The year 2012 is a Leap Year and February 29 is Leap Day. People born on Leap Days are known as leaplings or leapers. Do you know any leaplings or leapers?

Here are some fun facts about leap days, leap years, leaplings, and leapers.

1) February 29 is the date that is added to our calendar about once every four years. It is called leap day.

2) A leap year is a year containing one additional day. A leap year consists of 366 days, as opposed to a common year, which has 365 days.

3) Leap Years were first introduced over 2,000 years ago when we transitioned from the Roman Calendar to the Julian Calendar in 45 BCE. This day is added to the calendar in leap years as a corrective measure, because the earth does not orbit around the sun in precisely 365 days.

4) In the Gregorian calendar, the current standard calendar in most of the world, most years that are evenly divisible by 4 are leap years. Adding an extra day to the calendar every four years compensates for the fact that a period of 365 days is shorter than a solar year by almost 6 hours.

5) The Gregorian calendar was designed to keep the vernal equinox on or close to March 21, so that the date of Easter (celebrated on the Sunday after the 14th day of the first full moon that falls on or after March 21) remains correct with respect to the vernal equinox. The vernal equinox year is about 365.242374 days long (and increasing).

6) But the math is not perfect so there are some exceptions to this rule. Since the duration of a solar year is slightly less than 365.25 days, years that are evenly divisible by 100 are not leap years, unless they are also evenly divisible by 400, in which case they are leap years. For example, 1600 and 2000 were leap years, but 1700, 1800 and 1900 were not. Similarly, 2100, 2200, 2300, 2500, 2600, 2700, 2900 and 3000 will not be leap years, but 2400 and 2800 will be. Therefore, over two millennia, there will be 485 leap years. Using this rule, the average number of days per year will be 365 + 1/4 − 1/100 + 1/400 = 365.2425, which is 365 days, 5 hours, 49 minutes, and 12 seconds.

7) The difference of 0.000125 days between the Gregorian calendar average year and the actual year means that, in 8,000 years, the calendar will be about one day behind where it is now. But in 8,000 years, the length of the vernal equinox year will have changed by an amount that cannot be accurately predicted thus making 4000 a non-leap year will probably not be necessary.

Doesn’t this make you just love math?

8) Not all calendars treat the need to add time to them the same. The Julian calendar adds an extra day to February in years evenly divisible by four. The Coptic and Ethiopian calendars also add an extra day to the calendar; however they add it to the end of the year once every four years.

9) Chinese, Hindu, and Hebrew calendars are lunisolar so a leap year has an extra month. The formulas to add these extra months are complicated and include provisions to accommodate religious customs.

10) Leap Day has been associated with age-old Leap Day traditions and folklore. British, Danish and Finnish traditions allow for women to propose marriage in either leap years or on leap days. To avoid these marriages, men who refused these proposals often paid in gloves and fabrics.

11) In Greece it is considered unlucky to marry in a leap year. One in five couples will avoid marrying in a leap year.

12) 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 or March 1.

13) Technically, a leapling will have fewer birthday anniversaries than their age in years. This phenomenon is exploited when a person claims to be only a quarter of their actual age, by counting their leap-year birthday anniversaries only. In Gilbert and Sullivan’s 1879 comic opera, The Pirates of Penzance, Frederic the pirate apprentice who was a leapling discovers that he is bound to serve the pirates until his 21st birthday rather than until his 21st year.

Happy Leap Day and Leap Year! Hope you enjoy the extra day!

*1908 postcard from the Wikimedia Commons. Commons is a freely licensed media file repository.*

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Baker’s Dozen – Fun Facts About Leap Day, Leap Years, Leaplings, and Leapers