[LEAPSECS] the epoch of TAI, with no more doubt

[Steve Allen]

On Mon 2019-01-21T22:00:16+0000 Michael Deckers hath writ:
> [things that amount to wishful thinking that reality was simple]

The pages of Bulletin Horaire reveal that time is nowhere
near as simple as we would wish.
https://www.ucolick.org/~sla/leapsecs/bhpages.html

>  Do you happen to know in which tabulation the jump by 1.6 ms
>  occurs? A3 minus which other time scale?

The jump of 1.6 ms is clear in the tablulations of UT2 - A3 done
by both Stoyko and Guinot, and both of them point it out.
It was an inevitable side effect of changing from FK3 to FK4.

It means that all reported values of UT2 from before 1962 must
be adjusted if the desire is to have everything in a single
homogeneous system.  Stoyko and Guinot did not choose to do that.

Curiously there is not a big jump in the value of UT2 - A3 at that
same date which would have been caused by changing from the old
expression for UT2 - UT1 to the new expression.  I surmise that this
means Stoyko and Guinot did correct the old values of UT2 for the
change in that formula.

But more surprising is an obvious change in the rate of both
tabulations of UT2 - A3 at 1961-01-01.  This leaves me wondering if
the fix for the change of UT2 formula was done not by recomputing
UT2-UT1 for all past values, but simply by subtracting the difference
on that new years day.  The answer to this deserves a close look at
whether the slope difference matches the difference in the old and new
UT2 expressions, and also a close look at the BIH annual reports to
see whether they indicate the acquisition of computing machinery.

--
Steve Allen                    <sla at ucolick.org>              WGS-84 (GPS)
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