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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 or 0 January 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 for the ephemeris second, "1900 January 0 at 12 hours ephemeris time".^[1] 1900 January 0 (at Greenwich Mean Noon) was also the epoch used by Newcomb's Tables of the Sun, which became the epoch for the Dublin Julian day.^[2]

February 30

February 30 or 30 February is a date that does not occur on the Gregorian calendar, where the month of February contains only 28 days, or 29 days in a leap year.

The thirteenth-century scholar Johannes de Sacrobosco claimed that in the Julian calendar, February had 30 days in leap years from 45 BC until 8 BC, when 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 Sacrobosco, including dual dates with the Alexandrian calendar.^[3]

February 30 was a day that happened in Sweden, 1712.^[4] 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 days from 1700 to 1740, inclusive. 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.^[5]

To avoid confusion and further mistakes, the Julian calendar was restored in 1712 by adding an extra 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.^[5]^[6] The Swedish conversion to the Gregorian calendar was finally accomplished in 1753, when February 17 was followed by March 1.^[5]

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.^[7]

It also appears in some reform calendars.

February 31

February 31 or 31 February is exceptionally used on gravestones when the date is unknown,^[8]^{[better source needed]} or, in at least one case, out of supposed superstition (more likely a typo).^[9]^[10]

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 censored by the national government, and the event is normally referred to as June 4.^[11] It is also used in the title of The 35th of May, or Conrad's Ride to the South Seas, a German children's novel published in 1931.

December 31.5 GMT

"December 31.5 GMT" in 1924 almanacs was an instant defined to solve the contrast between two different conventions in defining the civil time of referring to midnight as zero hours.^[12]

December 32, 1980

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 the date was officially recorded by sympathetic British government officials as "December 32, 1980".^[13]

Software

In Microsoft Excel, the epoch of the 1900 date format is January 0, 1900.^[14]

February 31 is also used (along with February 32 and February 33) for calculating weather data.^[15]

March 0 or 0 March is an alternative name for the last day of February (February 28, or February 29 in leap years). It is used most often in astronomy, software engineering,^[16]^[17] and Doomsday algorithm calculations.^[18]

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.^[19]

February 30, 1951, is the last night of the world in Ray Bradbury's short story "Last Night of the World".^[20]

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.

December 32 or 32 December is the date of Hogswatchnight in Hogfather by Terry Pratchett. It has also been used as a 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 in^{[clarification needed]} the fictional month of Octember.

In popular culture

March 2 was celebrated as February 30 by Lin-Manuel Miranda and Weird Al Yankovic for the release date of Yankovic's "The Hamilton Polka".^[21]

Reform calendars

Because evening out the months is a part of the rationale for 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.

References

^ "Leap Seconds". Time Service Department, United States Naval Observatory. Archived from the original on February 28, 2012. Retrieved December 31, 2006.
^ Ransom, David H. Jr. (November 19, 1989). "Program ASTROCLK: Astronomical Clock and Celestial Tracking Program with Celestial Navigation". p. 110.
^ Roscoe Lamont, "The Roman calendar and its reformation by Julius Caesar", Popular Astronomy 27 (1919) 583–595. Sacrobosco's theory is discussed on pages 585–587.
^ "February 30 Was a Real Date". timeanddate.com. Retrieved April 25, 2016.
^ ^a ^b ^c Bauer, R. W. (1868). Calender for Aarene fra 601 til 2200. Copenhagen, Denmark: Dansk Historisk Fællesråd (1993 reprint). p. 100. ISBN 87-7423-083-2. {{cite book}}: ISBN / Date incompatibility (help)
^ Vallerius, Johannes (1711). Allmanach på åhret effter Christi födelse 1712. Lund, Sweden.
^ "Hadley Centre: GDT netCDF conventions". MetOffice.com. November 22, 2005. Archived from the original on November 22, 2005. Retrieved March 21, 2017.
^ "February 31 On Gravestone". Swampy Acres Farm Blog. December 19, 2018. Archived from the original on December 19, 2018. Retrieved June 13, 2019.
^ Troy Taylor (2005). Weird Illinois. Sterling Publishing Co., Inc. p. 212. ISBN 9780760759431.
^ McBride Jacobson, Molly (January 6, 2017). "St. Omer Cemetery Witch Grave". Atlas Obscura.
^ "China tightens information controls for Tiananmen anniversary". The Age. Australia. Agence France-Presse. June 4, 2009. Retrieved November 3, 2010.
^ Astronomical Supplement to the Astronomical Almanac. University Science Books. 1992. p. 76. ISBN 0-935702-68-7.
^ "Lear Fan 2100 (Futura)". The Museum of Flight. 2009. Archived from the original on July 12, 2009. Retrieved November 27, 2009.
^ Lowe, Scott (May 11, 2007). "How do I... Perform basic formatting in Excel 2003?". TechRepublic.
^ Everett, J. D. (January 1, 1863). "Description of a method of reducing observations of temperature". American Journal of Science. s2-35 (103): 17–31. Bibcode:1863AmJS...35...17E. doi:10.2475/ajs.s2-35.103.17. S2CID 130637323.
^ The Astronomical Almanac for the Year 2003: Data for Astronomy, Space Sciences, Geodesy, Surveying, Navigation and Other Applications. U.S. Government Printing Office. 2001. p. K2. Bibcode:2001asal.book.....U. ISBN 978-0-11-887320-8.
^ Tjia, John S. (2009). Building Financial Models. McGraw Hill Professional. p. 144. ISBN 978-0-07-160890-9.
^ Graham, S. W. (July 1995). "The Doomsday Rule". people.se.cmich.edu. Retrieved April 1, 2023.
^ Tolkien, J. R. R. (1965). "Appendix D". The Return of the King (2nd ed.). Boston: Houghton Mifflin Co. ISBN 978-0-395-08256-0.
^ "A Classic Ray Bradbury Esquire Story". esquire.com. June 6, 2012. Retrieved March 21, 2017.
^ Greene, Andy (March 2, 2018). "Lin-Manuel Miranda, 'Weird Al' Yankovic Talk New 'Hamilton Polka'". Rolling Stone. Retrieved March 2, 2018.

