Astrophysics in the 20th Century

Hubble's Discoveries:

Edwin Hubble (1889-1953) is a central figure in the development of observational cosmology. From 1922 to 1936 Hubble solved four of the central problems in cosmology.

From 1922 to 1925 Hubble devised a classification system for galaxies by grouping them according to their content, distance, shape, size, and brightness. The galaxy classification system had become the Hubble morphological (The study of form, structure and the like. ) sequence of galaxy types. Previous to this, no satisfactory system existed, thus Hubble's powerful, yet simple scheme was an incredibly important scientific achievement.

 By his discovery of Cepheids in 1924 and with parallel work in M33 and M31, Hubble proved decisively that these stars are outside of our galaxy. Thus bringing to a close the debate of whether there are other galaxies in the Universe beyond the Milky Way.

 From 1926 to 1936 Hubble spent studying the distribution of galaxies and...