Mezue ahịrịokwu na-esonụ: N'afọ 1920 a họpụtara ya ịbụ onye nduzi nke Allegheny Observatory. N'otu afọ ahụ, o sonyere na
Nnukwu arụmụka na Harlow Shapley (nke a na-akpọkwa Shapley <unk> Curtis Debate) banyere ọdịdị nke nebulae na ụyọkọ kpakpando, na oke nke eluigwe na ụwa. Curtis kwadoro echiche a na-anakwere ugbu a na e nwere ụyọkọ kpakpando ndị ọzọ ma e wezụga Milky Way.