Leap Seconds Bulletin

UTC stands for Universal Coordinated Time. UTC is the most commonly used time system in the world and is the one used by the Network Time Protocol (NTP). Leap second insertions are scheduled from time to time in order to keep UTC in alignment with the earth's rotation.

Leap second insertions occur on either June 30th or December 31st and do not happen very often.  The most recent occurrence was on December 31, 2008.  Before that it was on 12/31/2005, then 12/31/1998, and so on - back until 1960.  The International Earth Rotation Service (IERS) is responsible for notifying the public when a leap second will be inserted.  For your convenience this information is summarized below:

            The next possible leap second insertion date is June 30, 2012.
            There WILL be a leap second introduced into UTC on that date.
            The current number of leap seconds is 15.
            The future number of leap seconds (after next possible insertion date) is 16.

GPS-Synchronized Products
Our GPS-synchronized products precisely adjust for leap seconds to keep all Network Time Servers and Time & Frequency Equipment accurately synchronized to UTC. The next time there is a leap second insertion there is no special action you need to take - it will all be handled automatically.

CDMA-Synchronized Products
Timing information being transmitted by the CDMA base stations is guaranteed to be ultra-precise, except for the leap second information.  Our CDMA-synchronized products handle leap seconds in two different ways - automatically and manually (user-entered).  In automatic mode the unit will determine the leap second information from the CDMA base station transmissions.  Some CDMA base stations handle the leap second transition properly but some do not.  That is why the manual mode is the preferred mode.  For more information click here.

Background Information
Leap seconds are inserted in order to keep UTC, which is derived from atomic time (TAI), in agreement with the Earth's rotation rate. Relative to TAI, the Earth's rotation rate is slowing down. This means that UTC must be retarded periodically in order to maintain agreement between UTC and the apparent daylength. If this were not done, eventually UTC would drift out-of-sync with Earth's day and many astronomical and navigational problems would ensue.

The IERS is the organization responsible for measuring the relationship between UTC and the rotation rate of the Earth.  When the difference between UTC and apparent Earth time has exceeded a certain threshold, the IERS coordinates with the Bureau International of the Hour (BIH) to schedule the insertion of a leap second into the UTC time scale.  The IERS publishes Bulletin C about 6 months in advance of each possible leap second insertion point.  Leap seconds may only be inserted at UTC midnight of June 30 or December 31.  Bulletin C confirms whether a leap second will or will not be inserted at the next possible insertion point.  The IERS website is: http://hpiers.obspm.fr/eop-pc/.

The leap second information at the IERS website is actually the difference between atomic time (TAI) and UTC.  The leap seconds we are interested in are the difference between the Global Positioning System (GPS) time and UTC and is called the GPS-UTC Offset.  The GPS time scale began on January 6, 1980.  At that time, the UTC timescale had undergone 19 leap second insertion events (TAI-UTC).  So, if you are obtaining your leap second information from the IERS website, you will need to subtract 19 from the TAI-UTC leap second values published there to obtain the GPS-UTC Offset.  Here is a history of the leap second insertions since 1997:

Leap Second Insertion Date	TAI-UTC	GPS-UTC Offset
June 30, 1997	31 seconds	12 seconds
December 31, 1998	32 seconds	13 seconds
December 31, 2005	33 seconds	14 seconds
December 31, 2008	34 seconds	15 seconds
June 30, 2012	35 seconds	16 seconds