Dee ihe na-esote paragraf a - N'afọ 1920 a họpụtara ya onye nduzi nke Allegheny Observatory. N'otu afọ ahụ o sonyere na Great Debate
na Harlow Shapley (nke a na-akpọkwa Shapley <unk> Curtis Debate) banyere ọdịdị nke nebulae na ụyọkọ kpakpando, na nha nke eluigwe na ala. Curtis kwadoro echiche a na-anakwere ugbu a na e nwere ụyọkọ kpakpando ndị ọzọ ma e wezụga Milky Way.