Why Is There A Leap Year?

What Is A Leap Year & Why Does It Exist? We all know February has 28 days – except when it doesn’t. The leap year is a confusing concept for many people. Where does this …

Leap Year History

What Is A Leap Year & Why Does It Exist?

We all know February has 28 days – except when it doesn’t. The leap year is a confusing concept for many people. Where does this extra day come from? Why does it only happen every four years? These are questions that must have answers!

So, why is there a leap year? It takes 365 days, 5 hours, 48 minutes, and 46 seconds for the Earth to orbit around the Sun once. We have established that a year consists of 365 days, so where does that little bit of extra time go? The answer is that it accumulates over time, so after four years – or in other words, every fourth February 29th – we must have a leap day, also known as an extra day. This is why February 29th is called Leap Day.

Maybe like you, this whole leap year or leap day concept has always made my brain scramble a bit. Thankfully over hundreds of years, various groups of people made observations, created calendars, and researched how exactly we can solve this problem of extra time while still having a reliable and consistent calendar.

So, the leap year was invented, adopted, and eventually perfected from the Egyptians to Pope Gregory XIII. The history and science of the leap year are more interesting than you may think and some things about it may surprise you!

Who Discovered the Leap Year First?

Leap Year FAQsThe Egyptians were the first civilization who figured out how to solve this slow accumulation of time. This is not by coincidence. They invented many other things which are utilized today like geometry, medicine, and irrigation technology.

The ancient Egyptian astronomers decided that after four years, one leap day would be added to the calendar. At the time, this is exactly what they needed to do to keep pace with the sun.

However, this meant that their calendar was not exactly 365 days long each year. This is very important for religious festivals. Eventually, it got to a point where these festivals would randomly land on different days of the week each year.

The priests would use the civil calendar to predict the flooding of the Nile River, so this inaccuracy may have caused disasters. The Egyptians were forced to correct their calendars just like they had done many times before.

Although the ancient Egyptians were the first to recognize this problem and create a solution, that solution was slightly flawed. Every year except for those divisible by four would have a leap day added. This created a leap cycle of 3 years instead of 4 which is what we need!

Eventually, the Roman Empire took notice and updated their calendar to our current leap cycle, but by then it was off by a few more days than we need.

The Julian Calendar is Introduced

What is a Leap Year?The Romans adopted the idea of the leap year from the Egyptians, but they also saw that it was not perfect for them. After the priests of Egypt complained about their festivals being celebrated on different days, Julius Caesar took notice and decided to fix it.

He consulted with the Alexandrian astronomer Sosigenes, who was an expert in this field, about how to solve this issue.

According to legend, he said that they should take note of the observation that every fourth year was a leap year and make it consistent by adding a day to February of every fourth year, except for those years evenly divisible by 100; but those evenly divisible by 400 (e.g., 2000) would still have another day added, hence the term “leap” year.

Soon after the Julian Calendar was adopted, the Romans found that there were still problems with it. The Earth does not orbit around the Sun at a steady pace; it speeds up and slows down over time. Not by much, but it is still significant.

Sosigenes was not aware of this so he told the Romans that every 128 years there would be an extra day in February. This happened once in 46 BC and again in 8 AD, which was right before the Julian Calendar’s most accurate leap-cycle started over with errantly added leap days.

46 BC: The Longest Year

The cycle would be years that are divisible by 4 (except for those divisible by 100) having a leap day, while the other years in between would have no leap days. This meant that every 128th year there would be an extra leap day which was way too often; this inaccuracy grew over time.

Eventually, it got to the point where Julius Caesar had this problem fixed by adding 95 days instead of just one day (the year 46 BC was extended to 445 days). This is why every fourth year in the Julian Calendar has 98 or 99 days.

Eventually, people realized that this solution was not exactly accurate and at the time it took about 128 years for the Julian Calendar to have one day off from the astronomical vernal equinox. While one day off every 100 or so years seems insignificant, it starts to add up and someone of high prestige realized this.

Pope Gregory XII Creates The New Leap Year

Pope Gregory XII was not pleased with the accumulation of this extra time in the Julian Calendar. After consulting many astronomers and mathematicians about how to fix this problem, he and his advisors came up with an ingenious solution.

