International Atomic Time (TAI) The most accurate timekeeping system in use. It is based on the Systeme International (SI) second, which is defined as the duration of 9,192,631,770 cycles of radiation corresponding to the transition between two hyperfine levels of the ground state of cesium 133. Related category UNITS Also on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History Transport Concepts & Designs (partner site) |