NEW YORK (AP) — Leap year. It’s a delight for the calendar and math nerds among us. So how did it all start and why?

Take a look at some of the numbers, history and lore behind the (not quite) quadrennial phenomenon that adds a 29th day to February.

BY THE NUMBERS

The math is mind-boggling to a layman and goes down to fractions of days and minutes. Occasionally there is even a leap second, but when that happens there is no chaos.

According to the Jet Propulsion Laboratory at the California Institute of Technology, it’s important to know that leap years function largely to keep the months in sync with annual events, including the equinoxes and solstices.

It is a correction to address the fact that Earth’s orbit does not last exactly 365 days a year. According to NASA, the journey will take about six hours longer.

Contrary to what some may believe, however, there is not a jump every four years. According to the National Air & Space Museum, adding a leap day every four years would add more than 44 minutes to the calendar.

Later, in a calendar to come (we’ll get to that in a moment), it was decided that years divisible by 100 would not follow the four-year leap day rule unless they were also divisible by 400, the JPL notes. In the past 500 years, there was no leap day in the years 1700, 1800 and 1900, but there was in the year 2000. If the practice is followed, there will be no leap day in the years 2100, 2200, 2300 and 2500 in the next 500 years.

Still with us?

The next leap years are 2028, 2032 and 2036.

What would happen without a leap day?

Ultimately, there is no good when it comes to when major events take place, when farmers plant, and how the seasons align with the sun and moon.

“Without leap years, we will have summer in November after a few hundred years,” said Younas Khan, a physics lecturer at the University of Alabama at Birmingham. “Christmas will be in the summer. There will be no snow. There will be no Christmas feeling.”

Who came up with the leap year?

The short answer: It has evolved.

Ancient civilizations used the cosmos to plan their lives, and there are calendars dating back to the Bronze Age. They were based on either the phases of the moon or the sun, as is the case with various calendars today. Typically they were “lunisolar” and used both.

Now move on to the Roman Empire and Julius Caesar. He struggled with large seasonal variations in the calendars used in his area. They handled the drift poorly by adding months. He also navigated a variety of calendars, beginning in many ways in the vast Roman Empire.

He introduced his Julian calendar in 46 BC. a. It was purely solar powered and counted a year as 365.25 days, adding an extra day every four years. Previously, the Romans counted a year as 355 days, at least for a time.

But there was still drift under Julius. There have been too many leap years! The solar year doesn’t have exactly 365.25 days! It’s 365,242 days, said Nick Eakes, an astronomy educator at the Morehead Planetarium and Science Center at the University of North Carolina at Chapel Hill.

Thomas Palaima, a professor of classics at the University of Texas at Austin, said ancient times added periods to a year to reflect variations in the lunar and solar cycles. The Athenian calendar, he said, was used in the fourth, fifth and sixth centuries with 12 lunar months.

This didn’t work for seasonal religious rites. The drift problem resulted in an extra month being “slid in” at regular intervals to align with the lunar and solar cycles, Palaima said.

The Julian calendar was 0.0078 days (11 minutes and 14 seconds) longer than the tropical year, so errors in timekeeping still accumulated, according to NASA. But stability has increased, Palaima said.

The Julian calendar was the model of the Western world for centuries. Enter Pope Gregory XIII. into the game, which has calibrated itself even further. His Gregorian calendar came into effect in the late 16th century. It is still used today and is obviously not perfect, otherwise there would be no need for a leap year. But it was a big improvement as the drift was reduced to just a few seconds.

Why did he intervene? Well, Easter. As time went on, it came later in the year and he feared that events related to Easter, such as Pentecost, might conflict with pagan festivals. The Pope wanted Easter to stay in spring.

He eliminated some extra days that had accumulated in the Julian calendar and optimized the rules for leap days. It is Pope Gregory and his advisors who came up with the really tricky calculation of when there should be a leap year and when there should not be.

“If the solar year had the perfect value of 365.25, we wouldn’t have to worry about the complicated math involved,” Eakes said.

What’s the deal with leap years and marriage?

Oddly enough, Leap Day is associated with the legend of women asking men the marriage question. It was mostly harmless fun, but also had an edge that reinforced gender roles.

There is distant European folklore. One story places the idea of ​​women proposing marriage in fifth-century Ireland. St. Bridget appeals to St. Patrick to give women the opportunity to ask men to marry them, according to historian Katherine Parkin in a 2012 essay in the Journal of Family History.

Nobody really knows where it all began.

In 1904, syndicated columnist Elizabeth Meriwether Gilmer, aka Dorothy Dix, summed up the tradition this way: “Of course people will say…that a woman’s leap year privilege, like most of her freedoms, is but a glittering mockery.”

The pre-Sadie Hawkins tradition, no matter how serious or ironic, might have empowered women but merely perpetuated stereotypes. Proposals were supposed to be made by postcard, but many of these cards turned the tables and made fun of women instead.

The leap year marriage game was continued through advertising. A 1916 advertisement from the American Industrial Bank and Trust Co. stated, “On this day of the leap year, we encourage every girl to suggest to her father that he open a savings account in her name at our own bank.”

Because of Leap Day, there was no hint of independence for women.

Should we feel sorry for the Springlings?

Being born on a leap day in a leap year is certainly a topic of conversation. But from a paperwork perspective, it can be quite a hassle. Some governments and others that require filling out forms and specifying birthdays have stepped in to specify which date is used by Leaplings for things like driver’s licenses, be it February 28th or March 1st.

Technology has made it much easier for jump babies to write down their February 29 milestones, although there may be issues with health systems, insurance policies and other companies and organizations that don’t have this date built in.

There are about 5 million people worldwide who have a leap birthday, out of about 8 billion people on the planet. Shelley Dean, 23, of Seattle, Washington, chooses a rosy outlook on jumping. Growing up, she had normal birthday parties every year, but leap years had a special one. Because as an adult, she marks the switch-free period between February 28th and March 1st with a reserved “Phew”.

This year is different.

“It will be the first birthday in eight years that I will celebrate with my family, which is super exciting because last Leap Day I was on the other side of the country in New York studying,” she said. “It’s a very big year.”