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.
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