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quote:You have your facts and/or numbers wrong for some reason. Stellar aberration is a function of speed relative to the local gravity field, and rarely exceeds 0.01 degrees in the solar system. And nothing special happens at 53 au, which is also not any kind of limit. -|Tom|-
Thanks for checking, but I think my facts were approximately right. I refer not to the absolute value of stellar aberration ( 20.5" = 0.0057 deg ) but to a hypothetical error, of about 0.3 degrees, in the direction of that aberration (I'd estimated 0.2 but it's really 0.3 so I had to correct that above). That would amount to 0.0052 radians x 20.5" = 0.107". The hypothesis is, that we might be observing the aberration due to what Earth's velocity vector was 53 AU * 8.3 min/AU = 440 min ago.
If many data points on a sinusoid are known, the phase of that sinusoid can be determined to surprisingly high precision. Perhaps Bradley's, or some subsequent, demonstration of stellar aberration would reveal, on careful statistical analysis, that the aberration circle is 0.3 degrees out of phase with expected.
The second point is debatable (see my 2002 article in "Aircraft Engineering & Aerospace Technology" a journal which is unrefereed but does have an editorial board comprised mostly of college professors; and also the article by JD Anderson of Cal Tech cited as a reference therein). Anderson's article shows dramatic apparent speed fluctuations in Pioneer 10 occurring at about 53 AU but hardly anywhere else. I recall that others have suggested somewhat hesitantly that the probe encountered a cluster of comets there, however my estimate of the required number, large mass, and small distance between these alleged comets argued against that. Furthermore, Anderson's article shows that the probe began to have apparent sinusoidal fluctuations in speed, of period one year, then and thereafter. So indeed there is, or at least was, something there at 53 AU, and no one knows what.