Sorry about the delay, I didn't notice the reply initially. > I don't understand why you started with z = 0.076 and then calculated proper distance at z=0.078.

Sorry about the delay, I didn't notice the reply initially. > I don't understand why you started with z = 0.076 and then calculated proper distance at z=0.078. I also don't know what (a=0.928) there stands for a here is the FLRW scale factor: https://www.wikiwand.com/en/Scale_factor_(cosmology) https://www.wikiwand.com/en/Scale_factor_(cosmology) The two proper distances can be thought of as, for the larger, what a notional instantaneous (>> FTL) analogue of radar measurement would decide the distance to the galaxy we are observing is, and for the smaller, what we would read if we had optical telescopes that could read the display of such a measurement device showing a counterpart in the distant galaxy what the instantaneous distance to us is. (Or instead of an instant FTL analogue of radar, you could use a pair extremely long measuring tapes with the 0 end anchored on the observed party; if we look at a telescope at their tape's indicator, it would read 969.4 Mly, but looking at our own tape would read 1043 Mly.) The numbers are close because ~1 Gly is near enough that the metric expansion of space hasn't carried our galaxy cluster and theirs very far apart in the past billion years. They would see similar numbers looking at a galaxy at z=0.076 in a different part of their sky than where the Milky Way is; we would see a different and almost certainly higher redshift when looking at that galaxy from here.