February 29, also known as leap day or leap year day, is a date added to most years that are divisible by 4, such as 2016, 2020, and 2024. A leap day is added in various solar calendars (calendars based on the Earth’s revolution around the Sun), including the Gregorian calendar standard in most of the world. Lunisolar calendars (whose months are based on the phases of the Moon) instead add a leap or intercalary month. In the Gregorian calendar, years that are divisible by 100, but not by 400, do not contain a leap day. Thus, 1700, 1800, and 1900 did not contain a leap day; neither will 2100, 2200, and 2300. Conversely, 1600 and 2000 did and 2400 will. Years containing a leap day are called leap years. Years not containing a leap day are called common years. February 29 is the 60th day of the Gregorian calendar in such a year with 306 days remaining until the end of the year. In the Chinese calendar, this day will only occur in years of the monkey, dragon and rat.
A leap day is observed because the Earth’s period of orbital revolution around the Sun takes approximately six hours longer than 365 whole days. A leap day compensates for this lag, realigning the calendar with the Earth’s position in the Solar System; otherwise, seasons would occur later than intended in the calendar year. The Julian calendar used in Christendom until the 16th century added a leap day every four years; but this rule adds too many days (roughly three every 400 years), making the equinoxes and solstices shift gradually to earlier dates. By the 16th century the vernal equinox had drifted to March 11, and the Gregorian calendar was introduced both to shift it back by omitting several days, and to reduce the number of leap years via the ‘century rule’ to keep the equinoxes more or less fixed and the date of Easter consistently close to the vernal equinox.
Leap days can present a particular problem in computing known as the Leap year bug, when February 29 is not handled correctly in logic that accepts or manipulates dates. In Ireland and Britain, it is a tradition that women may propose marriage only in leap years. While it has been claimed that the tradition was initiated by Saint Patrick or Brigid of Kildare in 5th century Ireland, this is dubious, as the tradition has not been attested before the 19th century. Supposedly, a 1288 law by Queen Margaret of Scotland (then age five and living in Norway), required that fines be levied if a marriage proposal was refused by the man; compensation was deemed to be a pair of leather gloves, a single rose, £1 and a kiss. In some places the tradition was tightened to restricting female proposals to the modern leap day, February 29, or to the medieval (bissextile) leap day, February 24.
A person born on February 29 may be called a ‘leapling’ or a ‘leaper’. In common years, they usually celebrate their birthdays on February 28. In some situations, March 1 is used as the birthday in a non-leap year, since it is the day following February 28.
Most notable historic snippets or facts extracted from the book ‘On This Day’ first published in 1992 by Octopus Publishing Group Ltd, London, as well as additional supplementary information extracted from Wikipedia.
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