I have been sitting here thinking about that and doodling a bit. You are correct. There are no absolute distances. However, we can make useful distance measurements by assuming that the local FR is absolute. This trick of course only works if we use it for large enough distances and small enough differential velocity so that the relativistic dilation is negligible. So we can measure the 10 LY distance to Astra with enough confidence to use it in making all our measurements from Earth. The distance will vary in response to a whole lot of different variables, but the variation produced by those disturbances is still negligible.
Of course now I wonder if the relativistic dilation would affect our trajectory. Could we go straight there and then reverse the trajectory and come straight back? Or would our trajectory need to be adjusted?
Bill Gill
