Le 20/03/2011 05:59, Bruce Griffiths a écrit :
jimlux wrote:
A 10-12m diameter dish is probably close to the minimum feasible
aperture.
A 4m dish can be made to work in conjunction with a mauch larger dish
(eg 30m).
The original speculation was for measuring the small change in earth
rotation rate, for which some sort of interferometric measurement of
a stellar source could be used.
I sincerely doubt that it will be possible to get undisputed
verification of this speed up as the magnitude is swamped by the
irregular diurnal and sub-diurnal rotation rates induced by tidal
effects that are at lease a magnitude greater and for which the error
bars are of the same order or grater than the predicted shift.
There was a similarly predicted rotation shift predicted for the Chile
quake of 28 February 2010 (1,26us). There was IIRC no verification of
that AFAIK. Check the tidal effects at
http://bowie.gsfc.nasa.gov/ggfc/tides/intro.html for the tidal effect
and
http://hpiers.obspm.fr/ for rotational measured speed changes
http://hpiers.obspm.fr/eop-pc/index.php?index=news for the statement
of detectability.
The source has to be bright (so you can detect it with a practical
antenna.. not everyone has a 30m dish in their back yard)
The source has to be small angle (or at least something that you
could accurately determine the centroid of)
The source has to be "not moving" (which I think leaves out using
something like jupiter)
The frequency of measurement has to be somewhere that the atmosphere
won't dominate the uncertainty (leaving out optical, I think)
SO what's the brightest small angular radio source out there?
3C273
RA 12:29.1 DEC 02:03.1
As someone else has pointed out, measuring the earth surface position
relative to spacecraft orbits, e.g. GPS, would be another technique.
In fact, a high resolution measurement of the position of a geosync
sat might do.. If the earth's rotation rate changes you'd have to
adjust the height of the satellites in Clarke orbit to keep them
stationary.
Unfortunately, for earth orbiters, there's enough other perturbations
that you probably can't see it. They already have to move satellites
around to compensate for things like solar wind, air drag (for LEO),
etc.
But maybe for a spacecraft in deep space, between planets, which is
on a well understood trajectory?
Bruce
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
