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