History of the Leap Year: Why it Exists and Where it Originated

2024 is a leap year, meaning that it has 366 days compared to the common year, which has 365 days. While you probably got accustomed to seeing one extra day added to the calendar every four years, you probably never wondered how we got there. Let’s dive into the history of leap year and see why it exists and where it originated.

Why Do We Need Leap Years?

The common calendar follows the Earth’s orbit around the Sun. However, Earth doesn’t actually orbit the Sun in 365 days exactly; it needs roughly around 365.25 for one trip. If there were no leap years, those fractions would keep adding up, causing our months to go out of sync with annual events. For example, after several hundreds of years, the summer would start in December. By adding a leap year, we get to enjoy consistency in seasons and other annual events.

Where Did Leap Year Originated?

Roman emperor Julius Caesar is considered the “Father of Leap Year,” although he borrowed the idea from Egyptians, who followed the solar year. Romans used a 355-day calendar while adding an extra month with 22-23 days every second year to make sure their festivals and celebrations took place around the same time. Caesar decided to make the calendar simpler by distributing those extra days, creating a 365-day year, and adding one extra day to February in order to account for those extra six hours each year.

Modern Leap Year

However, Caesar’s calculation was slightly off, given that one Earth’s orbit around the Sun actually lasts 365.2422 days. While it doesn’t seem like a lot, it made a big impact throughout the centuries, causing the year to be short by one full day every 128 years.

In order to correct the issues, Pope Gregory XIII created the Gregorian calendar that accounted for the deviation by skipping some leap years. For example, every fourth year is a leap year unless it is divisible by 100, like 1800, 1900, and 2000. In that case, it also has to be divisible by 400 to be a leap year. 

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