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

[Michael Deckers]

    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, Série G, 241-245."
    That is probably a source you may have access to.

    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.

    Apparently, the origin J1958.0 was taken retrospectively, and
    did not just appply to the BIH atomic scales. Since atomic scales
    had an uncertainty of a few ms per year at the time, it should be
    possible to verify whether they all agreed at J1958.0 or at
    1960-01-01T20 -- it is unlikely that they all ever agreed on more
    than one instant.

    Michael Deckers.