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. In a leap year, February 29 is the 60th day of the Gregorian calendar, 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, so the Gregorian calendar was introduced both to shift it back by omitting several days, and to reduce the number of leap years via the aforementioned 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. For example, this has happened with ATMs and Microsoft's cloud system Azure.
Although most modern calendar years have 365 days, a complete revolution around the Sun (one solar year) takes approximately 365 days, 5 hours, 48 minutes, and 46 seconds (or, for simplicity's sake, approximately 365 days and 6 hours, or 365.25 days). An extra 23 hours, 15 minutes, and 4 seconds thus accumulates every four years (again, for simplicity's sake, approximately an extra 24 hours, or 1 day, every four years), requiring that an extra calendar day be added to align the calendar with the Sun's apparent position. Without the added day, in future years the seasons would occur later in the calendar, eventually leading to confusion about when to undertake activities dependent on weather, ecology, or hours of daylight.
Solar years are actually slightly shorter than 365 days and 6 hours (365.25 days), which had been known since the 2nd century BC when Hipparchus stated that it lasted 365 + 1/ − 1/ days, but this was ignored by Julius Caesar and his astronomical adviser Sosigenes. The Gregorian calendar corrected this by adopting the length of the tropical year stated in three medieval sources, the Alfonsine tables, De Revolutionibus, and the Prutenic Tables, truncated to two sexagesimal places, 365 14/ 33/ days or 365 + 1/ − 3/ days or 365.2425 days. The length of the tropical year in 2000 was 365.24217 mean solar days, Adding a calendar day every four years, therefore, results in an excess of around 44 minutes every four years, or about 3 days every 400 years. To compensate for this, three days are removed every 400 years. The Gregorian calendar reform implements this adjustment by making an exception to the general rule that there is a leap year every four years. Instead, a year divisible by 100 is not a leap year unless that year is also divisible by 400. This means that the years 1600, 2000, and 2400 are leap years, while the years 1700, 1800, 1900, 2100, 2200, 2300, and 2500 are not leap years.
Modern (Gregorian) calendarEdit
The Gregorian calendar repeats itself every 400 years, which is exactly 20,871 weeks including 97 leap days (146,097 days). Over this period, February 29 falls on Sunday, Tuesday, and Thursday 13 times; Friday and Saturday 14 times; and Monday and Wednesday 15 times. Except for a century mark that is not a multiple of 400, consecutive leap days fall in order Sunday, Friday, Wednesday, Monday, Saturday, Thursday, Tuesday, and repeats again.
Early Roman calendarEdit
The calendar of the Roman king Numa Pompilius had only 355 days (even though it was not a lunar calendar) which meant that it would quickly become unsynchronized with the solar year. An earlier Roman solution to this problem was to lengthen the calendar periodically by adding extra days to February, the last month of the year. February consisted of two parts, each with an odd number of days. The first part ended with the Terminalia on the 23rd, which was considered the end of the religious year, and the five remaining days formed the second part. To keep the calendar year roughly aligned with the solar year, a leap month, called Mensis Intercalaris ("intercalary month"), was added from time to time between these two parts of February. The (usual) second part of February was incorporated in the intercalary month as its last five days, with no change either in their dates or the festivals observed on them. This followed naturally, because the days after the Ides (13th) of February (in an ordinary year) or the Ides of Intercalaris (in an intercalary year) both counted down to the Kalends of March (i.e. they were known as "the nth day before the Kalends of March"). The Nones (5th) and Ides of Intercalaris occupied their normal positions.
The third-century writer Censorinus says:
When it was thought necessary to add (every two years) an intercalary month of 22 or 23 days, so that the civil year should correspond to the natural (solar) year, this intercalation was in preference made in February, between Terminalia [23rd] and Regifugium [24th].
The set leap day was introduced in Rome as a part of the Julian reform in the 1st century BCE. As before, the intercalation was made after February 23. The day following the Terminalia (February 23) was doubled, forming the "bis sextum"—literally 'twice sixth', since February 24 was 'the sixth day before the Kalends of March' using Roman inclusive counting (March 1 was the Kalends of March and was also the first day of the calendar year). Inclusive counting initially caused the Roman priests to add the extra day every three years instead of four; Augustus was compelled to omit leap years for a few decades to return the calendar to its proper position. Although there were exceptions, the first day of the bis sextum (February 24) was usually regarded as the intercalated or "bissextile" day since the 3rd century CE. February 29 came to be regarded as the leap day when the Roman system of numbering days was replaced by sequential numbering in the late Middle Ages, although this has only been formally enacted in Sweden and Finland. In Britain, the extra day added to leap years remains notionally the 24th, although the 29th remains more visible on the calendar.
