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

[Michael Deckers]

   On 2019-01-20 17:19, Steve Allen wrote:

> 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.

    Thanks for the pointer!

    Yes, Danjon wants a zero epoch defined, but Markowitz opines that
    this is of interest only ("uniquement") for the IAU who should
    decide upon it.

> 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.

    But this seems to state something about the inputs for the data
    reduction by the BIH. It does not say that the integrated atomic
    time scale of the BIH, the BIH output, has had a step at the time,
    or a step in rate, or does it?

    I understand that the BIH had to adapt every once in a while the
    constants for integrating the atomic time scales from their
    intermittent comparisons (because of the addition of new clocks,
    and because of the increasing accuracy). But I would assume that
    the goal in such adaptations must have been to keep the phase and
    rate of A3 without any noticeable steps over such a change.

> 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.


    Guinot must have known, but in 2004 he said (together with Arias)
    that the origin was J1958.0. Couldn't that mean that the change on
    1961-01-01 was designed to have no effect on A3 as published by
    the BIH?

    Michael Deckers.