|THE LEAP SECOND |
When should we introduce Leap second in UTC ?
On 30 June 2012, the last minute of the day has lasted 61 seconds.
leap second : see last
last Bulletin C
[ TAI - UTC ]
[ Offsets of UTC]
Universal Time (UTC, replacing GMT) is the reference time scale derived
from The Temps Atomique International (TAI) calculated by the Bureau International
des Poids et Mesures (BIPM) 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
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
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 1820) and secondly to the general slowing down of the Earth's
rotation, it has been necessary to add 25 s to UTC. The last additional
second has been introduced on 1 July 2012, at 0hUTC.
to introduce a leap second in UTC is the responsibility of the Earth Orientation Center of the International
Earth Rotation and reference System Service (IERS). This center is located at paris observatory.
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.
The leap second is announced in Bulletin