[teqc] no leap second insertion in UTC at end of Dec 2018

Lou Estey lou at unavco.org
Mon Sep 17 09:46:50 MDT 2018


Around this time of year I sometimes get questions about whether there will be another
leap second at the end of the year.  For those of you who don't know, the decision as
to whether or not to insert a leap second into UTC is made in order to keep UTC within
±0.9 second of the UT1 time scale, where UT1 is UT0 corrected for the Earth's polar motion,
and each leap second insertion has historically been in the last minute of December or
the last minute of June, depending on UT1-UTC drift.

Currently, UT1-UTC is about +0.05 second and slowly decreasing, with a projected value
around -0.04 s by the end of 2018 (see IERS Bulletin-A, e.g. http://maia.usno.navy.mil/ser7/ser7.dat).
Typically, a leap second has not been inserted until UT1-UTC is around -0.40 s ± a bit.
Thus, no leap second insertion is planned for the end of Dec 2018; e.g see

 From the IERS Bulletin-A and looking at the projected UT1-UTC, it looks like the earliest
the next leap second insertion would occur would be at the end of Dec 2019 or the end of
June 2020.  So it's at least 15 months and maybe 21 months from now.


Louis H. Estey, Ph.D.              office:  [+001] 303-381-7456
UNAVCO, 6350 Nautilus Drive           FAX:  [+001] 303-381-7451
Boulder, CO  80301-5554            e-mail:  lou  unavco.org

"If the universe is the answer, what is the question?"
                                                -- Leon Lederman

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