National Geographic : 1947 Sep
Split-second Time Runs Today's World BY F. BARROWS COLTON ANI) CATHERINE BELL PALMER E VERY night when the sky is clear, high on a hill above Washington, D. C., an astronomer takes a look at the stars to see if the Nation's clocks are right. His job is to check just how fast the earth is turning. From that turning the whole world gets its time. Our giant planet of solid rock, with its thin skin of continents and oceans, weighing well over six sextillion tons, turns at a speed that varies less than the works of the best clock ever made. On his lonely vigil while the Nation's Capi tal sleeps, the astronomer times this speed of turning. His is the most crucial timekeeping job done anywhere, for the turning earth is the master clock by which all other clocks are set. It is accurate to within one part in 30 million. This nightly task of timing the earth's rota tion is carried out at the U. S. Naval Observa tory, official keeper of the Nation's time. Astronomer Rides Merry-go-round Earth Think of the earth as a giant merry-go round, spinning around in space out among the stars. Riding around on it, you pass by the same point every time it completes a turn. As the astronomer rides around on the earth, he notes what time he passes directly under a certain star. Carrying him on around as it turns, the rotating earth brings him back the next night to the same position once more, and he notes again what time he passes under that same star. The interval between any two times when the astronomer passes under that star is always the same within an extremely tiny fraction of a second. By this standard the Naval Observatory regulates its radio time signals, sent out every two hours on the odd hour and heard all over the United States and the world. Those sig nals are accurate to within 8/1000 of a second. They are set, as near as is humanly possible, by the time of the earth's turning. A Signal Every Second All the world lives by this "earth time," which astronomers call star time or sidereal time. It is the most nearly accurate time available. No clock or watch can match the precision with which the turning earth brings that astronomer and his telescope back under the same star night after night, through the years and centuries, always "on the dot." But in today's split-second world, accurate time-telling is not enough. Time-measuring is equally important. To provide an accurate measure of time, the National Bureau of Standards broadcasts an other and far more frequent time signal that goes out each second (omitting the 59th of each minute), all day and all night, a con tinuous "tick-tick-tick." That signal provides a "yardstick of time." It is just as essential in today's world as the accurate telling of time. Very short intervals of time, tiny fractions of a second, are used in numerous ways, from calibrating parking meters so that you get exactly one hour for your nickel, to measuring the water under a ship's keel by timing an echo returning from the bottom. With its "signal-every-second" the Bureau of Standards provides a "standard second," accurate to one part in 1,000,000, just as it also makes available the standard foot, the standard meter, the standard pound, and the standard gallon. That time yardstick is coordinated closely with the Observatory's time signals, and so is based, too, on the master time of the earth's turning. Scientists and engineers use it con stantly to check their time-measuring devices. Astronomers, probing out into the unimagi nable depths of space, measure the universe with time-in years, "light years," the distance that light, flashing along at 186,000 miles per second, travels in a year. That comes out at six trillion miles, but so vast is the universe that the most distant galaxies of stars so far found are 500 million light years away.* Light from the Distant Past And with this light, coming to us from such incredible distances, we literally turn time backward and see into the past. For we see the more distant stars not as they are now but as they were long ago when the light from them now reaching us first started on its way. Light from some very distant stars began its journey before the human race existed on earth. It brings to our eyes today the images of those stars as they looked then. Today's world moves literally on split second timing. *See, in the NATIONAL GEOGRAPHIC MAGAZINE, "Heavens Above," by Donald H. Menzel, July, 1943; "Interviewing the Stars," by William Joseph Show alter, January, 1925; "News of the Universe," July, 1939, and "New Frontier in the Sky," September, 1946, both by F. Barrows Colton.