The Oxford Companion to the Year. Bonnie Blackburn & Leofranc Holford-Strevens. Oxford University Press 1999. ISBN 0-19-214231-3. Pages 98–99.

External links

Months in Order
30 days in February 1712
Change of calendars - Sweden (in Swedish)
30 February on Tolkien Gateway

[USNO-1] "Leap Seconds". Time Service Department, United States Naval Observatory. Archived from the original on February 28, 2012. Retrieved December 31, 2006.

[2] Ransom, David H. Jr. (November 19, 1989). "Program ASTROCLK: Astronomical Clock and Celestial Tracking Program with Celestial Navigation". p. 110.

[3] Roscoe Lamont, "The Roman calendar and its reformation by Julius Caesar", Popular Astronomy 27 (1919) 583–595. Sacrobosco's theory is discussed on pages 585–587.

[timeanddate-4] "February 30 Was a Real Date". timeanddate.com. Retrieved April 25, 2016.

[Bauer-5] Bauer, R. W. (1868). Calender for Aarene fra 601 til 2200. Copenhagen, Denmark: Dansk Historisk Fællesråd (1993 reprint). p. 100. ISBN 87-7423-083-2. {{cite book}}: ISBN / Date incompatibility (help)

[6] Vallerius, Johannes (1711). Allmanach på åhret effter Christi födelse 1712. Lund, Sweden.

[7] "Hadley Centre: GDT netCDF conventions". MetOffice.com. November 22, 2005. Archived from the original on November 22, 2005. Retrieved March 21, 2017.

[8] "February 31 On Gravestone". Swampy Acres Farm Blog. December 19, 2018. Archived from the original on December 19, 2018. Retrieved June 13, 2019.

[9] Troy Taylor (2005). Weird Illinois. Sterling Publishing Co., Inc. p. 212. ISBN 9780760759431.

[10] McBride Jacobson, Molly (January 6, 2017). "St. Omer Cemetery Witch Grave". Atlas Obscura.

[11] "China tightens information controls for Tiananmen anniversary". The Age. Australia. Agence France-Presse. June 4, 2009. Retrieved November 3, 2010.

[12] Astronomical Supplement to the Astronomical Almanac. University Science Books. 1992. p. 76. ISBN 0-935702-68-7.

[13] "Lear Fan 2100 (Futura)". The Museum of Flight. 2009. Archived from the original on July 12, 2009. Retrieved November 27, 2009.

[m-14] Lowe, Scott (May 11, 2007). "How do I... Perform basic formatting in Excel 2003?". TechRepublic.

[15] Everett, J. D. (January 1, 1863). "Description of a method of reducing observations of temperature". American Journal of Science. s2-35 (103): 17–31. Bibcode:1863AmJS...35...17E. doi:10.2475/ajs.s2-35.103.17. S2CID 130637323.

[16] The Astronomical Almanac for the Year 2003: Data for Astronomy, Space Sciences, Geodesy, Surveying, Navigation and Other Applications. U.S. Government Printing Office. 2001. p. K2. Bibcode:2001asal.book.....U. ISBN 978-0-11-887320-8.

[17] Tjia, John S. (2009). Building Financial Models. McGraw Hill Professional. p. 144. ISBN 978-0-07-160890-9.

[18] Graham, S. W. (July 1995). "The Doomsday Rule". people.se.cmich.edu. Retrieved April 1, 2023.

[19] Tolkien, J. R. R. (1965). "Appendix D". The Return of the King (2nd ed.). Boston: Houghton Mifflin Co. ISBN 978-0-395-08256-0.

[20] "A Classic Ray Bradbury Esquire Story". esquire.com. June 6, 2012. Retrieved March 21, 2017.

[21] Greene, Andy (March 2, 2018). "Lin-Manuel Miranda, 'Weird Al' Yankovic Talk New 'Hamilton Polka'". Rolling Stone. Retrieved March 2, 2018.

