U.S. NAVAL OBSERVATORY
                         WASHINGTON, D.C.  20392-5420
                                
                                                                  July 06, 2016
                                                                         No. 73

                      TIME SERVICE ANNOUNCEMENT SERIES 14

                                 UTC TIME STEP

1.  The International Earth Rotation and Reference Systems Service (IERS) has 
announced the introduction of a time step to occur at the end of December, 2016.

2.  Coordinated Universal Time (UTC) will be retarded by 1.0s so that the 
sequence of dates of the UTC markers will be:

                       2016 Dec  31   23h   59m   59s
                       2016 Dec  31   23h   59m   60s
                       2017 Jan  01    0h    0m    0s

3.  The difference between UTC and International Atomic Time (TAI) is:

      from 2015 01 Jul, UTC to 2017 01 Jan, UTC:           TAI-UTC= +36s
      from 2017 01 Jan, UTC until further notice:          TAI-UTC= +37s

4.  Information regarding current and predicted values of UT1-UTC is provided 
in IERS Bulletin A. 

5.  UTC and all time scales based on UTC will be affected by this adjustment.  
However, GPS will not be adjusted physically.  For GPS, the leap second 
correction contained within the UTC data of subframe 4, page 18 of the 
navigation message transmitted by satellites will change.

     Before the leap second
     GPS-UTC = +17s (i.e., GPS is ahead of UTC by seventeen seconds)

     After the leap second
     GPS-UTC = +18s (i.e., GPS will be ahead by eighteen seconds)