The Atlanta Journal-Constitution
Explaining what would happen if leap years didn’t exist
While math is involved, let’s simply say it wouldn’t be good.
NEW YORK — Leap year. It’s a delight for the calendar and math nerds among us. So how did it all begin and why?
Have a look at some of the numbers, history and lore behind the (not quite) every-four-year occurrence that adds a 29th day to February.
The math is mind-boggling and down to fractions of days and minutes. There’s even a leap second occasionally, but there’s no hullabaloo when that happens.
The thing to know is that leap year exists, in large part, to keep the months in sync with annual events, including equinoxes and solstices, says the Jet Propulsion Laboratory (JPL) at the California Institute of Technology. It’s a correction to counter that Earth’s orbit isn’t precisely 365 days a year; the trip takes about six hours longer than that, NASA says.
Contrary to what some might believe, though, not every four years is a leaper. Adding a leap day every four years would make the calendar longer by more than 44 minutes, said the National Air & Space Museum.
Now, get ready for math: Later, on a calendar yet to come (we’ll get to it), it was decreed that years divisible by 100 not follow the four-year leap day rule unless they also are divisible by 400, the JPL noted. In the past 500 years, there was no leap day in 1700, 1800 and 1900, but 2000 had one. In the next 500 years, if the practice is followed, there will be no leap day in 2100, 2200, 2300 and 2500.
Still with us?
The next leap years are 2028, 2032 and 2036.
What would happen without a leap day?
Eventually, nothing good in terms of when major events fall, when farmers plant and how seasons align with the sun and the moon.
“Without the leap years, after a few hundred years, we will have summer in November,” said Younas Khan, a physics instructor at the University of Alabama at Birmingham. “Christmas will be in summer. There will be no snow. There will be no feeling of Christmas.”
Who came up with it?
The short answer: It evolved. Ancient civilizations used the cosmos to plan their lives, and there are calendars dating to the Bronze Age. They were based on either the phases of the moon or the sun, as various calendars are today. Usually they were “lunisolar,” using both.
Now hop on over to the Roman Empire and Julius Caesar. He was dealing with major seasonal drift on calendars used in his neck of the woods. They dealt badly with drift by adding months. He also was navigating a vast array of calendars starting in a vast array of ways in the vast Roman Empire.
He introduced his Julian calendar in 46 BCE. It was purely solar and counted a year at 365.25 days, so once every four years an extra day was added. Before that, the Romans counted a year at 355 days, at least for a time.
But still, under Caesar, there was drift. There were too many leap years because the solar year isn’t precisely 365.25 days. It’s 365.242 days, said Nick Eakes, an astronomist at the Morehead Planetarium and Science Center at the University of North Carolina.
Thomas Palaima, a classics professor at the University of Texas, said adding periods of time to a year to reflect variations in the lunar and solar cycles was done by the ancients. The Athenian calendar, he said, was used in the fourth, fifth and sixth centuries with 12 lunar months.
But that didn’t work for seasonal religious rites. The drift problem led to “intercalating” an extra month periodically to realign with lunar and solar cycles, Palaima said.
The Julian calendar was 0.0078 days (11 minutes, 14 seconds) longer than the tropical year, so errors in timekeeping gradually accumulated, NASA says. But stability increased, Palaima noted.
The Julian calendar was the model used by the Western world for hundreds of years. Enter Pope Gregory XIII, who calibrated further. His Gregorian calendar took effect in the late 16th century. It remains in use today and, clearly, isn’t perfect or there would be no need for leap year. But it was a big improvement, reducing drift to mere seconds.
Why did he step in? Because of Easter. It was coming later in the year over time, and he fretted that events related to Easter, like the Pentecost, might bump up against pagan festivals. The pope wanted Easter to remain in the spring.
He eliminated some extra days accumulated on the Julian calendar and tweaked the rules on leap day. It was Pope Gregory and his advisers who came up with the math on when there should or shouldn’t be a leap year.
What’s the deal with leap year and marriage?
Bizarrely, leap day comes with lore about women popping the marriage question to men. It was mostly benign fun.
There’s distant European folklore. One story places the idea of women proposing in fifth century Ireland, with St. Bridget appealing to St. Patrick to offer women the chance to ask men to marry them, historian Katherine Parkin wrote in a 2012 paper 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 prerogative, like most of her liberties, is merely a glittering mockery.”
What about birthdays?
Being born on a leap day certainly is a talking point. But it can be kind of a pain from a paperwork perspective. Some governments and others requiring forms to be filled out stepped in to declare what date was used by leaplings for such things as drivers licenses, whether Feb. 28 or March 1.
Technology has made it far easier to jot down Feb. 29 milestones, though there can be glitches in terms of health systems, insurance policies and with other businesses and organization that don’t have that date built in.
There are about 5 million people worldwide (out of about 8 billion) who share the leap birthday.