Zeitstandards

Zeitstandards, or time standards, are formal references used to measure, synchronize, and coordinate time across devices, systems, and institutions. They support science, navigation, telecommunications, finance, and broadcasting. The foundation is the SI second, defined by the cesium-133 atomic transition and realized in atomic clocks worldwide.

Time scales and civil time: International Atomic Time (TAI) is a continuous time scale formed by combining hundreds of atomic clocks. Coordinated Universal Time (UTC) is the global civil time kept within about one second of UT1, a time scale tied to the Earth’s rotation. To compensate for irregularities in rotation, leap seconds are occasionally added to UTC. UT1 is used mainly in astronomy and geodesy, where the Earth's rotation matters.

Realization and dissemination: Time is realized by devices such as cesium and rubidium clocks and hydrogen masers. National metrology institutes contribute clocks to the international ensemble; the BIPM computes TAI and the offset of UTC. Time is disseminated through broadcast signals (DCF77, WWVB, MSF, CHU) and through satellite systems (GPS, Galileo, GLONASS), which provide precise time references to receivers and networks.

Governance and challenges: The global time framework is coordinated by the International Bureau of Weights and Measures (BIPM) and related committees. Ongoing challenges include refining accuracy, reducing dependence on leap seconds, and ensuring robust synchronization across digital infrastructures amid increasing demand for sub-microsecond timing.