1920 waxaa loo magacaabay madaxa Allegheny Observatory. Isla sanadkaas waxa uu ka qeyb galay dooddii weynayd
Harlow Shapley (oo sidoo kale loo yaqaano Shapley <unk> Curtis Debate) oo ku saabsan dabeecadda nebulae iyo galaxies, iyo cabirka caalamka. Curtis wuxuu taageeray aragtida hada la aqbalo ee ah in galaxyada kale ay jiraan marka laga reebo Milky Way.