How The Leap Day Keeps The World On Schedule

February 29th is known as Leap Day and it comes around every four years. 

2021 is not a leap year, which means that there are only 28 days in February. 

While it may seem unremarkable to most people, this one day that happens every four years keeps the world on schedule. 

Gregorian Calendar vs Astronomy & Seasons

We have become so accustomed to our neatly-organised seasons. In the northern hemisphere, July is always in the summer while in the southern hemisphere it is always in the winter. 

Basically, the reason we need a leap day is to keep our man-made calendar in tune with the natural world. 

Most of us believe that Earth takes 365 days to orbit around the sun. 

Every planet has a different number of days in a year based on its orbit around the sun. 

It takes exactly 365.256 days for Earth to complete its orbit around the sun. 

That pesky quarter of a day is why every four years, we need to add a day to ‘make up’ that extra time. 

And since it’s not quite a quarter of a day, leap day is skipped once every century.

When Did Leap Days Begin?

The first officially recorded leap day took place in 1752 in Great Britain. 

This was when the Gregorian calendar was adopted by Britain and its colonies. 

Instead of adding one day to February, a whopping 11 days were ‘lost’ from September. 

Although personally, I know many people who would have enjoyed this ‘fast forward’ to Halloween and Christmas, this was a dramatic way to catch up to the Earth’s natural rhythm.

What Would Happen Without A Leap Day?

In our lifetimes, it wouldn’t make a huge difference if the leap day was suddenly cancelled. 

However, over time, summer would become winter and the equinox would be at a weird time of the year. If we abandoned leap day, so much of our current calendar would no longer be relevant.

The deviation of just six hours per year would shift seasons by 24 hours within just 100 years. 

Since it happens so slowly, it would not be a shocking difference. However, it would disrupt the way we celebrate holidays and create unnecessary confusion. 

What Are Leap Seconds?

Removing 11 days from a year is extreme and even adding a day seems pretty crazy. Sometimes, to help our calendar ‘calibrate’ to the natural world, something more subtle is needed. 

The first leap second was added in 1998 to help keep our clock-time aligned with the time measured by the sun. 

There was also one added on December 31st in 2005 and one in 2008, 2012, and 2015. A lot of science goes into deciding to add even just a second to our previous calendar.

As the sun’s gravity weakens over time, Earth moves about 15 cm away from it every year. Thids doesn’t seem particularly significant. 

However, in the future, we may be seeing leap minutes, leap hours and who knows, maybe even leap weeks. 

The leap day is a fascinating human invention that stems from a lot of scientific research. 

It functions to keep our man made constructs of holidays and calendars in sync with the Earth’s natural orbit around the sun. 

Next leap year, which will take place in 2024, take the day to marvel at the passing of time and how just one day can change everything forever.

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