They also provide a reliable time reference in scientific research applications, such as measuring variations in the frequencies of pulsars. Perhaps the most important is in Earth's Global Positioning System (GPS), which require atomic clocks to provide accurate measurements of distance. There are many immediately practical uses for extremely accurate clocks. To learn more about the science of Cesium clocks, visit Hyperphysics. Still, the atomic clocks using Cesium keep time within an accuracy of 2 to 3 parts in 10 14: this means it may only lose a second once every 1.4 million years! Note that this frequency occurs when the Cesium-133 atom is in isolation at absolute zero temperature in reality corrections for this are necessary. Upon observing exactly 9,192,631,770 periods (or cycles) of this electromagnetic wave, a second is said to have passed. In simpler terms, radiant energy, or light, in the form of microwaves is emitted at a very precise frequency from this particular atomic transition. The second is 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 caesium 133 atom. Nowadays, Cesium-133 is used as the definition for the second due to the reliable frequency of microwave it emits. Aside from the fact that there are different definitions for what a "day" is, using the Earth's rotation as a definition for time is not practical due to irregularities in the frequency of its rotation. Our most common unit of time, the second, was originally defined based on the Earth's rotation the Earth rotates around its axis once per day, with the second being defined as 1/86,400 of a (mean solar) day. Cesium is the standard for atomic clocks, and actually provides the definition for the second! Some of its properties are listed below: Atomic weight Ĭesium is the 55 th element on the periodic table of elements. Cesium, with atomic number 55 and atomic weight of 132.905.
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