cesium
chemical elementalso spelled caesium (Cs)
chemical element of Group 1 (also called Group Ia) of the periodic table, the alkali metal group, and the first element to be discovered spectroscopically (1860), by German scientists Robert Bunsen and Gustav Kirchhoff, who named it for the unique blue lines of its spectrum (Latin caesius, “sky-blue”).
Atomic cesium is employed in the world’s time standard, the cesium clock. The microwave spectral line emitted by the isotope cesium-133 has a frequency of 9,192,631,770 hertz (cycles per second). This provides the fundamental unit of time. Cesium clocks are so stable and accurate that they are reliable to 1 second in 1.4 million years. Primary standard cesium clocks, such as NIST-F1 in Boulder, Colo., are about as large as a railroad flatcar. Commercial secondary standards are suitcase-sized.
Currently there are 5 Atomic clocks around the world. 2 in Japan, 1 in the US, 1 in the UK and 1 in Germany.
Perhaps the following clocks are not as accurate but somehow they exude more charm, interest and fun.
3.16 Billion Cycles
Thermal Clock
Cinematic Timepiece
Counting to a Billion
