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

[Michael Deckers]

    On 2019-01-22 05:17, Steve Allen wrote:


> Curiously there is not a big jump in the value of UT2 - A3 at that
> same date which would have been caused by changing from the old
> expression for UT2 - UT1 to the new expression.  I surmise that this
> means Stoyko and Guinot did correct the old values of UT2 for the
> change in that formula.

    In [https://www.ucolick.org/~sla/leapsecs/taiepoch.html], the
    table F on page 74 in fact does not show a step in ΔA3 = UT2 - A3
    between the lines for 1961 January 00 and January 05 (which is
    why you could interpolate linearly to obtain UT2 - A3 = -1.4123 s
    for 1961-01-01).

    And the column "WWV3" equally shows no step at 1961-01-01,
    and since it is probably meant to be "BIH integrated atomic time
    - time signaled by WWV3" (where the latter should include the
    step down by 5 ms), the point of tabulation "Janvier 0" may
    actually be the instant when UT2 was 1960 Dec 31 - 5 ms.
    So yes, the entry may have been "corrected".

    Anyway, a jump down by 5 ms occurred in (what was later baptized)
    UTC on 1961-01-01 (see [Explanatory Supplement 1992, p 87]).
    I always thought that this was done to adapt to the jump in UT2
    caused by the change in the formula for UT2 - UT1, but from the
    graphs in [https://www.ucolick.org/~sla/leapsecs/seasonal.html]
    (thanks!) I have to conclude that UT2 must have made an
    upward jump by about 5 ms, while the step by 5 ms in UTC
    at 1961-01-01 definitely was a downward jump (it is also included
    as such in the SOFA function iauDat()). Did I make a sign error?

    Michael Deckers.