DUT1 (sometimes also written DUT) is a time correction equal to the difference between
Universal Time
Universal Time (UT or UT1) is a time standard based on Earth's rotation. While originally it was mean solar time at 0° longitude, precise measurements of the Sun are difficult. Therefore, UT1 is computed from a measure of the Earth's angle wit ...
(
UT1), which is defined by
Earth's rotation, and
Coordinated Universal Time
Coordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. It is within about one second of mean solar time (such as UT1) at 0° longitude (at the IERS Reference Meridian as the currently use ...
(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 betwe ...
s.
:DUT1 = UT1 − UTC
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 observ ...
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
Tidal acceleration is an effect of the tidal forces between an orbiting natural satellite (e.g. the Moon) and the primary planet that it orbits (e.g. Earth). The acceleration causes a gradual recession of a satellite in a prograde orbit away fro ...
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 DUT1 for the past week, and daily forecast values for the coming year, are published by
IERSbr>
Bulletin A
Several
time signal service
A radio clock or radio-controlled clock (RCC), and often (incorrectly) referred to as an atomic clock is a type of quartz clock or watch that is automatically synchronized to a time code transmitted by a radio transmitter connected to a time s ...
s 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.
Notes
References
* ITU-R Recommendation TF.460-4: Standard-frequency and time-signal emissions.
International Telecommunication Union
The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Unio ...
.
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
* https://web.archive.org/web/20161115072453/http://maia.usno.navy.mil/ser7/deltat.data
{{Time measurement and standards
Time scales