[time-nuts] Re: possible negative leap second

[Steve Allen]

On Thu 2024-03-28T11:03:26-0700 Tom Van Baak via time-nuts hath writ:
> The modern version of UTC started in 1972 and from the beginning had the
> provision for either positive or negative leap seconds, without favor. The
> goal was simply to keep the stable atomic time scale that we all use roughly
> in sync with unstable earth rotation time.

Alas, that is the UTC goal stated public presentations.
The actual goal was to have a single international time scale which
would be legal according to the laws of all nations.

Physicists did not want leap seconds.
Radio time signal providers did not want leap seconds.
Astronomers did not want leap seconds.
Astronomers produced a paper pretty much predicting that leap seconds
would become the disaster that we saw in 2012.

All of that was irrelevant because several nations had just made
inconsistent changes to their laws defining their legal time scale.
The only option for a single broadcast time scale which would be legal
to use in all countries was the leap second.

Despite concerns about the effect of leap seconds on navigation it is
not true that the leap second was instituted for navigators.
It would have been easier to produce almanacs for navigation if the
broadcast time signals had gone to purely atomic time without leaps.

Afterwards the principals in the decision process went to the meetings
of international agencies and begged them to approve of the leap
second.  The 1970 IAU meeting erupted into chaos when they learned of
the change, but that was redacted from the proceedings, and they were
coerced to vote for a resolution that approved.  The international
meeting concerned with navigation was forced into a similar approval.

Ever since the IAU approved the existence of Ephemeris Time the
practitioners of astronomical time have tacitly known that UT
(nowadays UT1) is not and never has been the mean solar time of the
Greenwich meridian.  The difference has been increasing.  Since
that inception the pracitioners have taken pains to make sure that
fact is expressed in language so obscure that only a close read of the
mathematical expressions would reveal it and the proceedings
have been edited to omit discussions of it.

If in either the 1950s or the 1970s astronomers had made it clear that
UT1 was not the mean solar time of the Greenwich meridian the likely
outcome would be chaos.  The UK Parliament and other legislative
bodies might have changed their laws to demand that their national
time bureau produce some peculiar version of time.  If different
countries produced different values for the time then each of those
countries would need to compute its own set of almanacs or else tables
of offsets for use with its own time scale.

The most important goal of the folks who are charged by their
governments with producing time scales for navigation and legal
purposes has been to produce values that agree with the values
produced by the pracitioners in other countries.

The meaning of the time scale is less important than the agreement.

UTC with leap seconds is the time scale that was "good enough for
international government work" until it became expedient to rewrite
national laws about time.  That was the goal in 1970.

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