LEAP SECOND ALERT!

  
                     U.S. NAVAL OBSERVATORY
                  WASHINGTON, D.C.  20392-5420
                                
                                             July 23, 1998
                                             No. 64

               TIME SERVICE ANNOUNCEMENT SERIES 14
                                
                          UTC TIME STEP

1.  The International Earth Rotation Service (IERS) has announced the 
introduction of a time step to occur at the end of December, 1998.

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

               1998 December 31   23h   59m   59s
               1998 December 31   23h   59m   60s
               1999 January  01    0h    0m    0s

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

from 1997   01 Jul, UTC to 1999 01 January, UTC:       TAI-UTC= +31s
from 1999   01 Jan, UTC until further notice:          TAI-UTC= +32s

4.  The insertion of one leap second will be evident by the change of 
sign of the DUT1 correction which will become positive.  Extrapolated 
values of DUT1 are distributed weekly in the IERS Bulletin A.

5.  All coordinated time scales will be affected by this adjustment.  
However, Loran-C and GPS will not be adjusted physically.  Times of 
Coincidence for LORAN-C are available on the Time Service Web Page 
(http://tycho.usno.navy.mil/loran.html).  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 = +12 (i.e., GPS is ahead of UTC by twelve seconds)

     After the leap second
     GPS-UTC = +13s (i.e., GPS will be ahead by thirteen seconds)



                              DENNIS D. McCARTHY
                              Director
                              Directorate of Time

Time Service Dept., U.S. Naval Observatory, Washington, DC