Editing List of non-standard dates

{{Short description|none}} <!-- "none" is preferred when the title is sufficiently descriptive; see [[WP:SDNONE]] -->
{{Use mdy dates|date=September 2020}}
[[File:Feb31OnTombstone.jpg|thumb|February 31 on a tombstone]]
Several '''non-standard dates''' are used in [[calendars]] for various purposes: some are expressly fictional, some are intended to produce a rhetorical effect (such as [[sarcasm]]), and others attempt to address a particular mathematical, scientific or accounting requirement or discrepancy within the calendar system.

==Historical==
===January 0===
'''January 0''' is an alternative name for [[December 31]]. January 0 is the day before [[January 1]] in an annual [[ephemeris]]. It keeps the date in the year for which the ephemeris was published, thus avoiding any reference to the previous year, even though it is the same day as [[December 31]] of the previous year. January 0 also occurs in the [[Epoch (astronomy)|epoch]] for the [[Second#Fraction of an ephemeris year|ephemeris second]], "1900 January 0 at 12 hours ephemeris time".<ref name="USNO">{{cite web|title=Leap Seconds |publisher=Time Service Department, [[United States Naval Observatory]] |url=http://tycho.usno.navy.mil/leapsec.html |access-date=December 31, 2006 |url-status=dead |archive-url=https://web.archive.org/web/20120228195938/http://tycho.usno.navy.mil/leapsec.html |archive-date=February 28, 2012 }}</ref> 1900 January 0 (at Greenwich Mean Noon) was also the epoch used by [[Newcomb's Tables of the Sun|Newcomb's ''Tables of the Sun'']], which became the epoch for the [[Julian day#Variants|Dublin Julian day]].<ref>{{cite web|url=https://textfiles.meulie.net/computers/DOCUMENTATION/astroclk.dc2 |title=Program ASTROCLK: Astronomical Clock and Celestial Tracking Program with Celestial Navigation | first=David H. Jr. | last=Ransom |date=November 19, 1989 |page=110}}</ref>

===February 30===
{{see also|Swedish calendar}}
[[File:feb1712.jpg|thumb|right|300px|Swedish calendar for February 1712]]

'''February 30''' is a day that does not occur on the [[Gregorian calendar]], where the month of [[February]] contains only 28 days, or 29 days in a [[leap year]]. However, from a historical perspective February 30 has been used at least once and appears in some [[#Reform calendars|reform calendars]].

The thirteenth-century scholar [[Johannes de Sacrobosco]] claimed that in the [[Julian calendar#Sacrobosco's incorrect theory on month lengths|Julian calendar]], [[February]] had 30 days in leap years from 45 BC until 8 BC, when [[Caesar Augustus|Augustus]] allegedly shortened [[February]] by one day to give that day to the month of [[August]] named after him so that it had the same length as the month of [[July]] named after his adoptive father, [[Julius Caesar]]. However, all historical evidence refutes [[Johannes de Sacrobosco|Sacrobosco]], including dual dates with the [[Coptic calendar|Alexandrian calendar]].<ref>Roscoe Lamont, "[http://articles.adsabs.harvard.edu//full/1919PA.....27..579P/0000583.000.html The Roman calendar and its reformation by Julius Caesar]", ''[[Popular Astronomy (US magazine)|Popular Astronomy]]'' '''27''' (1919) 583–595. Sacrobosco's theory is discussed on pages 585–587.</ref>

February 30 was a day that happened in [[Sweden]] in 1712.<ref name = timeanddate>{{cite web
 |url=http://www.timeanddate.com/date/february-30.html
 |title=February 30 Was a Real Date
 |publisher=timeanddate.com
 |access-date=2024-07-11
 |first=Vigdis
 |last=Hocken
 |url-status=live
 |archive-url=https://web.archive.org/web/20240329043659/https://www.timeanddate.com/date/february-30.html
 |archive-date=2024-03-29
}}</ref> This occurred because, instead of changing from the [[Julian calendar]] to the [[Gregorian calendar]] by omitting a block of consecutive days, as had been done in other countries, the [[Swedish Empire]] planned to change gradually by omitting all [[leap day]]s from 1700 to 1740, inclusive, so that the next leap year after 1696 would not be until 1744. Although the leap day was omitted in February 1700, the [[Great Northern War]] began later that year, diverting the attention of the Swedes from their calendar so that they did not omit leap days on the next two occasions; 1704 and 1708 remained leap years.<ref name="Bauer">{{cite book|last1=Bauer|first1=R. W.|title=Calender for Aarene fra 601 til 2200|date=1868|location=Copenhagen, Denmark|publisher=Dansk Historisk Fællesråd (1993 reprint)|isbn=87-7423-083-2|page=100}}</ref>

