Great Debate
astronomy debate held on 26 April 1920 at the Smithsonian Museum of Natural History between Harlow Shapley and Heber Curtis about whether spiral nebulae were different galaxies or part of the Milky Way
en-US/ˈɡɹeɪt dɪˈbeɪt/
en-GB/ˈɡɹeɪt dɪˈbeɪt/