A leap year is a year that has one extra day. On the Gregorian calendar, the standard calendar for most of the world, common years have 365 days. A leap year, however, has 366 days, with the extra day designated as February 29. A leap year generally occurs every four years in the years evenly divisible by four.
Leap year was originally designed to keep the calendar year synchronized with the solar year, or the time it takes the earth to complete its orbit about the sun. Because the solar year is about a quarter of a day longer than the calendar year, the seasons will not match the calendar after many years have passed. The Gregorian calendar was specifically created to keep the vernal equinox, or the time when the sun is directly above the Earth’s equator, as close to March 21 as possible so that Easter celebrations will coincide with the equinox.
The idea of adding a leap year to the calendar is nothing new. The Egyptian ruler King Ptolemy III first added an extra day to the year back in 238 BC. The Romans later adopted this solution for their calendar in order to maintain correct seasonal changes. In other ancient cultures, it was customary to have lunar calendars with twelve months to a year. To align the calendar with the seasons, a thirteenth month, called a "leap month," was inserted every two or three years. Many countries, including Asia, still use such calendars.
The day of February 29, commonly called Leap Day, has long been associated with particular superstitions and traditions. In Scotland, for example, it has always been considered extremely unlucky for someone to be born on Leap Day. In Greece, it is still believed that getting married in a leap year means nothing but bad luck for the couple.
The most popular leap year tradition, however, spans back to the days when the rules of courtship were extremely strict. In many cultures, women were allowed to propose to men only on the rare date of February 29. On this day, which is sometimes referred to as “Bachelors’ Day,” a man had to pay a penalty such as a kiss, a pair of silk gloves, or a monetary fine if he refused a marriage offer from a woman.
This tradition’s origins most likely stems from the old Irish folktale which tells of Saint Bridget striking a deal with Saint Patrick to allow women to propose to men once every four years. This old custom may have been used to balance the traditional male and female roles much like Leap Day is used to balance the calendar. In the United States, some people call Leap Day “Sadie Hawkin’s Day” after a chronically unmarried female in the popular Li’l Abner comic strip.
Leap Day is considered a very special day for those "leapers" and "leaplings" born on February 29. There is a big debate on whether these birthdays should be celebrated on February 28 or on March 1. Many leapers, however, only celebrate their birthday during official leap years because they believe there is no substitute for a February 29 birthday. Most countries make special amendments for those born on Leap Day so they can be considered eligible for driving, marriage, and other activities requiring a legal age.