Today is a strange day, as it's February 29th - a Leap Day. A day which only happens once every four years. Why you ask? Well during a Leap Year a Leap Day is added, this is to keep our calendars in order. To look into the shenanigans of a Leap Year, let's break it down a bit more.
Where did Leap Year come from?
Over 2,000 years ago, Julius Caesar introduced Leap Years to the Romans, but they utilized the Julian calendar, which was flawed.
With the Julian calendar any year evenly divisible by 4 was a Leap Year. This led to far too many, but this problem wasn't corrected until the introduction of the Gregorian Calendar some 1,500 years later.
Our modern day Gregorian calendars only has 365 days, but it takes approximately 365.242199 days - or 365 days, 5 hours, 48 minutes, and 46 seconds to circle once around the Sun. So in order to keep our calendars in alignment with the Earth's revolutions around the sun, Leap Years are needed.
For instance, if we didn't add a day every four years, you would lose almost six hours off our calendar every year. Time and Date states that after only 100 years, our calendar would be off by nearly 24 days.
The Gregorian calendar was designed to keep the vernal equinox on or close to March 21st, this is so the date of Easter remains correct
How does one know if it's a leap year? (This could get a little complicated)
If the year is divisible by 100, it is not a Leap Year, unless it is also evenly divisible by 400, in which case it would be a Leap Year. For example years 1700, 1800 and 1900 weren't Leap Years, but 1600 and 2000 were. Make sense?
What if someone is born on a Leap Day?
Short answer: they only have a birthday day once every four years. (Okay, that's not entirely accurate.)
Individuals born on February 29th are known as "Leapers". They'll either celebrate their birthday on either February 28th or March 1st, with most celebrating on the 1st.
For those of you who are more visual, you should check out the video below, which explains Leap Year / Leap Day quite well.