[LEAPSECS] [time-nuts] Why 9,192,631,770 ??

[mike cook]

Le 11/05/2012 07:14, Peter Monta a écrit :

> Are there better estimates of the ET second nowadays (relative to the

> SI second)?  It would be interesting to know what the cesium frequency

> "should have been" if much better estimates of the ephemeris-time

> second were available at the time.  One would think that with all the

> solar-system data JPL and others have had at their disposal since the

> 1970s, a very good ET-second number could be cooked up; better than

> 1950s Moon cameras at any rate.

>

>

There are various refs in the pedia to later estimates. Markowitz (1988) 
calculated an agreement to 1x10-10.  but looking at the article I see 
there were still some uncertainty in terms used to calculate ET and 
depending on what was chosen gave 2x10-11 .  Accordingly he concludes 
conservatively that ET has been equal to Si within 1x10-9.
The uncertainties will have been reduced since then but not eliminated 
and so "should have been"  is a moving target but it would appear from 
the above that the chosen SI value would still be preferred if the 
decision was to be reappraised.