George Hale hosted a series of lectures about the scale of the Universe.
The Kapteyn universe is all there is, and it is relatively small, with the sun close to the center. Shapley's universe is also all there is, but it is immense: remember, I used his term "the big galaxy."
Heber Curtis (Lick Observatory):
-spiral nebulae were separate galaxies
-believed in the Kapteyn Universe (small galaxies in a big universe)
-edge-on spirals look like the Milky Way
-other galaxies have solar spectra
-supernovae in other galaxies are similar to ours, but further from us
-slipher's spiral velocities
-Shapley's calibration curve was wrong
Harlow Shapley (Mt Wilson):
-spirals are part of the Milky Way, which is huge
-the objects in the spirals are in motion (Adriaan von Maanan)
-- the spirals could not be separate, distant, island universes and had to be part of our own galaxy. Nobody has ever discovered just how van Maanan managed to mis-measure the photographs.
Great Debate was a draw, and not resolved until 1923.