The first division of the day’s 24 hours (known in Latin as partes minutae primae) gave them the length of the minute, which was one-1,440th of an average solar day. The second division (partes minutae secundae) provided them the duration — and name — of the second, which was one-86,400th of a day. Earth is gradually slowing in its daily rotation; days are growing slightly longer and so the astronomical second is, too. Scientists put cesium atoms in a vacuum and exposed them to the energy of microwaves, in the nonvisible range of the electromagnetic field. The task was to figure out which wavelength, or frequency, would excite as many cesium atoms as possible into emitting a packet of light, or photon.

Source: International New York Times April 25, 2022 09:25 UTC