RR Lyrae
Beginning in 1914, Harlow Shapley began a series of studies of globular clusters, published across about 40 scientific papers. He examined the clusters' RR Lyrae variables—stars which he assumed were Cepheid variables—and used their luminosity and period of variability to estimate the distances to the clusters. It was later found that RR Lyrae variables are fainter than Cepheid variables, causing Shapley to overestimate the distances.