Observability of parameters Strictly speaking, neither nor in the formula are directly observable, because they are properties of a galaxy, whereas our observations refer to the galaxy in the past, at the time that the light we currently see left it.
obseRvabILItY Of paramEteRs STrIctLy sPeaKIng, NeITher noR in thE formulA are dIreCtlY obServable, becAUsE ThEy arE prOPeRties of a gaLaxY, WherEas OuR OBseRvAtions RefEr to tHe Galaxy in tHe Past, aT tHE tiMe that The lIght we CurrENtly see lEft iT.