Editing Leap year (section)

== Leap day in the Julian and Gregorian calendars <span class="anchor" id="Leap day"></span> ==
{{Main|February 29|Bissextus}}
{{Redirect|Leap day|other uses|Leap Day (disambiguation){{!}}Leap Day}}
[[File:Calendar-leapyeardate.jpg|thumb|right|A Swedish pocket calendar from 2008 showing 29 February]]
[[File:Japanese Calendar with Verses by Osman Edwards 1900 February.jpg|thumb|February 1900 calendar showing that 1900 was not a leap year]]

The intercalary day that usually occurs every four&nbsp;years is called leap day and is created by adding an extra day to February. This day is added to the calendar in leap years as a corrective measure because the Earth does not orbit the Sun in precisely 365&nbsp;days. Since about the 15th century, this extra day has been 29 February, but when the Julian calendar was introduced, the leap day was handled differently in two respects. First, leap day fell {{em|within}} February and not at the end: [[Bissextus|24 February was doubled]] to create, strangely to modern eyes, two days both dated 24 February.{{sfnp|Pollard|1940|p=188}} Second, the leap day was simply not counted so that a leap year still had 365&nbsp;days.{{sfnp|Cheney|2000|loc=p 145, footnote 1}}

===Early Roman practice===
{{further|Julian calendar#Motivation}}
The early [[Roman calendar]] was a lunisolar one that consisted of 12&nbsp;months, for a total of 355&nbsp;days. In addition, a 27- or 28-day [[intercalary month]], the {{lang|la|[[Mercedonius|Mensis Intercalaris]]}}, was sometimes inserted into February, at the first or second day after the {{lang|la|[[Terminus (mythology)|Terminalia]]}} {{lang|la|a. d. VII Kal. Mar.}} (23 February), to resynchronise the lunar and solar cycles. The remaining days of Februarius were discarded. This intercalary month, named {{lang|la|Intercalaris}} or {{lang|la|[[Mercedonius]]}}, contained 27&nbsp;days. The religious festivals that were normally celebrated in the last five&nbsp;days of February were moved to the last five&nbsp;days of Intercalaris. The lunisolar calendar was abandoned about 450&nbsp;BC by the {{lang|la|[[decemviri]]}},<ref>According to [[Christian Ludwig Ideler]] (1825)</ref> who implemented the [[Roman calendar|Roman Republican calendar]], used until 46&nbsp;BC. The days of these calendars were counted down (inclusively) to the next named day, so 24 February was {{lang|la|ante diem sextum Kalendas Martias}} ["the sixth day before the calends of March"] often abbreviated {{lang|la|a. d. VI Kal. Mart.}} [[Ancient Rome|The Romans]] counted days inclusively in their calendars, so this was the fifth day before 1 March when counted in the modern exclusive manner (i.e., not including both the starting and ending day).<ref name=Key>{{citation |first = Thomas Hewitt |last = Key |url=https://penelope.uchicago.edu/Thayer/E/Roman/Texts/secondary/SMIGRA*/Calendarium.html |title=Calendarium |publisher=University of Chicago| orig-year = 1875 |date=2013 |quote=the intermediate days are in all cases reckoned backward upon the Roman principle already explained of counting both extremes.}}</ref> Because only 22 or 23&nbsp;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.{{citation needed|date=February 2024}}

===Julian reform===
In Caesar's revised calendar, there was just one intercalary day{{snd}}nowadays called the leap day{{snd}}to be inserted every fourth year, and this too was done after 23 February. To create the intercalary day, the existing {{lang|la|ante diem sextum Kalendas Martias}} (sixth day (inclusive: i.e., what we would call the fifth day before) before the {{lang|la|[[Kalends]]}} (first day) of March, i.e., what we would call 24 February) was doubled,{{sfnp|Pollard|1940|p=186}} producing {{lang|la|ante diem bis sextum Kalendas Martias}} [a second sixth day before the ''Kalends''. This {{lang|la|bis sextum}} ("twice sixth") was rendered in later languages as "[[bissextile]]": the "bissextile day" is the leap day, and a "bissextile year" is a year which includes a leap day.{{sfnp|Cheney|2000|loc=Page 145, Footnote 1}} This second instance of the sixth day before the Kalends of March was inserted in calendars between the "normal" fifth and sixth days. By legal fiction, the Romans treated both the first "sixth day" and the additional "sixth day" before the Kalends of March as one day. Thus a child born on either of those days in a leap year would have its first birthday on the following sixth day before the Kalends of March. In a leap year in the original Julian calendar, there were indeed two&nbsp;days both numbered 24 February. This practice continued for another fifteen to seventeen centuries, even after most countries had adopted the Gregorian calendar.{{citation needed|date=February 2024}}

