[LEAPSECS] the epoch of TAI, with no more doubt

[Steve Allen]

On Sun 2019-01-20T15:15:54+0000 Michael Deckers hath writ:
> On 2019-01-20 00:50, Steve Allen wrote:
> > I took a closer read and cross reference of the relevant
> > issues of Bulletin Horaire and finalized my web page.
> > The epoch at which TAI was set is definitely 1961-01-01T20:00:00 UT2
>
> Arias and Guinot say in "Coordinated Universal Time UTC: Historical
> Background And Perspectives", online at
> [https://syrte.obspm.fr/journees2004/PDF/Arias2.pdf]:
>
>   "In 1961, the BIH assigned a common origin to these time scales
>   [atomic time A1 of USNO for other integrated atomic times]
>   by coincidence with UT2 on the 1st of January 1958 (Stoyko, 1961).
>   The same origin was used for the BIH mean atomic time."
>
>  The reference is to:
>      "Stoyko A., 1961, Bulletin Horaire du BIH, Serie G, 241-245."
>  That is probably a source you may have access to.

Those pages are a response to Recommendation 2 from the second CCDS
meeting held 1961-04-11/1961-04-12.  At the CCDS meeting BIH presented
an initial effort to integrate and compare all the cesium standards
for which data were available, and BIH was the only place with the
timing data from all the labs.  The BIPM has now scanned and published
the proceedings from all the CCDS meetings, so anybody can look at this.

During those CCDS proceedings is the discussion on what value to give
to an atomic time scale:
    The president [Danjon] insists on the need to define a zero, even
    arbitrary, for the time scale; it is necessary to date terrestrial
    and astronomical events in a certain calendar.

Guinot was working with BIH since 1952, so he must have been
aware of Anna Stoyko's atomic time scale in 1961, and he may
even have been one of the computers.

>  The quote implies that the BIH scale A3 (precursor of TAI) was taken
>  to agree with UT2 at J1958.0, but of course this does not rule out
>  that the two time scales also agreed at some later instant.

The table with the inception of A9 in my web page from Bulletin
Horaire ser 5 no 13 was created scant months after the original
table in ser G no 8.  The intro to the A9 table discusses the
difference between the "5 anciens" standards and the 4 new ones.
The intro explicitly states that the BIH is choosing to reset their
value of all these atomic time scales at 1961-01-01T20:00:00 UT2.

Guinot knew this, in part because after Anna Stoyko decided to create
A3 and sync it with A9 Guinot later re-interpolated A3.  More
unquestionably, in Bulletin Horaire ser J no 1 p 3 Guinot wrote
that the origin of A3 and all other BIH TAi values was 1961 Jan 1
and he referred to Bulletin Horaire ser 5 no 13.

--
Steve Allen                    <sla at ucolick.org>              WGS-84 (GPS)
UCO/Lick Observatory--ISB 260  Natural Sciences II, Room 165  Lat  +36.99855
1156 High Street               Voice: +1 831 459 3046         Lng -122.06015
Santa Cruz, CA 95064           https://www.ucolick.org/~sla/  Hgt +250 m