Short answer: February 29.
Scientific answer (sort of): Every year, calendar folks grab the surplus 5 hours 48 minutes and 45 seconds that accumulate annually with the earth’s orbit around the sun, and stash them somewhere where we can’t see them. You see, it takes the Earth approximately 365.242189 days to circle the sun. Those spare hours need to be placed somewhere, so they’re gathered up, held in time-out or a safety deposit box or something, and after four years, the calendar crew compacts them into a full day, and sticks them at the end of the shortest month, February. This is done because, so far, no one has been able to put those hours, minutes, and seconds into a pretty desktop or wall calendar.
Folks have known about this time discrepancy for thousands of years, at least since the Egyptians. Finally, in 45 BCE, Julius Caesar did something about it. He (or one of his advisers) created the Julian calendar system and included one Leap Day every four years. Without it, 100 years down the road, the solstices and equinoxes would be off by 24 days, and farmers wouldn’t know when to plant their peas and potatoes.
Oh, and those few extra seconds add up, too. Pope Gregory XIII and his astronomers—who introduced the Gregorian calendar in 1582, replacing Caesar’s self-named calendar—decided we needed to lose three Leap Days every 400 years. So, Leap Years are years divisible by 100, but not 400. That little tweak took care of most of the leftover seconds from the formula, but not all of them. In 10,000 years, someone else will have to do another adjustment. But we won't be around then, so really don't need to be concerned.
Oh, and the very unscientific, but traditional explanation of Leap Day: It’s the day a woman may ask a man to marry her or go to the Sadie Hawkins Dance… As if a bold woman ever needed a special day for that!
So, enjoy the extra day in February this year. And if he’s the right man for you, ask him out. But be prepared to pay. This is the 21st century, after all.
Naked in the Winter Wind, first book in The Fairies Saga, the tale of time travelers who pop back and forth between the 18th century and current times.
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