Allan R. Sandage
Allan Sandage has defined the fields of observational cosmology and extragalactic astronomy for most of the last forty years. Modern cosmological research had its beginnings with the great work of Edwin Hubble in the 1920’s and 1930’s, which established what were then called spiral nebulae as separate distant “island universes”, i.e., galaxies. Hubble demonstrated the expansion of the universe, and laid the roots of galaxy classification still used today. Using the powerful Hale 200-inch telescope at Palomar Observatory in Southern California, Sandage continued and expanded upon Hubble’s program on a large number of fronts.
Sandage has quantified the expansion of the universe in many important ways. In particular, in close collaboration with Gustaf Tammann of the University of Basel, Switzerland, he relentlessly pursued the value of the Hubble Constant, which determines the rate of expansion, through detailed observations of galaxies. He made the essential measurements of globular cluster stars to determine their ages, and showed the correspondence with the expansion age of the universe from the Hubble Constant.
Sandage was the first to recognize the existence of quasars without strong radio emission, leading the way to the discovery of some of the most distant objects in the universe. He has thoroughly explored the observational characteristics of galaxies, their stellar populations, their clustering properties and their evolutionary history. He led the first major redshift survey of galaxies, creating a three-dimensional map of the galaxy distribution, and used it to explore the dynamics of the local Universe. He developed new observational techniques and opened new areas of inquiry in fields ranging from the pulsations of stars, to tests of cosmological models at great distances, to searches for quasars.
Sandage’s papers have set the research agenda for hundreds of astronomers in all these areas. His lifetime contribution to extragalactic astronomy and cosmology, and his influence on his colleagues, is unmatched by any other astronomer.
By Michael Strauss
Department of Astrophysical Sciences