But where the "sun actually is" doesn't really move that much, relative to the Earth. Don't let the apparent "movement" of the sun across the sky as the Earth rotates fool you.
The Sun pretty much sits in the same spot (i.e., right in the middle of the solar system), so there's no testable difference between the effect its gravity has on our orbit if "instantaneous", versus the effect it would have 8.3 minutes delayed.
If the Sun actually *were* circling the Earth in the way it *appears* to, then yeah, an 8.3 minute difference in gravity would be measurable. But then, it would also be circling us at over two million miles per hour (3% of the speed of light)...
Summary
- S. Kopeikin misquotes Van Flandern as predicting that cg (Kopeikins speed of gravity) will be infinity. Van Flandern and Vigier are in print showing that six experiments better than Kopeikins already show that the speed of gravity is >> c (c = speed of light). But in posted discussions with Kopeikin and in USENET newsgroups, Van Flandern clearly states that Kopeikins cg parameter cannot be the speed of gravity and will certainly come out near the value c, as it did.
n Asada followed up Kopeikins Astrophysical Journal paper with his own paper in the same journal showing that Kopeikin was simply measuring a quantity that propagated at the speed of light, and was definitely not measuring the speed of gravity.
n Kopeikin has mostly ignored these well-founded corrections, apparently because he justified funding for his experiment by the claim that it would measure the speed of gravity.
n Kopeikin new paper at the Los Alamos archive shockingly revises his protocol, equations, and methodology. Scientific method forbids changing the protocol after the results are in, especially when it is done to avoid an unwanted or unexpected result.
n Kopeikins new equations introduce a new factor, c/cg, for time in the Einstein equations. This factor drives time intervals to zero for large values of cg, thereby making large cg results *impossible* for any experimental data regardless of reality.
n Kopeikins now-forced results do a great disservice to science in general and the advancement of physics in particular because they no longer represent what his own experiment showed, much less the speed of gravity.