Reading Nature, Observing Science: Examining Material Practices in the Lick Observatory Archives and Kenneth S. Norris Papers

Note about the term "nebula"

Astronomers did not yet understand the size of the universe--they thought the Milky way comprised most of the universe; accordingly, they could not differentiate between nebulae and galaxies. In other words, most astronomers believed that structures like the Andromeda Galaxy or Whirlpool Galaxy were part of the Milky Way, and of the same nature as structures like the Orion nebula or Horsehead nebula. In the early years of the 20th century, some astronomers began to argue that some of these objects were "island universes" outside of the Milky Way; this was known as the "Great Debate." As the Lick Observatory astronomers continued to take measurements and photographs of these objects, they eventually helped to confirm that these "island universes" are in fact galaxies in themselves. 

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