A matter of good timing
- By Bob Brewin
- Jul 18, 1999
Dennis McCarthy stood in front of the Master Clock time display at the U.S. Naval Observatory in Washington, D.C., looked at his watch and again at the display and declared his watch 40 seconds fast.
Most folks would accept a 40-second deviation, but not McCarthy, who serves as director of the Directorate of Time at USNO. The observatory's Master Clock - a rather nondescript piece of electronic equipment - keeps time with an accuracy far beyond that of even the most expensive and flashy Rolex.
The Master Clock tracks time to the nanosecond by measuring the cycles of a cesium atom. Although McCarthy declares himself "not a time freak," he can tell you exactly how many of those cycles make up one tick of a clock. "The frequency we get out of cesium is 9 billion cycles a second," he said.
He then scrambled through the files on his cluttered desk and quickly clarified: "That's exactly 9,192,631,770 cycles per second.''
Precision weapons, Global Positioning System satellites and the synchronization requirements of a networked economy have driven the demand for ultra-accurate timekeeping to the extent that the Directorate of Time at the observatory - a lushly landscaped oasis that includes the residence of the vice president - has become a global asset, McCarthy said.
McCarthy explained that the observatory has been keeping time for the Navy at its circular site on Massachusetts Avenue in Washington, D.C., since 1843. Navigation is time-dependent, and the Navy needs the most accurate time that science and technology can produce. That push for precision led to the circular design of the Naval Observatory site, he said. When the observatory was built, ships' clocks were brought there for adjustment, and the adjustments were done inside a well at the epicenter of observatory. All roads and buildings on the grounds were built outside a 1,000-foot perimeter surrounding the well so vibration would not affect the clocks, McCarthy explained.
In a city where the output of many an organization is measured in linear feet of paper, the Directorate of Time produces a commodity with real value, McCarthy said. He explained that the telecommunications networks that carry services ranging from phone calls to World Wide Web-driven electronic commerce would collapse without the timing signals provided by the Master Clock at the observatory and about 60 other Master Clocks around the world.
Providing an example of how much the Directorate of Time has become a utility, McCarthy said the two observatory-operated, Web-based time servers - named Tick and Tock - receive almost a half a billion hits a month.
One of McCarthy's first jobs, he said, was operating the optical telescopes that were used at the observatory's Earth Orientation Department to monitor the speed of the rotation of the Earth and its orientation to the stars - the original basis of celestial time-keeping. He said the observatory now does this with a network of radio telescopes in West Virginia, Alaska and Hawaii that focus on quasars at the outer reaches of space - "landmarks at the edge of the universe," as McCarthy described them.
Sophisticated measurements obtained from these radio telescopes help the observatory determine the speed of the Earth, McCarthy said, which in turn helps to determine when to insert a "leap second" into the atomic clocks. Leap seconds, which McCarthy called "a great story on a slow news day," are inserted whenever the difference between the time defined by atomic clocks differs from the Earth's rotational time by nine-tenths of a second.
McCarthy predicted that "people are eventually going to become annoyed with the whole concept of the leap second." Because the Earth's rotation continues to slow, McCarthy said the directorate will have to insert "two leap seconds per year within 50 years compared to a leap second every 1.5 years today."
This could impact the operation of communications networks, McCarthy said. If networks do not pick up a new second, which is added to the last minute of the last day of the year, they could suffer a loss of network interoperability from a failure to operate on the same time base.
Keeping track of time in terms of nanoseconds has not kept McCarthy from using his spare time to pursue distinctly non-work-related avocations. He relishes biking and camping on the Chesapeake and Ohio Canal towpath, where time stands still enough for him to observe birds and enjoy the Potomac River valley with his adult son, Duncan.
For years McCarthy has spent a lot of his spare time as a Civil War "re-enactor,'' rising to the rank of colonel in a Confederate group. But lack of time, he ruefully admitted, has caused him to cut back on that hobby, and he's been reduced in rank to private.
While a man who devotes himself to precision in his work life might be assumed to prefer the musical precision of Bach, McCarthy said he prefers the lushness of Mozart as well as Celtic music by the Chieftains and others.
Although eligible for retirement after more than 30 years of service at the observatory, McCarthy intends to stay in the time business for the foreseeable future.
McCarthy said he views his job as an enviable one. He recalled a phone call from someone "who was convinced we had inserted a leap second without announcing it because his watch was one second off.''
"People really have an intense interest in time," McCarthy concluded.