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Leap Second
The adjustment between Atomic & Earth Time
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INFORMATION ON UTC - TAI
The last additional second was introduced on 1
January 1999, at 0h.
Paris, 4 July 2005
Bulletin C 30
To authorities responsible for the measurement and distribution of
time
UTC TIME STEP on the 1st of January 2006
A positive leap second will be introduced at the end of December
2005.
The sequence of dates of the UTC second markers will be:
2005 December 31, 23h 59m 59s
2005 December 31, 23h 59m 60s
2006 January 1, 0h 0m 0s
The difference between UTC and the International Atomic Time TAI is:
from 1999 January 1, 0h UTC, to 2006 January 1 0h UTC : UTC-TAI = -
32s
from 2006 January 1, 0h UTC, until further notice : UTC-TAI = - 33s
Leap seconds can be introduced in UTC at the end of the months of
December or June, depending on the evolution of UT1-TAI.
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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in USA & Canada until:
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