For legal purposes, the two&nbsp;days of the {{lang|la|bis sextum}} were considered to be a single day, with the second sixth being intercalated; but in common practice by the year 238, when [[Censorinus]] wrote, the intercalary day was followed by the last five&nbsp;days of February, ''a.'' ''d.'' ''VI'', ''V'', ''IV'', ''III'', and {{lang|la|pridie Kal. Mart.}} (the days numbered 24, 25, 26, 27, and 28 from the beginning of February in a common year), so that the intercalated day was the ''first'' of the doubled pair. Thus the intercalated day was effectively inserted between the 23rd and 24th days of February. All later writers, including [[Macrobius]] about 430, [[Bede]] in 725, and other medieval [[computus|computists]] (calculators of Easter), continued to state that the bissextum (bissextile day) occurred before the last five&nbsp;days of February.{{citation needed|date=December 2022}}

In England, the Church and civil society continued the Roman practice whereby the leap day was simply not counted, so that a leap year was only reckoned as 365&nbsp;days. [[Henry III of England|Henry III]]'s 1236 {{lang|la|[[Statute De Anno et Die Bissextili]]}}{{efn|''Statute concerning [the] leap year and leap day''<br />The day of the leap year, and the day before, shall be holden for one day.<ref name=Bissextili>{{citation |last1=Ruffhead |first1=Owen |title=The Statutes at Large, from Magna Charta to the End of the Last Parliament |date=1763 |publisher=Mark Basket |page=20 |url=https://archive.org/details/statutesatlargef01grea/page/20/mode/1up |access-date=21 October 2021}} (21 Hen, III)</ref>}} instructed magistrates to treat the leap day and the day before as one day.<ref name=Bissextili />{{sfnp|Cheney|2000|loc=Page 145, Footnote 1}} The practical application of the rule is obscure. It was regarded as in force in the time of the famous lawyer Sir [[Edward Coke]] (1552–1634) because he cites it in his ''[[Institutes of the Lawes of England]]''. However, Coke merely quotes the Act with a short translation and does not give practical examples.
{{blockquote|text= ... and by (b) the statute {{lang|la|de anno bissextili}}, it is provided, {{lang|la|quod computentur dies ille excrescens et dies proxime præcedens pro unico dii}}, so as in computation that day [[wiktionary:excrescent|excrescent]] is not accounted.<ref>{{cite book | title = First Part of the [[Institutes of the Lawes of England]] | date = 1628 | chapter-url= https://archive.org/details/firstpartofinsti011628coke/page/116/mode/1up?view=theater | chapter = Cap. 2, ''Of Villenage'' | page = [https://archive.org/details/firstpartofinsti011628coke/page/n287/mode/2up?view=theater 136 left (Sect. 202, line 3)] | first = Edward |last=Coke | author-link = Edward Coke }}</ref>}}

===29 February===
Replacement (by 29 February) of the awkward practice of having two days with the same date appears to have evolved by custom and practice; the etymological origin of the term "bissextile" seems to have been lost.{{sfnp|Pollard|1940|p=188}} In England in the fifteenth century, "29 February" appears increasingly often in legal documents{{snd}}although the records of the proceedings of the [[House of Commons of England]] continued to use the old system until the middle of the sixteenth century.{{sfnp|Pollard|1940|p=188}} It was not until the passage of the [[Calendar (New Style) Act 1750]] that 29 February was formally recognised in British law.<ref>{{Citation |url=https://archive.org/details/in.ernet.dli.2015.69034/page/n226/mode/1up |title=The Statutes at Large: from the 23rd to the 26th Year of King George II |publisher=Charles Bathurst |year=1765 |editor-last=Pickering |editor-first=Danby |editor-link=Danby Pickering |volume=20 |location=Cambridge |access-date=28 January 2020 |page=194}} (calendar at the end of the Act)</ref>{{efn|Though it appears in earlier Government proclamations, such as one of 1619.<ref>{{Citation |last=Bond |first=John James |url=https://archive.org/details/handybookrulesa00bondgoog/page/n6/mode/2up |title=Handy Book of Rules and Tables for Verifying Dates With the Christian Era Giving an Account of the Chief Eras and Systems Used by Various Nations...' |chapter=Preface |page=[https://archive.org/details/handybookrulesa00bondgoog/page/n22/mode/2up xix] |edition=4th|publisher=George Bell & Sons |year=1875 |location=London |author-link=John James Bond }}</ref>}}

