[tz] [PROPOSED] Cite Rec. ITU-R TF.460-6 for leap seconds

Steve Allen sla at ucolick.org
Thu Jul 4 22:06:13 UTC 2019

On Thu 2019-07-04T21:18:42+0000 Michael H Deckers hath writ:
> Certainly the parameters in the modern definition of UT1 were
> chosen so that UT1 is continuous in phase and rate with Newcomb's
> definition of UT based on his tables of the Sun. But I find it
> a bit misleading to imply that only this match was the goal of
> the modern definition of UT1. The rotating body, the reference
> for measuring rotation angle, and the rotation axis have all
> been changed significantly since Newcomb's time around 1900.

In the change from FK3 to FK4 there was a step of 0.0016 s in UT2(BIH)
at 1962-01-01, but that was inconsequentially small by comparison with
the systematic offsets that had previously existed between time
services of different nations up to that point
Bulletin Horaire series 5 number 16 indicates that as part of the
change from FK3 to FK4 BIH had been instructed to recalculate the
longitude of every observatory in a globally-consistent fashion
so that the longstanding systematic offsets between their time
values would be nulled.

In section 3 Aoki et al. explicitly say that matching rate and value
of UT1 was part of the agreement in the change from FK4 to FK5

In section 7 Capitaine et al.  note that in the change from FK5 to
ICRS continuity of value was possible but that continuity of rate was
only possible as a mean over an interval (instead of instantaneously)

At each change the papers explaining the new system explicitly note
the goal to preserve UT1 as continuous in rate and value with
Newcomb's expressions in Tables of the Sun inasmuch as was possible
while adopting a more precise set of conventions.  Comments in tz
do not need to review a century of changes of nomenclature and
conventions, but they can legitimately say that much.

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