Leap year

The early Roman calendar was a lunisolar one that consisted of 12 months, for a total of 355 days. In addition, a 27- or 28-day intercalary month, the Mensis Intercalaris, was sometimes inserted into February, at the first or second day after the Terminalia a. d. VII Kal. Mar., (23 February), to resynchronise the lunar and solar cycles. The remaining days of Februarius were discarded. This intercalary month, named Intercalaris or Mercedonius, contained 27 days. The religious festivals that were normally celebrated in the last five days of February were moved to the last five days of Intercalaris. The lunisolar calendar was abandoned about 450 BC by the decemviri,[16] who implemented the Roman Republican calendar, used until 46 BC. The days of these calendars were counted down (inclusively) to the next named day, so 24 February was ante diem sextum Kalendas Martias ["the sixth day before the calends of March"] often abbreviated a. d. VI Kal. Mart. The Romans counted days inclusively in their calendars, so this was actually the fifth day before 1 March when counted in the modern exclusive manner (i.e., not including both the starting and ending day).[17] Because only 22 or 23 days were effectively added, not a full lunation, the calends and ides of the Roman Republican calendar were no longer associated with the new moon and full moon.

In Caesar's revised calendar, there was just one intercalary day – nowadays called the leap day – to be inserted every fourth year, and this too was done after 23 February. To create the intercalary day, the existing ante diem sextum Kalendas Martias (sixth day (inclusive: i.e. what we would call the fifth day before) before the Kalends (first day) of March, i.e. what we would call 24 February) was doubled,[18] producing ante diem bis sextum Kalendas Martias [a second sixth day before the Kalends . This bis sextum ("twice sixth") was rendered in later languages as "bissextile": the "bissextile day" is the leap day, and a 'bissextile year' is a year which includes a leap day.[19] This second instance of the sixth day before the Kalends of March was inserted in calendars between the "normal" fifth and sixth days. By a legal fiction, the Romans treated both the first "sixth day" and the additional "sixth day" before the Kalends of March as one day. Thus a child born on either of those days in a leap year would have its first birthday on the following sixth day before the Kalends of March. In a leap year in the original Julian calendar, there were indeed two days both numbered 24 February. This practice continued for another fifteen to seventeen centuries, even after most countries had adopted the Gregorian calendar.

For legal purposes, the two days of the bis sextum were considered to be a single day, with the second sixth being intercalated; but in common practice by the year 238, when Censorinus wrote, the intercalary day was followed by the last five days of February, a. d. VI, V, IV, III and pridie Kal. Mart. (the days numbered 24, 25, 26, 27, and 28 from the beginning of February in a common year), so that the intercalated day was the first of the doubled pair. Thus the intercalated day was effectively inserted between the 23rd and 24th days of February. All later writers, including Macrobius about 430, Bede in 725, and other medieval computists (calculators of Easter), continued to state that the bissextum (bissextile day) occurred before the last five days of February.

In England, the Church and civil society continued the Roman practice whereby the leap day was simply not counted, so that a leap year was only reckoned as 365 days. Henry III's 1236 Statute De Anno et Die Bissextili[lower-alpha 1] instructed magistrates to treat the leap day and the day before as one day.[20][19] The practical application of the rule is obscure. It was regarded as in force in the time of the famous lawyer Sir Edward Coke (1552–1634) because he cites it in his Institutes of the Lawes of England. However, Coke merely quotes the Act with a short translation, and does not give practical examples.[21]

' ... and by (b) the statute de anno bissextili, it is provided, quod computentur dies ille excrescens et dies proxime præcedens pro unico dii, so as in computation that day excrescent is not accounted.'

Replacement (by 29 February) of the awkward practice of having two days with the same date appears to have evolved by custom and practice, the etymological origin of the term "bissextile" seeming to have been lost.[14] In England in the course of the fifteenth century, "29 February" appears increasingly often in legal documents – although the records of the proceedings of the House of Commons of England continued to use the old system until the middle of the sixteenth century.[14] It was not until passage of the Calendar (New Style) Act 1750 that 29 February was formally recognised in British law.[22][lower-alpha 2]

In the older Roman Missal, feast days falling on or after 24 February are celebrated one day later in a leap year.

