Astrophysics (Index)About

Great Debate

(Shapley-Curtis Debate, Curtis-Shapley Debate)
(historical debate regarding the nature of galaxies)

The Great Debate (or Shapley-Curtis Debate or Curtis-Shapley Debate) was an event held in 1920, with two astronomers, Heber Curtis and Harlow Shapley debating the size of the universe, in particular, the nature of galaxies, whether they are distant objects made up of stars versus whether they were closer objects relatively close to the known expanse of stars (the Milky Way).

At the debate, a reported observation of visible rotation of the Pinwheel Galaxy seemed to constitute proof of the latter view as visible rotation of a distant, large object is untenable, implying velocities beyond the speed of light. Edwin Hubble's collection and presentation of the evidence based on observations was key in settling the matter some time after the debate, observing that other measures of distances to galaxies (using their maximally-bright stars, and using Cepheid variables) generally correspond to their redshift, suggesting that the further away the galaxies are, the faster their radial velocity away from us, and at speeds that preclude them remaining as close as was supposed.

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Referenced by page:
Kapteyn universe