February 30 occurs in some calendars but not in the Gregorian calendar, where February contains only 28 or, in a leap year, 29 days. February 30 is usually used as a sarcastic date for referring to something that will never happen or will never be done.
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 for the entire period 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 and 1704 and 1708 remained leap years.
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 30th of February in history. That date corresponded to February 29 in the Julian calendar and to March 11 in the Gregorian calendar.
The Swedish conversion to the Gregorian calendar was finally accomplished in the usual way in 1753, by omitting the last 11 days of February.
Although many sources erroneously state that 30-day months were used in the Soviet Union for part or all of the period 1929–1940, in fact the Soviet calendar with 5- and 6-day weeks was only used for assigning workdays and days of rest in factories. The traditional calendar remained for everyday use—surviving physical calendars from that period only show the irregular months of the Gregorian calendar, including a 28- or 29-day February, so there was never a February 30 in the Soviet Union.
Early Julian calendar
The 13th century scholar Sacrobosco claimed that in the Julian calendar February had 30 days in leap years between 45 BC and 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. (See Julian calendar.)
Due to evening out the months being 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 contains a 35-day February.
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.
In J.R.R. Tolkien's Middle-earth legendarium, the Hobbits have developed the Shire Reckoning. According to Appendix D to The Lord of the Rings written by Tolkien, this calendar has arranged the year neatly 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.
- "Thirty Days Hath February 2000?". About.com. Retrieved 7 November 2013.
- Bauer, R.W. (1868). Calender for Aarene fra 601 til 2200. Dansk Historisk Fællesråd (1993 reprint). p. 100. ISBN 87 7423 083 2.
- Vallerius, Johannes (1711). Allmanach på åhret effter Christi födelse 1712. Lund, Sweden.
- See Soviet calendar for a comprehensive list of sources, both for and against 30-day months.
- Return of the King, Appendix D
- The Oxford Companion to the Year. Bonnie Blackburn & Leofranc Holford-Strevens. Oxford University Press 1999. ISBN 0-19-214231-3. Pages 98–99.
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