A CliffsNotes Version of Leap Year

By Grace Bernstein

Today is February 29, 2020 (well, when this article was posted it was February 29, 2020). Normally, February only has 28 days, but every four years our calendar has what is commonly known as a “Leap Year”. In reality, a leap year only adds one extra day in February to keep the Gregorian calendar in line with the astronomical calendar. 

This begs the questions: what is an astronomical calendar, why does it change our calendar every four years, and what exactly is the Gregorian calendar? To start off, the Gregorian calendar is the most used calendar in the world. In 1582 Pope Gregory XIII named the Gregorian calendar as the new way to mark dates. It was very different from its predecessor, the Julian calendar, as it had four less days, and it did not properly reflect the actual time it takes the Earth to circle once around the Sun. Our current calendar focuses on the accurate timeframe for how long it takes the Earth to rotate around the Sun, which gives us approximately 365 days, 5 hours, 48 minutes, and 45 seconds each year (but who’s really counting?). Because of that, every four years we have a leap year (in reality, it’s more of a leap day) in order to match the astronomical calendar.

The astronomical calendar is actually a grouping of calendars that follow celestial events like moon phases, eclipses, and other astronomy occurrences. It doesn’t help that astronomical cycles are incredibly inconsistent and aren’t always in tune with each other. The lunar calendar and Julian calendar are just two examples of calendars that make up the aforementioned “grouping”, which is different from the solar Gregorian calendar. 

Because the two calendars are different, but the world uses both of them, the Gregorian calendar has a leap year every four years (but only when the year is divisible by four) in order to keep the calendars in sync with the rest of the world. The next leap year occurs in 2024, then 2028, and so on.

And now you know…and knowing is half the battle!