Leaping into the year: Why do we have an extra day?

The Gregorian calendar we have today is thus crucial to keep our calendars and seasons in sync.

Marina Snyder
4th March 2024
Image Credit: Pixabay - TheDigitalArtist https://pixabay.com/illustrations/leap-jump-leaping-silhouette-4052923/
Every four years, it gets to that time in February, and you get that little surprise…an extra day! Having a leap year is one of these things you learn about in school; however, how much do we understand about leap years? Why do we have them? And what’s the history behind them?

A leap year is defined as the extra day we have every four years, where the 28th of February is suddenly followed by the ‘29th’. These leap years are essential because they ensure our calendar matches our solar year

People often think a solar year is 365 days; however, that’s a rounded number. A solar year is 365.25 days, so to make up for the missing, partial day, one day is added to the Calander approximately every four years.

But why are leap years so crucial? The earth completes one orbit around the sun in approximately 365 days and 6 hours whilst rotating on its axis in about 24 hours (constituting a day). Because we round down to 365 days, we remove approximately ¼ (6 hours) of a day.

However, if we kept subtracting 6 hours every year and didn’t have a leap year, all those missing hours would eventually add to days, weeks, and months. This means that our seasons would be different; August would be freezing cold in a couple of hundred years.

Leap years have arguably been a process of trial and error. For instance, the Roman system was initially going to have 445 days instead of 365, known as the ‘Year of Confusion’. Julius Caesar then made a 365.25-day year, having a leap day every fourth year.

But even this system was not entirely accurate, as years were still 11 minutes shorter than our current calendar, which meant that eventually, an entire day would be short every 128 years.

The Gregorian calendar we have today is thus crucial to keep our calendars and seasons in sync. That is not to say it’s an entirely perfect system; there’s still a 30-second drift each year. Even with these imperfections, though, the calendar won’t be off for more than a day for another 3,300 years – who knew leap years were so important?

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