The Period-Luminosity Relationship
					• Relationship discovered by Henrietta Leavitt in 1912 – stars in Small Magellanic Cloud – all at roughly same distance – but didn’t have absolute M, just apparent M – need absolute M to get distances • Calibrated by Harlow Shapley – If you can find distance (so M-m) for just one nearby Cepheid, you can convert Leavitt’s “m” scale to the “M” you want.