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The original was posted on /r/todayilearned by /u/No-Maximum-9087 on 2023-06-27 09:39:39+00:00.

Original Title: TIL that until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Doust Curtis, observations by Edwin Hubble showed that the Milky Way is just one of many galaxies.