More Developments with Time Systems
Following UT1, the concept of “UT2” was developed to correct certain seasonal variations for better time accuracy. Mechanical clocks are more regular than the sun so the atomic clock is more accurate than the Earth. The concept of Atomic Time was established with the development of mechanical clocks.
The most accurate clocks use an atomic transition in a caesium vapor, which defines a very accurate frequency. This frequency is then divided down to give seconds and minutes. Many atomic clocks are used to define a local time standard time service. There are many separate time services throughout the world and a combined mean version of their time measurement is used as International Atomic Time (TAI). TAI is the International Atomic Time scale, a statistical timescale based on a large number of atomic clocks. However, this takes no notice of the Earth’s rotation as measured by UT1 so another standard for civil time, known as Coordinated Universal Time (UTC), is used.