Extra day keeps season in sync
Romans added the day to keep our calendar in sync with the seasons. Why to February? Because it was the last month of the Roman year.
The Earth takes 365.2421897 days to make a trip around the sun every year - not an easy number for a calendar to accommodate. For the sake of simplicity, we round it down to 365, but then each year we "lose" six hours. So we add them into one day roughly each four years: the leap day makes up the lost time. Only on years with numbers that can be exactly divided by four - such as 2012 - does February have 29 days. Years ending with 00 can only be leap years if they can be divided by 400. So 1900 was not a leap year, but 2000 was.
Chances against leap birthdays
The chance of being a leapling is one in 1,461. Four million worldwide share this special birthday, according to an American census in 2000. But few live under the same roof, like members of the two different families, the Henriksens and Keoghs.
Norway's three Henriksen siblings were recognised by Guinness World Records, the organisation that checks notable achievements, for being born on three consecutive leap days - Heidi in 1960, Olav in 1964 and Leif-Martin in 1968.
The Keogh family has three consecutive generations born on February 29. Peter Anthony was born in Ireland in 1940; his son, Peter Eric, in Britain, in 1964; and his granddaughter, Bethany Wealth, in Britain, in 1996.
When asked whether they are born lucky or not, leaplings are spilt. Many leap day babies say they enjoy special privileges such as free meals, free admission and discounts.
Yet imagine waiting four years for your real birthday and hearing endless jokes about being aged four when you are really 16.
Worse still, leaplings' birthdays fall on March 1 in normal years in many countries including Hong Kong. This brings leaplings problems when applying for birth certificates, driver's licences or filling in the entry fields on websites.
The February 29th birth of famous leaplings over the years include:
1988: Superman, American fictional superhero and cultural icon.
1976: Ja Rule, an American rapper and actor.
1916: Dinah Shore, an American singer and actress.
1904: Hubert Wolfe+585 Snr, an American whose full name (including a 590-letter surname) totals 746 letters. It is the longest official name: his parents gave him a name for every letter of the alphabet.
Make the most of a leap day
Women can embrace the Irish leap-year tradition and propose to their boyfriends today!
Officially, the leap day was the only day when Irishwomen could ask their beloveds for their hand in marriage.
Legend has it that St Bridget complained to St Patrick that women had to wait far too long for a man to pop the question about getting married. So St Patrick gave women a chance to propose instead every four years.
However, if a man turns the proposal down, he needs to pay a fine or give the woman a beautiful piece of clothing. In the United States, it is possible to attend a special party with other leaplings in Anthony, Texas.
Since 1988, the self-proclaimed Leap Year Capital of the World celebrates the special day with a gathering of leaplings that includes a parade, hot-air-balloon rides and a carnival.
Additional sources from McClatchy-Tribune