[LEAPSECS] presentations from AAS Future of Time sessions

[Brooks Harris]

On 2014-01-12 08:49 AM, Steve Allen wrote:

> 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.


Thanks Steve, that's a great summary.

So it appears the reference to the International Astronomical Union (13th
General Assembly, Prague, 1967) is where the recommendations from BIH 
come to the statement in

l.A.2. Recommendations of the 5th Session
of the Consultative Committee for the
Definition of the Second

RECOMMENDATION S 4 (1970)

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.

So the 1958 origin was made *official* by this Recommendation. Is that 
your understanding?


>

> --

> 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

> _______________________________________________

> LEAPSECS mailing list

> LEAPSECS at leapsecond.com

> http://six.pairlist.net/mailman/listinfo/leapsecs

>

>