Every four years, the day of February 29th graces our calendars and gives us one extra day to the year. But why does this happen? It takes the Earth 365.25 days to fully orbit the sun. Since it’s difficult to have a one-quarter day, those .25 are saved up until they equal one day, then are acknowledged every fourth year on February 29th.
Before Julius Caesar came to power over the Roman Empire, people used a 355-day calendar that included an additional 22-day month every two years. However, due to the movement of the stars and the shifting of feast days as they fell into different seasons, Caesar’s astronomer, Sosigenes, was tasked with created a more simplistic solution. Sosigenes developed the 365-day calendar that would save each year’s extra hours until they created an extra day.
Like any mathematical equation, there are rules. Generally, every fourth year is a Leap Year. However, a potential Leap Year that is divisible by 100 does not qualify as a Leap Year unless it is divisible by 400. Since Earth’s orbit around the sun is slightly less than 365.25 - 365.2422 to be exact - Pope Gregory XIII’s astronomers established the Gregorian calendar in 1582, which loses three leap days every 400 years to remain mathematically sound and astrologically aligned.
