[LEAPSECS] [Non-DoD Source] D.H. Sadler in 1954

[Warner Losh]

On Fri, Mar 16, 2018 at 10:16 AM, Matsakis, Demetrios N CIV NAVOBSY, N3TS <
demetrios.matsakis at navy.mil> wrote:

> I was surprised to find phrases in the Lick web pages:  "CCIR ignored the
> advice that astronomers " and "squelched astronomers who insisted that leap
> seconds would cause trouble".
>
> I realize their author is not the only person with a strong emotional
> bias, but even so I question the tone of these web pages because they are
> inconsistent with the following:
>
> 1. There was a progression in thought as technology advanced and atomic
> clocks proved their reliability.
>
> 2. It should be obvious that ephemeris time would need a flywheel system
> to get practical time to the users, and GMT could be part of that.  Today
> individual labs realize UTC(k) for the same reason - to flywheel before the
> monthly computations of UTC are published.  WWVB, GPS, and your local cell
> towers are all part of the system as well.  (Even so, I think everyone
> today agrees that Ephemeris time was a mistake.)
>
> 3.  According to references in Nelson et al’s Metrologia article, which
> was peer-reviewed, it looks to me like the switch to UTC was by universal
> agreement among the institutions.  The IAU, URSI, CIPM(=CGPM), and CCIR(=
> ITU) all agreed to the current system in the late 60's, and I would guess
> that the timing of their resolutions probably depended more on the
> (generally) 3-year spacing of their general assemblies than anything else.
> Note that many of those groups had overlapping membership.  It would
> however be unusual if all individual members of these bodies ever agreed to
> any resolution, even if passed "by consensus".
>

The adaptation of UTC was by consensus. The leap second stuff was a rush
job in 1971 with the first leap second on Jan 1, 1972. I think that rush
job is what the Lick pages refer to.

For more trivia, the dynamic  Gernot Winkler of the USNO was both a
> practical clock man and astronomer.  He was not the only one, and he was a
> very active member of the IAU who chaired commissions, served on working
> groups, etc.  He told me personally that he and Essen independently came up
> with the idea of leap seconds.   He also said a big reason was to win the
> support of the mariners, who in the pre-GNSS days actually did celestial
> navigation and who in the pre-internet days could not easily get access to
> tables that incorporated the difference between UT1 and UTC.
>

UT1 - UTC was known to .1s based on WWV and other broadcasts. At the time,
the < 1s error was so that you limited your error in navigation to
something acceptable. Though one also had LORAN-C (which had it's own
time-scale based on UTC w/o leapseconds to compute the TOCs, but whose
operational bases had atomic clocks set to UTC).

Warner


> To: Leap Second Discussion List
> Subject: [Non-DoD Source] [LEAPSECS] D.H. Sadler in 1954
>
> In 1954 D.H. Sadler produced a monograph on the changes in time
> that had been resolved at the 1952 IAU General Assembly.
> His writeup is clearer than almost anything else for the next 60 years.
> It was published in Occasional Notices of the RAS, and it has been hard
> to find until now.
> https://www.ucolick.org/~sla/leapsecs/twokindsoftime.html
> This is one of the series of documents produced starting in 1948 and
> proceeding through the next 20 years where astronomers explained that
> two kinds of time would be needed to satisfy all applications.
>
> --
> Steve Allen                    <sla at ucolick.org>              WGS-84 (GPS)
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