On 2017-01-12 12:18 PM, Michael Shields via LEAPSECS wrote:
On Wed, Jan 11, 2017 at 5:03 PM, Warner Losh <i...@bsdimp.com> wrote:
On Wed, Jan 11, 2017 at 3:28 PM, Zefram <zef...@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.
As I understand it, it's pretty complicated. IERS is the top node in a
hierarchy of entities; there are many contributing organizations
including the participating observatories and interaction with BIPM. The
IERS conventions guide the procedures, and those are large and
complicated documents. It's a pretty big administrative and technical
apparatus. It would be nice to understand it better, but the bottom line
for practical timekeeping discussions seems to be the IERS products.
Maybe someone can inform us better?
-Brooks
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).
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