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The
Shapley-Curtis Debate: 1920
•Are
spiral nebulae really other galaxies, or just swirling clouds of gas and dust within our own galaxy?
•Many
spiral galaxies had much larger radial velocities than other objects within our own galaxy
•Answered by new observations:
•In 1923/4 Edwin Hubble photographed and identified
Cepheids in the Andromeda
Galaxy:
–Distance to Cepheids cleared showed Andromeda was
outside our own galaxy
