- The year must be evenly divisible by 4;
- If the year can also be evenly divided by 100, it is not a leap year; unless ...
- The year is also evenly divisible by 400. Then it is a leap year.
Using this logic, the year 2000 was a leap year, while 1900 and 2100 both will not be.
The system still isn’t quite perfect, though. By 4909, the Gregorian calendar will be a full day ahead of the solar year.
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The Gregorian calendar makes scientific sense, but its history is intertwined with politics.
Leap year was introduced by Roman emperor Julius Caesar in 45 BCE to replace a complicated calendar that relied on equinoxes and moon positions to determine how long months would be. Prior to the Julian calendar, "leap months" were sporadically used to keep the seasons in check with the calendar.
This is an undated sketch of Julius Caesar, the Roman general and statesman who is known as “The Father of Leap Years.”
Caesar’s calendar was replaced by Pope Gregory XIII in 1582 because he wanted Easter to better align with the spring equinox (the Julian calendar miscalculated the tropical year by about 11 minutes).
"Though Pope Gregory's papal bull reforming the calendar had no power beyond the Catholic Church, Catholic countries — including Spain, Portugal and Italy — swiftly adopted the new system for their civil affairs. European Protestants, however, largely rejected the change because of its ties to the papacy, fearing it was an attempt to silence their movement." — History.com
Protestant countries Germany and England waited almost 200 years to switch to the Gregorian calendar. Allegedly, riots broke out in England when Parliament was forced to advance the calendar overnight from Sept. 2 to Sept. 14, 1752, to catch up to the correct date.
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Superstitions and celebrations
Feb. 29, also called “Leap Day,” holds a host of superstitions based on this extra day.
One popular tradition holds that on Feb. 29, women can propose to men. The legend comes from Irish roots. According to 24/7 Wall Street, the story goes that St. Brigit of Kildare complained to St. Patrick that women were constantly being strung along, waiting for their man to pop the question. St. Patrick ruled that women should get the chance to propose, if only once every four years. Legend says if the man refused, he had to buy the woman 12 new gloves to cover up the shame of being seen without an engagement ring.
Other cultures claim that leap year as a whole should be avoided for weddings and romance, claiming it as unlucky. Greek traditions hold that a leap year marriage will end either in divorce or with untimely death.
In Italy, a leap year goes by the name “anno finesto,” which means fatal or doomed year.
"Farming, fertility, and family are most at risk, according to one belief. According to another, women are erratic during leap years," says one article.
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Superstitions aside, many choose to instead celebrate the extra day in February, especially in Anthony, Texas, which is the “Leap Year Capital of the World.”
The small town near El Paso sets aside Feb. 29 to celebrate those with leap year birthdays with a parade and festival.
Other leap year babies, called “leaplings” or “twenty-niners” can take advantage of deals Feb. 29.
On Feb. 29, Krispy Kreme will deliver free doughnuts to hospitals where babies are born.
Taste of Home also reports that Lay's Potato Chips will host a giveaway through Facebook to those born on a leap year.
Olive Garden also reportedly promises to give away four free desserts to leaplings, three extra for every birthday they've missed.
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