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SESK: Stuff Everyone Should Know · sesk.info/wt-utc

What is the world's reference time scale, kept by atomic clocks, called?

UTC, Coordinated Universal Time.

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  1. EST
  2. BST
  3. UTC ✔

Why: Coordinated Universal Time runs at the rate of atomic clocks and took effect internationally in 1972. Local time zones are often written as offsets from it, such as UTC minus 5.

Huh, didn't know that: When atomic time and Earth's rotation drift nearly a second apart, a leap second is added to UTC.

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UTC is the time zone for people who think local time is too emotional.
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References

Answer: UTC. Coordinated Universal Time runs at the rate of atomic clocks and took effect internationally in 1972. Local time zones are often written as offsets from it, such as UTC minus 5.

  1. A Walk Through Time: World Time Scales (NIST) www.nist.gov/pml/time-and-frequency-division/popular-links/walk-through-time/walk-through-time-world-time-scales
    UTC runs at the rate of the atomic clocks
    Checked 2026-10-12.

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