tidkilder

Tidkilder, literally “time sources” in Danish, is a term used to describe systems or signals that supply verified time information for synchronizing clocks and timekeeping infrastructure. In modern metrology and telecommunications, tidkilder are essential for ensuring consistent time across devices, networks, financial markets, navigation, and broadcasting.

Common tidkilder include atomic time scales such as TAI and UTC; astronomical time references; radio time signals; and satellite time signals. Atomic time sources rely on cesium or rubidium atomic clocks to realize precise timescales. TAI provides a continuous atomic timescale; UTC is the civil time standard that incorporates leap seconds to stay close to mean solar time.

Radio and satellite time signals provide widespread dissemination. Examples include longwave time signals from national laboratories (e.g., DCF77 in Germany, MSF in the United Kingdom, WWVB in the United States) and satellite time through GPS time, and other GNSS like Galileo or GLONASS. GPS time is a continuous timescale; civil time is UTC. Local time servers and network time protocols (NTP, PTP) use these tidkilder to synchronize computer systems and networks.

Organization and governance: the international time scale is maintained by organizations such as the BIPM, in cooperation with national metrology institutes, to realize TAI and UTC. Standards bodies like ITU and ISO coordinate dissemination and synchronization practices. Leap seconds are applied in UTC to adjust for Earth's slowing rotation.

See also: timekeeping, metrology, NTP, PTP.