February 30
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February 30 occurs in some calendars, unlike the Gregorian calendar, where February contains only 28 or 29 days.
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[edit] Swedish calendar
The Swedish Empire (which included Finland at the time) planned to change from the Julian calendar to the Gregorian calendar beginning in 1700 by omitting the leap days for the next 40 years. The plan was successfully followed in 1700. However, under the influence of the Great Northern War, which began later that year, the Swedes were focused too much on the war and could not focus on removing leap days, and so 1704 and 1708 were still leap years.
To avoid confusion and further mistakes, the Julian calendar was restored when, in 1712, one extra leap day was added, thus giving that year a 30th of February. That date corresponded to February 29 in Julian and March 11 in Gregorian counting. The Swedish changeover to the Gregorian calendar was finally accomplished in 1753.
[edit] Soviet calendar
Although many sources state that 30-day months were used in the Soviet Union for part or all of the period 1929–1940, other sources as well as all surviving physical calendars from that period only show the irregular months of the Gregorian calendar, including a 28- or 29-day February, so the Soviet calendar never had a February 30.
[edit] 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 shortened February to give the month of August named after him the same length as the month of July named after his adoptive uncle Julius Caesar. However, all other historical evidence relating to the Julian calendar during this period refutes Sacrobosco, including dual dates with the Alexandrian calendar. See Julian calendar: Month lengths.
[edit] Artificial calendars
Artificial calendars may also have thirty February dates. For example, in a climate model the statistics may be simplified by having twelve months of thirty days. The Hadley Centre General Circulation Model is an example.
[edit] References
- The Oxford Companion to the Year. Bonnie Blackburn & Leofranc Holford-Strevens. Oxford University Press 1999. ISBN 0-19-214231-3. Pages 98-99.
