Tue Apr 26, 2016 SHAPLEY-CURTIS DEBATE

On April 26th in the year 1920, a great debate took place concerning the earth's place in our Milky Way Galaxy. Some astronomers such as Heber Curtis thought we were at the center of our galaxy, for when you looked along the milky band of stars that defines the galactic disc, you saw roughly the same number of stars throughout. Curtis also thought that spiral nebulae were distant galaxies, like our Milky Way, but very far away. Other astronomers, notably Harlow Shapley, suggested that interstellar dust clouds blocked our view of the galactic center, and that a concentration of star clusters in the direction of the constellation Sagittarius was where the true center of the galaxy was. It turns out that our solar system is not at the center of the Milky Way, but about two-thirds of the way out, in one of its spiral arms. And those other spiral nebulas – they really are other galaxies, other island universes, far, far away.