[LEAPSECS] Leap seconds have a larger context than POSIX

[Michael Deckers]

On 2020-02-02 22:30, Steve Allen wrote:
> On Sun 2020-02-02T17:59:20+0000 Michael Deckers hath writ:
>> The maximum deviation |UTC - UT1| <= 0.9 s as stipulated in
>> 1974 by CCIR Rec. 460-1 has never been violated until now.
> That violates the agreement that the difference between
> UTC and UT1 would be encoded as part of the time broadcasts.


    Actually, the difference |UTC - UT1| has always been < 0.8 s
    except around 1973-01-01.

    And DUT1 has assumed the value 0.8 s only once, for a few days
    on and after 1994-07-01, as specified in Bulletin D46 (online at
    [https://datacenter.iers.org/data/17/bulletind-046.txt]).

    That Bulletin is remarkable in several respects: it describes
    two switches of DUT1, not just one, and it was issued on 1994-06-21,
    only 10 days before the first switch (rather than a month before
    it, as was requested -- from the BIH -- in CCIR Rec 460-4 of 1986).



>>> In one case it was broken specifically because a high official at CCIR
>>> conceded to a high official from USSR and directed the BIH to violate
>>> the wording of the existing agreement.
>> Do you mean the only violation of applicable CCIR rules, the
>> introduction of a leap second into UTC at 1973-01-01?
> Right.  Sadler covers this in his memoir and in several contemporary
> publications.
>
> Delving into this reveals more of the fear in the process.
>
> Several memoirs show that the principals involved with the creation of
> UTC with leaps were very concerned that the change of broadcast time
> signals might cause havoc with ships using celestial navigation.
> Reading through those shows palpable relief when they managed to evoke
> from the Maritime Safety Committee of the IMCO a statement that Rec.
> 460 would not cause difficulties with navigation predicated on the
> expectation that governments whose radio broadcasts used new UTC would
> issue notices about the change of their broadcasts.  That meant that
> the Time Lords did not have their arses on the line if a ships might
> collide as a result of the new system.  With the maximum difference of
> 0.7 s that could be encoded in the radio broadcasts not being able to
> handle the 0.9 s difference that put their arses back on the line.
>
> Other concern was expressed that exceeding the 0.7 limit might be
> blamed on the BIH and might trigger governmental review of the
> operation and funding of the BIH.  At that time about 80% of the funds
> for BIH were coming from Observatoire de Paris as slush from their
> allotment from the French government.  That was hardly an
> "international" arrangement, but BIH had only just been handed the
> responsibility for maintaining TAI specifically because any other
> arrangement would have required effectively duplicating the
> expertise and hardware of the BIH and finding a way to fund that.
>
> Prompting governments or journalists to open an investigation into the
> process of writing an international "technical" specification that was
> violated in less than two years was not a welcome notion.



    Very interesting, thanks for these details!

    Concerning the technical expertise of the CCIR with time scales: one
    of the early proposals of the CCIR has been a "stepped atomic time"
    with steps of 1 s and maximal difference of 0.5 s from UT2 (as mentioned
    in the 1970 report of commission 31 available via your web site on
[https://ui.adsabs.harvard.edu/link_gateway/1970IAUTA..14..343Z/ADS_PDF])
    -- apparently they had not consulted any astronomer, even though they
    used to "request" many actions from the BIH in their specifications of
    time scales.

    The 1970 report also contains the proposal that the CIPM should be
    responsible for the definition of UTC, and 49 years later, the CGPM
    in 2019 seems to have taken on that task with the resolution
    [https://www.bipm.org/en/CGPM/db/26/2/] which notably has no
    requirement that |UTC - UT1| be bounded.

    Michael Deckers.