First of all, what are leap years?
A leap year is a year that has an additional day, which is February 29th. This results in the year having 366 days instead of the typical 365. In the Gregorian calendar (the one we use), leap years usually occur within four years.
Why do we need leap years?
The purpose of leap years is to balance the calendar year with the time it takes for Earth to orbit the sun, which is known as an astronomical year. If you dont know, it doesn’t take exactly 365 days for the earth to orbit the sun, it takes 365 and a quarter (365.2425). This is why it happens every 4 years. We try and do this to balance our year so we can keep the days of seasonal events like solstices and equinoxes the same.
How were leap years discovered?
The process of discovering leap years involved two different types of calendars proposed by two different people:
- The Julian Calendar: The Julian Calendar was introduced around 45 BCE (Before the Common Era). Julius Caesar is responsible for putting this calendar in place. The proposed calendar involved a 365-day year with an extra day added every four years. However, this calendar wasn’t the most accurate as it was about 11 minutes from the true time of the year. 11 minutes may not seem like a lot but in the long run, it would impact us a lot. Because of this, someone introduced a new calendar to correct it.
- The Gregorian Calendar: The Gregorian Calendar was introduced by Pope Gregory XIII. The purpose of this calendar as mentioned was to correct the mistakes in the Julian Calendar. The biggest change to it was to make it so years divisible by 100 are not leap years except if they are divisible by 400. This is to take in the fact that an astronomical year is slightly less than 365.25.
In the end…
Leap years are introduced to balance the relationship between astronomical years and calendar years. Two types of calendars have been introduced but we have only stuck with one, the Gregorian Calendar. Leap years are an integral part of how we live life and our calendar system.