Do you know why a leap year happens and when it occurs? In this post, we explain you the curiosities less familiar about leap year.

In addition to the new decade, 2020 is a leap year, and that means we will have an extra day to do great things. But, what is the origin of all this? Keep reading, we explain you what a leap year is and why it occurs.

The history and origin of leap year

The leap year responds to the necessity to balance out a gap between the tropical year – 365 days, 5 hours, 48 minutes, and 45.10 seconds, and the 365 days’ year. In order to find out more about its origin, we need to go back to the Rome of Julius Caesar, who realised that the Roman calendar wasn´t completely aligned with the solar calendar. In one of his first visits to Egypt, Caesar asked to the astronomer Sosigenes of Alexandria to elaborate a new and accurate calendar. In order to do so, he based it on the Egyptian calendar, maintaining the name of the Roman months, and added an extra day every four years to balance out the gap, although the result wasn´t quite accurate.

Centuries later, Pope Gregory XIII decided to further improve it by papal bull (thus the origin of the Gregorian calendar). Advised by the Jesuit astronomer Christopher Calvius, he established that the 4^th of October of 1582 was followed by the 15^th of October. With the suppression of these days, the 11-minute’s gap accumulated over the beginning of the Julian calendar was balanced out.

So it didn´t happen again, Pope Gregory XIII created a system of exceptions for leap years, as there is not always a 29^th of February every four years. He established that leap years are all years divisible by four, with the exception that these are also divisible by 100, unless they are divisible by 400.

We know that this formula may be a bit tricky. Fortunately, everything is already calculated and we don´t have to worry about maths, only about enjoying an extra day!