The second (s) is characterized by taking the addressed numerical value of the cesium frequency ∆νCs, the unperturbed ground-state hyperfine shift frequency of the cesium-133 atom, to it is in 9,192,631,770 as soon as expressed in the unit Hz, i beg your pardon is same to s−1.

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The variety of periods or cycles per second is referred to as frequency. The SI unit for frequency is the hertz (Hz). One hertz is the exact same as one cycle per second. Standard frequencies and the correct time space broadcast by radio stations WWV and WWVB in Colorado, and also WWVH in Hawaii. it is intended digital time signals by telephone and through the internet.

Official U.S. Government time is noted by and also USNO. also offers an internet Time organization (ITS) and an Automated computer Time business (ACTS) the allow setting of computer and other clocks with the web or over traditional commercial telephone lines. Complimentary software for using these services on several types of popular computer systems can be downloaded there. Information about these services can be uncovered on the Time and Frequency department Web site.

Resources for Students and Teachers


What is the present Coordinated universal Time? and the U.S. Naval Observatory jointly operate a website that offers the main U.S. Time. Readings indigenous the clocks that these two agencies contribute to world time, dubbed Coordinated universal Time (UTC). Learn more...How to get the time utilizing a telephone, computer or radio signals? What is a leap second? What space the daylight conserving time rules? Visit the Time and also Frequency department FAQs for more information.

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League of SI Superheroes – Professor Second

This comic book-style video clip animation collection has been emerged to help middle college students learn around the 7 SI base measurement units. By analysis the vibrations of her laser-cooled cesium atoms, Professor second can synchronize any type of frequency and also correct any type of clock. A 2nd is the time it take away an excited cesium atom come vibrate 9,192,631,770 times.

Navigate to an ext SI base unit information:
Metric and also Time and also frequency metrology


developed April 12, 2010, updated July 6, 2021


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