DUT1 is a time correction equal to the difference between
Universal Time (
UT1), which is defined by
Earth's rotation
Earth's rotation or Earth's spin is the rotation of planet Earth around its own Rotation around a fixed axis, axis, as well as changes in the orientation (geometry), orientation of the rotation axis in space. Earth rotates eastward, in progra ...
, and
Coordinated Universal Time
Coordinated Universal Time (UTC) is the primary time standard globally used to regulate clocks and time. It establishes a reference for the current time, forming the basis for civil time and time zones. UTC facilitates international communicat ...
(UTC), which is defined by a network of precision
atomic clock
An atomic clock is a clock that measures time by monitoring the resonant frequency of atoms. It is based on atoms having different energy levels. Electron states in an atom are associated with different energy levels, and in transitions betwee ...
s, with a precision of +/- 0.1s.
:DUT1 = UT1 − UTC (with a precision of +/- 0.1s)
UTC is maintained via
leap second
A leap second is a one-second adjustment that is occasionally applied to Coordinated Universal Time (UTC), to accommodate the difference between precise time (International Atomic Time (TAI), as measured by atomic clocks) and imprecise solar tim ...
s, such that DUT1 remains within the range −0.9 s < DUT1 < +0.9 s. The reason for this correction is partly 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, and partly because the
SI second (as now used for
UTC) was, when adopted, a little shorter than the current value of the second of mean solar time.
Daily observed values of UT1 - UTC for the past week, and daily forecast values for the coming year, are published by
IERSbr>
Bulletin A with more digits than for DUT1. Final values are published in the monthly IER
Bulletin B DUT1 forecasts are published in IER
Bulletin D
Several
time signal services broadcast values of DUT1.
CHU (Canada),
HLA (South Korea),
MSF (United Kingdom), and
WWV (United States) transmit DUT1 with 0.1 s precision. In Russia,
RWM,
RTZ and the longwave
RBU transmit DUT1 with 0.1 s precision and an additional correction dUT1 in 0.02 s increments.
See also
*
Notes
References
* ITU-R Recommendation TF.460-4: Standard-frequency and time-signal emissions.
International Telecommunication Union
The International Telecommunication Union (ITU)In the other common languages of the ITU:
*
* is a list of specialized agencies of the United Nations, specialized agency of the United Nations responsible for many matters related to information ...
.
External links
IERS Bulletins including Bulletin A – latest and past versions, and graphical plots
* Latest version o
Bulletin AIERS Rapid Service/Prediction Center via the US Naval ObservatoryArchived version
available for non-US readers)
* http://scienceworld.wolfram.com/astronomy/Time.html
{{Time measurement and standards
Time scales