INTERNATIONAL EARTH ROTATION SERVICE (IERS) SERVICE INTERNATIONAL DE LA ROTATION TERRESTRE BUREAU CENTRAL DE L'IERS OBSERVATOIRE DE PARIS 61, Av. de l'Observatoire 75014 PARIS (France) Tel. : 33 (0) 1 40 51 22 26 FAX : 33 (0) 1 40 51 22 91 Internet : iers@obspm.fr Paris, 17 July 1998 Bulletin C 16 To authorities responsible for the measurement and distribution of time UTC TIME STEP on the 1st of January 1999 A positive leap second will be introduced at the end of December 1998. The sequence of dates of the UTC second markers will be: 1998 December 31, 23h 59m 59s 1998 December 31, 23h 59m 60s 1999 January 1, 0h 0m 0s The difference between UTC and the International Atomic Time TAI is: from 1997 July 1, 0h UTC, to 1999 January 1, 0h UTC : UTC-TAI = - 31s from 1999 January 1, 0h UTC, until further notice : UTC-TAI = - 32s 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 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. Daniel GAMBIS Director Central Bureau of IERS