Born on February 29Edit
A person born on February 29 may be called a "leapling", a "leaper", or a "leap-year baby". Some leaplings celebrate their birthday in non-leap years on either February 28 or March 1, while others only observe birthdays on the authentic intercalary date, February 29.
The effective legal date of a leapling's birthday in non-leap years varies between jurisdictions.
In New Zealand, a person born on February 29 is deemed to have their birthday on February 28 in non-leap years, for the purposes of Driver Licensing under §2(2) of the Land Transport (Driver Licensing) Rule 1999. The net result is that for drivers aged 75, or over 80, their driver licence expires at the end of the last day of February, even though their birthday would otherwise fall on the first day in March in non-leap years. Otherwise, New Zealand legislation is silent on when a person born on February 29 has their birthday, although case law would suggest that age is computed based on the number of years elapsed, from the day after the date of birth, and that the person's birth day then occurs on the last day of the year period. This differs from English common law where a birthday is considered to be the start of the next year, the preceding year ending at midnight on the day preceding the birthday. While a person attains the same age on the same day, it also means that, in New Zealand, if something must be done by the time a person attains a certain age, that thing can be done on the birthday that they attain that age and still be lawful.
In Taiwan, the legal birthday of a leapling is February 28 in common years:
- If a period fixed by weeks, months, and years does not commence from the beginning of a week, month, or year, it ends with the ending of the day which proceeds the day of the last week, month, or year which corresponds to that on which it began to commence. But if there is no corresponding day in the last month, the period ends with the ending of the last day of the last month.
Thus, in England and Wales or in Hong Kong, a person born on February 29 will have legally reached 18 years old on March 1. If they were born in Taiwan they legally become 18 on February 28, a day earlier.
In the United States, according to John Reitz, a professor of law at the University of Iowa, there is no "... statute or general rule that has anything to do with leap day." Reitz speculates that "March 1 would likely be considered the legal birthday in non-leap years of someone born on leap day," using the same reasoning as described for the United Kingdom and Hong Kong. However, for the purposes of Social Security, a person attains the next age the day before the anniversary of birth. Therefore, Social Security would recognize February 28 as the change in age for leap year births, not March 1.
There are many instances in children's literature where a person's claim to be only a quarter of their actual age turns out to be based on counting only their leap-year birthdays.
A similar device is used in the plot of Gilbert and Sullivan's 1879 comic opera The Pirates of Penzance: as a child, Frederic was apprenticed to a band of pirates until his 21st birthday. Having passed his 21st year, he leaves the pirate band and falls in love. However, since he was born on February 29, his 21st birthday will not arrive until he is eighty-eight (since 1900 was not a leap year), so he must leave his fiancée and return to the pirates.
- 1504 – Christopher Columbus uses his knowledge of a lunar eclipse that night to convince Jamaican natives to provide him with supplies.
- 1644 – Abel Tasman's second Pacific voyage begins.
- 1704 – Queen Anne's War: French forces and Native Americans stage a raid on Deerfield, Massachusetts Bay Colony, killing 56 villagers and taking more than 100 captive.
- 1712 – February 29 is followed by February 30 in Sweden, in a move to abolish the Swedish calendar for a return to the Julian calendar.
- 1720 – Ulrika Eleonora, Queen of Sweden abdicates in favour of her husband, who becomes King Frederick I on March 24.
- 1752 – King Alaungpaya founds Konbaung Dynasty, the last dynasty of Burmese monarchy.
- 1768 – Polish nobles form the Bar Confederation.
- 1796 – The Jay Treaty between the United States and Great Britain comes into force, facilitating ten years of peaceful trade between the two nations.
- 1864 – American Civil War: Kilpatrick–Dahlgren Raid fails: Plans to free 15,000 Union soldiers being held near Richmond, Virginia are thwarted.
- 1892 – St. Petersburg, Florida is incorporated.
- 1912 – The Piedra Movediza (Moving Stone) of Tandil falls and breaks.
