Dee ihe na-esote paragraf a - N'afọ 1920 arụmụka weere ọnọdụ n'etiti Harlow Shapley na Heber Curtis (The Great Debate
), banyere ọdịdị nke Milky Way, nebulae spiral, na akụkụ nke eluigwe na ala. Iji kwado ihe o kwuru nke bụ́ na Nnukwu Igwe ojii Andromeda bụ ụyọkọ kpakpando dị n'èzí, Curtis kwuru na e nwere ụzọ ndị gbara ọchịchịrị yiri ígwé ojii ájá nke Milky Way, nakwa na e nwere nnukwu mgbanwe Doppler.