Leap year: The importance of one extra day and what would happen without it

2024 is a leap year, the year with an extra day. But where does it come from and what if we ignore it?

For most of us, mathematics in the initial years of schooling was all about learning how a year has 365 days and some, known as leap years, don't. These years have 366 days, with an extra one in February. But where do these extra days come from, and what happens if we do not consider it? Well, without it, after some years most of us might have to celebrate Christmas in the summer.

Why do we have a leap year?

Contrary to what we have been taught, a year does not have 365 days. According to the National Aeronautics and Space Administration (Nasa), Earth's one revolution around the Sun takes a bit longer than that. 365 days, 5 hours and 48 minutes to be precise.

 

So, to correct the calculations, we add one day to every four years, making the fourth one 366 days long. It is known as a leap year.

But does leap year come every four years? Not quite.

Do leap years come every four years?

To find out if a year is a leap year or not, we need to see if it is divisible by 4. But for centuries, we need to divide it by 400. For example, 1300 is divisible by 4 but not by 400. So, it was not a leap year.

According to NASA, the current calendar system was actually made for the Roman Empire by Julius Caesar around 46 BC. But the Julian calendar was 11 minutes and 14 seconds longer than the actual tropical year.

It led to errors in timekeeping and they gradually accumulated.

Between 46 BC and 1582 AD, this error became a total of 12.7 days. So, in 1582, Pope Gregory XIII specified that all years divisible by 4 are to be leap years except for century years, which must be divisible by 400.

But what happens if we do not consider that one extra day?

Sure, it would be convenient to leave the complex calculations and keep all years uniform. However, researchers say that it would lead to peculiar shifts in our idea of a year.

The one extra day would keep adding and shifting the calibration between our seasons and the calendar. According to the Jet Propulsion Laboratory at the California Institute of Technology, "After only a century without leap day, summer wouldn't start until mid-July." 

A video from planetary scientist James O'Donoghau recently showed that, eventually, December would drift into summer.

Would that not be very strange, albeit exciting?