Coordinated Universal Time

Coordinated Universal Time (UTC) is the international time standard derived from atomic clocks and adjusted by leap seconds to remain close to Earth’s rotation-based time.

International Atomic Time: International Atomic Time is a continuous time scale calculated from atomic clocks worldwide. UTC is derived from this atomic time scale, with leap seconds inserted to limit their divergence.
Second: The second is the SI base unit of time, defined by a fixed cesium-133 transition frequency. UTC counts seconds using the international atomic definition.
Greenwich Mean Time: Greenwich Mean Time is a time standard historically based on the mean solar time at Greenwich. UTC inherited GMT’s role as a global reference while adopting atomic timekeeping.
Network Time Protocol: Network Time Protocol synchronizes computer clocks over packet-switched networks. NTP distributes UTC-related time to computers and network devices.
Leap-second abolition: Leap-second abolition is the proposal to stop inserting leap seconds into UTC. Ending insertions would remove a source of complexity in systems that use UTC.
Leap second: A leap second is a one-second adjustment occasionally added to or subtracted from UTC. This adjustment keeps UTC close to time measured by Earth’s rotation.
International System of Units: The International System of Units is the globally agreed framework for standard measurement units. UTC’s seconds and its formal realization depend on this measurement system.
Atomic timekeeping: Atomic timekeeping uses stable atomic transition frequencies to define and measure time. Its precision made a time standard independent of daily Earth rotation practical.
Global Positioning System time: Global Positioning System time is a continuous atomic time scale used by GPS satellites and receivers. GPS time stays continuous rather than inserting UTC leap seconds, so conversion requires their offset.
Leap smear: A leap smear gradually spreads a leap-second adjustment across a longer interval. It avoids a one-second step for some systems but creates temporary differences from official UTC.

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