Why Leap Year: The Planetary Connection

from Wildlife Promise

This year promises to be a long one—a full day longer than usual—because 2012 is a Leap Year, composed of 366 days instead of the typical 365.

And wouldn’t you know that U.S. presidential election cycles pop up during Leap Years, giving us an extra day of campaigning and attack ads, especially onerous because in politician years, a day is like 12 months.

But it can’t be helped. The need for Leap Year is an excellent example of how the natural world just won’t fall neatly in line with human plans, schemes and machinations. The Earth circles the sun at the rate of about 365.242199 days—just roughly speaking, you see—which means our 365-day calendars fall six hours behind each year. In a century, the calendar would be off by 24 days—nearly a month. So every four years we add the otherwise elusive February 29th to the calendar, allowing our appointments to catch up with the orbiting speed of the planet, which, by the way, is more or less 66,486.717569 miles per hour.

Where’d Leap Year Come From?

leap year, georgia, okefenokee swamp, sunset

The sun sets behind trees at Georgia's Okefenokee Swamp in a photo entered by Jack T. Sandow in the NWF Annual Photo Contest. Variations in the Earth's orbit around the sun make Leap Years a chronological necessity.


Leap Year has been with us for more than 2,000 years, introduced in 45 B.C. when the Roman emperor Gaius Julius Caesar revised the calendar (and named one of the months after himself—July). Equally famed for his association with the final words “Et tu, Brute,” Gaius put in a Leap Day every four years, though the process of keeping the calendar on track with the Earth proved more complicated than that.  His plan led to too many Leap Years, so the calendar had to be adjusted by nearly two weeks in the early 1700s.

Now the injection of a Leap Day occurs in every year evenly divisible by 4, unless the year also can be evenly divided by 100, in which case it’s not a Leap Year, unless it also can be evenly divided by 400, in which case it is a Leap Year. If this sounds confusing, well, you can perhaps forgive Gaius for his oversight, which must not have been made easier by the use of Roman numerals.

Luck of the 29th

Of course, a date as wayward in its recurrence as February 29th is bound to have some myth attached to it, the human mind being as superstitious as it is. In Scotland, being born on Leap Day is considered unlucky. In Greece, marrying during a Leap Year is a bad sign, and marrying on Leap Day is even worse (though it would simplify anniversary celebrations). In some European nations, Leap Day is a sort of Sadie Hawkins event in which women propose to men. This day is also called Bachelors’ Day in some nations where, according to tradition, if the man turns down the woman, he must give her gifts (you can see the potential for abuse of this system). Among the upper classes in some countries, the demurring man was supposed to give the woman a dozen gloves, which she could wear to conceal her lack of a wedding ring.

Planetary Changes

The vagaries of the Earth’s rush around the sun isn’t the only factor that can remind us that what happens in space doesn’t stay in space. For example, the spin of the Earth on its axis, currently at a speed of about 1,070 miles per hour at the Equator, is slowing down. During the age of dinosaurs, a day was probably around 23 hours long. In the Devonian period, some 370 million years ago—long before dinosaurs—the day was around 22 hours long. So when someone complains, “There are only so many hours in the day,” you may smugly reply, “It could be worse.”

Other factors affect the measuring of time. Last November, scientists who study this sort of thing discovered that the Earth’s axial spin actually sped up after the Antarctic Circumpolar Current, a powerful stream of ocean water, slowed down. Each day from roughly November 8 to the 20 was about 0.1 millisecond shorter than usual. Before the planet resumed normal speed, we lost a good 1.2 milliseconds, which can ruin a two-week vacation. Such shifts may become more common as climate changes in the wake of global warming, because some scientists suspect that warming trends caused the alterations in the sea current’s velocity.

Record Leap Day Births

A Norwegian family holds the world’s record for the official number of children born within a family on Leap Day—Mrs. Karin Henriksen, from the town of Andenes, gave birth to three children on consecutive Leap Days—1960, 1964 and 1968.

Were you born on Leap Day?  If so, perhaps you can tell us in the comment section how, or when, you celebrate your birthday anniversary.

To see more photos like those in this blog, or to enter the 42nd Annual NWF Photo Contest, visit the NWF Photo Contest.

Much of the information in this blog comes from the Time and Date website,  which has tons of data on, well, time and dates.

National Wildlife magazine online offers you more information on animals and birds.