Universal Time Coordinated
UTC (Universal Time Coordinated) is the international time standard. UTC is equivalent to mean solar time at the prime meridian (0° longitude), formerly expressed in GMT. It is also equivalent to Z time (Zulu time). When it is 0 UTC, it is midnight in Greenwich (England), on the meridian line of longitude zero.
UTC is calculated at the Bureau International des Poids et Mesures (BIPM) from the data of approximately two hundred clocks, distributed in nearly fifty national laboratories.
Time Service Department, U.S. Naval Observatory, (USA), gives UTC in real time.