What time is it?

Coordinated Universal Time (UTC), maintained by the BIPM (Bureau International des Poids et Mesures), is the time scale that forms the basis for the coordinated dissemination of standard frequencies and time signals. The UTC scale is adjusted by the insertion of leap seconds to ensure approximate agreement with the time derived from the rotation of the Earth. These leap seconds are inserted on the advice of the International Earth Rotation and Reference Systems Service (IERS).

Physical realizations of UTC – named UTC(k) – are maintained in national metrology institutes or observatories contributing with their clock data to the BIPM.