I use the word characterise because it means more than just measure, which illustrates my central thesis in this discussion: we know very little. It's probable IMHO that we grossly misunderstand cosmology in very fundamental ways today, and the measurements we make may well be wildly inaccurate as a result. Understanding the character of light is what makes it possible for us to measure interstellar distances, because we seem to have grasped the concept of spectral shift (redshift, the Doppler effect). However I have read arguments that point out flaws with our characterization of light and redshift, which involve gravity and may have merit. Characterization is more fundamental understanding which enables measurement, and that's why I use that word in this context.

I dunno. I'm not a physicist, and can't do that math. All I do know is that we sure as hell don't have it nailed down to settled science. There's a plethora of cosmological theories rational expert physicists wrangle over today, which supports my thesis. What we have learned seems like a lot, but we're tiny motes of obscene glop incapable of really grasping even the scale of what there is to know. Worse, a lot of what we think we know for sure just isn't so at all, and we're afflicted with hubris as a species, which Mark Twain noted makes it a lot easier to fool us than to convince us we've been fooled.

The difference between Newton and Einstein well illustrates the dilemma of science. Newton proved he was absolutely right, and folks were convinced his characterization of physics was settled science for centuries, but he was completely wrong in his understanding - although his measurements are still today considered close enough for government work.