EndRun Meridian II, User Manual

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M e r i d i a n I I U s e r M a n u a l 183
"Smarter Timing Solutions"
Appendix
F
Leap Seconds
UTC stands for Coordinated Universal Time. UTC is the international time standard most commonly
used in the world and by the Network Time Protocol (NTP). A leap second insertion is scheduled
about every one-and-a-half to three years in order to keep UTC in alignment with the Earth’s rota-
tion. Possible leap second insertions can be scheduled at 23:59:59 UTC on June 30 or December 31.
Automatic
Leap Second Insertion
Your GPS-synchronized Meridian II precisely adjusts for leap seconds if and when they occur. There
is nothing you need to do in order to keep your Meridian II time server accurately synchronized to
UTC.
You can see the current GPS-UTC parameters that are downloaded from the satellites by using the
gpsutcinfo
command. See
Chapter 3 - Console Port Control and Status
for details on this com-
mand or type
help gpsutcinfo
at the console port.
Background Information
Leap seconds are inserted from time-to-time 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 International Earth Rotation and Reference Systems Service (IERS) is the organization respon-
sible for measuring the relationship between UTC and the rotation rate of the Earth. When the differ-
ence 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. Bulletin C confirms whether a leap second will or will not be inserted at the
next possible insertion point. The IERS website is:
http://www.iers.org
EndRun summarizes this information at this link:
http://www.endruntechnologies.com/leap.htm