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

Peter Monta pmonta at gmail.com
Fri May 11 05:14:02 UTC 2012


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.

For that matter, what are the inherent long-term limits on ET as a
timescale?  I gather the observation noise is very high on short
timescales, but what is the situation for, say, tau>1year?  It's not
as if the Earth's orbit is randomly perturbed very much, I'm guessing,
and any deterministic perturbations or relativistic corrections would
be compensated for; it's the noiselike processes that would be
interesting.  (Solar wind?)

Cheers,
Peter



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