The Andromeda nebula was studied using a 100-inch telescope and ordinary stars were identified within it. Although Hubble's estimate that Andromeda was 750,000 ly away turned out to be an underestimate, it was still far enough to be well outside our galaxy. The general structure of the Universe came to be understood, and it was far greater than previously thought.
A visual chronology of Asimov's ~1500 scientific inventions and discoveries.
