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

mike cook 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 mailing list