ok - I have not been studying astrophysics in any real sense but I have been an amateur enthusiast for ten years or more.

I have a burning question :

Our measurements of Universal bodies (stars, nebulae etc) comes from the measurements we have learned to make with our knowledge of Electromagnetic radiation here on earth and in the surrounding solar system. Now we revolve around our Sun with a discernable regularity - the Sun is our fixed point for measurement of this.

But our measurements into the Universe cannot be based on the same calculations as
1) we dont know whether Electromagnetic radiation behaves the same around other, much different celestial bodies (eg does the speed of light in space change in proximity of a black hole) and
2) we dont have a fixed point anywhere in the Universe to base our measurements from.

If the Sun is moving through the Universe and all the other things we are looking at are moving, we dont know what direction or speed they are moving (vector geometry without a fixed point?) and thus, what distance they are.

Before I try to hypothesise myself into oblivion, can someone tell me why I am wrong (as I think I must be or all Astronomy needs a rethink)?

Thanks.

Paul