[LEAPSECS] next leap second

[John Sauter]

On Wed, 2017-01-11 at 13:07 +0000, Zefram wrote:
> John Sauter wrote:
> > While it is impossible to know for certain when the next leap
> > second
> > will occur, I predict it will be December 31, 2022.
> 
> I find that a surprising prediction.  What is your basis for it?
> 
> The extrapolating expression from the current Bulletin A
> <https://datacenter.iers.org/eop/-/somos/5Rgv/getTX/6/bulletina-xxx-0
> 01.txt>,
> which projects a linear evolution of UT2-TAI, suggests that UT1-TAI
> will approach -37.5 in early 2019 (actually passing it on 2019-02-
> 03),
> and then pass that value twice more early in the second half of 2019.
> So I'd expect the next leap second to happen on 2018-12-31 or 2019-
> 06-30.
> If there is no leap, this projection suggests that the UT1-UTC bound
> would
> be exceeded on 2020-01-19.  Extending all the way out to your
> proposed
> leap date, which is a dubious exercise given the crudity of the
> model,
> yields UT1-TAI ~= -39.228 at 2023-01-01, implying that we'd need to
> have
> two leaps between now and then, with 2022-12-31 being an early
> candidate
> for the *third* leap from now.
> 
> -zefram

My prediction is based on combining the information from two sources. 
The first is the IERS predictions for UT1-UTC, at this URL:

https://datacenter.iers.org/eop/-/somos/5Rgv/latestXL/7/finals.all/csv


It shows the value of UT1-UTC was -0.4078580 on December 31, 2016, and
0.5911620 on January 1, 2017, immediately after the leap second.  It
predicts a value of 0.1021884 on January 13, 2018, which is a decrease
of 0.4889736.  If the rate of decrease is constant the next leap second
will be around December 31, 2018 or perhaps June 30, 2019, which is the
same as your estimate.

My second source is the estimates of delta T from Stephenson, Morrison
and Hohenkerk.  Their data is at this URL:

http://astro.ukho.gov.uk/nao/lvm/

If you look at their projections from 1950 to 2016, they expect delta T
to be 68.04 at the beginning of 2016.  Looking at the projections for
2017 to 2500, they expect delta T to be 67 at 2017, then 68 until 2020,
and increase to 70 by 2030.  I regard the decrease from 2016 to 2017 as
a glitch in the join between two tables, so I regard their paper as
predicting no change in delta T from 2016 to 2020.  

In order to create my table of leap seconds before 1972, I simulated
the IERS process using historical delta T data.  Extending that
simulation forward, I predict December 31, 2022 as the next leap
second.

It will be interesting to see what actually happens.
    John Sauter (John_Sauter at systemeyescomputerstore.com)

-- 
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