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This year, there's an extra day in the calendar: February 29, 2024.
That's because 2024 is a "leap year," an occurrence that happens every four years...sort of.
But why is exactly is that? According to experts, it has to do with the fact that 365 is a rounded number.
Now, with 24 hours to go, here are all your leap year questions, answered.
What is a leap year and why do we have them?
A leap year means there's an extra day in the calendar.
"A calendar year is typically 365 days long," an article from Smithsonian Magazine titled "The Science of Leap Year" reads. "These so called 'common years' loosely define the number of days it takes the Earth to complete one orbit around the Sun. But 365 is actually a rounded number. It takes Earth 365.242190 days to orbit the Sun, or 365 days 5 hours 48 minutes and 56 seconds."
The article goes on to say that the extra time known as a "sidereal" year must be accounted for somehow. Otherwise, seasons could be impacted.
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"If we didn’t account for this extra time, the seasons would begin to drift," the article goes on to say. "This would be annoying if not devastating, because over a period of about 700 years our summers, which we’ve come to expect in June in the northern hemisphere, would begin to occur in December."
What is a leap day?
During a leap year, the month of February has an extra day added to it. So this year, there will be 29 days in February, rather than 28. That 29th day is also referred to as a "leap day."
When are leap years, and why don't they happen every four years exactly?
Leap years happen almost every four years. That means 2024 and 2028 will both be leap years.
But still, there are some exceptions to the once-every-four-years rules.
"Some simple math will show that over four years the difference between the calendar years and the sidereal year is not exactly 24 hours," the article goes on to say. "Instead, it’s 23.262222 hours."
If we added a "leap day" every four years, we'd actually make the calendar longer by over 44 minutes, Smithsonian said.
"Over time, these extra 44+ minutes would also cause the seasons to drift in our calendar," the article goes on to say. "For this reason, not every four years is a leap year."
How do you calculate a leap year?
The rule is that if the year is divisible by 100 and not divisible by 400, leap year is skipped, the magazine says.
"The year 2000 was a leap year, for example, but the years 1700, 1800, and 1900 were not," the article states. "The next time a leap year will be skipped is the year 2100."
Why is it called a 'leap year'?
A typical year is 52 weeks and one day long. "That means, if your birthday were to occur on a Monday one year, the next year it should occur on a Tuesday."
But, an extra day during a leap year means your birthday now "leaps" over a day, Smithsonian said.
What if you are born during a leap year?
It's not that those birthdays are celebrated only every four years. Rather, those born on a leap day typically celebrate on March 1, the magazine said.
According to the Almanac, people born on a leap day during a leap year are known as "leaplings." Some cultures see the birthday as a sign of good luck.
