Animation shows what would happen if we didn't have leap years

February 29th, 2024, marked another leap year since 2020.

On this extra day, people born on February 29th could celebrate their birthdays, and according to St. Patrick legends, women can propose to men if they wish.

But why exactly do we have leap years? And what would happen if we didn't?

An interesting animation posted by James O'Donoghue on X shows what happens if we don't add a leap year into our Earth's calendar.

The physicist captioned: 'Tomorrow we add a leap day, as 2024 is a leap year. I made a video to show why we do that and what happens when we don't. Have a nice extra day tomorrow!'

Physicist James O'Donoghue explains why we have leap years in an animation / Nora Carol Photography/Getty

The animation starts in 2020 and shows the Earth's orbit with a leap year.

Earth's orbit takes approximately 365.24 days to complete, not just 365. So without a leap year, we'd gradually fall behind by about 0.24 days each year.

So, the year 2021 would be 0.48 days behind, 2022 would be 0.73 days behind and so on.

However, with the leap year, we reach 0.03 days ahead in 2024. That extra time known as a 'sidereal' year must be accounted for somehow - which is the reason we have an extra day.

Then, part two of the video shows what happens if we don't add in the leap year.

Instead, the time continues from 2024 for around 500 years, and seasons begin to drift out of sync. Winter months eventually become summer months and vice versa.

Without a leap year, our seasons would shift out of sync /@physicsJ/X

According to a science article in the Smithsonian magazine: 'If we didn’t account for this extra time, the seasons would begin to drift.

'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.'

As a result, Christmas would be an entirely different experience for us all.

However, leap years don't always occur every four years.

The article added: 'If we added a "leap day" every four years, we'd actually make the calendar longer by over 44 minutes.'

'Over time, these extra 44+ minutes would also cause the seasons to drift in our calendar. For this reason, not every four years is a leap year.'

If the year is divisible by 100 but not by 400, the leap year is skipped.