Much to the disgust of one of my colleagues, I was recently listening to The Pirates of Penzance (“I understand equations, both the simple and quadratical!”). A key plot point of Gilbert & Sullivan’s opera is that the hero, Frederic, indentured to the pirate king until his 21st birthday, was born on February 29th – a leap year – meaning that his 21st birthday is 63 years away.
As it happens, last week had a February 29, making this year a leap year. But what is a leap year, and why do we have them? It’s one of those things we rarely give much thought to, but there’s some fascinating history behind it.
First off, the obvious: A leap year is a year with 366 days instead of 365. No doubt you know the rhyme by heart: 30 days hath September… except for February, which has 28, 29 on a leap year. But, why? Because the Earth doesn’t take exactly 365 days to orbit the Sun. It takes 365 days plus six hours. Do the maths: four times six hours equals 24 hours, or one extra day every four years.
But it’s even more complicated than that. Because it’s not exactly six hours.
Adding a leap day every four years would make the calendar longer by more than 44 minutes, according to the National Air and Space Museum.
It was decreed that years divisible by 100 not follow the four-year leap day rule unless they are also divisible by 400, the JPL notes.
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.
Don’t even get started on leap-seconds.
Why not just drop the whole crazy business?
What would happen if we didn’t have a leap day?
Eventually, the seasons would be out of sync with the months – but that would take a bit of time.
“Without the leap years, after a few hundred years, we [in the Northern Hemisphere] will have summer in November,” Younas Khan, a physics instructor at the University of Alabama, said.
“Christmas will be in summer.”
So we’d finally have a white Christmas here in the Southern Hemisphere?
Who started all this nonsense, anyway?
Ancient civilisations 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 various calendars are today. Usually they were “lunisolar,” using both.
Our calendar is a modified version of the Julian calendar, named for good reason: it’s all Julius Caesar’s fault.
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 was also 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.
If you’ve ever wondered why September, Latin for seventh, is the ninth month and October and December (Latin for eight and 10) the 10th and 12th, the answer is again Julius. He added July (after himself, modest fellow that he was), August (for Augustus) and November (new month).
The actual calendar we use now is not the original Julian, but the Gregorian calendar. You guessed it, named after some bloke named Greg. Pope Gregory XIII, to be precise.
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 years. But it was a big improvement, reducing drift to mere seconds.
Why did he step in? Well, 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’s Pope Gregory and his advisers who came up with the really gnarly math on when there should or shouldn’t be a leap year.
Finally: why February?
Well, going back to the rhyme, poor February only has 28 days. It was just convenient to whack the extra day onto an already weirdly short month.
Another theory is that it’s based on Roman superstitions, author Alexander Boxer said in an interview with US public broadcaster NPR.
He says the Romans used to see February as an unlucky month.
Back then, the February they observed only went for 23 days.
And apparently they were suspicious of odd numbers.
So adding the extra day to February would have made the month go for 24 days in a leap year – making it a month with an even number of days.
ABC Australia
And so it is that Frederic, former pirate apprentice, would have celebrated his 42nd birthday last week.
