A

David

Darling

second

The second is the base unit of time (symbol: s) in the SI system. It is defined as 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 cesium-133 atom.

 

A second is also a unit of angle (symbol: ") equal to 1/3600 of a degree or 1/60 of a minute.