Severalnon-standard dates are used incalendars for various purposes: some are expressly fictional, some are intended to produce a rhetorical effect (such assarcasm), and others attempt to address a particular mathematical, scientific or accounting requirement or discrepancy within the calendar system.
January 0 is an alternative name forDecember 31. January 0 is the day beforeJanuary 1 in an annualephemeris. 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 asDecember 31 of the previous year. January 0 also occurs in theepoch for theephemeris second, "1900 January 0 at 12 hours ephemeris time".[1] 1900 January 0 (at Greenwich Mean Noon) was also the epoch used byNewcomb'sTables of the Sun, which became the epoch for theDublin Julian day.[2]
February 30 is a day that does not occur on theGregorian calendar, where the month ofFebruary contains only 28 days, or 29 days in aleap year. However, from a historical perspective February 30 has been used at least once and appears in somereform calendars.
The thirteenth-century scholarJohannes de Sacrobosco claimed that in theJulian calendar,February had 30 days in leap years from 45 BC until 8 BC, whenAugustus allegedly shortenedFebruary by one day to give that day to the month ofAugust named after him so that it had the same length as the month ofJuly named after his adoptive father,Julius Caesar. However, all historical evidence refutesSacrobosco, including dual dates with theAlexandrian calendar.[3]
February 30 was a day that happened inSweden in 1712.[4] This occurred because, instead of changing from theJulian calendar to theGregorian calendar by omitting a block of consecutive days, as had been done in other countries, theSwedish Empire planned to change gradually by omitting allleap days 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, theGreat 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.[5]
To avoid confusion and further mistakes, theJulian 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 theJulian calendar and to March 11 in theGregorian calendar.[5][6] The Swedish conversion to theGregorian calendar was finally accomplished in 1753, when February 17 was followed by March 1.[5]
Artificial calendars may also have 30 days inFebruary. For example, in a climate model the statistics may be simplified by having 12 months of 30 days. TheHadley Centre General Circulation Model is an example.[7]
May 35 is also used in the title ofThe 35th of May, or Conrad's Ride to the South Seas, a German children's novel published in 1931.[citation needed]
July 36 refers to 5 August 2024, when the Bangladeshquota reform movement celebrated Prime MinisterSheikh 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.[8][9][10]
December 31.5 GMT in 1924 almanacs was an instant defined to resolve the contrast between two different conventions in defining thecivil time of referring to midnight as zero hours.[11]
TheLearAvia 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".[12]
Microsoft Excel displays the day before January 1, 1900 (the earliest date it can represent) as January 0, 1900.[13] 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 ofFebruary 28. This means March 1, 1900 is the earliest date that can be used reliably in Excel.
February 31, 32, and 33 were used to calculate weather data by making each month the same length.[14]
Other non-standard dates are sometimes used insoftware engineering. For example,Java (specifically the java.util.Calendar class) allows dates such as February 0 (= January 31) and April 31 (= May 1).
February 31 or31 February is exceptionally used on gravestones when the date is unknown,[15][better source needed] or, in at least one case, out of supposed superstition (more likely an error).[16][17]
March 0 or0 March is used inastronomy.[18][clarification needed]
May 35 or35 May is used in mainland China to avoid censorship when referring to theTiananmen Square protests of 1989, where the official names are strictlycensored by thenational government, and the event is normally referred to asJune 4.[19]
In the works ofJ. R. R. Tolkien, theHobbits have developed theShire Reckoning. According to Appendix D ofThe Lord of the Rings, this calendar has arranged the year in 12 months of 30 days each. The month the Hobbits callSolmath is rendered in the text asFebruary, and therefore the date February 30 exists in the narrative.[20]
February 30, 1951, is the last night of the world inRay Bradbury's short story "Last Night of the World".[21]
June 31 is a fictional date in the Soviet film31 June. It is also the date of a fictional RAF raid on Germany inLen Deighton's 1970 novelBomber.
December 32 or32 December is the date of Hogswatchnight inHogfather by Terry Pratchett. It has also been used as atitle for various works.
The children's bookPlease Try to Remember the First of Octember! byDr. 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 sitcomParks 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.
March 0 is used inDoomsday algorithm calculations.[22]March 2 was celebrated as February 30 byLin-Manuel Miranda andWeird Al Yankovic for the release date of Yankovic's "TheHamilton Polka".[23]
In November 2010 it was discovered that aHanshin Tigers wall calendar incorrectly included the dateNovember 31. Fans who had bought the calendar were given a sticker to cover up the date, and reprinted calendars were sent.[24]
Soul bandBlack Pumas included a song named "OCT 33" on theirGrammy-nominated 2019eponymous album.
The 1998 French-language filmAugust 32nd on Earth was written and directed byDenis Villeneuve, and was his feature film directoral debut.
Because evening out the lengths of the months is part of the rationale forreforming the calendar, some reform calendars, such as theWorld Calendar and theHanke–Henry Permanent Calendar, contain a 30-day February. TheSymmetry454 calendar assigns 35 days to February, May, August, and November, as well as December in a leap year.
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