- 1916 – Tokelau is annexed by the United Kingdom.
- 1916 – Child labor: In South Carolina, the minimum working age for factory, mill, and mine workers is raised from 12 to 14 years old.
- 1920 – Czechoslovak National Assembly adopts the Constitution.
- 1936 – February 26 Incident in Tokyo ends.
- 1940 – 12th Academy Awards: For her performance as "Mammy" in Gone with the Wind, Hattie McDaniel becomes the first African American to win an Academy Award.
- 1940 – Finland initiates Winter War peace negotiations.
- 1940 – In a ceremony held in Berkeley, California, physicist Ernest Lawrence receives the 1939 Nobel Prize in Physics from Sweden's Consul General in San Francisco.
- 1944 – World War II: The Admiralty Islands are invaded in Operation Brewer led by American General Douglas MacArthur.
- 1960 – The 5.7 Mw Agadir earthquake shakes coastal Morocco with a maximum perceived intensity of X (Extreme), destroying Agadir, and leaving 12,000 dead and another 12,000 injured.
- 1972 – Vietnam War: Vietnamization: South Korea withdraws 11,000 of its 48,000 troops from Vietnam.
- 1980 – Gordie Howe of the Hartford Whalers makes NHL history as he scores his 800th goal.
- 1984 – Pierre Trudeau announces his retirement as Liberal Party leader and Prime Minister of Canada.
- 1988 – South African archbishop Desmond Tutu is arrested along with one hundred other clergymen during a five-day anti-apartheid demonstration in Cape Town.
- 1988 – Svend Robinson becomes the first member of the House of Commons of Canada to come out as gay.
- 1992 – First day of Bosnia and Herzegovina independence referendum.
- 1996 – Faucett Flight 251 crashes in the Andes; all 123 passengers and crew die.
- 1996 – Siege of Sarajevo officially ends.
- 2000 – Second Chechen War: Eighty-four Russian paratroopers are killed in a rebel attack on a guard post near Ulus Kert.
- 2004 – Jean-Bertrand Aristide is removed as President of Haiti following a coup.
- 2008 – The United Kingdom's Ministry of Defence decides to withdraw Prince Harry from a tour of Afghanistan "immediately" after a leak leads to his deployment being reported by foreign media.
- 2008 – Misha Defonseca admits to fabricating her memoir, Misha: A Mémoire of the Holocaust Years, in which she claims to have lived with a pack of wolves in the woods during the Holocaust.
- 2012 – Tokyo Skytree construction is completed. It is the tallest tower in the world, 634 meters high, and the second-tallest artificial structure on Earth, next to Burj Khalifa.
- 1468 – Pope Paul III (d. 1549)
- 1528 – Albert V, Duke of Bavaria (d. 1579)
- 1528 – Domingo Báñez, Spanish theologian (d. 1604)
- 1572 – Edward Cecil, 1st Viscount Wimbledon (d. 1638)
- 1576 – Antonio Neri, Florentine priest and glassmaker (d. 1614)
- 1640 – Benjamin Keach, Particular Baptist preacher and author whose name was given to Keach's Catechism (d. 1704)
- 1692 – John Byrom, English poet and educator (d. 1763)
- 1724 – Eva Marie Veigel, Austrian-English dancer (d. 1822)
- 1736 – Ann Lee, English-American religious leader, founded the Shakers (d. 1784)
- 1792 – Gioachino Rossini, Italian composer (d. 1868)
- 1812 – James Milne Wilson, Scottish-Australian soldier and politician, 8th Premier of Tasmania (d. February 29, 1880)
