PARIS, France (AFP) — An extra day every four years, what’s not to love?

The calendar quirk of February 29 keeps us in sync with the seasons but it has also spawned a host of rituals and superstitions, not to mention computer glitches, which
AFP unpacks here:

Why one day more?

Leap years have been with us since the 16th century, an invention of the Gregorian calendar and introduced to deal with a troublesome fraction in the solar year.

Bearing in mind it takes around 365.2422 days each year for the Earth to revolve around the sun, the extra snippet (around six hours a year) adds up over time.

Leap days regulate things; without them we would fall out of sync with the seasons, causing havoc for farmers and their crops as well as school holidays.

Most leap years fall every four years but as the extra snippet is not exactly six hours, they exclude years exactly divisible by 100.

However, years such as 1600, 2000 or 2400 are leap years as they are exactly divisible by 400.

Forever young

For leap day babies, or leaplings, being born on 29 February may mean four times fewer birthdays — but it is also, as some like to claim, the key to eternal youth.

At least that’s what much-loved French screen star Michele Morgan liked to say during her lifetime, which lasted till the ripe old age of 96.

Among other famed or notorious leaplings are Spanish premier Pedro Sanchez, US rap star Ja Rule, and serial killer Aileen Wuornos, incarnated by Charlize Theron in her Oscar-winning performance for
Monster.

With the chance of babies being born on a leap day at one in around 1,500, there are an estimated five million leaplings in the world today.

Marry me!

In Ireland February 29 is known as Bachelor’s Day or Ladies Privilege, when (tradition has it) women can propose to men rather than waiting to be wooed.

While some claim only a “Yes” answer is allowed, others say the man can decline, but must buy his admirer a gift.

The tradition received the Hollywood treatment in 2010 with
Leap Day, starring Amy Adams who follows her beau to Dublin in a bid to ensnare him into marriage by popping the question on the day.

The Irish Government in 2004 celebrated the 10th anniversary of the International Year of the Family by gifting 100 euros to every child born on February 29 .

Freebies

Rare days on the calendar are also a chance for businesses to try to drum up trade.

In north-eastern US the Legal Sea Foods restaurant chain is offering discounts on the region’s beloved dish, lobsters, on February 29.

Pizza chain Papa John’s in 2008 used leap day to launch its Perfect Pan Pizza, with the tag line: “One Giant Leap for Pankind.”

Leap years also generate special deals in hotels and on flights.

As US flyer Virgin America put it in one of its promotions: “Why leap when you can fly?”

System can’t compute

The existence of an extra day around twice a decade has also created its fair share of online mayhem, never more so than in 2000.

The prediction from doomsayers that January 1 would see a total information shutdown never came to pass, but on February 29 an alarming succession of system errors took place across the globe. This included Japan’s meteorological service sending out faulty weather reports and Montreal’s tax service shutting down.