ARlogo Annu. Rev. Astron. Astrophys. 1999. 37: 445-486
Copyright © 1999 by Annual Reviews. All rights reserved

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Today astronomy and astrophysics is vastly different than it was in 1950. Although at that time much of the astrophysics of the stars was known through the spectacular advances in the basic physics (reviews by Stromgren 1951, Chandrasekhar 1951), little was yet understood about origins or evolution or the grand synthesis involving stars and galaxies that dominates the current climate. In that period the emphasis was on physical processes (see Aller 1956, Osterbrock 1974 for reviews of the physics of gaseous nebulae following Menzel, Aller, Goldberg, and Baker in the 1940s), classification systems, absolute magnitude calibrations (cf. Adams et al 1935 for the HR diagram), and surveys for the extant types of astronomical objects. Furthermore, observational cosmology had only just begun with galaxy classification, proof that galaxies and their distribution form the last great hierarchy in the organization of matter, and that the expansion exists (Hubble 1925, 1926a, 1926b, 1929a, 1929b, 1934, 1936a, 1936b, 1936c; cf. Sandage 1998b).

All this was the prelude to the 50 years that has now just ended. The tremendous change that we have witnessed can only be compared with the paradigm shift in geology and biology in the Darwinian era of the 1850s and the developments in relativity and quantum physics from 1900 to 1940. Astronomy's turn has been the last half century.

Of course, Mount Wilson and Palomar were not the only places where the first great advances into the new astronomy would take place, but the Observatories did have an enormous advantage in the first twenty years of Palomar. Radio astronomy hardly existed in 1950 and X-ray astronomy was not to be for 15 years. The first orbiting Astronomical Observatories (OAOs) were not operational until 1969. Computers had just been invented using von Neumann's concepts of stored programs.

In addition, most of today's large telescopes did not exist before approximately 1970. Those in existence before 1970 were not highly productive until after the 1960s. Hence, in 1950, Mount Wilson, Palomar, Lick, and Yerkes and McDonald were still the major centers of observational astronomy and astrophysics in America, with Radcliffe (Pretoria) and Stromlo just beginning in the southern hemisphere.

In this review I cannot cover even a fair fraction of the research done in the past half century, either at Palomar or worldwide. This account is necessarily highly restricted to stellar evolution, observational cosmology, and the beginnings of high energy astrophysics. It is primarily a retrospective on the programs set for the Palomar telescopes by Baade and Hubble 50 years ago.

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