===Liturgical practices===
[[File:MissaleLeapYear.jpg|thumb|right|In the older [[Roman Missal]], feast days falling on or after 24 February are celebrated one day later in a leap year.]]
In the [[liturgical calendar]] of the Christian churches, the placement of the leap day is significant because of the date of the feast of [[Saint Matthias]], which is defined as the sixth day before 1 March (counting inclusively). The Church of England's ''[[Book of Common Prayer]]'' was still using the "two days with the same date" system in its 1542 edition;<ref>{{Citation |last1=Campion |first1=Rev W M |url=https://archive.org/details/prayerbookinter01unkngoog/page/n50/mode/2up |title=The Prayer Book interleaved |last2=Beamont |first2=Rev W J |date=1870 |location=London |publisher=Rivingtons |page=31 |via=[[Archive.org]]}}</ref> it first included a calendar which used entirely consecutive day counting from 1662 and showed leap day as falling on 29 February.<ref name="Baskerville">{{Citation |last=Church of England |url=https://archive.org/details/bookcommonpraye00chur/page/n25/mode/1up |title=Book of Common Prayer |publisher=[[John Baskerville]] |year=1762 |location=Cambridge |orig-year=1662 |via=[[Archive.org]]}}</ref> In the 1680s, the Church of England declared 25 February to be the feast of St Matthias.{{sfnp|Cheney|2000|p=8}}
Until 1970, the [[Roman Catholic Church]] always celebrated the feast of Saint Matthias on {{lang|la|a. d. VI Kal. Mart.}}, so if the days were numbered from the beginning of the month, it was named 24 February in common years, but the presence of the {{lang|la|bissextum}} in a bissextile year immediately before {{lang|la|a. d. VI Kal. Mart.}} shifted the latter day to 25 February in leap years, with the [[Vigil]] of St. Matthias shifting from 23 February to the leap day of 24 February. This shift did not take place in pre-Reformation Norway and Iceland; [[Pope Alexander III]] ruled that either practice was lawful.<ref>[[Liber Extra]], 5. 40. 14. 1</ref> Other feasts normally falling on 25–28 February 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.{{citation needed|date=February 2024}}

In the [[Eastern Orthodox Church]], the feast of St. [[John Cassian]] is celebrated on 29 February, but he is instead commemorated at Compline on 28 February in non-leap years. The feast of St. Matthias is celebrated in August, so leap years do not affect his commemoration, and, while the feast of the [[Beheading of John the Baptist#Related feasts|First and Second Findings of the Head of John the Baptist]] is celebrated on 24 February, the Orthodox church calculates days from the beginning of the current month, rather than counting down days to the Kalends of the following month, this is not affected. Thus, only the feast of St. John Cassian and any movable feasts associated with the Lenten or Pre-Lenten cycles are affected.

===Folk traditions===
[[File:Bob Satterfield cartoon about leap year traditions.jpg|right|thumb|upright|A [[spinster]] eagerly awaits the upcoming leap day, in this 1903 cartoon by [[Bob Satterfield (cartoonist)|Bob Satterfield.]]]]
In Ireland and Britain, it is a [[tradition]] that women may [[Proposal of marriage|propose marriage]] only in leap years. While it has been claimed that the tradition was initiated by [[Saint Patrick]] or [[Brigid of Kildare]] in 5th century Ireland, this is dubious, as the tradition has not been attested before the 19th century.<ref>{{citation | last1 = Mikkelson |first1=B. | last2 = Mikkelson | first2 = D.P. | date = 2010 | url = http://www.snopes.com/oldwives/february29.asp | title = The Privilege of Ladies | website = The Urban Legends Reference Pages | publisher = snopes.com}}</ref> Supposedly, a 1288 law by Queen [[Margaret, Maid of Norway|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 was deemed to be a pair of leather gloves, a single rose, £1, and a kiss.<ref>{{Cite web |last=Ha-Redeye |first=Omar |date=28 February 2016 |title=The Leap Year Proposal Law |url=https://www.slaw.ca/2016/02/28/the-leap-year-proposal-law/ |access-date=8 April 2024 |website=Slaw |language=en-US}}</ref>{{efn|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).}} In some places the tradition was tightened to restricting female proposals to the modern leap day, 29 February, or to the medieval (bissextile) leap day, 24 February.{{citation needed|date=December 2022}}

