Why do we have leap year? Blame the Earth and sun
February has an extra day in 2024 because it is a leap year, but what would happen if we didn't add an extra day to the calendar once every four years?
A leap year occurs once every four years, adding an extra day to the short month of February. Why do leap years exist?
Once every four years, an extra day is tacked on at the end of February, resulting in a leap year that is 366 days as opposed to the typical 365 days. But where does this leap day come from?
The extra day can be traced back to the way the Earth orbits the sun. It takes approximately 365.25 days for the Earth to complete one trip around the sun, which is slightly different than the human-made Gregorian calendar which is 365 days.
A calendar shows the month of February, including leap day, Feb. 29, 2024. (AP Photo/Gregory Bull)
To make up for the slight difference between the celestial calendar and the Gregorian calendar, once every four years, February has 29 days instead of 28 days.
What would happen if we didn't have leap year?
A difference of one-quarter of a day is virtually imperceptible on a year-to-year basis, but in the long run, it would wreak havoc on the seasons.
The one-quarter of a day would add up over decades and centuries and cause the seasons to shift on the calendar.
"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," the Smithsonian explained on its website.
One of a set of teaching cards published by James Reynolds & Sons, London, England around 1860. Titled 'The Seasons', the chart was drawn and engraved by John Emslie. The diagram shows how the Earth's axis of rotation is tilted with respect its path around the Sun, but its direction in space is fixed. (Photo by SSPL/Getty Images)
Loopholes to leap year
There are exceptions to the rule that a leap year is once every four years. On occasion, we leap over a leap year as it takes the Earth closer to 365.24 days to complete one orbit around the sun, instead of exactly 365.25 days. If left unchecked, this fraction of a day would throw off the calendar.
"The rule is that if the year is divisible by 100 and not divisible by 400, leap year is skipped," the Smithsonian said. "The year 2000 was a leap year, for example, but the years 1700, 1800, and 1900 were not. The next time a leap year will be skipped is the year 2100."
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