Wait Just a Second . . .


Greenwich Clock

Shepherd gate clock at the Royal Observatory, Greenwich, UK.

Image: Joaquim Alves Gaspar

Wait a second. The start of next year will be delayed by circumstances beyond everyone's control. Time will stand still for one second on New Year's Eve, as we ring in the New Year on that Wednesday night. As a result, you'll have an extra second to celebrate because a Leap Second will be added to 2008 to let a lagging Earth catch up to super-accurate clocks.

By international agreement, the world's timekeepers, in order to keep their official atomic clocks in step with the world's irregular but gradually slowing rotation, have decreed that a Leap Second be inserted between 2008 and 2009.

The extra second, ordered by the world's nominal timekeeper, the International Earth Rotation and Reference Systems Service, will be marked officially at the stroke of midnight on Wednesday in Greenwich, England, the home of what is popularly known as Greenwich Mean Time (GMT)—Coordinated Universal Time (UTC) to the more technically inclined—the standard time for the planet.

So at precisely 23:59:60 at Greenwich, England, on New Year's Eve, there will be a one-second void before the onset of midnight and the start of the New Year. Wednesday will see the 24th Leap Second that has been needed since the practice was initiated in 1972, and will be the first in three years.

Keeping the Earth on time

Around the world, to satisfy the requirements of navigators, communication organizations and scientific groups, about 200 atomic clocks in over 50 national laboratories worldwide will be adjusted at local times corresponding to midnight to local times at Greenwich. On New Year's Eve, the master clock at the United States Naval Observatory will be adjusted at 6:59:60 p.m. EST, or 23:59:60 GMT.

The extra second is needed to keep the world's clocks in time with the rotation of the planet. Time measured by the rotation of the Earth is not uniform when compared to time kept by atomic clocks. Today's atomic clocks have an inaccuracy of less than one second in 200 million years.

But for various reasons—the sloshing molten core, the rolling of the oceans, the melting of polar ice and the effects of solar and lunar gravity—our planet rotates on its axis at irregular rates, and on average has been falling behind atomic time at a rate of about two milliseconds per day. It now trails the official clock by about six-tenths of a second.

As a result of this difference, atomic clocks can get out of sync with the Earth and periodically have to be adjusted. Since it's the atomic clocks that are used to set all other clocks, a Leap Second has to be added from time to time to make up the difference.

Adding the extra second between 23:59:59 on Dec. 31 and midnight on Jan. 1 will put Mother Earth about four-tenths of a second ahead of the clock, giving her a bit of a head start as 2009 begins.

Who said chivalry is dead?

How to see and hear the extra second

Today many retailers market radio clocks as atomic clocks;" though the radio signals they receive usually come from true atomic clocks, they are not atomic clocks themselves. Typical radio atomic clocks require placement in a location with a relatively unobstructed atmospheric path to the transmitter, perform synchronization once a day during the night-time, and need reasonably good atmospheric conditions to receive the time signals.

If you own such a device, you might want to watch what your clock displays just before 0 hours GMT, Jan. 1, which corresponds to 7 p.m. Eastern standard time on Dec. 31. The minute beginning at 6:59 p.m. EST will contain 61 seconds. When a Leap Second was added in 2005, I watched my own clock closely during that minute as the seconds ticked off. When the final second of that minute was reached, the number 59 flashed not once, but twice!

If you don't have a radio clock, you can bring up a time display on your computer by going to NIST, the National Institute of Standards and Technology.

You can also listen for the Leap Second by tuning in to a shortwave time signal station. In North America, the extra tick can be heard by listening either to station WWV out of Fort Collins, CO at 2.5, 5, 10, 15 and 20 megahertz, CHU in Ottawa, Canada 3330, 7335, and 14670 kilohertz, or see other shortwave time signal stations for other parts of the world. (Note that CHU 7335 will cease broadcast on this frequency immediately after the leap second and move to 7,850 kHz thereafter.)

Should you encounter poor reception, try preparing a seconds pendulum by hanging a small weight on a string about 39.1 inches (99.3 centimeters) in length. Adjust the string length beforehand until the swings exactly match the time signal ticks. If the beeps denoting the start of each minute occur at the left extreme of a swing before the final (GMT) minute of 2008, they will be heard at the right extremes thereafter. (Although the swing amplitude will be steadily dying down, this does not affect a free pendulum's oscillation period.)

Ball Drop too early?

New Years Eve Ball 1978

New Year’s Eve Ball, 1978.

Photo credit: The New York Times.

By the time the transition from 2008 to 2009 arrives in North America the Leap Second will have already been inserted into the world's timescale. But there was a bit of confusion about all this back in 1972 when the first Leap Second to be inserted on a New Year's Eve took place. One of our astronomers here at the Hayden Planetarium took a phone call that day from one of the engineers who was assigned to drop the famous illuminated ball in Times Square (in those days, the ball was slowly lowered using an old fashioned rope and pulley). This can affect our jobs, he reportedly said. So we want to be sure we don't drop that thing one second too soon!

Regardless of how you use your extra second, just keep this one indisputable fact in mind: Whenever you note the time on the clock, realize that it is now—right now—later than it has ever been.

Happy New Year!

Tags: time, calendar