Return of the Leap Year

January 18, 2012

Each and every year, we come together to celebrate the arrival of the New Year. This year may seem to be just like any other, but it has an interesting story. While 2012 is both the hundred year anniversary of the sinking of the Titanic and the focus of the entertainment industry on numerous apocalyptic theories, it is unique for a different reason. Instead, 2012 is a leap year, meaning it is one day longer than a normal year. Next month, we will be rewarded with an extra 24 hours on February 29th.

What exactly is a Leap Year? The term ‘leap year’ refers to a year that includes an extra day for a total of 366 days. While a year with the normal 365 days is called a ‘common year,’ every leap year has a ‘leap day,’ and it is always the same: February 29th. It is an interesting phenomenon that occurs in an effort to solve problems of time over hundreds or thousands of years. While we are all familiar with the leap year term, we may not know the story behind it.

How do we know when a year becomes a leap year? The rules tend to be slightly complicated, so get ready to practice some mathematics. If a year is evenly divisible by the number four, it is most likely a leap year. However, if it is also evenly divisible by 100, it would not be a leap year. Unless of course it was also evenly divisible by 400, in which case it would be a leap year. This means that during a period of 400 years, there will be 97 leap years and 303 common years.

The story begins in 45 B.C. when Julius Caesar reformed the complex Roman calendar. For many years, it consisted of 355 days with an additional month of 22 or 23 days being created each year to keep festivals constant with the changing seasons. In an attempt to simplify the calendar, Caesar added days to certain months to create a year with 365 days after consulting with the astronomer Sosigenes of Alexandria. Because the calculation came out to 365 and 1/4 days, an extra day would be added to the end of the Roman month of Februarius during every fourth year. This change became known as the Julian calendar.

Since that time, a calendar year was calculated to be exactly 365 days, 5 hours, 49 minutes and 12 seconds. The 11 minute difference between the actual year and the Julian calendar meant that after hundreds of years there would be an error of a few days. By the late 1500s, the calendar was inaccurate by nearly 10 days with the spring equinox falling on March 11th instead of its normal date of March 20th or 21st. To fix this problem, another reform was necessary. On February 24th, 1582, Pope Gregory XIII introduced by papal decree what would become known as the Gregorian calendar so that Easter would fall on or after the spring equinox. Since then, this has become the modern calendar that we still use today.

In the end, the leap year is an important part of our existence. Without the extra day, the year as we know it would change over time, shifting the seasons further away from what we are used to. While many of us are familiar with extra day on February 29th, the reasoning and history behind the leap year is more complex. Now that you have read a little more about the leap year, I hope you make plans to celebrate the extra day!