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Rounding down to leap year

Thursday, February 29, marks another leap year, 366 days versus 365 in 2024. For most, it is just an extra day in the shortest month that occurs every four years.

But its history and evolution are worth revisiting.

The science behind leap year: It takes 365.2422 days for the earth to circle the sun. The .2422 (5 hours, 48 minutes and 56 seconds) may seem insignificant, but it adds up over time, according to  Eventually, seasons would not fall in their usual months. Imagine the school year beginning in springtime or farm harvesting in May?

The Egyptians are thought to have been the first to practice a leap year using a solar calendar of 365 days adding an extra day every four years.

Taking a cue from the Egyptians, Julius Caesar created his western calendar in 45 BCE but he rounded up to 365.25 with the rule that any year evenly divisible by four would have an extra day in it. Ultimately, the Cesarean calendar did not work because even the small difference between 365.25 and 365.2422 made the year shorter by 11 minutes, losing one day every 128 years.

By the 16th century, some of the important dates and holidays had shifted on the calendar. Therefore, Pope Gregory XIII removed Caesar’s three calendar days and created the Gregorian calendar adding one extra day in February, using the 365.2422 metric. This is the calendar most of us use today.

But the Gregorian calendar has its challenges, too. “There is still a 30-second drift every year. But even with that, the calendar won’t be off for more than a day for another 3,300 years,” according to National Geographic.

Although having a birthday on February 29 is one of the rarest occasions, approximately five million “leaplings” celebrate a leap-day birthday every year, according to the History Channel.



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