- 1828 – Emmeline B. Wells, American journalist, poet, and activist (d. 1921)
- 1836 – Dickey Pearce, American baseball player and manager (d. 1908)
- 1852 – Frank Gavan Duffy, Irish-Australian lawyer and judge, 4th Chief Justice of Australia (d. 1936)
- 1860 – Herman Hollerith, American statistician and businessman, co-founded the Computing-Tabulating-Recording Company (d. 1929)
- 1876 – William Stewart, Scottish footballer
- 1884 – Richard S. Aldrich, American lawyer and politician (d. 1941)
- 1892 – Augusta Savage, American sculptor (d. 1962)
- 1896 – Morarji Desai, Indian civil servant and politician, 4th Prime Minister of India (d. 1995)
- 1896 – William A. Wellman, American actor, director, producer, and screenwriter (d. 1975)
- 1904 – Jimmy Dorsey, American saxophonist, composer, and bandleader (d. 1957)
- 1904 – Pepper Martin, American baseball player and manager (d. 1965)
- 1908 – Balthus, French-Swiss painter and illustrator (d. 2001)
- 1908 – Dee Brown, American historian and author (d. 2002)
- 1908 – Alf Gover, English cricketer and coach (d. 2001)
- 1908 – Louie Myfanwy Thomas, Welsh writer (d. 1968)
- 1916 – Dinah Shore, American singer and actress (d. 1994)
- 1916 – James B. Donovan, American lawyer (d. 1970)
- 1916 – Leonard Shoen, founder of U-Haul Corp. (d. 1999)
- 1920 – Fyodor Abramov, Russian author and critic (d. 1983)
- 1920 – Arthur Franz, American actor (d. 2006)
- 1920 – James Mitchell, American actor and dancer (d. 2010)
- 1920 – Michèle Morgan, French-American actress and singer (d. 2016)
- 1920 – Howard Nemerov, American poet and academic (d. 1991)
- 1920 – Rolland W. Redlin, American lawyer and politician (d. 2011)
- 1924 – David Beattie, New Zealand judge and politician, 14th Governor-General of New Zealand (d. 2001)
- 1924 – Carlos Humberto Romero, Salvadoran politician, President of El Salvador (d. 2017)
- 1924 – Al Rosen, American baseball player and manager (d. 2015)
- 1928 – Joss Ackland, English actor
- 1928 – Jean Adamson, British writer and illustrator
- 1928 – Vance Haynes, American archaeologist, geologist, and author
- 1928 – Seymour Papert, South African mathematician and computer scientist, co-created the Logo programming language (d. 2016)
- 1932 – Gene H. Golub, American mathematician and academic (d. 2007)
- 1932 – Masten Gregory, American race car driver (d. 1985)
- 1932 – Reri Grist, American soprano and actress
- 1932 – Jaguar, Brazilian cartoonist
- 1932 – Gavin Stevens, Australian cricketer
- 1936 – Jack Lousma, American colonel, astronaut, and politician
- 1936 – Henri Richard, Canadian ice hockey player (d. 2020)
- 1936 – Alex Rocco, American actor (d. 2015)
- 1936 – Nh. Dini, Indonesian writer (d. 2018)
- 1940 – Sonja Barend, Dutch talk show host
- 1940 – Bartholomew I of Constantinople
- 1940 – William H. Turner, Jr., American horse trainer
- 1944 – Ene Ergma, Estonian physicist and politician
- 1944 – Dennis Farina, American police officer and actor (d. 2013)
- 1944 – Nicholas Frayling, English priest and academic
- 1944 – Phyllis Frelich, American actress (d. 2014)
- 1944 – Steve Mingori, American baseball player (d. 2008)
- 1944 – Paolo Eleuteri Serpieri, Italian author and illustrator
- 1944 – Lennart Svedberg, Swedish ice hockey player (d. 1972).
