Why do we have a leap day every four years? What’s the story of ‘leap year skip’

The year 2024 will have February 29 on our calendars, and its existence may spark curiosity about the significance of leap days and the scientific reason behind adding one day to our calendars every four years. 

According to National Geographic, beyond being an extra day on the calendar, leap years hold a vital scientific purpose, aiming to align Earth’s orbit with the human calendar. This additional day ensures synchronicity between seasons, holidays, and agricultural activities.

The scientific reason behind leap day

Leap years, occurring roughly every four years, result from the Earth’s orbit taking approximately 365 days and 6 hours. The quarter-day surplus accumulates over time, and leap years serve as a corrective measure, preventing a misalignment between our calendars and the Earth’s orbit. Without leap years, a gradual shift in seasons and solstices would disrupt familiar timelines.

The tradition of leap days extends beyond mere calendar adjustments. While not an official holiday in the United States, various cultures celebrate it uniquely. 

In Ireland, women challenge traditional gender norms by proposing to their partners. In parts of China, children express affection to parents through gifts, and leap days have become popular wedding choices.

History of leap day

Leap Day’s roots trace back to ancient civilizations grappling with calendar discrepancies. Pope Gregory XIII’s implementation of the Gregorian calendar, incorporating leap years, proved to be an effective solution.

However, not all cultures adhere to the Gregorian calendar, devising alternative methods to account for the Earth’s orbital intricacies. The Hebrew calendar, for instance, introduces an extra month within a 19-year cycle to maintain alignment with solar seasons.

What is a Leap Year skip?

While leap years typically occur every four years, exceptions exist because the Earth’s orbit takes approximately 365.2422 days. The rule of skipping a leap year if divisible by 100 but not by 400 ensures a more accurate alignment. The next leap year skip is projected for 2100.