Computer & Digital
Atomic Time (TAI)
International Atomic Time · 37 seconds ahead of UTC
The time caesium actually keeps. There is no atomic day or atomic year — TAI is simply an unbroken count of SI seconds, dressed in ordinary hours and dates. Its one peculiarity is that it never pauses: UTC has inserted 27 leap seconds since 1972 to stay in step with a very slightly slowing planet, and TAI has taken none of them. Add the ten seconds the two were already apart when UTC took its present form that year, and that is the 37 seconds TAI now runs ahead. GPS froze its own offset at 18 seconds in 1980.
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At a glance
- Type
- A clock — an unbroken count of SI seconds
- Origin
- Atomic clocks worldwide, combined by the BIPM near Paris
- Day
- Exactly 86,400 SI seconds — no leap seconds
- Counts from
- Set level with Universal Time on 1 January 1958
- Where it’s used
- Timekeeping laboratories; the reference beneath UTC
- How it’s worked out here
- Your device’s clock plus the 37 seconds TAI runs ahead of UTC
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