<Li> 1785--William Herschel carried the first attempt to describe the shape of the Milky Way and the position of the Sun in it by carefully counting the number of stars in different regions of the sky . He produced a diagram of the shape of the galaxy with the solar system close to the center . </Li> <Li> 1845--Lord Rosse discovers a nebula with a distinct spiral shape </Li> <Ul> <Li> 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, </Li> <Li> 26 April 1920--Harlow Shapley and Heber Curtis debate whether or not the Andromeda Nebula is within the Milky Way, </Li> <Li> 1923--Edwin Hubble resolves the Shapley--Curtis debate by finding Cepheids in the Andromeda Galaxy </Li> <Li> 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, </Li> <Li> 1932--Karl Guthe Jansky discovers radio noise from the center of the Milky Way, </Li> <Li> 1933--Fritz Zwicky applies the virial theorem to the Coma Cluster and obtains evidence for unseen mass, </Li> <Li> 1936--Edwin Hubble introduces the spiral, barred spiral, elliptical, and irregular galaxy classifications, </Li> <Li> 1939--Grote Reber discovers the radio source Cygnus A, </Li> <Li> 1943--Carl Keenan Seyfert identifies six spiral galaxies with unusually broad emission lines, named Seyfert galaxies, </Li> <Li> 1949--J.G. Bolton, G.J. Stanley, and O.B. Slee identify NGC 4486 (M87) and NGC 5128 as extragalactic radio sources, </Li> </Ul> <Li> 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, </Li>

When were galaxies discovered to be large separate structures in the universe