Is the expansion rate slowing?
		• Look “into the past” to see if expansion rate was faster in early history. • To “look into the past”  look very far away: – Find “Ho” for very distant objects, compare that to “Ho” for closer objects • Remember – we found Ho by plotting velocity (vr) vs. distance – We found velocity vr from the red shift (z) – We found distance by measuring apparent magnitude (mv) of known brightness objects – We can test for changing Ho by measuring mv vs. z