Happy Intercalary Day!
Civilization has been observing Leap Year since the time of Julius Caesar (44 BC). Back in his day, a 22 or 23-day month was added every second year to their standard 355-day calendar in order to keep the festivals seasonal. Still time kept on slipping. In 45 BC the great leader had to extend the year to 445 days, just to get the schedule completely back on track. Not surprisingly it was referred to as the Year of Confusion. Caesar decided that this was a bit laborious, and so he set his astronomer Sosigenes to working on a viable alternative for the future. In this instance he was following the example of the Egyptians, who were said to have been the first to realize the necessity of an adjustment. The 400-year corrective was instituted under the reign of Pope Gregory XIII in 1582. Thanks in part to him, we only have to worry about a divergence (between the Gregorian calendar and solar years) of about one day every eight thousand years . I'm sure someone's keeping track of that.
The timing of the intercalary (added) day is confounding. Hell... February is a notoriously unpleasant month (at least in the climate I live in), and I'd be happy with keeping it at 28 days for all of eternity. It appears that Caesar picked the time of year because of religious festivals that were held during the last five days of February. The added day was the ante diem bis sextum Kalendas Martii, which was basically a doubling of February 24th (making the added day the first Feb 24th, the sixth day before the Calends of March). The following day was the traditional Feast of St. Matthias.
Despite the rather complex reasoning for its timing, there are surprisingly few historical traditions associated with Leap Year. Reportedly there is a tradition in the English-speaking world that women can only propose during Leap Days. The "rule" is apocryphally attributed to Queen Margaret of Scotland in the Thirteenth Century. It is said that she levied a fine upon men who refused a marriage proposal from a woman. Some men were apparently aghast at the severity of the punishment, so a law was supposedly passed restricting women to offering betrothal only on February 24th. In Greece it is thought unlucky to marry during a leap year, and so it is claimed that many couples wait for it to pass.
Due to the proportion of "common years" to "leap years", your chance of being born on February 29th is approximately 1 in 1461. When I was a kid I remember one little boy who seriously insisted that those whose birthdays fell on February 29th would remain young forever. However such "leaplings" usually choose to celebrate 75% of their birthdays on either the day before, or on March 1st. One would expect many fewer celebrities to have been born on the 29th of February- but there are a surprising number throughout history, including Jah Rule, Simon Gagne, "Rocket Richard", Antonio Sabato, Jr., Tony Robbins, Dennis Farina, Senator William Hathaway, Dinah Shore, General Montcalm, Pope Paul III, and some German guy* that had a Christian name for every letter in the alphabet.
*Adolph Blaine Charles David Earl Frederick Gerald Hubert Irvin John Kenneth Lloyd Martin Nero Oliver Paul Quincy Randolph Sherman Thomas Uncas Victor William Xerxes Yancy Zeus Wolfeschlegelsteinhausenberdorft Sr.