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]]{{snd}}fair warning, if you will."<ref>{{citation | last = Felten | first = E. | date = 23 February 2008 | url = https://www.wsj.com/articles/SB120371485815386581 | title = The Bissextile Beverage | website = Wall Street Journal | access-date = 12 August 2017 | archive-date = 12 August 2017 | archive-url = https://web.archive.org/web/20170812135932/https://www.wsj.com/articles/SB120371485815386581 | url-status = live }}</ref>

In Finland, the tradition is that if a man refuses a woman's proposal on leap day, he should buy her the fabrics for a skirt.<ref>{{citation | last = Hallett | first = S. | date = 29 February 2012 | url = http://www.huffingtonpost.com/2012/02/27/leap-year-proposal-tradition_n_1305525.html | title = Leap Year Proposal: What's The Story Behind It? | website = Huffington Post | access-date = 21 December 2015 | archive-date = 21 October 2014 | archive-url = https://web.archive.org/web/20141021183428/http://www.huffingtonpost.com/2012/02/27/leap-year-proposal-tradition_n_1305525.html | url-status = live }}</ref>

In France, since 1980, a satirical newspaper titled ''[[La Bougie du Sapeur]]'' is published only on leap year, on 29 February.<ref>{{cite web|url=http://www.france24.com/en/20120229-mediawatch-bougie-du-sapeur-newspaper-once-four-years|title=La Bougie du Sapeur: the world's least frequent newspaper|last=Creedon|first=James|date=29 February 2012|work=[[France 24]]|archive-url=https://web.archive.org/web/20120404003951/http://www.france24.com/en/20120229-mediawatch-bougie-du-sapeur-newspaper-once-four-years|archive-date=4 April 2012|url-status=live|access-date=4 June 2024}}</ref>

In Greece, marriage in a leap year is considered unlucky.<ref>{{citation | url = http://www.anagnosis.gr/index.php?la=eng&pageID=151 | title = A Greek Wedding | website = Anagnosis Books | access-date = 12 January 2012 | archive-date = 10 February 2012 | archive-url = https://web.archive.org/web/20120210092205/http://www.anagnosis.gr/index.php?pageID=151&la=eng | url-status = live }}</ref> One in five engaged couples in Greece will plan to avoid getting married in a leap year.<ref>{{citation | url = http://www.developingteachers.com/tips/pasttips63.htm | title = Teaching Tips 63 | website = Developing Teachers | access-date = 12 January 2012 | archive-date = 2 March 2012 | archive-url = https://web.archive.org/web/20120302215023/http://www.developingteachers.com/tips/pasttips63.htm | url-status = dead }}</ref>

In February 1988 the town of [[Anthony, Texas]], declared itself the "leap year capital of the world", and an international leapling birthday club was started.<ref>{{citation|url=http://www.timeanddate.com/date/leap-year-capital.html|title=Anthony – Leap Year Capital of the World|publisher=Time and Date|date=2008|access-date=6 November 2011|archive-date=9 November 2011|archive-url=https://web.archive.org/web/20111109194902/http://www.timeanddate.com/date/leap-year-capital.html|url-status=live}}</ref>

<gallery mode="packed" widths="350px" caption="1908 postcards">
File:PostcardLeapYearBeCarefulClara1908.jpg|Woman capturing man with butterfly-net
File:PostcardLeapYearMaidensAre1908.jpg|Women eagerly awaiting the coming leap year
File:PostcardTheMaidensVowIn1908.jpg|Histrionically preparing
</gallery>

===Birthdays===
A person born on 29 February may be called a "leapling" or a "leaper".<ref>{{citation | date = 28 February 2012 | article = 29 February: 29 things you need to know about leap years and their extra day | title = Mirror | access-date = 7 December 2015 | url = https://www.mirror.co.uk/news/uk-news/leap-years-29-things-you-746716 | archive-date = 2 January 2016 | archive-url = https://web.archive.org/web/20160102001559/http://www.mirror.co.uk/news/uk-news/leap-years-29-things-you-746716 | url-status = live }}</ref> In common years, they celebrate their [[birthday]]s on 28 February or 1 March.

