Nearly every four years, we add an extra day to the calendar in the form of February 29, also known as Leap Day. Put simply, these additional 24 hours are built into the calendar to ensure that it stays in line with the Earth’s movement around the sun.
While the modern calendar contains 365 days, the actual time it takes for Earth to orbit its star is slightly longer—roughly 365.2421 days. The difference might seem negligible, but over decades and centuries that missing quarter of a day per year can add up. To ensure consistency with the true astronomical year, it is necessary periodically to add in an extra day to make up the lost time and get the calendar back in sync with the heavens.
According to an old Irish legend, St. Brigid struck a deal with St Patrick to allow women to propose to men every four years. This is believed to have been introduced to balance the traditional roles of men and women in a similar way to how leap day balances the calendar.
In some places, Leap Day has been known as “Bachelors’ Day” for the same reason. A man was expected to pay a penalty (money), if he refused a marriage proposal from a woman on Leap Day.
In many European countries, especially in the upper classes of society, tradition dictates that any man who refuses a woman's proposal on February 29 has to buy her 12 pairs of gloves. The intention is that the woman can wear the gloves to hide the embarrassment of not having an engagement ring. During the middle ages there were laws governing this tradition.