Caesium Archive

Time

Time is traditionally accounted for by counting periodic motion of a planetary mass in the solar system. One rotation of Earth is a day, one revolution about the sun is a year. In the current era, it has its progress tracked by atomic clocks, the principles of which is founded upon the periodic motion of subatomic particles. I recall learning at one point in school that the relevant international standard is based on energy transitions of a particular isotope of caesium, and identifying over nine billion periods of its radiation as one second.