New definition of the second

Since 1967, the new definition of the second has been based on the frequency of the cesium-133 atom. Time is no longer determined by observing the movement of the stars but by measuring the Earth's variations. The time to which clocks are set in specialist centres (International Time Bureau, observatories) is atomic time. Conversely, Earth's time-keeping is corrected according to changes in its rotational speed. For several years the Earth has been slowing at a rate of around 1 second per year, which is why clocks are regularly delayed by 1 second on 1 January at midnight. In Switzerland, the LSRH frequency standard group, overseen by J. Bonanomi, has developed NH3 masers and a laboratory cesium standard. At Neuchâtel, these developments have led to an industrial application, resulting in the manufacture of cesium atomic clocks that are still the only ones produced in Europe.