Technically, a leapling will have fewer ''birthday anniversaries'' than their age in years. This phenomenon may be exploited for dramatic effect when a person is declared to be only a quarter of their actual age, by counting their leap-year birthday anniversaries only. For example, in [[Gilbert and Sullivan]]'s 1879 [[comic opera]] ''[[The Pirates of Penzance]]'', Frederic (the pirate apprentice) discovers that he is [[Indentured servitude|bound to serve]] the pirates until his 21st ''birthday'' (that is, when he turns 88&nbsp;years old, since 1900 was not a leap year) rather than until his 21st ''year''.

For legal purposes, legal birthdays depend on how local laws count time intervals.

==== Taiwan ====
{{Wikisource|Civil Code Part I General Principles}}
The Civil Code of [[Taiwan]] since 10 October 1929,<ref>{{citation |title=Legislative History of the Civil Code of the Republic of China |url=http://law.moj.gov.tw/Eng/LawClass/LawHistory.aspx?PCode=B0000001 |access-date=19 July 2011 |archive-date=28 December 2016 |archive-url=https://web.archive.org/web/20161228131414/http://law.moj.gov.tw/Eng/LawClass/LawHistory.aspx?PCode=B0000001 |url-status=live }}</ref> implies that the legal birthday of a leapling is 28 February in common years:

{{Blockquote|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 precedes 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.<ref>{{citation | article = Article 121 Civil Code | url = http://law.moj.gov.tw/Eng/LawClass/LawAll.aspx?PCode=B0000001 | title = Part I General Principles of the Republic of China | access-date = 2011-07-19 | archive-date = 2021-03-04 | archive-url = https://web.archive.org/web/20210304113355/https://law.moj.gov.tw/Eng/LawClass/LawAll.aspx?PCode=B0000001 | url-status = live }}</ref>}}

==== Hong Kong ====
Since 1990 non-retroactively, [[Hong Kong]] considers the legal birthday of a leapling 1 March in common years:<ref>{{citation |title=Age of Majority (Related Provisions) Ordinance (Ch. 410 Sec. 5) |date=30 June 1997 |url=http://www.legislation.gov.hk/blis_ind.nsf/E1BF50C09A33D3DC482564840019D2F4/22F10EC537B1BEBAC825648300339AA3?OpenDocument |publisher=Hong Kong Department of Justice |access-date=19 July 2011 |archive-date=18 May 2013 |archive-url=https://web.archive.org/web/20130518152417/http://www.legislation.gov.hk/blis_ind.nsf/E1BF50C09A33D3DC482564840019D2F4/22F10EC537B1BEBAC825648300339AA3?OpenDocument |url-status=live }} (Enacted in 1990).</ref>
{{blockquote|
# The time at which a person attains a particular age expressed in years shall be the commencement of the anniversary corresponding to the date of [their] birth.
# Where a person has been born on February 29 in a leap year, the relevant anniversary in any year other than a leap year shall be taken to be March 1.
# This section shall apply only where the relevant anniversary falls on a date after the date of commencement of this Ordinance.}}

====UK====
In the UK 1 March is considered to be a leapling's legal birthday.<ref>{{cite web |title=Leap day birthdays: 'How old are you really?' |url=https://www.bbc.com/news/uk-england-51176188 |publisher=BBC |access-date=3 September 2024 |date=28 February 2020}}</ref>

===Revised Julian calendar===
The [[Revised Julian calendar]] adds an extra day to February in years that are multiples of four, except for years that are multiples of 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.

This rule gives an average year length of 365.242222&nbsp;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, for the time being, does not do as good a job as the Gregorian calendar at keeping the vernal equinox on or close to 21 March.