To avoid confusion and further mistakes, the [[Julian calendar]] was restored in 1712 by adding a second leap day, thus giving that year the only known actual use of February 30 in a calendar. That day corresponded to February 29 in the [[Julian calendar]] and to March 11 in the [[Gregorian calendar]].<ref name="Bauer"/><ref>{{cite book|last1=Vallerius|first1=Johannes|title=Allmanach på åhret effter Christi födelse 1712|date=1711|location=Lund, Sweden}}</ref> The Swedish conversion to the [[Gregorian calendar]] was finally accomplished in 1753, when February 17 was followed by March 1.<ref name="Bauer"/>

Artificial calendars may also have 30 days in [[February]]. For example, in a climate model the statistics may be simplified by having 12 months of 30 days. The [[Hadley Centre]] General Circulation Model is an example.<ref>{{cite web|url=http://www.metoffice.com/research/hadleycentre/models/GDT/ch23.html|title=Hadley Centre: GDT netCDF conventions|date=November 22, 2005|work=MetOffice.com|access-date=March 21, 2017|url-status=dead|archive-url=https://web.archive.org/web/20051122015007/http://www.metoffice.com/research/hadleycentre/models/GDT/ch23.html|archive-date=November 22, 2005}}</ref>

===May 35===
'''May 35''' is used in the title of ''[[The 35th of May, or Conrad's Ride to the South Seas]]'', a German children's novel published in 1932.{{cn|date=March 2025}}

===July 36===
{{Main|July 36}}
'''July 36''' refers to 5 August 2024, when the Bangladesh [[2024 Bangladesh quota reform movement|quota reform movement]] celebrated Prime Minister [[Sheikh Hasina]] resigning and fleeing to India after mass protests, which began with the reinstatement of the quota system in June and escalated despite the Supreme Court's ruling on 21 July in favor of quota reform.<ref>{{Cite web |date=2024-12-01 |title='Bangladesh Reborn: Pathway to July 36' photo exhibition by BJIM starts tomorrow |url=https://www.tbsnews.net/events/bangladesh-reborn-pathway-july-36-photo-exhibition-bjim-starts-tomorrow-1007386 |access-date=2024-12-04 |website=The Business Standard |language=en}}</ref><ref>{{Cite web |title=Photo exhibition 'Saluting the Brave Hearts, 36 days of July' inaugurated |url=https://www.dhakatribune.com/bangladesh/event/366734/photo-exhibition-%E2%80%98saluting-to-brave-hearts-36 |access-date=2024-12-04 |website=Dhaka Tribune |language=en}}</ref><ref>{{Cite web |date=2024-08-20 |title='New Bangladesh', '36 July': Artworks grow on Dhaka walls to memorialise protests |url=https://www.mid-day.com/news/world-news/article/new-bangladesh-36-july-artworks-grow-on-dhaka-walls-to-memorialise-protests-23377626 |access-date=2024-12-04 |website=Mid-day |language=en}}</ref>

===December 31.5 GMT===
{{see also|Greenwich Mean Time#Ambiguity in the definition of GMT}}
'''December 31.5 GMT''' in 1924 almanacs was an instant defined to resolve the contrast between two different conventions in defining the [[civil time]] of referring to midnight as zero hours.<ref>{{cite book |title=Astronomical Supplement to the Astronomical Almanac |publisher=University Science Books |year=1992 |isbn=0-935702-68-7 |page=76}}</ref>

===December 32===
The [[LearAvia Lear Fan]] aircraft test flight had British government funding that expired at the end of that year. After the cancellation of a planned test flight on December 31, 1980, due to technical issues, the first prototype made its maiden flight on January 1, 1981, but a sympathetic government official recorded the date as "December 32, 1980".<ref>{{cite web |url=http://www.museumofflight.org/aircraft/lear-fan-2100-futura|title=Lear Fan 2100 (Futura) |archive-url=https://web.archive.org/web/20090712041304/http://museumofflight.org/aircraft/lear-fan-2100-futura |archive-date=July 12, 2009 |work=The Museum of Flight |date=2009 |access-date=November 27, 2009}}</ref>

==Software==
===January 0===
[[Microsoft Excel]] displays the day before January 1, 1900 (the earliest date it can represent) as January 0, 1900.<ref name="m">{{cite web |url=http://www.techrepublic.com/article/how-do-i-perform-basic-formatting-in-excel-2003/ |work=[[TechRepublic]] |title=How do I... Perform basic formatting in Excel 2003? |first=Scott |last=Lowe |date=May 11, 2007}}</ref> It also treats 1900 incorrectly as a leap year (whereas only centuries divisible by 400 are), so it displays the day before March 1, 1900, as the non-existent February 29 instead of [[February 28]]. This means March 1, 1900 is the earliest date that can be used reliably in Excel.

