This graph shows the historical evolution of DUT1 between 1985 and 2005. The vertical segments are due to leap seconds.

The time correction DUT1 (sometimes also written DUT) is the difference between Universal Time (UT1), which is defined by Earth's rotation, and Coordinated Universal Time (UTC), which is defined by a network of precision clocks.

DUT1 = UT1 ? UTC

UTC is maintained via leap seconds, such that DUT1 remains within the range ?0.9 s < DUT1 < +0.9 s. The reason for this correction is that the rate of rotation of the Earth is not constant, due to tidal braking and the redistribution of mass within the Earth, including its oceans and atmosphere.

Forecast values of DUT1 are published by IERS Bulletin A. Weekly updated values of DUT1 with 0.1 s precision are broadcast by several time signal services, including WWVB.

References

• ITU-R Recommendation TF.460-4: Standard-frequency and time-signal emissions. International Telecommunication Union.

External links

• http://scienceworld.wolfram.com/astronomy/Time.html

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