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Making Up for Lost Time

Today marks first time in 28 years that February has five Fridays.

Posted: February 29, 2008 7:48 p.m.
Updated: May 1, 2008 5:02 a.m.
It sounds like the ultimate mathematical riddle. Take a year, divide it by four. If the year is divisible by four, add one day. Otherwise leave it alone.

If the year is a century, such as 1600 or 2000, divide it by 400. If it is divisible by 400, add one day. Otherwise leave it alone.

While some may hop around trying to solve the riddle, the easiest thing to do is look at a calendar. Today's date would fall within the purview of the above riddle, which is the mathematical science behind the leap year.

This year - 2008 - is divisible by four, therefore one day is added in February. Coincidentally, today is that added day, also known as "leap day."

Also for the first time in 28 years, February began and ended on a Friday. That will not happen again until 2036.

Yet why have an extra day every four years?

"Leap years keep modern calendars in alignment with the earth's revolutions around the sun," said Steffen Thorsen of Time and Date AS.

Why February?
Under the Roman calendar, which preceded the Gregorian and Julian calendars in Western civilizations, February was the final month of the year. Accordingly, it made sense to add an extra day - leap day - to the final day of the year. Only in recent calendars was February changed to the second month of the year. In Ancient Rome, that extra day was Feb. 24.

Thorsen added that the original Roman calendar compensated for calendar errors and seasonal changes by adding an extra month every few years.

When Did Leap Year Start?
While the Roman calendar adjusted every few years to keep up with seasonal changes, it was not until the Julian calendar that leap day became a regular occurrence.

Implemented in the year 45 (BC), the Julian calendar added one day in February every four years, including century years.

In 1582, when the Gregorian calendar was introduced, Pope Gregory XIII adjusted the Julian calendar with a new rule - a century year is not a leap year unless it is evenly divisible by 400.

Accordingly, under the Gregorian calendar, the following years would not have a leap day even though it is divisible by four: 1800, 1900, 2100, 2200, 2300 and 2500. However, 2000 and 2400 are both leap years.

Vernal Quinox
The leap year is based upon the vernal equinox, which is when the sun is directly above the Earth's equator as it moves from the southern hemisphere to the northern.

The time between vernal equinoxes is 365.2422 days -the basis of the Gregorian calendar year. However, only 365 days are used in the calendar, meaning there is a loss of 0.2422 days each year.

Over the course of four years, approximately one full day would be lost; over 100 years, approximately 24 days would be lost, meaning the calendar would be ahead of season and inaccurate.

Adding an extra day to the calendar every four years compensates for the lost time.

"The difference between the calendar and the seasons can be reduced significantly," Thorsen said. "The calendar will align with the seasons much more accurately."

Imperfect Calendars
While the leap year definitely compensates for lost time, it does not mean the calendar is perfect. According to Thorsen, time is still lost.

For example, the Gregorian calendar, which most of the world relies upon, is approximately 365.2422 days in tropical years - the time between two successive vernal equinoxes. Following this calendar exactly means there will be an error of 27 seconds each year, or one day every 3,236 years.

The Julian calendar, which preceded the Gregorian calendar, the length of a year was 365.25 days, which resulted in an error of 11 minutes per year - or one day every 128 years.

Lunar calendars, which are based on the moon and still relied on in countries such as India and China, vary between 12 and 13 months per year depending upon moon location. The error varies year-by-year.

Mondays & Wednesdays
While this year's leap day is on a Friday, Thorsen points out that leap days are likely to occur on a Monday or Wednesday.

"A leap day is more likely to occur on Mondays or Wednesdays rather than other days because the Gregorian calendar repeats itself every 400 years," he said. "Therefore Feb. 29 can occur 15 times on a Monday or Wednesday, 14 times on a Friday or Saturday and 13 times on a Sunday, Tuesday or Thursday."

Leap Year Births
An age-old question abound each leap year is when do leap day babies celebrate their birthdays?
Thorsen stated that people born on Feb. 29 celebrate their birthdays in a variety of ways. Some celebrate on Feb. 28, since it is the last day of the month in non-leap years. Some will celebrate on March 1, since they believe they did not actually "turn years" on Feb. 28. Others will only celebrate on leap years, since their is no true substitute on the calendar for Feb. 29.

Bachelor's Day
Leap day is the one day that women should not expect a knight in shining armor to ride in on that white horse and propose to them. According to Thorsen, a tradition was once introduced to allow women to propose to men on leap day.

Called "Bachelor's Day," a man could not refuse a marriage proposal by a woman on leap day. If he did refuse the proposal, he was expected to pay a penalty, either in the form of a gown or money.

"The tradition's origin stemmed from an old Irish tale referring to St. Bridget striking a deal with St. Patrick to allow women to propose to men every four years," Thorsen added. "This old custom was probably made to balance the traditional roles of men and women in a similar way to how the leap day balances the calendar."

St. Oswald's Day
One of two holidays - St. Oswald's Day - is observed on Feb. 29. St. Oswald, a 10th century archbishop of York, died on Feb. 29, 992. People around the world have a feast in his name on leap day.

Under the Baha'i calendar, Feb. 29 is the fourth day of a five day holiday called Ayyám-i-Há, which is a period dedicated to fasting, charity, hospitality and gift-giving,

Scotland and Greece had superstitions about leap year, which are still current. Babies born on leap day are considered unlucky in Scotland, while it is unlucky for couples to marry during leap year in Greece.

Come Back, Soon!
After today, leap day will not return until 2012, coincidentally the same year as the next Summer Olympiad and Presidential election in the United States.

Until then, enjoy the remainder of today's "bonus" day.


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