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December 2005 15 In the 1920s, Rudy Valle had a major hit with his recording of the song "My Time Is Your Time." Life was simpler then. After all, the dispute between the Julian calendar and the Gregorian calen- dar had been resolved some 200 years before. As mechanical clocks came into widespread use at about the same peri- od, people started scheduling their days by reference to the clock, rather than the sun - hence the term "o'clock" when telling time. Time zones were officially established by international treaty in the 1880s. In the United States, time zone boundaries are designated by the Secretary of Transportation. The dates for daylight savings time are controlled by Congress (daylight seems to be the only thing these legislators can save). Timekeeping in general, as with so many other things, revolved around the sun. That changed with the arrival of the Atomic Age. Scientists discovered that certain atoms vibrated with amazing consisten- cy. Engineers started developing highly accurate clocks based not on a pendu- lum, but on these vibrating atoms. They soon discovered that there was a differ- ence between these atomic clocks and the rotation of the Earth on its axis. It seems that, for a variety of reasons that are not germane to this article, the rota- tion of Earth is slowing down, although not consistently. It takes slightly longer today for the Earth to rotate 360 degrees on its axis (a full solar day) than it took on the same day last year. The differ- ence is so slight that I, for one, did not notice. Mechanical clocks do not detect this slowing either. But atomic clocks do register the difference. In 1967, before the implications of the slow lengthening of the solar day were fully appreciated, the General Conference on Weights and Measures decided, in the interest of scientific accuracy, to change the definition of the second from "1/86,400 of a mean solar day" to "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom." Soon, it was apparent that the atomic clocks and the Earth were getting out of synchronization. The process of adding leap seconds (generally at the end of various years) commenced in 1972. To date, 22 leap seconds have been added in an attempt to keep the atomic clocks and the Earth in sync. Why does, or should, the mariner care? Because life is no longer simple. Technologies that mariners have grown to rely on themselves rely on atomic clocks to perform their missions. LORAN-C and especially the Global Positioning System (GPS) utilize atom- ic clocks to synchronize their highly precise signals. These atomic clocks do not utilize leap seconds. LORAN-C clocks are calibrated to zero-hour on January 1, 1958. There is now a 22 sec- ond difference between the LORAN-C clocks and Coordinated Universal Time (UTC). GPS clocks are calibrated to zero-hour on January 6, 1980. There is now a 13 second difference between GPS clocks and UTC. At the speed Circle 225 on Reader Service Card My Time Is NOT Your Time Government Update MR DECEMBER2005 #2 (9-16).qxd 11/30/2005 11:01 AM Page 15