===February 31===
February 31, 32, and 33 were used to calculate weather data by making each month the same length.<ref>{{cite journal |last1=Everett |first1=J. D. |title=Description of a method of reducing observations of temperature |journal=American Journal of Science |date=1 January 1863 |volume=s2-35 |issue=103 |pages=17–31 |doi=10.2475/ajs.s2-35.103.17 |bibcode=1863AmJS...35...17E |s2cid=130637323 |url=https://zenodo.org/record/1621032 }}</ref>

===Other non-standard dates===
Other non-standard dates are sometimes used in [[Application software|software engineering]]. For example, [[Java (programming language)|Java]] (specifically the java.util.Calendar class) allows dates such as February 0 (= January 31) and April 31 (= May 1).

==Other uses==
===February 31===
'''February 31''' or '''31 February''' is exceptionally used on gravestones when the date is unknown,<ref>{{cite web |title=February 31 On Gravestone |url=http://www.swampyacresfarm.com/wordpress/tag/february-31-on-gravestone/ |website=Swampy Acres Farm Blog |access-date=June 13, 2019 |archive-url=https://web.archive.org/web/20181219214313/http://www.swampyacresfarm.com/wordpress/tag/february-31-on-gravestone/ |url-status=dead |archive-date=December 19, 2018 |date=December 19, 2018}}</ref>{{Better source needed|date=June 2019|reason=This claim needs references to better sources. A blog is not generally considered a reliable source.}} or, in at least one case, out of supposed superstition (more likely an error).<ref>{{cite book |title=Weird Illinois |author=Troy Taylor |page=212 |publisher=Sterling Publishing Co., Inc. |year=2005 |isbn=9780760759431 |url=https://books.google.com/books?id=gE4P1bhDCB4C&pg=PA212}}</ref><ref>{{cite web |last1=McBride Jacobson |first1=Molly |title=St. Omer Cemetery Witch Grave |url=https://www.atlasobscura.com/places/st-omer-cemetery-witch-grave |work=Atlas Obscura |date=6 January 2017 }}</ref>

===March 0===
'''March 0''' or '''0 March''' is used in [[astronomy]].<ref>{{cite book |title=The Astronomical Almanac for the Year 2003: Data for Astronomy, Space Sciences, Geodesy, Surveying, Navigation and Other Applications |date=2001 |publisher=U.S. Government Printing Office |isbn=978-0-11-887320-8 |page=K2 |bibcode=2001asal.book.....U }}</ref> {{Clarify|reason=How is it used?|date=October 2024}}

===May 35===
'''May 35''' or '''35 May''' is used in mainland China to avoid censorship when referring to the [[Tiananmen Square protests of 1989]], where the official names are strictly [[Censorship in China|censored]] by the [[Government of China|national government]], and the event is normally referred to as [[June 4]].<ref>{{cite news
 |url=http://www.theage.com.au/world/china-tightens-information-controls-for-tiananmen-anniversary-20090604-bvxf.html
 |title=China tightens information controls for Tiananmen anniversary
 |agency=Agence France-Presse
 |date=2009-06-09
 |work=The Age
 |location=Australia
 |access-date=2025-03-20
 |url-status=live
 |archive-url=https://web.archive.org/web/20090930185040/http://www.theage.com.au/world/china-tightens-information-controls-for-tiananmen-anniversary-20090604-bvxf.html
 |archive-date=2009-09-30
}}</ref>

==Fictional calendars==
In the works of [[J. R. R. Tolkien]], the [[Hobbits]] have developed the [[Shire Reckoning]]. According to Appendix D of ''[[The Lord of the Rings]]'', this calendar has arranged the year in 12 months of 30 days each. The month the Hobbits call ''Solmath'' is rendered in the text as ''February'', and therefore the date February 30 exists in the narrative.<ref>{{cite book|last1=Tolkien|first1=J. R. R.|title=The Return of the King|date=1965|publisher=Houghton Mifflin Co.|location=Boston|isbn=978-0-395-08256-0|edition=2nd|chapter=Appendix D|url=https://archive.org/details/returnofking00tolk}}</ref>

February 30, 1951, is the last night of the world in [[Ray Bradbury]]'s short story "Last Night of the World".<ref>{{cite web|url=http://www.esquire.com/entertainment/books/a14340/ray-bradbury-last-night-of-the-world-0251/|title=A Classic Ray Bradbury Esquire Story|date=June 6, 2012|work=esquire.com|access-date=March 21, 2017}}</ref>

''June 31'' is a fictional date in the Soviet film ''[[31 June]]''. It is also the date of a fictional RAF raid on Germany in [[Len Deighton]]'s 1970 novel ''[[Bomber (novel)|Bomber]]''.

