INTERNATIONAL EARTH ROTATION AND REFERENCE SYSTEMS SERVICE (IERS) SERVICE INTERNATIONAL DE LA ROTATION TERRESTRE ET DES SYSTEMES DE REFERENCE SERVICE DE LA ROTATION TERRESTRE DE L'IERS OBSERVATOIRE DE PARIS 61, Av. de l'Observatoire 75014 PARIS (France) Tel. : +33 1 40 51 23 35 e-mail : services.iers@obspm.fr http://hpiers.obspm.fr/eop-pc Paris, 6 July 2016 Bulletin C 52 To authorities responsible for the measurement and distribution of time UTC TIME STEP on the 1st of January 2017 A positive leap second will be introduced at the end of December 2016. The sequence of dates of the UTC second markers will be: 2016 December 31, 23h 59m 59s 2016 December 31, 23h 59m 60s 2017 January 1, 0h 0m 0s The difference between UTC and the International Atomic Time TAI is: from 2015 July 1, 0h UTC, to 2017 January 1 0h UTC : UTC-TAI = - 36s from 2017 January 1, 0h UTC, until further notice : UTC-TAI = - 37s 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. Christian Bizouard Head Earth Orientation Center of IERS Observatoire de Paris, France