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@@ Line 4: / Line 4: @@
 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.
-==January 0==
+==Historical==
+===January 0===
-'''January 0''' or '''0 January''' is an alternative name for [[December 31]].
+'''January 0''' or '''0 January''' 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>
-===In an ephemeris===
+===February 30===
-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>
-===In software===
-In [[Microsoft Excel]], the [[Epoch (computing)|epoch]] of the 1900 date format is 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>
-==February 30==
-'''February 30''' or '''30 February''' is a date that does not occur on the [[Gregorian calendar]], where the month of [[February]] contains only 28 days, or 29 days in a [[leap year]]. February 30 is usually used as a sarcastic date for referring to something that will never happen or will never be done.{{cn|date=April 2023}} It also appears in some [[#Reform calendars|reform calendars]].
-===Swedish calendar===
 {{see also|Swedish calendar}}
 [[File:feb1712.jpg|thumb|right|300px|Swedish calendar for February 1712]]
-February 30 was a day that happened in Sweden, 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=April 25, 2016}}</ref>
+'''February 30''' or '''30 February''' is a date that does not occur on the [[Gregorian calendar]], where the month of [[February]] contains only 28 days, or 29 days in a [[leap year]].
-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. 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>
+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 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>
-To avoid confusion and further mistakes, the Julian calendar was restored in 1712 by adding an extra 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>
+February 30 was a day that happened in Sweden, 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=April 25, 2016}}</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. 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>
-The Swedish conversion to the Gregorian calendar was finally accomplished in 1753, when February 17 was followed by March 1.<ref name="Bauer"/>
+To avoid confusion and further mistakes, the Julian calendar was restored in 1712 by adding an extra 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===
 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>
+It also appears in some [[#Reform calendars|reform calendars]].
-===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 31===
-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>
+[[File:Feb31OnTombstone.jpg|thumb|February 31 on a tombstone]]
+'''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 a typo).<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>
-===Myths===
+===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 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=June 4, 2009 |work=The Age |location=Australia |access-date=November 3, 2010 }}</ref> It is also used in the title of ''[[The 35th of May, or Conrad's Ride to the South Seas]]'', a German children's novel published in 1931.
-====Soviet calendar====
-Although many sources state that 30-day months were used in the Soviet Union for part or all of the period from 1929 to 1940, the [[Soviet calendar]] with 5- and 6-day weeks was used only for assigning workdays and days of rest in factories. The Gregorian calendar (since 1918) remained for everyday use: surviving physical calendars from that period show only the irregular months of the Gregorian calendar, including a 28- or 29-day February, suggesting there was never a February 30 in the Soviet Union.{{cn|date=March 2022}}
-====Early Julian calendar====
+===December 31.5 GMT===
+{{see also|Greenwich Mean Time#Ambiguity in the definition of GMT}}
-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 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>
+'''"December 31.5 GMT"''' in 1924 almanacs was an instant defined to solve 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>
-===Other===
+=== December 32, 1980 ===
+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 the date was officially recorded by sympathetic British government officials 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>
-[[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>
-==February 31==
+==Software==
+In [[Microsoft Excel]], the [[Epoch (computing)|epoch]] of the 1900 date format is 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>
-[[File:Feb31OnTombstone.jpg|thumb|February 31 on a tombstone]]
-'''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 a typo).<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>
-It is also used (along with February 32 and February 33) for calculating weather data.<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>
+February 31 is also used (along with February 32 and February 33) for calculating weather data.<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>
-==March 0==
 '''March 0''' or '''0 March''' is an alternative name for the last day of February ([[February 28]], or [[February 29]] in [[leap year]]s). It is used most often in [[astronomy]], [[Application software|software engineering]],<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><ref>{{cite book |last1=Tjia |first1=John S. |title=Building Financial Models |date=2009 |publisher=McGraw Hill Professional |isbn=978-0-07-160890-9 |page=144 |url=https://books.google.com/books?id=tZ7ss5KihJ0C&pg=PT144 }}</ref> and [[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>
-==May 35==
+==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>
-'''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 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=June 4, 2009 |work=The Age |location=Australia |access-date=November 3, 2010 }}</ref> It is also used in the title of ''[[The 35th of May, or Conrad's Ride to the South Seas]]'', a German children's novel published in 1931.
+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==
-'''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]]''.
+'''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 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 solve 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==
 '''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 in{{clarify|reason=Is this a specific date?|date=December 2023}} the fictional month of Octember.
-=== December 32, 1980 ===
-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 the date was officially recorded by sympathetic British government officials 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>
+==In popular culture==
-==Octember 1==
+[[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>
-The children's book ''Please Try to Remember the First of Octember!'' by [[Dr. Seuss]] narrates many delightful things which are supposed to happen in{{clarify|reason=Is this a specific date?|date=December 2023}} the fictional month of Octember.
 ==Reform calendars==

v t e Months and days of the year
Today: June 27, 2026 [refresh]
January	1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
February	1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
March	1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
April	1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
May	1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
June	1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
July	1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
August	1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
September	1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
October	1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
November	1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
December	1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Related: List of non-standard dates