ROANOKE TIMES
Copyright (c) 1995, Roanoke Times
DATE: Saturday, December 30, 1995 TAG: 9601020048
SECTION: NATIONAL/INTERNATIONAL PAGE: A-1 EDITION: METRO
DATELINE: WASHINGTON (AP)
SOURCE: SIBELLA C. GIORELL RICHMOND TIMES-DISPATCH
`AULD LANG SYNE' can wait, at least until the 'leap second' that will be tacked onto the end of 1995 passes.
When the countdown begins on New Year's Eve ... 4 ... 3 ... 2 ... 1 ... pause a second.
Literally.
Between the last second of December 1995 and the first second of January 1996, a leap second will be added to the Master Clock of the United States.
The Master Clock, as the name suggests, is the undisputed authority for exact time in this country. Its time is combined with times from other international time-keeping labs, though the Master Clock's time is given the most weight in averaging for Universal Time.
Provided they're not sports referees, most people don't have to pay attention to a second here or a second there.
``A lot of people take time for granted,'' said Dennis McCarthy of the U.S. Naval Observatory in Washington, home of the Master Clock.
But there are those who rely on ultra-precise time-keeping.
Navigators, for instance, chart course with methods related to time. Similarly, satellite signaling and transportation of high-speed electronic data are highly time-dependent. In those cases, an inaccuracy of even one-millionth of a second can create a positioning error of a quarter-mile.
Besides, what would happen if nobody kept track of time - how would we know it was dinner time?
``Somebody has to be able to tell people what time it really is. We can't all be keeping our own time,'' McCarthy said .
Head of the observatory's Earth Orientation Department, McCarthy spends his time watching the Earth, specifically how the Earth is behaving from time to time.
``Our job is to keep track of how the Earth is spinning in space,'' he said. ``Not only its rate but how it's tipping and turning in space.''
Why is that timely?
Because Earth has a mind of its own.
The Master Clock, which is actually about 60 atomic clocks averaged for accuracy, keeps such consistent time it can shame all of Switzerland's. But occasionally the atomic time-keeping has to be synchronized with Earth's time, which changes all the time.
``The Earth is not a uniform rotator,'' McCarthy said.
Since 1972, when the first leap second was added, Earth has been slowing - contrary to the perception of most people that the world has mercilessly speeded up on them.
When the rate of Earth's slacking off - for lack of a less scientific term - equals about one second, the leap second is added. Of course, the Master Clock sees that second differently, specifically as 9,192,631,770 cycles per second of the Cesium atom.
The leap second is usually inserted at the end of the calendar year, and synchronizes the Master Clock with Earth's rotation. The reason time is added to the Master Clock is that, as the saying goes, you can't change the world.
In appearance, the Master Clock hardly lives up to its domineering name. Basically, visitors to the Naval Observatory see a mass of computer machinery with a red digital display of the exact time to the nearest second, although the clock knows the time to the billionth of a second. The machinery is kept behind a window of plexiglass; even minor environmental changes such as body heat can throw off the clock.
While most people don't pay much attention to the Master Clock's timing, they would eventually clamor for synchronization of scientific times with Earth time.
Seconds lead to minutes. Minutes lead to hours. Hours lead to days, and days lead to years.
And leap years.
``With leap years, what we're trying to do is make the Earth's rotation coincide with the calendar,'' McCarthy said.
``The calendar is based on how the Earth is traveling around the sun. In 365 days, the Earth appears to be back in the same position. But it's really 365 and a quarter days. How do we make up for this quarter-day? We put another day on the calendar every four years.''
What if we didn't?
``Eventually, it would be December and we'd be sitting around in shirt sleeves and it would be warm enough for it. The man-made calendar would get out of sync with the Earth's rotation. We'd be coming up on noon and it would be dark outside.''
McCarthy admits that scenario is ``millions of years'' away. But it's nice to know we have one less worry for the new year.
In the meantime, when Sunday night comes to a close, remember to count slowly.
LENGTH: Medium: 89 linesby CNB