Why is there a leap day?

Why is there a leap day?

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 to periodically add in an extra day to make up the lost time and get the calendar back in synch with the heavens. 

 Who introduced leap year?

Julius Caesar introduced Leap Day, with help from the Egyptians...

The Mercedonius-when-we-feel-like-it system apparently irked Caesar, the general-turned-consul-turned-dictator of Rome who drastically altered the course of European history. In addition to conquering Gaul and transforming Rome from a republic into an empire, Caesar re-ordered the Roman calendar, giving us the blueprint off of which much of the world still operates to this day.

During his time in Egypt, Caesar became convinced of the superiority of the Egyptian solar calendar, which featured 365 days and an occasional intercalary month which was inserted when astronomers observed the correct conditions in the stars. Caesar and the philosopher Sosigenes of Alexandria made one important modification: instead of relying on the stars, they would simply add a day to every fourth year. In keeping with the Roman tradition of messing with the length of February, that day would fall in the second month of the year—thus Leap Day was born. Caesar added two extra-long months to the year 46 BCE to make up for missed intercalations, and the Julian Calendar took effect on January 1st, 45 BCE.

 What is a leap day?

Leap Day is often associated with marriage, proposals and flipping gender roles

Curiously, many Leap Day customs have revolved around romance and marriage. Tradition holds that in 5th-century Ireland, St. Bridget lamented to St. Patrick that women were not allowed to propose marriage to men. So legend has it that St. Patrick designated the only day that does not occur annually, February 29, as a day on which women would be allowed to propose to men. In some places, Leap Day thus became known as Bachelor's Day.

This tradition hopped the Irish Sea to Scotland and England, where the British added a twist—if a man rejected a woman's proposal, he owed her a debt of several pairs of fine gloves, perhaps to hide the fact that she did not have an engagement ring. In Greek tradition, however, it is considered bad luck to marry on Leap Day, and statistics suggest that Greek couples continue to take this superstition seriously.

 What is people called born on leap day?

People born on Leap Day are called 'Leaplings'

There are only about 5 million people in the whole world who were born on February 29, with the odds of being born on Leap Day standing at about 1-in-1,461. Several famous people—including actress and singer Dinah Shore (born 1916), motivational speaker Tony Robbins (born 1960) and hip-hop artist Ja Rule (born 1976)—are leaplings. Leaplings technically only get to celebrate their birthdays once every four years, but they do get to be part of an elite group.

How to find a leap year?

The following pseudocode determines whether a year is a leap year or a common year in the Gregorian calendar (and in the proleptic Gregorian calendar before 1582). The year variable being tested is the integer representing the number of the year in the Gregorian calendar.

if (year is not divisible by 4) then (it is a common year)
else if (year is not divisible by 100) then (it is a leap year)
else if (year is not divisible by 400) then (it is a common year)
else (it is a leap year)