TAIUTC

TAIUTC is an informal term used to denote the offset between International Atomic Time (TAI) and Coordinated Universal Time (UTC). It is not a separate time scale, but a numeric difference that appears in timing calculations, data timestamps, and some software applications.

TAI and UTC are two distinct time standards. TAI is a continuous atomic time scale maintained by laboratories around the world. UTC is the civil time standard used for daily life and many technical applications, and it incorporates leap seconds to keep within about 0.9 seconds of Earth's rotation (UT1). This means UTC occasionally steps forward by one second to realign with observed rotational time.

The TAIUTC offset is defined as TAI minus UTC. It increases by one second at every leap second event, since UTC advances by a leap second while TAI does not. As of 2017-01-01, the offset has been 37 seconds, and it remains 37 seconds today. The exact value at any moment is published by the International Earth Rotation and Reference Systems Service (IERS) and is used in precise timekeeping, astronomy, satellite navigation, and related fields.

In practice, TAIUTC is used to convert between TAI-based timestamps and UTC-based civil time, to model time scales in scientific computations, and in the interpretation of historical time data where a fixed offset between TAI and UTC is required.

See also: International Atomic Time (TAI), Coordinated Universal Time (UTC), leap second, IERS.