[LEAPSECS] presentations from AAS Future of Time sessions

[Magnus Danielson]

On 12/01/14 09:26, Brooks Harris wrote:

> Thanks very much Steve. Great info....

>

> On 2014-01-11 10:45 PM, Steve Allen wrote:

>> On Sat 2014-01-11T21:43:02 -0800, Brooks Harris hath writ:

>>> Any help getting to the bottom of this appreciated.

>> It's history, and it's confused.  Measurement techniques were crude

>> and people were not cognizant that there was more than one thing being

>> measured.  Measurement techniques are vastly improved and some people

>> understand better, but even the best current knowledge cannot

>> unconfuse the folks in the past or be sure how to interpret their

>> understanding using a modern vocabulary and reference frame.

>>

>> NASA technical report number 70 by Hans D.  Preuss of the Department

>> of Geodetic Science at Ohio State University "The Determination and

>> Distribution of Precise Time" is relevant to read to see how badly

>> confused the situation was in the 1960s

>> http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19670028967_1967028967.pdf

>>

>>

>> NIST has many of the old NBS publications scanned and online at their

>> website, and many of the announcements of rationales and dates when

>> decisions were made to change the radio broadcasts are scattered among

>> those.  Their publication with most dense collection of such facts is

>> NBS Monograph 140 which can be found at

>> http://digicoll.manoa.hawaii.edu/techreports/PDF/NBS140.pdf

>>

>> But nobody is going to reset their clocks based on a new understanding

>> of when an epoch was nor what kinds of seconds were being counted.

>> Tabulating historic differences between the values of various time

>> scales is of little relevance to the decision before the ITU-R.

>> How they handle the leap second issue will assert whether humanity has

>> any intent of keeping the meaning of the word "day" to be based on the

>> rotation of the earth.

>

> Yes. Its only relevant in substantiating the standards provance in the

> interest of completeness.

>

> The specific question I was trying to get at was about the 1958 origin

> of TAI.

>

> I had said "So that essentially establishes a proleptic TAI timescale

> from 1958-01-0100:00:00 (TAI) to 1972-01-01T00:00:10 (TAI)."

>

> And Warner said "I don't think TAI is proleptic during that time."

>

> 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.

>

> And I think I've found it in the material you sent. (thanks again, I've

> been hunting for that for too long.)

>

> TIME AND FREQUENCY:

> Theory and Fundamentals

>

> ANNEX l.A

> DEFINITION OF THE SECOND AND TAI

>

> l.A.2. Recommendations of the 5th Session

> of the Consultative Committee for the

> Definition of the Second

>

> RECOMMENDATION S 4 (1970)

>

> Mise en Pratique (Putting into Practice) of

> International Atomic Time

>

> 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 this suggests that the TAI origin was indeed retroactively declared,

> although it seems there was unofficial agreement about it as far back as

> 1961.

>

> So I'm not sure which part of TAI might be called proleptic, or if its

> useful to characterize it that way. But the history seems to explain the

> gap in the TIA/UTC tables between 1958 and 1961. The 1958 origin was put

> in place when there was enough information and agreement to declare it

> as such. 1961 is the start of the accumulation of data.


You have to realize that experiments on atomic timescale goes back to 
1956, so as they figured things out they sketched out how it needs to 
work. Only then you can formulate definitions and even then it takes 
time before formalization can be done as it becomes clear. It's ongoing 
research. So, it's not proleptic, but rather formalization of informal 
agreement.

I've too found the lack of early formal definitions disturbing until 
realizing as they where inventing it as they go.

Once you know that the formalization just came afterhand, then helps to 
see the cause-action pattern better and the formalization does operate 
in the span.

I have not found any TAI-UT1 data, but it is probably hidden in some 
obscurity considering the labs being involved. Would be a nice find to make.

Cheers,
Magnus