[ad_1]
The same astronomical thinking led them to patch the clock, the ancient Babylonian method of counting to 60, the sexagesimal system. Just as they divided a circle, or the sphere of the Earth, into 60 parts and then 60 again – making 360 degrees – they also divided the hour.
The first division of the 24 hours of the day (known in Latin as partes minutae primae) gave them the length of the minute, which is 1,440 of an average solar day. The second part (partes minutae secundae) gave them the name and duration of a second, which is 86,400 of a day. This definition was valid until 1967. (There was a brief diversion into something called ephemeris time, which is so complex that even metrologists don’t use it.)
But there were problems with the definition. The earth is slowly slowing down in its daily rotation; The days are getting a little longer and so are the astronomical seconds. These small differences add up. Based on extrapolations from historical eclipses and other observations, Earth has lost more than three hours in one hour over the past 2000 years.
Therefore, the standard unit of time based on astronomical calculation is not fixed; This is a reality that became increasingly unbearable for metrologists in the first decades of the 20th century as they discovered how erratic the Earth’s rotation was. Science demands stability, reliability and repeatability. So was time – and by the late 1960s, society was becoming increasingly dependent on the frequencies of radio signals, which demanded extremely precise timings.
Metrologists turned to the much more predictable movement of atomic particles. Atoms never wear out or slow down. Its properties do not change over time. They are perfect watches.
In the mid-20th century, scientists persuaded cesium 133 atoms to reveal their hidden internal ticks. Cesium, a silvery-gold metal that is liquid at about room temperature, has heavy, slow atoms, which means it’s relatively easy to track them down.
Scientists put cesium atoms in a vacuum and exposed them to the energy of microwaves in the invisible range of the electromagnetic field. The task was to find out which wavelength or frequency would excite as many cesium atoms as possible to emit a packet of light, or photon. Photons were received and counted by a detector.
[ad_2]
Source link