- 1948 – Hermione Lee, English author, critic, and academic
- 1948 – Manoel Maria, Brazilian footballer
- 1948 – Patricia A. McKillip, American author
- 1948 – Henry Small, American-born Canadian singer
- 1952 – Sharon Dahlonega Raiford Bush, American journalist and producer
- 1952 – Tim Powers, American author and educator
- 1952 – Raisa Smetanina, Russian cross-country skier
- 1952 – Bart Stupak, American police officer and politician
- 1956 – Jonathan Coleman, English-Australian radio and television host
- 1956 – Bob Speller, Canadian businessman and politician, 30th Canadian Minister of Agriculture
- 1956 – Aileen Wuornos, American serial killer (d. 2002)
- 1960 – Lucian Grainge, English businessman
- 1960 – Khaled, Algerian singer-songwriter
- 1960 – Richard Ramirez, American serial killer (d. 2013)
- 1964 – Dave Brailsford, English cyclist and coach
- 1964 – Lyndon Byers, Canadian ice hockey player and radio host
- 1964 – Mervyn Warren, American tenor, composer, and producer
- 1968 – Chucky Brown, American basketball player and coach
- 1968 – Pete Fenson, American curler and sportscaster
- 1968 – Naoko Iijima, Japanese actress and model
- 1968 – Bryce Paup, American football player and coach
- 1968 – Howard Tayler, American author and illustrator
- 1968 – Eugene Volokh, Ukrainian-American lawyer and educator
- 1968 – Frank Woodley, Australian actor, producer, and screenwriter
- 1972 – Mike Pollitt, English footballer and coach
- 1972 – Sylvie Lubamba, Italian showgirl
- 1972 – Antonio Sabàto, Jr., Italian-American model and actor
- 1972 – Pedro Sánchez, Prime Minister of Spain
- 1972 – Dave Williams, American singer (d. 2002)
- 1972 – Saul Williams, American singer-songwriter
- 1972 – Pedro Zamora, Cuban-American activist and educator (d. 1994)
- 1976 – Vonteego Cummings, American basketball player
- 1976 – Gehad Grisha, Egyptian soccer referee
- 1976 – Katalin Kovács, Hungarian sprint kayaker
- 1976 – Terrence Long, American baseball player
- 1976 – Ja Rule, American rapper and actor
- 1980 – Çağdaş Atan, Turkish footballer and coach
- 1980 – Chris Conley, American singer-songwriter and guitarist
- 1980 – Patrick Côté, Canadian mixed martial artist
- 1980 – Simon Gagné, Canadian ice hockey player
- 1980 – Rubén Plaza, Spanish cyclist
- 1980 – Peter Scanavino, American actor
- 1980 – Clinton Toopi, New Zealand rugby league player
- 1980 – Taylor Twellman, American soccer player and sportscaster
- 1984 – Rica Imai, Japanese model and actress
- 1984 – Cullen Jones, American swimmer
- 1984 – Nuria Martínez, Spanish basketball player
- 1984 – Adam Sinclair, Indian field hockey player
- 1984 – Rakhee Thakrar, English actress
- 1984 – Dennis Walger, German rugby player
- 1984 – Cam Ward, Canadian ice hockey player
- 1984 – Mark Foster, American singer, songwriter and musician
- 1988 – Lena Gercke, German model and television host
- 1988 – Benedikt Höwedes, German footballer
- 1988 – Brent Macaffer, Australian Rules footballer
- 1988 – Bobby Sanguinetti, American ice hockey player
- 1988 – Milan Melindo, Filipino boxer
- 1992 – Sean Abbott, Australian cricketer
- 1992 – Ben Hampton, Australian rugby league player
- 1992 – Eric Kendricks, American football player
- 1992 – Caitlin EJ Meyer, American actress
- 1996 – Nelson Asofa-Solomona, New Zealand rugby league player
- 1996 – Reece Prescod, British sprinter
- 1996 – Claudia Williams, New Zealand tennis player
- 2000 – Ferran Torres, Spanish footballer
- 468 – Pope Hilarius
- 992 – Oswald of Worcester, Anglo-Saxon archbishop and saint (b. 925)
- 1212 – Hōnen, Japanese monk, founded Jōdo-shū (b. 1133)
- 1460 – Albert III, Duke of Bavaria-Munich (b. 1401)
- 1528 – Patrick Hamilton, Scottish Protestant reformer and martyr (b. 1504)
- 1592 – Alessandro Striggio, Italian composer and diplomat (b. 1540)
- 1600 – Caspar Hennenberger, German pastor, historian and cartographer (b. 1529)
- 1604 – John Whitgift, English archbishop and academic (b. 1530)
- 1740 – Pietro Ottoboni, Italian cardinal (b. 1667)
- 1744 – John Theophilus Desaguliers, French-English physicist and philosopher (b. 1683)
- 1792 – Johann Andreas Stein, German piano builder (b. 1728)
- 1820 – Johann Joachim Eschenburg, German historian and critic (b. 1743)
- 1848 – Louis-François Lejeune, French general, painter and lithographer (b. 1775)
- 1852 – Matsudaira Katataka, Japanese daimyō (b. 1806)
- 1868 – Ludwig I of Bavaria (b. 1786)