In the liturgical calendar of the Christian churches, the placement of the leap day is significant because of the date of the feast of Saint Matthias, which is defined as the sixth day before 1 March (counting inclusively). The Church of England's Book of Common Prayer was still using the "two days with the same date" system in its 1542 edition;[24] it first included a calendar which used entirely consecutive day counting from 1662 and showed leap day as falling on February 29.[25] In the 1680s, the Church of England declared 25 February to be the feast of St Matthias.[26] Until 1970, the Roman Catholic Church always celebrated the feast of Saint Matthias on a. d. VI Kal. Mart., so if the days were numbered from the beginning of the month, it was named 24 February in common years, but the presence of the bissextum in a bissextile year immediately before a. d. VI Kal. Mart. shifted the latter day to 25 February in leap years, with the Vigil of St. Matthias shifting from 23 February to the leap day of 24 February. This shift did not take place in pre-Reformation Norway and Iceland; Pope Alexander III ruled that either practice was lawful.[27] Other feasts normally falling on 25–28 February in common years are also shifted to the following day in a leap year (although they would be on the same day according to the Roman notation). The practice is still observed by those who use the older calendars.

A spinster eagerly awaits the upcoming leap day, in this 1903 cartoon by Bob Satterfield.

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.[28] 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.[lower-alpha 3] In some places the tradition was tightened to restricting female proposals to the modern leap day, 29 February, or to the medieval (bissextile) leap day, 24 February.

According to Felten: "A play from the turn of the 17th century, 'The Maydes Metamorphosis,' has it that 'this is leape year/women wear breeches.' A few hundred years later, breeches wouldn't do at all: Women looking to take advantage of their opportunity to pitch woo were expected to wear a scarlet petticoat – fair warning, if you will."[29]

In Finland, the tradition is that if a man refuses a woman's proposal on leap day, he should buy her the fabrics for a skirt.[30]

In France, since 1980, a satirical newspaper titled La Bougie du Sapeur is published only on leap year, on 29 February.

In Greece, marriage in a leap year is considered unlucky.[31] One in five engaged couples in Greece will plan to avoid getting married in a leap year.[32]

In February 1988 the town of Anthony in Texas, declared itself "leap year capital of the world", and an international leapling birthday club was started.[33]

• 1908 postcards
• 
  Woman capturing man with butterfly-net
• 
  Women anxiously awaiting January 1
• 
  Histrionically preparing

A person born on February 29 may be called a "leapling" or a "leaper".[34] In common years, they usually celebrate their birthdays on 28 February. In some situations, 1 March is used as the birthday in a non-leap year, since it is the day following 28 February.

Technically, a leapling will have fewer birthday anniversaries than their age in years. This phenomenon may be exploited for dramatic effect when a person is declared to be only a quarter of their actual age, by counting their leap-year birthday anniversaries only. For example, in Gilbert and Sullivan's 1879 comic opera The Pirates of Penzance, Frederic (the pirate apprentice) discovers that he is bound to serve the pirates until his 21st birthday (that is, when he turns 88 years old, since 1900 was not a leap year) rather than until his 21st year.

For legal purposes, legal birthdays depend on how local laws count time intervals.

Wikisource has original text related to this article:

Civil Code Part I General Principles

The Civil Code of Taiwan since 10 October 1929,[35] implies that the legal birthday of a leapling is 28 February 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 precedes 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.[36]

Since 1990 non-retroactively, Hong Kong considers the legal birthday of a leapling 1 March in common years:[37]

1. The time at which a person attains a particular age expressed in years shall be the commencement of the anniversary corresponding to the date of [their] birth.
2. Where a person has been born on February 29 in a leap year, the relevant anniversary in any year other than a leap year shall be taken to be March 1.
3. This section shall apply only where the relevant anniversary falls on a date after the date of commencement of this Ordinance.

The Revised Julian calendar adds an extra day to February in years that are multiples of four, except for years that are multiples of 100 that do not leave a remainder of 200 or 600 when divided by 900. This rule agrees with the rule for the Gregorian calendar until 2799. The first year that dates in the Revised Julian calendar will not agree with those in the Gregorian calendar will be 2800, because it will be a leap year in the Gregorian calendar but not in the Revised Julian calendar.

This rule gives an average year length of 365.242222 days. This is a very good approximation to the mean tropical year, but because the vernal equinox year is slightly longer, the Revised Julian calendar, for the time being, does not do as good a job as the Gregorian calendar at keeping the vernal equinox on or close to 21 March.