It Happens Every Four Years – And It Happened 2 Years

2016 was a leap year, and that means we had an extra day in February. This only happens every four years, so it is customary for people to celebrate in different ways on February 29. But many people are unaware of how this curious custom started.

Why do we have a leap year every four years in the first place?

To answer this question we need to go a few hundred years back. For the sun to make a full circle around our planet it takes 365 days plus a little more – about five to six hours.

But as you already know, the Gregorian Calendar (the calendar used by most countries as a calendar system) only contains 365 days spread out over 12 months. So what happens to that one-third of an hour?

You’re already figuring it out, I can tell. It takes three years for this 0.24 of a day to make up a whole day. We add an extra day to February every fourth year to make up for this discrepancy.

Why does it matter?

Calendars have one goal: to ensure people can properly understand and predict the seasons and the weather. If we were to omit adding one day every four years, eventually the seasons would not be in sync with our calendars.

On paper it would say May, but in terms of seasonal temperatures, it might feel like August or December, depending on how out of synch it was that year. Imagine the chaos!

If you’re a bit of a history nerd you’ll love this. Back in the days of the Roman Empire the calendar had only 355 days. To account for those extra days that the sun needed to complete its orbit, the Romans use to add a whole month – yes, a whole month – to their calendars every two years.

But when Julius Caesar became emperor of Rome in the 1st century AD, he decided that he wanted a more straightforward system. That’s when Sosigenes, the astronomer Caesar employed, created the Julian calendar, with 365 days in normal years and 366 days every fourth year.

But wait – we don’t use the Julian calendar today!

That’s because for some people, even this Julian adjustment wasn’t enough. About five hundred years later, the Gregorian calendar was created to account for a much smaller (0.002%) discrepancy.

It was a change driven by the needs of the Roman Catholic Church, which decreed that the Easter celebrations were to be held on or close to the spring equinox (end of March).

After five centuries of observing the Julian Calendar, Easter was getting farther and farther from the spring equinox, something the Church was not happy with. That’s why Pope Gregory XIII introduced the Gregorian Calendar. It was first adopted by Catholic countries in Europe, and eventually by most countries around the world, as a way to make international trade and communication more convenient.

Why the extra day is added to February and not another month?

This is a question many people have. Today, every other month has 30 or 31 days – but this was not always the case.

When Julius Caesar was emperor, July – the month named after him – had 31 days and August had 29. When Caesar Augustus succeeded Julius Caesar, he too wanted the month named after him (August) to have more than just 29 days. So he borrowed two days from February.

It’s good to be king! (Or emperor, in this case.)