- 1880 – James Milne Wilson, Scottish-Australian soldier and politician, 8th Premier of Tasmania (b. February 29, 1812)
- 1920 – Ernie Courtney, American baseball player (b. 1875)
- 1940 – E. F. Benson, English archaeologist and author (b. 1867)
- 1944 – Pehr Evind Svinhufvud, Finnish lawyer, judge and politician, 3rd President of Finland (b. 1861)
- 1952 – Quo Tai-chi, Chinese politician and diplomat, Permanent Representative of China to the United Nations (b. 1888)
- 1956 – Elpidio Quirino, Filipino lawyer and politician, 6th President of the Philippines (b. 1890)
- 1964 – Frank Albertson, American actor and singer (b. 1909)
- 1972 – Tom Davies, American football player and coach (b. 1896)
- 1976 – Florence P. Dwyer, American politician (b. 1902)
- 1984 – Ludwik Starski, Polish screenwriter and songwriter (b. 1903)
- 1988 – Sidney Harmon, American screenwriter and producer (b. 1907)
- 1992 – Ruth Pitter, English poet and author (b. 1897)
- 2000 – Dennis Danell, American guitarist (b. 1961)
- Wenn V. Deramas, Filipino director and screenwriter (b. 1966)
- Gil Hill, American police officer, actor and politician (b. 1931)
- Josefin Nilsson, Swedish singer (b. 1969)
- Louise Rennison, English author (b. 1951)
- Mumtaz Qadri, Pakistani assassin, was allegedly executed on Feb 29 to deny his supporters an anniversary.
Holidays and observancesEdit
- As a Christian feast day:
- The fourth day of Ayyám-i-Há (Bahá'í Faith) (observed on this date only if Bahá'í Naw-Rúz falls on March 21)
- Rare Disease Day (in leap years; celebrated in common years on February 28)
- Bachelor's Day (Ireland, United Kingdom)
There is a popular tradition known as Bachelor's Day in some countries allowing a woman to propose marriage to a man on February 29. If the man refuses, he then is obliged to give the woman money or buy her a dress. In upper-class societies in Europe, if the man refuses marriage, he then must purchase 12 pairs of gloves for the woman, suggesting that the gloves are to hide the woman's embarrassment of not having an engagement ring. In Ireland, the tradition is supposed to originate from a deal that Saint Bridget struck with Saint Patrick.
- Lerner, Ed. K. Lee; Lerner, Brenda W. (2004). "Calendar". The Gale Encyclopedia of Science. Detroit, MI: Gale. pp. 679–82.CS1 maint: ref=harv (link)
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- Conrad Bullock (January 7, 1993). "Leap Year Causes Problems for ATM Machines".
- Gene Wirchenko (March 2, 2012). "Windows Azure Leap-Year Glitch Takes Down G-Cloud".
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- Ptolemy (1998), Ptolemy's Almagest, translated by Toomer, G. J., Princeton University Press, p. 139, ISBN 0-691-00260-6
- North, J. D. (1983), "The Western calendar – "intolerabilis, horribilis, et derisibilis"; four centuries of discontent", in Coyne, G. V.; Hoskin, M. A.; Pedersen, O. (eds.), Gregorian reform of the calendar, Vatican Observatory, p. 99
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- Censorinus, The Natal Day, 20.28, tr. William Maude, New York 1900, available at .
- Bonnie Blackburn and Leofranc Holford-Strevens, The Oxford companion to the year (Oxford: Oxford University Press, 1999) 678–680.
- "Ante Diem Bis Sextum Kalendras Martii", News, The British Sundial Society, February 24, 2016.
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- Sullivan, Arthur; Gilbert, W.S. (August 20, 2011). "The Pirates of Penzance". Gilbert and Sullivan Archive. Archived from the original on November 15, 2011. Retrieved February 6, 2012.
- Narcisse, Evan (February 29, 2016). "The Goofy Reason DC Comics Says Today Is Superman's Birthday". Retrieved February 28, 2020.
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- "'Excuse Me, But I Think You're Sitting on My Hershey Bar' and Other Openers", The Washington Post, February 29, 1980. p. D5
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- Krucoff, Carol. "By Leaps and Seconds: It's Feb. 29: Call It a Time-Consuming Day", The Washington Post. February 29, 1984, p. F9. "Leap Day was not created, as rumor has it, to give women one day out of 1,461 to chase men (who needs a special day for that?)—even though the town of Aurora, Ill., deputizes single women and allows them to arrest bachelors (fine, $4) every Feb. 29."[better source needed]
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