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Leap Second
The adjustment between Atomic & Earth Time
INFORMATION ON UTC - TAI
Paris, 5 January 2012
Bulletin C 43
To authorities responsible
for the measurement and distribution of time
UTC TIME STEP
on the 1st of July 2012
A positive leap second will be introduced at the end of June 2012.
The sequence of dates of the UTC second markers will be:
2012 June 30, 23h 59m 59s
2012 June 30, 23h 59m 60s
2012 July 1, 0h 0m 0s
The difference between UTC and the International Atomic Time TAI is:
from 2009 January 1, 0h UTC, to 2012 July 1 0h UTC : UTC-TAI = - 34s
from 2012 July 1, 0h UTC, until further notice : UTC-TAI = - 35s
Leap seconds can be introduced in UTC at the end of the months of December or
June, depending on the evolution of UT1-TAI.
Bulletin C is mailed every six months,
either to announce a time step in UTC or
to confirm that there will be
no time step at the next possible date.
Information provided by: INTERNATIONAL EARTH ROTATION SERVICE
(IERS), Paris, France |
The Coordinated Universal Time (or UTC) replaced Greenwich Mean Time (GMT) as the reference time
scale derived from The Temps Atomique International (TAI) calculated by
the Bureau International des Poids et Mesures (BIPM) in Paris, France
using a worldwide network of atomic clocks. UTC differs from TAI by an
integer number of seconds; it is the basis of all activities in the world.
UT1 is the time scale based on the observation of the Earth's
rotation. It is now derived from Very Long Baseline Interferometry (VLBI).
The various irregular fluctuations progressively detected in the rotation rate
of the Earth lead in 1972 to the replacement of UT1 as the reference time scale
. However, it was desired by the scientific community to maintain the difference
UT1-UTC smaller than 0.9 second to ensure agreement between the physical and
astronomical time scales.
Since the adoption of this system in 1972, firstly due to the
initial choice of the value of the second (1/86400 mean solar day of the year
1900) and secondly to the general slowing down of the Earth's rotation, it has
been necessary to add 21s to UTC.
The decision to introduce a leap second in UTC is the
responsibility of the International Earth Rotation Service (IERS). According to
international agreements, first preference is given to the opportunities at the
end of December and June, and second preference to those at the end of March and
September. Since the system was introduced in 1972, only dates in June and
December have been used.
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News:
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USA & Canada clocks
on Standard Time until:
Sunday 11 March 2012 2am local time
Europe / UK clocks
on Standard Time until:
Sunday 25 March 2012 01:00 GMT
Australia clocks
on Daylight Saving Time
Western Samoa changed time zone on
29 December 2011
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Related Websites:
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