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The Renaissance of General Relativity and Cosmology Published online by Cambridge University Press: 15 December 2009
Galaxies are the building blocks of the Universe, and most of what we know about them has been discovered since Dennis Sciama became a research student. In the space available to me it is not possible to cover even in outline all significant developments during this period. So I have tried to concentrate on what seem to me to be the most important themes. My choice must surely be heavily influenced by personal taste and experience; I hope only that my prejudices are not too glaringly evident.
THE STRUCTURE OF THE MILKY WAY
Galactic astronomy in the 1950s was dominated by the discovery (Ewen & Purcell, 1951) of the 21 cm line predicted by H. C. van der Hulst in 1944. This made it possible for the first time to study the large-scale kinematics of the Milky Way. For the most part the 21 cm observations confirmed the picture of a disk in differential rotation developed by Oort more than twenty years before. However, there were surprises — most notably the discovery that the disk is warped rather than being perfectly flat (Burke, 1957; Kerr, 1957).
Extinction of stars by dust had first betrayed the existence of the interstellar medium (Trumpler 1930).
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