[LEAPSECS] presentations from AAS Future of Time sessions

[Brooks Harris]

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.

-Brooks



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