Question: when were galaxies discovered to be large separate structures in the universe
Answer: 1918 -- Harlow Shapley demonstrates that globular clusters are arranged in a spheroid or halo whose center is not the Earth , and decides , correctly , that its center is the Galactic Center of the galaxy , 26 April 1920 -- Harlow Shapley and Heber Curtis debate whether or not the Andromeda Nebula is within the Milky Way , 1923 -- Edwin Hubble resolves the Shapley -- Curtis debate by finding Cepheids in the Andromeda Galaxy 1930 -- Robert Trumpler uses open cluster observations to quantify the absorption of light by interstellar dust in the galactic plane ; this absorption had plagued earlier models of the Milky Way , 1932 -- Karl Guthe Jansky discovers radio noise from the center of the Milky Way , 1933 -- Fritz Zwicky applies the virial theorem to the Coma Cluster and obtains evidence for unseen mass , 1936 -- Edwin Hubble intro