The Bulletin C announce leap second. It is sent by email two times a year :
- At the beginning of january to announce if there will be or will not be a leap second on 30 june at midnight
- At the beginning ot july to announce if there will ve or will not be a leap second on 31 december at midnight
To be advised of leap second on internet, you can also consult our Leap_Second.dat :
https://hpiers.obspm.fr/iers/bul/bulc/Leap_Second.dat
Be careful : The limit date of validity of a bulletinc C or Leap_Second.dat is "nearly" one year :
- The limit date of validity of the bulletin C/Leap_second.dat published at the beginning of january is 28 december
- The limit date of validity of the bulletin C/Leap_second.dat published at the beginning of july is 28 june
TAI is the atomic time scale of BIPM; its unit interval is exactly
one SI second at sea level. The origin of TAI is such that UT1-TAI is
approximately 0 on 1958 January 1. The instability of TAI is about 6 orders
of magnitude smaller than that of UT1.The terrestrial Dynamical Time TDT is
presently defined as TAI + 32.184s. Discussion is taking place in the IAU
Working Group on Reference Systems (WGRS) about improved definition of time.
UTC is defined by the CCIR Recommendation 460-4 (1986). It differs
from TAI by an integral number of seconds, in such a way that UT1-UTC stays
smaller than 0.9s in absolute value. The decision to introduce a leap second
in UTC to meet this condition is the responsability of the IERS. According to
the CCIR Recommendation, 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.