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Panoramic view of the clock hall at PTB with the four caesium clocks CS1, CS2, CSF1 and CSF2.

Will there be a leap second any time soon?

The global and uniform basis for the determination of time is disseminated by the International Bureau for Weights and Measures in Paris as Coordinated Universal Time (acronym UTC). It is realized with the support of eighty time institutes, among these also the Time and Frequency Department of PTB. Since our everyday life – despite atomic clocks – now as ever follows the position of the sun, the atomic time scale (realized by atomic clocks) is occasionally adjusted with leap seconds to the Earth's rotation which is not uniform in time. The atomic second is on an average somewhat shorter than the calculated second of the mean solar day. Since 1.1.1958, a time difference of about 37 seconds has accumulated up to now: The clock designated as TAI (Temps Atomique International) is, in comparison to the clock designated as UTC, 37 seconds faster. Central European Time is thus UTC + 1 hour, Central European Summer Time + 2 hours.

The International Earth Rotation and Reference Systems Service (IERS) announced with its Bulletin C 67 of 8 January 2024 that no leap second will be introduced at the end of June 2024.

Three clocks showing the time scales TAI, UTC and CEST