Shapley, Curtis and Hubble  About a hundred years ago,
astronomers were becoming increasingly divided over the nature
of the "nebulae." The nebulae were fuzzy patches of light --
some smooth and featureless and some spiral in form -- that were
scattered around the sky. Many astronomers thought that the
nebulae were clouds of gas or star-forming regions distributed
within the Milky Way, similar to the Orion Nebula. Others
thought that they might be "island universes," or vast
collections of stars located far beyond the boundaries of the
Milky Way.  In April 1920, the National Academy of Sciences held
a debate in Washington, D.C. Harvard astronomer Harlow Shapley
argued that the nebulae were nearby objects located in the Milky
Way. The spiral forms were presumed to represent the swirling
material of a star-forming region. By identifying Cepheid
variable stars within the globular clusters -- and using the
period-luminosity relation to estimate their intrinsic
brightness -- Shapley was able to measure distances t