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Science, Maths & Technology
Understanding science: what we cannot know
...Temps atomique international) officially began on 1 January 1958 and has been running steadily ever since. In 1967, the second was redefined as the duration of 9 192 631 770 periods of the radiation from the caesium atom. The definition, part of the International System of Units (or SI, from Système international), was chosen to match the duration of the astronomical...