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May8-10, 05:19 PM
Sci Advisor
P: 1,910
DrGreg, I'm not referring to how bright the sun is, but the exact time when it is directly overhead.
DrGred had something else in mind. Is there day and night because the sun is revolving around the earth, or is earth rotating? What does this mean for your experiment?

Further, it's a bit more difficult than you think.
For example, if the sun were electrically charged, and we could measure the field of this charge here on earth, we would measure its direction to be not where we see the sun, but (almost exactly) where it ought to be now. For gravity, this "coincidence" is even more exact.
It's hard to explain in a few words, but those "forces" point to the momentary position rather than the retarded position of the source. Has to do with the absence of the respective modes in the radiation (no monopole radiation in EM, no monopole or quadrupole radiation in Gravity).
Read this paper.