[LEAPSECS] epoch of TAI, and TAI vis a vis GPS

Steve Allen sla at ucolick.org
Wed Mar 4 03:13:33 EST 2015

On Wed 2015-03-04T07:42:46 +0000, michael.deckers via LEAPSECS hath writ:
>   On 2015-03-04 02:23, Steve Allen wrote on the

> >Getting meaninglessly pedantic, in Survey Review v19 #143 p7 (1967)
> >A.R. Robins had been talking with Sadler and Smith and with that
> >information in hand he wrote that atomic time was identical to UT2 at
> >1958-01-01 T 20:00:00 Z

>   Well, there is not only personal recollections:
>   RECOMMENDATION S 4 (1970) of the 5th Session of the
>   Consultative Committee for the Definition of the Second:
>       4. The origin of International Atomic Time is
>       defined in conformance with the recommendations
>       of the International Astronomical Union (13th
>       General Assembly, Prague, 1967) that is, this scale
>       was in approximate agreement with 0 hours UT2
>       January 1, 1958.

A resolution does not change what had been done by the folks running
the broadcasts over a decade earlier, nor does it repair the
deficiencies in what they had done over that entire interval.  A.R.
Robins talked with H.M. Smith.  Smith had been there making the UK
time broadcasts happen.  If Smith said that the UK versions of the
atomic time scale and the UT2 time scale were aligned at 1958-01-01T20
then that is likely the way the calculations to do that alignment were
performed, and likely based on the hour of the day that the
ionospheric conditions were most conducive to allowing the best
comparison with other transmitters.

It is instructive to read BIH Bulletin Horaire for the actual history;,
to see the ways that the radio broadcasters attempted, succeeded, and
failed at their mandate of maintaining continuously operating
transmitters based on continuously operating chronometers; to see the
issues with Anna Stoyko's initial, painstaking efforts to reconstruct
the history of received radio time signals into the first atomic time
scale; to see the number of times that the broadcasters changed their
strategies and the number of times that the BIH changed their
algorithms and recomputed what past issues should have said the time

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

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