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Happy New Year!

Le Bureau International des Poids et Mesures vous présente ses meilleurs vœux pour la Nouvelle Année


400th publication of Circular T by the BIPM in 2021


The scientific and artistic experiment “Equation of Time”
has been created by Raphaël DALLAPORTA with researchers
from the LNE-SYRTE at Observatoire de Paris - PSL
and is reproduced with their permission.

The track of the Sun photographed over a year at the Observatoire de Paris - PSL illustrates the "equation of time". It is caused by the difference between the period of 24 hours indicated by a clock, and the duration of the day based on observation of the Sun at local noon.

In the 20th century, timekeeping passed from astronomical observations to measurements of atomic clocks, and the International Bureau of Weights and Measures (BIPM) was given the unique role of computing Coordinated Universal Time (UTC).

In April 2021, the BIPM celebrated the 400th monthly publication of the reference values for UTC in its Circular T.

This international cooperation of more than 85 national institutes allows the coordinated dissemination of reference frequencies and time signals throughout the world.