[LEAPSECS] [time-nuts] Why 9,192,631,770 ??
michael.cook at sfr.fr
Fri May 11 02:44:42 EDT 2012
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.
More information about the LEAPSECS