Excerpt:
Hubble's role. This year marks the centennial of the birth of Edwin Hubble. There can be no doubt that future historians, writing about the scientific advances of this age will describe the 20th century as epoch-changing in giving us the first correct view of how the universe is organized. The principal cosmological problem of discovering the large scale content of the universe was solved observationally between 1920 and 1936. Hubble was a major figure in this development. Knowledge that galaxies mark the space and provide the means to measure it was gained by the first convincing analysis of new data on the nature of the nebulae - knowledge that came directly from the sky rather than by dialectic discussion or revelation.