Length measure in Astronomy

In cosmology, we have a couple of different length measures. Among them, comoving and proper distnlances seem to be good fit to real world use cases in astronomy.

So my quesion is which length measure are we using in astronomy? For instance, when we say a certain galaxy is # light yrs distant from the Earth, what does it actually mean?

Thanks!

• In astronomy it seems to me that we intend proper distances. When the objects are too far the only sensible value is z. The rest comes from the model and parameters used. – Alchimista Aug 31 at 10:38

By making observations we can determine the luminosity distance of an object $$d_L$$. And the $$d_L$$ is related to the transvverse comoving distance $$r$$ via $$d_L = r(1+z)$$ For flat universe $$r = c\int_0^z dz/H(z)$$