Hubble Sees Andromeda: Universe Expands Beyond the Milky Way
Edwin Hubble presented evidence on November 23, 1924, that the Andromeda 'nebula' was actually a separate galaxy far outside the Milky Way, instantly expanding the known universe from one galaxy to billions. Using the 100-inch Hooker telescope at Mount Wilson Observatory, Hubble identified Cepheid variable stars in Andromeda and calculated their distance at roughly 900,000 light-years, well beyond the Milky Way's boundaries. The prevailing scientific consensus, championed by Harlow Shapley, held that the universe consisted entirely of the Milky Way. Hubble demolished it with a photograph. His measurement was actually too low; Andromeda is 2.5 million light-years away. But the fundamental insight was correct: the universe contains hundreds of billions of galaxies, and we occupy an unremarkable corner of one of them.
November 23, 1924
102 years ago
Key Figures & Places
What Else Happened on November 23
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