11/29/2023 0 Comments Atomic clock dcThe realization that Earth's rotation was not constant and therefore could not serve as an accurate measure of time became clear in the 1930s, when clocks had become sufficiently sophisticated to demonstrate the discrepancy, notes Dennis McCarthy, an astronomer who heads the Directorate of Time at the Naval Observatory, established in 1830 to cooperate with observatories around the world in charting astronomical time. In the U.S., each city and town kept its own time based on direct observation of the sun until 116 years ago, when the uniform time zones were established.Ī little more than 100 years ago, industrialization made timepieces widely available to ordinary families and began to draw attention away from nature to "clock time," said Carlene Stephens, curator of a new exhibit on time at the Smithsonian Institution. Time was linked to natural processes that could be readily observed. To do so, it needs clocks that are more sensitive than most in use today.Īll this is pretty heady stuff, from a historical perspective.Īlthough mechanical clocks have been around since the late 1600s, until the 1800s most people across the planet kept time by watching the movement of the sun across the sky and the path of the stars over the heavens. Naval Observatory, the official timekeeper for the military. military uses the satellite system to guide ships, aircraft or missiles with an accuracy range of about 10 yards, but it would like to bring that down to a yard or two at most, said Geoff Chester, public affairs officer at the U.S. The distance is computed by how long it takes light to travel to a certain point. The Global Positioning System, a network of 24 satellites that circle Earth twice a day, depends on atomic clocks aboard each satellite to help mark precisely where they are in orbit, and how far they are from any given point on Earth. Air traffic controllers use top-of-the-line clocks to help them guide planes. Radio and television stations rely on time to set broadcast schedules. The optical fiber networks that transmit vast amounts of data depend on clocks that synchronize the sending and receiving of in-formation. Time as infrastructure? Consider that all stock transactions on the major exchanges, where prices can change in an instant, are time-stamped.Įlectric companies maintain standard frequencies, which allow everything from televisions to computers to work when plugged into outlets, based on precise timekeeping. "And yet, they have become an essential piece of infrastructure today, which has made possible things like satellite navigation and telecommunications." "If you go back and talk to the people who built these atomic clocks, no one could justify them on the basis of a known industrial need," Sullivan said. The meter, for instance, is considered the amount of distance that light, which speeds along at 186,347 miles per second, covers in a certain time.īut the physicists who have dreamed up ever finer ways to slice time in this atomic age have always been in the lead. In fact, international standards for both the meter (a unit of distance) and voltage (a unit of electricity) are defined in terms of time because of the clocks' reliability. No means of measuring distance, or weight, or any other physical property even comes close. Today's atomic clocks already generate the most sensitive, sophisticated measures known to man. It's difficult to imagine the uses to which this extraordinary precision will be put.
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