On 2018-07-21 01:08, Steve Allen wrote:
At that same meeting IAU Comm 31 was led to yield that they had no
influence over the leap seconds that the CCIR had instituted, and IAU
Comm 31 was pressed to produce a statement declaring that leap seconds
were "the optimum solution."
http://adsabs.harvard.edu/abs/1971IAUTB..14..198W
Thanks for that document!
I note the typo on page 198 where it says under the heading
"9. Designation of the epoch of steps in UTC":
"9.1. If UTC is to be advanced, then second 00 will follow
23h 59m 58s of the previous day."
"9.2. If UTC is to be retarded, then the second of the previous day
23h 59m 58s will be followed by the next second 0h 00m 00s
of the first day of the month."
And the text
"9.4. The time of an event given in the old scale, before the
leap second, will be given as a data in the previous month,
exceeding 24h if necessary. The time of an event given in the
scale after the step will be given as a data in the new month,
with a negative time, if necessary."
gives not only the leap second notation long before CCIR codified it
in 1978, but also shows an alternative notation.
All of the above strike me as "something is seriously wrong here."
Looking deeper into the history and memoirs by folks who were involved
it becomes clear that the inception of leap seconds was the
culmination of a 20 year game of international regulatory and
scientific agency pinball. After the CCIR introduced them that game
continued for another 10 years as other agencies and governments were
led to approve the notion of UTC with leap seconds using words like
"parfaitment recommandable".
I do not see what you mean here. Before 1972, the BIH (under control
of the IAU) had defined UTC. The document (above) you quoted contains
the approval by IAU Commissions 4 and 31 to the leap second scheme as
proposed by the CCIR. The introduction of leap seconds happened
with the
support of the BIH, and all the discrepancies among disseminated radio
time scales vanished on 1972-01-01. Not much gaming.
The recommendation of the 15th CGPM in 1975 that "this usage
[of UTC] can be strongly endorsed" does not appear to me to have
been forced upon the CGPM. The resolution does not even call UTC a
time scale, it merely states what was obvious at the time:
• that the system called “Coordinated Universal Time” (UTC)
is widely used,
• that it is broadcast in most radio transmissions of time signals,
• that this wide diffusion makes available to the users not only
frequency standards but also International Atomic Time and an
approximation to Universal Time (or, if one prefers, mean solar
time),
• that this Coordinated Universal Time provides the basis of
civil time,
the use of which is legal in most countries.
Compare this with the proposed resolution B of the 26th CGPM in
2018 November which declares that:
• UTC produced by the BIPM, based on TAI, is the only recommended
time scale for international reference and the basis of civil
time in most countries,
This latter resolution can in fact be seen as the BIPM claiming
the defining authority for UTC from ITU-R, by making it clear that
the realization of UTC (except for the encoding of time signals)
is already completely controlled by data from Bulletin T of
the BIPM. If I were looking for a competition between
standardizing bodies, I would rather point to this resolution.
I have found nothing that directly explains why it was repeatedly
deemed impossible for any of these agencies to explain and recommend
the existence of two kinds of time scales, but it seems clear that
the legal considerations led toward the notion of a compromise.
I do not think that there was any disagreement around 1970 about
the need for multiple time scales, neither among astronomers
(who used many more time scales than just two) nor among radio
people (who would at least distinguish TAI, UT0, UT1, UT2 and UTC).
The CCIR wanted to select a reference time scale to be disseminated
world-wide in order to achieve global synchronization in phase and
frequency. Disseminating two different reference time scales
for that purpose does not make sense: a single globally available
reference time scale allows for the dissemination and comparison of
the readings of any number of time scales across the globe (up to
the uncertainty of the rate of the reference time scale and only
as far as these time scales use the same concept of synchronicity
near the surface of the Earth).
So we have betrayal, eroded trust, and reduced usefulness because some
folks wanted to take what looked like a politically expedient shortcut
which was full of unexplained technical complexities. It is not clear
who can remedy things.
I do not take such a grim view of the history of UTC.
It is certainly true that (international) commissions do not
always work efficiently and unbiased, and that powerful
people like Gernot Winkler can have a dominating influence
on their decisions. But there was general agreement in 1970
that the rates of UTC and TAI should be made equal, and the only
realistic alternative to the leap second proposal at the time
would have been to make UTC a fixed translate of TAI -- which
would have been the greater change to existing practice. No
wonder that no alternative to Winkler's UTC was proposed.
And one also has to admit that the 1972 definition of UTC
has been remarkably successful: arguably all countries now
use UTC as their basis for legal time, and many even formally
admit that they do so; UTC is used globally to date all kinds
of observations in astronomy, geodesy, meteorology, space
technology; and it is widely taken as the time base for
computers. The previous time scale definition that lasted
for more than 50 years was that of UT, defined by Newcomb
in terms of Greenwich mean sidereal time.
Michael Deckers.
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