[LEAPSECS] next leap second

[Michael Shields]

On Wed, Jan 11, 2017 at 5:03 PM, Warner Losh <imp at bsdimp.com> wrote:
> On Wed, Jan 11, 2017 at 3:28 PM, Zefram <zefram at fysh.org> wrote:
>> It would be nice to have more sophisticated projections from IERS more
>> than a year ahead.  It would particularly help in evaluating the proposals
>> that have been made involving scheduling leap seconds further ahead.
>
> Especially if they had error bars that reflect the current confidence
> levels, perhaps tested on historic data.

It might also be helpful if we understood better how these models are
used to decide when to announce leap seconds.  I don't know currently
what criteria the IERS uses, except the overall parameters of keeping
|UT1-UTC| < 0.9 s and preferring to have leap seconds in June or
December instead of other months.

For example, here's Bulletin A from 2016-06-30:

https://datacenter.iers.org/eop/-/somos/5Rgv/getTX/6/bulletina-xxix-026.txt

2016-12-31 (MJD 57753): -0.45079 s
2017-06-30 (MJD 57934): -0.73759 s

You might have expected either of these days to have leap seconds.
The next week, Bulletin C Number 52 announced a leap second for
2016-12-31.  The actual value of UT1-UTC on that day was about
-0.407858 s.

The predictions looked similar on 2014-06-26:

https://datacenter.iers.org/eop/-/somos/5Rgv/getTX/6/bulletina-xxvii-026.txt

2014-12-31 (MJD 57022): -0.46583 s
2015-06-26 (MJD 57199): -0.67258 s

Again, either December 2014 or June 2015 could have had leap seconds.
But in this case the leap second was deferred.  It happened on
2015-06-30, when UT1-UTC was -0.6760362 s
(https://datacenter.iers.org/eop/-/somos/5Rgv/getTX/207/bulletinb-330.txt).