The start of 2020 brings a lot of excitement and interest to many people. For some, it’s the anticipation of what this next decade brings. For others it’s the fact that Halloween is on a Saturday this year. But there’s another reason why 2020 is interesting to some people; it’s a Leap Year. 

 For those who don’t know, a Leap Year is when we add on an extra day to February. So instead of the calendar going February 28 then March 1, it goes February 28, 29, then March 1. There is a Leap Year roughly every four years.  

The reason we have a Leap Year is so the Gregorian calendar, the one we typically use in the U.S., stays aligned with Earth’s rotations around the sun. In a non-Leap Year, there are 365 days. But is actually takes Earth around 365 days, five hours, 48 minutes, and 45 seconds to make a full rotation around the sun. This is measured using the March Equinox when the sun shines directly on the equator and the length of the day is almost exactly equal to the length of the night.  

If we didn’t have a Leap Year roughly every four years, we would be losing about six hours off the calendar every year. After 100 years, our calendar would be off by about 24 days. 

The idea of having Leap Years was introduced by the Roman general, Julius Caesar, over 2,000 years ago. But according to his calendar, the only rule to make a year a Leap Year is if it’s evenly divisible by four. This created too many Leap Years but it wasn’t corrected until over 1,500 years later with the introduction of the Gregorian calendar.  

Now, there are three criteria a year must meet in order to be considered a Leap Year. One is if it can be evenly divided by four, it’s a Leap Year. But if the year is evenly divisible by 100, it isn’t a Leap Year; unless it can also be evenly divisible by 400, in which case it is a Leap Year.  

Those using the Gregorian calendar aren’t the only ones who have Leap Years. There’s a Chinese Leap Year that adds an entire month to the calendar every three years, the Jewish Leap Year adds a 13th month seven times in a 19-year cycle. One of the most accurate calendar systems comes from the Iranians. Their Leap Year isn’t based on mathematical rules like many of the other calendars, but rather by the timing of the equinoxes.  

While a Leap Year in the Gregorian calendar occurs roughly every four years and for only one day, it isn’t impossible to have babies born on that extra day, in fact there are roughly 187,000 people born on February 29, known as Leaplings. So then the question is asked, what do these people do for their birthdays when it isn’t a Leap Year? It depends on the individual Leapling, but some will just celebrate a day early or a day late, some will make their birthday a two-day event, and others will get together with other Leaplings and have an all out celebration.  

Regardless of if Leap Years are common knowledge in your household or not, they are important events in our lives that help to keep us synchronized with our planet’s orbit around the sun.