Astrophysics (index)

Great Debate

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

The Great 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).

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. Edwin Hubble later settled the matter by observing that the dimness of galaxies generally corresponds 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 sufficiently close.