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Time, the international atomic age, the universal age, what is this?

UTC Time, International Atomic Time, Universal Time What is it? -Charlie Paris

UTC Time, International Atomic Time or Universal Time, you don't know what the difference is? Don't worry, we will enlighten you on their role and the characteristics of each.

  1. What is UTC time, atomic time, and universal time?
  2. But what is International Atomic Time?
  3. But what is the role of TU in defining UTC time?
  4. What about UTC time in the middle of that?


1. What is UTC, Atomic Time, and Universal Time?

UTC time is the world reference time. It is determined among other things thanks to some 500 atomic clocks placed in 70 laboratories around the world. UTC replaced the time given by the greenwich meridian in 1982, but UTC + 0 is still the time in the greenwich time zone. The time within each time zone is therefore defined in relation to UTC time. UTC time is actually a clever mix of International Atomic Time (TAI) and Universal Time (UTC).


2. But what is International Atomic Time?

International atomic time is a time scale relative to the duration of one second. It was determined in 1967 by the 13th General Conference on Weights and Measuresthat one second would be "equivalent to the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom".

To put it simply: A Cesium 133 atom receives a frequency of 9,192,631,770 Hz which allows it to change its energy state. The time between the F3 and F4 energy state of the cesium-133 atom is exactly one second.

The advantage of the atomic clock is that it is exceptionally precise: it shifts less than one second every 30 million years. Researchers have even developed a strontium atomic clock with an accuracy of less than one second every 15 billion years!

TAI is calculated by the BInternational ureau for Weights and Measures. It corresponds to the average of 500 atomic clocks present across the globe. The TAI is however not used as is because it does not take into account the time of rotation of the earth in a day.


3. But what is the role of UTC in defining UTC time?

Universal Time or UTC is an improved version of Greenwich Mean Time. The UT is also a measure of time except that it is not an atomic measurement but a measurement relating to the rotation of the earth on itself (which takes place in 24 hours). The problem is that the Earth's rotation is not very regular, it may slow down under the effects of tides, earthquakes or other internal disturbance on the Earth (even if this delay remains tiny).


4. What about UTC time in the middle of that?

UTC time is a mix of these two hours so that the sun is at the Greenwich meridian within 0.9 s at 12:00 UTC. The second of UTC time is the same as that given by TAI. Only to find the UTC time we subtract or add whole seconds to the TAI so that the difference between the TAI and the TU is less than 0.9s.

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