What was the central question addressed by the Great Debate of 1920?

Answer

Whether faint spiral nebulae were nearby collections of stars within the Milky Way or separate 'island universes' far away.

The Great Debate centered on the true nature and scale of spiral nebulae—whether they were relatively close components of our own galaxy or massive, independent star systems located at great distances.

What was the central question addressed by the Great Debate of 1920?
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