calculate the day of the week for any calendar date. ...

References

  1. ^ Royal Observatory, Greenwich: Which years are leap years?
  2. ^ USNO (U.S. Naval Observatory): Leap Years
  3. ^ E.G. Richards, Mapping time: The calendar and its history, p. 240, ISBN 0-19-282065-7
  4. ^ Thomas Hewitt Key, Calendarium (1875)
  5. ^ Google search for 4000-year rule.
  6. ^ The Straight Dope with 4000-year rule
  7. ^ Julian Date Calculator
  8. ^ The Privilege of Ladies by Barbara Mikkelson
  9. ^ Virtually no laws of Margaret survive. Indeed, none concerning her subjects are recorded in the twelve volume Acts of the Parliaments of Scotland (1814–75) covering the period 1124–1707 (two laws concerning young Margaret herself are recorded on pages 424 & 441–2 of volume I).
  10. ^ The Bissextile Beverage - WSJ.com
  11. ^ Hall, Christina (2008-02-29), "Leap year babies hop through hoops of joy, pain of novelty birthday", Detroit Free Press, <http://www.freep.com/apps/pbcs.dll/article?AID=/20080229/NEWS05/802290352>. Retrieved on 29 February 2008
  12. ^ Article 121 of the Civil Code Part I General Principles of the Republic of China in effect in Taiwan

For the Chinese civilization, see China. ...

External links

A tropical year is the length of time that the Sun, as viewed from the Earth, takes to return to the same position along the ecliptic (its path among the stars on the celestial sphere). ... For other uses, see Equinox (disambiguation). ... “Summer solstice” redirects here. ... This article is about days of the week. ... This article details various mathematical algorithms to calculate the day of the week for any particular date in the past or future. ... The days of the year are sometimes designated letters A, B, C, D, E, F and G in a cycle of 7 as an aid for finding the day of week of a given calendar date and in calculating Easter. ... The International Commission on Stratigraphy concerns itself with stratigraphy on a global scale. ... // For other uses, see time scale. ... Dating material drawn from the archaeological record can made by a direct study of a artifact or may be deduced by association with materials found in the context the item is drawn from or inferred by its point of discovery in the sequence relative to datable contexts. ... The precession of Earths axis of rotation with respect to inertial space is also called the precession of the equinoxes. ... Sidereal time is time measured by the apparent diurnal motion of the vernal equinox, which is very close to, but not identical with, the motion of stars. ... // Galactic time NGC 4414, a typical spiral galaxy alike our Milky Way Galactic time, not to confuse with siderial time, is the time that is described by our spin relative to the center of the galaxy. ... The Furlong/Firkin/Fortnight (FFF) system is a set of units that uses impractical and outdated measurements. ... A fortnight is a unit of time equal to two weeks: that is 14 days, or literally 14 nights. ... The term jiffy (or jiffie) is used in different applications for various different short periods of time, usually 1/60 of a second. ... Lustrum was a sacrifice for expiation and purification offered by one of the censors of Rome in name of the Roman people at the close of the taking of the census, and which took place after a period of five years, so that the name came to denote a period... A saeculum is a length of time roughly equal to the lifetime of a person, or about 90 years. ... A shake is an informal unit of time equal to 10 nanoseconds, or 10-8 seconds. ... A tide is an obsolete or archaic term for time, period or season, such as eventide, shrovetide, Eastertide, etc. ... For the novel by Michael Crichton, see Timeline (novel). ... A duration is an amount of time or a particular time interval. ... In computer science and computer programming, system time represents a computer systems notion of the passing of time. ... // Definition and history Psychologists have investigated mental chronometry for over 100 years. ... The time value of money is the premise that an investor prefers to receive a payment of a fixed amount of money today, rather than an equal amount in the future, all else being equal. ...

  Results from FactBites:
 
Why Leap Years? (898 words)
Between 1904 and 2096, leap years with same day of week for each date repeat every 28 years which means that the last time February had 5 Fridays was in 1980 and next time will be in 2036.
A leap year is a year with one extra day inserted into February, the leap year is 366 days with 29 days in February as opposed to the normal 28 days.
This means that year 1800, 1900, 2100, 2200, 2300 and 2500 are NOT leap years, while year 2000 and 2400 are leap years.
NationMaster - Encyclopedia: Leap year starting on Monday (407 words)
A leap year (or intercalary year) is a year containing an extra day or month in order to keep the calendar year in sync with an astronomical or seasonal year.
Leap years (which keep the calendar in sync with the year) should not be confused with leap seconds (which keep clock time in sync with the day).
Thus 1996 was a leap year whereas 1999 was not, and 1600, 2000 and 2400 are leap years but 1700, 1800, 1900 and 2100 are not.
  More results at FactBites »

 
 

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