Leap year. It adds a 29th day to February roughly every four years. So how did it all begin—and why?
Have a look at some of the numbers and history behind the day.
Leap day is . . . math.
It’s mind-boggling math! We measure each year using 365 24-hour periods, or days. But Earth’s orbit isn’t precisely 365 days long. The trip around the Sun takes about six hours longer than that. Leap year adjusts the calendar to fit the Earth’s movements. It exists to keep the months in sync with events that happen every year, such as equinoxes and solstices. (Those mark the beginning of each season.)
The next leap years are 2028, 2032, and 2036. But not every four years is a leaper. Adding a leap day every four years would make the calendar longer by more than 44 minutes.
Years divisible by 100 do not follow the four-year leap day rule . . . unless they are also divisible by 400. In the past 500 years, there was no leap day in 1700, 1800, and 1900. But 2000 had one. In the next 500 years, there will be no leap day in 2100, 2200, 2300, or 2500.
Is your brain melting yet?
Leap day is . . . necessary.
What would happen without leap day? Nothing good. Especially for people who plant crops! The calendar would get really confusing.
“Without the leap years, after a few hundred years we will have summer in November,” says physics instructor Younas Khan. “Christmas will be in summer. There will be no snow.”
Leap day is . . . history.
The Bible tells us that God “made the Moon to mark the seasons” and that “the Sun knows its time for setting.” (Psalm 104:19) For all of history, people have used the motions of the Earth and Moon to make calendars and plan their lives. Ancient calendars were based on the phases of the Moon or the Sun.
Now hop on over to the Roman Empire. Emperor Julius Caesar’s part of the world was having a problem with “calendar drift.” So he introduced his Julian calendar in 46 B.C. It used only the Sun to guide its dates. It set each year at 365.25 days. Once every four years, an extra day was added.
But still, under Julius, there was drift. There were too many leap years! That’s because the solar year isn’t precisely 365.25 days. It’s 365.242.
People in the Western world used the Julian calendar for hundreds of years. Enter Pope Gregory XIII. He noticed that Easter was coming later in the year than it used too. He wanted to keep it in the spring. His Gregorian calendar took effect in the late 16th century. We still use it. It isn’t perfect though, because we still need a leap year.
Do you know anyone who was born on a leap day? About five million people worldwide share the leap birthday.
