[RadioAstronomer]

So the question is whether the Earth rotates in an orbital plane around where the Sun was 8.3 minutes ago, which will always be 78,186 miles away from its current position (if your math is valid), or whether the Earth orbit is centered more closely to the actual position of the Sun at the present time.

Remember it takes one year for the earth to orbit the sun once. Visualize it as a combined system (earth/sun) orbiting about a common point of mass moving as a whole relative to the center of the galaxy. Don't forget the galaxy is also moving linearly as a "whole" as well.

[Southack]

That's correct and fine and well and good, but either the Earth is orbiting around where the Sun was centered 8.3 minutes ago at any given point in time, or it is orbiting around a point closer to the center of the Sun at the present time, and the differnece, if any, between those two points will enable us to calculate, from observable phenomena, the speed of Gravity.