''December 32'' or ''32 December'' is the date of Hogswatchnight in ''[[Hogfather]]'' by Terry Pratchett. It has also been used as a [[December 32 (disambiguation)|title for various works]].

The children's book ''Please Try to Remember the First of Octember!'' by [[Dr. Seuss]] narrates many delightful things which are supposed to happen starting on the first day of the fictional month of Octember.

In the episode "[[94 Meetings]]" of the sitcom [[Parks and Recreation]], [[Ron Swanson]] is forced to deal with 94 meetings in a single day because his assistant, [[April Ludgate]], scheduled them all for March 31st instead of the common fake date of February 31, mistakenly believing it was not a real date.

==In popular culture==
March 0 is used in [[Doomsday algorithm]] calculations.<ref>{{Cite web |last=Graham |first=S. W. |date=July 1995 |title=The Doomsday Rule |url=http://people.se.cmich.edu/graha1sw/pub/doomsday/doomsday.html |access-date=2023-04-01 |website=people.se.cmich.edu}}</ref> [[March 2]] was celebrated as February 30 by [[Lin-Manuel Miranda]] and [[Weird Al Yankovic]] for the release date of Yankovic's "The ''[[Hamilton (musical)|Hamilton]]'' Polka".<ref>{{cite magazine |url=https://www.rollingstone.com/music/features/lin-manuel-miranda-weird-al-yankovic-on-hamilton-polka-w517343 |title=Lin-Manuel Miranda, 'Weird Al' Yankovic Talk New 'Hamilton Polka' |first=Andy |last=Greene |date=March 2, 2018 |access-date=March 2, 2018 |magazine=[[Rolling Stone]]}}</ref>

In November 2010 it was discovered that a [[Hanshin Tigers]] wall calendar incorrectly included the date ''November 31''. Fans who had bought the calendar were given a sticker to cover up the date, and reprinted calendars were sent.<ref>{{cite web|archiveurl=https://web.archive.org/web/20190227104628/https://www.nikkei.com/article/DGXNSSXKA0041_Y0A121C1000000/|archivedate=February 27, 2019|url=https://www.nikkei.com/article/DGXNSSXKA0041_Y0A121C1000000/|title=阪神タイガース、来年のカレンダーに|work=Nikkei|language=Japanese|date=November 28, 2010|accessdate=December 13, 2023}}</ref>

Soul band [[Black Pumas]] included a song named "OCT 33" on their [[Grammy]]-nominated 2019 [[Black Pumas (album)|eponymous album]].

The 1998 French-language film [[August 32nd on Earth]] was written and directed by [[Denis Villeneuve]], and was his feature film directoral debut.

==Reform calendars==
Because evening out the lengths of the months is part of the rationale for [[Calendar reform|reforming the calendar]], some reform calendars, such as the [[World Calendar]] and the [[Hanke–Henry Permanent Calendar]], contain a 30-day February. The [[Symmetry454]] calendar assigns 35 days to February, May, August, and November, as well as December in a leap year.

==See also==
*[[Ides of March]]
*[[List of calendars]]
*[[List of idioms of improbability]], including various nonexistent dates
*[[Time formatting and storage bugs]]
*[[System time]]
*[[Tibb's Eve]], a day said to occur neither before nor after Christmas
*[[Undecimber]]

==References==
{{reflist}}
{{refbegin}}
* ''The Oxford Companion to the Year''. Bonnie Blackburn & Leofranc Holford-Strevens. Oxford University Press 1999. {{ISBN|0-19-214231-3}}. pp.&nbsp;98–99.
{{refend}}

==External links==
{{commons}}
* [https://www.monthsinorder.com/ Months in Order]
*[https://web.archive.org/web/20120303010051/http://hem.fyristorg.com/hok/lee/calender.htm#30%20days 30 days in February 1712]
*[https://web.archive.org/web/20010418192946/http://www.algonet.se/~hogman/tiderakning_eng.htm Change of calendars - Sweden (in Swedish)]
*[http://tolkiengateway.net/wiki/30_February 30 February] on Tolkien Gateway

{{months}}

{{DEFAULTSORT:Non-standard dates}}
[[Category:February]]
[[Category:1712 in Sweden]]
[[Category:English-language idioms]]
[[Category:January|January 00]]
[[Category:December]]
[[Category:0 (number)]]
[[Category:Lists of things considered unusual|Dates]]