What are Atomic Clocks?
By Scott Childs Dec 1, 2003, 09:28 Scott Childs QUESTION: What are Atomic Clocks and Radio-Controlled Clocks? ANSWER: Long ago, we used to measure time by measuring the Earth’s rotation. Today we use a method which basically measures the number of vibrations a certain element gives off. The most common element used in atomic clocks is Cesium 133, whose vibrations are remarkably stable over time. This allows us to keep incredibly accurate time. As of January, 2002, NIST’s latest cesium standard clock was capable of keeping time to about 30 billionths of a second per year. Now the cost of a typical cesium atomic clock could keep everyone from having one sitting on their mantle, so the NIST–the National Institute of Standards and Technology, located in Fort Collins, Colorado–worked out a way for all of us to achieve “atomic time.” Each day, the NIST sends out a radio broadcast telling any clock that will listen what time it is. Inside one of these “radio controlled” clocks is a small an
