Blame Leap Year on Mismatched Solar, Lunar, and Seasonal Cycles


It’s hard to think of anything as complex, and yet as humdrum, as the calendar. These days, clocks and calendars are so ubiquitous—the screen you’re looking at right now can instantly tell you the time and date—that we’re blissfully unaware of the centuries-old intellectual struggle involved in their creation. What better day than February 29—a day that comes only once every four years—to reflect on the story behind our seemingly esoteric method of counting the days of the year.


The complexity of our timekeeping systems isn’t really humanity’s fault. If you’re looking for a scapegoat, I’d blame the solar system. The urge to keep track of time is probably as old as our species, and the most obvious signs of time’s passage are the cycles we observe in nature, especially the regularities we see in the night sky.

Most obvious are the day (measured by the rising or setting of the Sun); the month (measured by tracking the phases of the Moon); and the year (the annual cycle of the seasons). But timekeeping soon gets complicated, because none of these cycles fit neatly into one another: The lunar month is about 29.5 days long (actually 29.5306); the average year as defined by the seasons—also known as the “solar” or “tropical” year—is about 365.25 days long (actually a smidgeon less, at 365.2422 days). And the month refuses to fit neatly into the year, too, for that matter (there are more than 12, but less than 13, lunar cycles in a year). Over the centuries, different civilizations tried every possible trick to try to reconcile these incongruent cycles.

It would have been nice if there were 360 days in a year: The math would be wonderfully simple, since 360 can be divided by 2, 3, 4, 5, 6, 8, 9, 10, and—well, I won’t list them all, but 360 has 22 divisors in all (not counting 1 and 360). But no such luck; the year actually has a bit more than 365 days.


The ancient Egyptians had a fairly elegant solution: Use a 360-day calendar, with 12 months of 30 days each, and then enjoy five days of feasts and celebrations at the end of each year. But it still wasn’t perfect: The resulting year of 365 days is still about a quarter-day short of the true solar year.

The Egyptians recognized this discrepancy early on, and realized that adding an extra day every four years would bring the average length of the year to within just a few minutes of the true solar (tropical) year. It wasn’t until 238 BCE, however, that the Egyptian king Ptolemy III pushed for the adoption of a leap-year system. The Romans—whose empire would eventually encompass Egypt—tried a variety of calendar systems, eventually adopting the now-familiar leap year system, in which every fourth year has 366 days, instead of the usual 365. They’re also responsible for the peculiar lengths of the months. Initially, the idea was to have alternating 30-day and 31-day months, but successive rulers fiddled with those lengths. (For example: July, named for Julius Caesar, had 31 days; naturally, his successor, Augustus, demanded that August must have 31 also—the extra day being taken away from lowly February.)

The Roman calendar wasn’t perfect. Its average year of 365.25 days was just slightly shorter—by about 11 minutes—than the true solar year. By the time of Pope Gregory XIII, in the late 1500s, that discrepancy added up to 10 full days. Springtime holidays like Easter were drifting awkwardly into summer. Gregory convened a council of mathematicians and astronomers, who eventually found a way to make the average year just slightly longer: In the old system, “century years” like 1500, 1600, and 1700 would be leap years because they’re divisible by 4; under the new plan, only those century years divisible by 400 (such as 1600 and 2000) would be leap years.

The proposed reform was adopted in 1582—at which point 10 days were dropped from the calendar to let it “synch up” with the seasons (and so October 4, 1582, was followed by October 15). Some people were distressed at what seemed to be “lost” time. Merchants puzzled over the calculation of profits and losses; bankers were befuddled by interest rates.


While Catholic countries quickly adopted the Gregorian calendar, Protestant countries held off. In Britain, the new calendar wasn’t adopted until 1752—at which point 11 days had to be dropped from the year, in order to “catch up.” Protests broke out in London and Bristol, with workers shouting, “Give us back our 11 days!” Interestingly, such tensions have not entirely disappeared; as The Telegraph points out, some people resent having to work an extra day for no pay in leap years.