It turns out that there was a 14-day discrepancy between the astronomical vernal equinox and the Julian Calendar’s first day of the year. Pope Gregory XII decided to do something about it.

The last day of February in 1582 would be cut short from 28 days to only 24. Those leap years divisible by 100 were still going to be 366 days, but years divisible by 400 would only have 365.

This “Gregorian Calendar,” as it is called today, was a huge improvement from the Julian Calendar. There were no more adding of leap days every four years and the average year length was much closer to that of the astronomical vernal equinox.

Gregorian Calendar & the Vernal Equinox

Over 200 years later, the difference between the Gregorian Calendar’s average year length and that of the astronomical vernal equinox is about 10 minutes. This was fixed in part by reducing all months to 30 days except for March, May, July, August, October, and December which are still 31 days each.

These months were chosen because they roughly correspond to the vernal equinox and autumnal equinox. February, though it is still 28 days long, now only contains the astronomical vernal equinox as opposed to what was once February 1st of the old Julian Calendar.

It is also interesting to note that the other main reason Pope Gregory XIII altered the calendar was to better account for Easter. Currently, Easter can be celebrated as early as March 22nd or as late as April 25th, but it must always fall on a Sunday between these dates.

For Catholics who used the Julian Calendar before switching to the Gregorian Calendar, Easter could frequently fall too early or too late, even as much as 8 days off. Since the switch, Easter falls much closer to its date: between March 22nd and April 25th.

Why Is The Leap Day On February 29?

Now, of course, everyone always wonders how and why February was chosen to account for the leap day. It turns out, February was chosen simply because it was the shortest month in the already adopted calendar year.

Adding it to the shortest month of the year makes perfect sense when considering this concept: when adding an extra day to this month every four years, there is no effect on any of the months around it.

How Common Are Leap Day Birthdays?

What is Leap Year?It comes as no surprise that it is pretty uncommon to be born on a leap day, the chances are about one in 1,461.

There are only a handful of well-known people who were born on this day, but it is still interesting to note that some celebrities do share this unique birthday.

Some celebrities who share the February 29th birthday include Mark Twain (writer), Tony Robbins (motivational speaker), Mae West (actress), Ja Rule (musical artist) Michelangelo (artist), and Napoleon Bonaparte (emperor).

What do leap day births do for a birthday then? Well legally and logically, most will simply celebrate their birthday on March 1st on non-leap years. Some will throw an extra celebratory party on leap years where their actual day of birth can be celebrated!

When Will Another Leap Year Occur?

Now that we have a better understanding of why there is a leap year, let’s go over how it works. A year with a leap day is defined as a leap year if it is divisible by four. If a year isn’t divisible by four, then the number of days in February will be 29 instead of 28.

This rule remains true even if the year is also divisible by 100 but not divisible by 400. This means that the last leap year was in 2020 and the next few will be as follows: 2024, 2028, 2032, 2036, 2040, 2044, and 2048.

Celebrating Leap Day Traditions

On February 29th, many people all over the world like to celebrate leap day traditions. These traditions harken back to the days of old when people would take advantage of that extra day in February to spend time with loved ones or do something spontaneous.

A popular tradition born in Ireland, that has ever since allowed the subversion of traditional gender roles once every four years (though for 24 hours only) goes like this: every February 29th, ladies can propose to their lovers and the gentlemen must say yes.

In some countries, people will also celebrate Leap Day with events such as leap races in which people leap over an object. Others choose to dance or leap over fires, but Leap Day has also been known to involve dancing on rooftops or dressing up in disguises, and pranking others.

Other popular traditions are having Leap Day birthday parties and trying out new things that you normally wouldn’t try (like skydiving, etc.) Leap years are an amazing feat to witness in our lives.

We can take this extra day and use it for things like celebrating our birthday, spending time with loved ones, or trying out new activities that we normally wouldn’t do. So remember, when you see February 29th on the calendar next year, go out there and take advantage of that extra day!


Are you still looking to learn more interesting facts? Find more answers to life’s questions here!