Second

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For other uses of "second", see second (disambiguation).

The second (symbol: s) is a unit of time, and one of the seven SI base units. It is defined as the time taken by 9,192,631,770 cycles of radiation that comes from electrons moving between two energy levels of the caesium-133 atom.

A second is also 1/60 of a minute, and 1/3600 of an hour.