Leap years, which have been a part of our timekeeping system for more than 2000 years, barely warrant notice these days— although today’s Google Doodle serves as a cute reminder. Of course, if you’re one of the 4 million or so living leap day babies, known as “leaplings” or “leapers,” you’re likely hyper-aware of leap years. (Calculating the number of people with a February 29 birthday is tricky, by the way: The fraction of babies born on February 29 isn’t 1 in 365, but rather, about one in 1460, since February 29 occurs only once every four years—or, to be precise, 97 times every 400 years.) Famous leap-babies include motivational speaker Tony Robbins, rapper Ja Rule, and the 16th-century pope Paul III. Intriguingly, two major events—the Summer Olympics and U.S. national elections—are always held in leap years.

Dan Falk (@danfalk) is a science journalist based in Toronto. He explored time and timekeeping in his 2008 book, In Search of Time.

Ralph Heimans/Buckingham Palace/PA Wire via Getty Images
Pop Culture
The Cult of Prince Philip
Ralph Heimans/Buckingham Palace/PA Wire via Getty Images
Ralph Heimans/Buckingham Palace/PA Wire via Getty Images

For seven decades, Prince Philip has been one of the more colorful figures in Britain's Royal Family, prone to jarring remarks and quips about women, the deaf, and overweight children.

"You're too fat to be an astronaut," he once told a boy sharing his dream of space travel.

British media who delighted in quoting him are still lamenting the 96-year-old's recent retirement from public duties. But the people of the Pacific Island nation of Vanuatu are likely to be optimistic he'll now have the time to join them: They worship him as a god and have based a religion on him.

Followers of the Prince Philip Movement, which started in the 1960s, believe that the prince was born to fulfill an ancient prophecy: that the son of an ancient mountain spirit would one day take the form of a pale-skinned man, travel abroad, marry a powerful lady, and eventually return to the island. When villagers saw the prince’s portrait, they felt the spirit in it, and when he visited Vanuatu in 1974, they were convinced.

Chief Jack Naiva, a respected warrior in the culture, greeted the royal yacht and caught sight of Philip on board. "I saw him standing on the deck in his white uniform," Naiva once said. "I knew then that he was the true messiah."

True believers assign large world movements to the machinations of Philip. They once claimed his powers had enabled a black man to become president of the United States and that his "magic" had assisted in helping locate Osama bin Laden. The community has corresponded with Buckingham Palace and even sent Philip a nal-nal, a traditional club for killing pigs, as a token of its appreciation. In return, he sent a portrait in which he’s holding the gift.

Sikor Natuan, the son of the local chief, holds two official portraits of Britain's Prince Philip in front of the chief's hut in the remote village of Yaohnanen on Tanna in Vanuatu.

The picture is now part of a shrine set up in Yaohnanen in Vanuatu that includes other photos and a Union flag. In May 2017, shortly after the Prince announced his retirement, a cyclone threatened the island—and its shrine. But according to Matthew Baylis, an author who has lived with the tribe, the natives didn't see this so much as a cause for concern as they did a harbinger of the prince's arrival so he can bask in their worship.

To date, Prince Philip has not announced any plans to relocate.

A version of this story ran in a 2012 issue of Mental Floss magazine.

The Secret World War II History Hidden in London's Fences

In South London, the remains of the UK’s World War II history are visible in an unlikely place—one that you might pass by regularly and never take a second look at. In a significant number of housing estates, the fences around the perimeter are actually upcycled medical stretchers from the war, as the design podcast 99% Invisible reports.

During the Blitz of 1940 and 1941, the UK’s Air Raid Precautions department worked to protect civilians from the bombings. The organization built 60,000 steel stretchers to carry injured people during attacks. The metal structures were designed to be easy to disinfect in case of a gas attack, but that design ended up making them perfect for reuse after the war.

Many London housing developments at the time had to remove their fences so that the metal could be used in the war effort, and once the war was over, they were looking to replace them. The London County Council came up with a solution that would benefit everyone: They repurposed the excess stretchers that the city no longer needed into residential railings.

You can tell a stretcher railing from a regular fence because of the curves in the poles at the top and bottom of the fence. They’re hand-holds, designed to make it easier to carry it.

Unfortunately, decades of being exposed to the elements have left some of these historic artifacts in poor shape, and some housing estates have removed them due to high levels of degradation. The Stretcher Railing Society is currently working to preserve these heritage pieces of London infrastructure.

As of right now, though, there are plenty of stretchers you can still find on the streets. If you're in the London area, this handy Google map shows where you can find the historic fencing.

[h/t 99% Invisible]


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