Saturday, 01 January, 1972, Coordinated Universal Time (UTC) was adopted worldwide.
Current official world time reference for civil and scientific purposes.
Coordinated Universal Time is measured from six standard atomic clocks at the International Bureau of Weights and Measures (BIPM) in Paris, France.
English language: Coordinated Universal Time (UTC)
French language: Temps Universel Coordonné.
Time zone boundaries as used by nations are drawn according to political considerations. Leap seconds are added to UTC periodically, about once each 18 months, so the highly accurate atomic clock time matches the time measured by Earth's rotation, which is very slightly variable due to tidal forces with the Moon.
Bureau International des Poids et Mesures UTC/TAI Time Server