[LEAPSECS] presentations from AAS Future of Time sessions

[Steve Allen]

On Sun 2014-01-12T00:26:29 -0800, Brooks Harris hath writ:

> I had seen refernce to the fact the 1958 origin was retroactively

> declared, and this might throw light on why there is a gap in the

> TIA/UTC tables between 1958 and 1961. So I was hunting for the

> actual statement in the standards.


There was nothing that could be called UTC before several months into
the year 1960.  US and UK agencies had agreed to coordinate in 1959
August, but buried in those old NBS publications is an acknowledgement
that they did not get that working until sometime in 1960.

Until that date in 1960 all available time scales looked like the
plot at the bottom of
http://www.ucolick.org/~sla/leapsecs/amsci.html
where that depicts NBS only.  USNO was different.  UK was
different.  Every other broadcast in the world was different.

It was during 1960 that BIH accepted the responsibility for doing the
coordination, and they started doing it as of 1961.  This is evident
in Guinot's 2000 memoire and in the contemporary proceedings of the
IAU.

Also note in Guinot's memoire that the BIH did not start combining the
various different sources of AT into an atomic time scale with unified
epoch until 1961.  (If I'm not mistaken that new responsibility for
tracking atomic time was what prompted BIH to hire Guinot.)
Therefore BIH has nothing to say about UTC before 1961.

The only way to proclaim a difference of AT and UT before 1961 is to
adopt the clocks of a single agency or to go back through all the
numbers gathered by the BIH and try to reconstruct what that
difference might have been.  Doing that sort of thing is rare and
often only accomplished as part of somebody's PhD thesis or
academic research.  The task delegated to time service bureaus is
to provide the best value of time now, not to try to compensate for
inadequacies of data from long ago.

Even after 1961 the USNO and NBS were not attempting to provide the
coordinated time scale as specified on paper by the BIH.  In NBS140
there are several documents noting that it was not until 1968-10-01
that USNO and NBS started making adjustments so that they would agree
with each other, and not until two months later that NBS began to
acknowledge that they were providing UTC according to the BIH.

--
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