Leap year: Difference between revisions

{{Short description|Calendar year containing an additional day}}

{{other uses}}

 

An astronomical year lasts slightly less than 365{{sfrac|4}} days. The historic [[Julian calendar]] has three [[common year]]s of 365 days followed by a leap year of 366 days, by extending February to 29 days rather than the common 28. The [[Gregorian calendar]], the world's most widely used civil calendar, makes a further adjustment for the small error in the Julian algorithm. Each leap year has 366 days instead of 365. This extra leap day occurs in each year that is a multiple of 4, except for years evenly divisible by 100 but not by 400.

 

 

 

The length of a day is also occasionally corrected by inserting a [[leap second]] into [[Coordinated Universal Time]] (UTC) because of variations in Earth's [[rotation period]]. Unlike leap days, leap seconds are not introduced on a regular schedule because variations in the length of the day are not entirely predictable.

==Julian calendar==

{{main|Julian calendar}}

 

Prior to Caesar's creation of what would be the Julian calendar, February was already the shortest month of the year for Romans. In the [[Roman calendar]] (after the reform of [[Numa Pompilius]] that added January and February), all months except February had an odd number of days{{snd}}29 or 31. This was because of a [[Religion in ancient Rome|Roman superstition]] that even numbers were unlucky.<ref>{{Citation|title=Why Are There Only 28 Days in February? |encyclopedia=[[Encyclopedia Britannica]] |last=Hogeback |first=Jonathon |url=https://www.britannica.com/story/why-are-there-only-28-days-in-february |access-date=31 May 2023}}</ref> When Caesar changed the calendar to follow the solar year closely, he made all months have 30 or 31&nbsp;days, leaving February unchanged except in leap years.

The Gregorian calendar was designed to keep the [[vernal equinox (Northern Hemisphere)|vernal equinox]] on or close to 21 March, so that the date of [[Easter]] (celebrated on the Sunday after the ecclesiastical [[full moon]] that falls on or after 21 March) remains close to the vernal equinox.<ref>{{citation | first = E. G. | last = Richards | date = 1998 | title = Mapping time: The Calendar and its History | publisher = Oxford University Press | pages = 250–1 | isbn = 0-19-286205-7}}</ref> The "[[Gregorian calendar#Accuracy|Accuracy]]" section of the "[[Gregorian calendar]]" article discusses how well the Gregorian calendar achieves this design goal, and how well it approximates the [[tropical year]].

 

{{Main|February 29|Bissextus}}

{{Redirect|Leap day|other uses|Leap Day (disambiguation){{!}}Leap Day}}

The intercalary day that usually occurs every 4&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}}

 

{{more|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 5&nbsp;days of February were moved to the last 5&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}}

===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.]]

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}}

 

===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.]]]]

 

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>

<gallery mode="packed" widths="350px" caption="1908 postcards">

File:PostcardLeapYearBeCarefulClara1908.jpg|Woman capturing man with butterfly-net

File:PostcardTheMaidensVowIn1908.jpg|Histrionically preparing

</gallery>

 

===Birthdays===

 

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''.

# 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.}}

===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.

* [[Sansculottides]]

* [[Zeller's congruence]]

 

* [[Leap year starting on Monday]]