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DUT1

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Time scale with correction

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Graph showing the difference in seconds betweenUT1 andUTC over time. A vertical transition indicates the use of aleap second. The red portion of the graph indicates predicted values.

DUT1 is a time correction equal to the difference betweenUniversal Time (UT1), which is defined byEarth's rotation, andCoordinated Universal Time (UTC), which is defined by a network of precisionatomic clocks, with a precision of +/- 0.1s.^[1]^[2]

DUT1 = UT1 − UTC (with a precision of +/- 0.1s)

UTC is maintained vialeap seconds, 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 totidal braking and the redistribution of mass within the Earth, including its oceans and atmosphere, and partly because theSI second (as now used forUTC) was, when adopted, a little shorter than the current value of the second of mean solar time.^[a]

Daily observed values of UT1 - UTC for the past week, and daily forecast values for the coming year, are published byIERS Bulletin A, with more digits than for DUT1. Final values are published in the monthly IERSBulletin B. DUT1 forecasts are published in IERSBulletin D.

Severaltime signal services broadcast values of DUT1.CHU (Canada),HLA (South Korea),MSF (United Kingdom), andWWV (United States) transmit DUT1 with 0.1 s precision. In Russia,RWM,RTZ and the longwaveRBU transmit DUT1 with 0.1 s precision and an additional correction dUT1 in 0.02 s increments.^[3]

Notes

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^(1) In "The Physical Basis of the Leap Second", by D D McCarthy, C Hackman and R A Nelson, in Astronomical Journal, vol.136 (2008), pages 1906–1908, it is stated (page 1908), that "the SI second is equivalent to an older measure of the second of UT1, which was too small to start with and further, as the duration of the UT1 second increases, the discrepancy widens." :(2) In the late 1950s, the cesium standard was used to measure both the current mean length of the second of mean solar time (UT2) (result:9192631830 cycles) and also the second ofephemeris time (ET) (result:9192631770±20 cycles), see"Time Scales", by L. Essen, in Metrologia, vol.4 (1968), pp.161–165, on p.162. As is well known, the9192631770 figure was chosen for theSI second. L Essen in the same 1968 article (p.162) stated that this "seemed reasonable in view of the variations in UT2".

References

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^"Bulletin D - Product metadata".IERS. 1996-07-17.Archived from the original on 2024-03-03. Retrieved2024-11-26.
^"Leap second and UT1-UTC information".NIST. 2024-11-15.Archived from the original on 2024-09-30. Retrieved2024-11-26.
^"Time Signal Transmitter".www.meinbergglobal.com. Retrieved21 March 2022.

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

External links

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IERS Bulletins, including Bulletin A – latest and past versions, and graphical plots
Latest version ofBulletin A
IERS Rapid Service/Prediction Center via the US Naval Observatory (Archived version available for non-US readers)
http://scienceworld.wolfram.com/astronomy/Time.html

v t e Time measurement andstandards
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Obsolete standards	Ephemeris time Greenwich Mean Time Prime meridian
Time in physics	Absolute space and time Spacetime Chronon Continuous signal Coordinate time Cosmological decade Discrete time and continuous time Proper time Theory of relativity Time dilation Gravitational time dilation Time domain Time-translation symmetry T-symmetry
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Archaeology and geology	Chronological dating Geologic time scale International Commission on Stratigraphy
Astronomical chronology	Galactic year Nuclear timescale Precession Sidereal time
Otherunits of time	Instant Flick Shake Jiffy Second Minute Moment Hour Day Week Fortnight Month Year Olympiad Lustrum Decade Century Saeculum Millennium
Related topics	Chronology Duration music Mental chronometry Decimal time Metric time System time Time metrology Time value of money Timekeeper