Leap year, explained

February 20, 2016

Many think of leap day as a mysterious extra day that is added to the calendar almost every four years. But the origin of the leap year goes back to ancient history.

After coming into power, Julius Caesar created a new calendar because the previous one was inaccurate. On Caesar’s calendar, there were 12 months with 365 days in a year. An extra day was added every four years to account for the earth’s rotation.

It takes the earth one year to go around the sun. In that single year, the earth rotates 365.2425 times; adding the extra day helped keep the calendar on track.

But there was a problem.

Adding the extra day every four years created an excess of about 11 minutes for that year. This meant that every 128 years, a day drifted off course. Over time, the days added up.

By 1582, the vernal (spring) equinox was off 10 days and was on March 11 instead of March 21. After this occurrence, one man altered the calendar and developed what we use today, the Gregorian calendar.

Pope Gregory XIII acknowledged the problems with the calendar and changed it to better align with the Earth’s rotation. The only difference between the two calendars is that in the Gregorian calendar, leap years occurred every year divisible by four.

Century years were calculated differently. In order for it to be a leap year, the century year must be divisible by both 100 and by 400.

Sound confusing? Look at the year 1900. There was no extra day added that year because 1900 is divisible by 100, but not 400. The same goes for 1700, 1800 and so on. The year 2000 did have the extra day because it is divisible by both 100 and 400.

Even with these improvements, the calendar is still not perfect. There are inconsistencies in our calendar system, but they don’t occur very often. About every 10,000 years, the problems will need to be remedied by future generations.

There are a few interesting facts relative to this leap day, or intercalary day. There is a one-in-1461 chance of being born on a leap day. People whose birthday falls on Feb. 29 usually celebrate it on the Feb. 28 or March 1. And, in some countries, it is traditionally acceptable for women to propose on leap day. Yet, the ancient Greeks believed that it was unlucky to be married in a leap year.

For those who want a few more hours in a day, or say, “I wish I had one more day to ...” well, this year you do. Let’s make that extra day count!

Happy birthday, leap day babies.

By Matthew Marasco

Sophomore, Washington



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