Sandage was one of the most influential astronomers of the 20th century. He was born in
Iowa City, Iowa, United States. He graduated from the
University of Illinois in 1948. In 1953 he received a
PhD from the
California Institute of Technology; the
German-born Wilson Observatory-based astronomer
Walter Baade was his advisor. During this time Sandage was a graduate student assistant to cosmologist
Edwin Hubble. He continued Hubble's research program after Hubble died in 1953. In 1952 Baade surprised his fellow astronomers by announcing (at the 1952 Conference of the
International Astronomical Union, in Rome) his determination of two separate populations of
Cepheid variable stars in the
Andromeda Galaxy, resulted in a doubling of the estimated
age of the universe (from 1.8 to 3.6 billion years). Hubble had posited the earlier value; he had considered only the weaker Population II Cepheid variables as
standard candles. After Baade's pronouncements, Sandage showed that astronomers' previous assumption, that the brightest stars in galaxies were of approximately equal inherent intensity, was mistaken in the case of
H II regions which he found not to be stars and inherently brighter than the brightest stars in distant galaxies. This resulted in another 1.5-fold increase in the calculated age of the universe, to approximately 5.5 billion years. Throughout the 1950s and well into the 1980s Sandage was regarded as the pre-eminent observational
cosmologist, making contributions to all aspects of the cosmological distance scale, ranging from calibrators within our own
Milky Way Galaxy, to cosmologically distant galaxies. Sandage began working at the
Palomar Observatory. In 1958 he published the first good estimate for the
Hubble constant, revising Hubble's value of 250 down to 75 km/s/Mpc, which is close to today's accepted value. Later he became the chief advocate of an even lower value, around 50, corresponding to a
Hubble age of around 20 billion years. At the time, many, especially Sandage, believed that the
cosmological constant was zero. In such a case, a low Hubble constant is necessary in order for the age of the universe (as opposed to the
Hubble age) to be at least as old as the oldest objects it contains, i.e. ca. 14 billion years. Sandage performed photometric studies of
globular clusters, and calculated their age to be at least 25 billion years. This led him to speculate that the universe did not merely expand, but actually expanded and contracted with a period of 80 billion years. The current cosmological estimates of the age of the universe, in contrast, are typically of the order of 14 billion years. As part of his studies concerning the formation of galaxies in the early universe, he co-wrote the paper now referred to as ELS after the authors
Olin J. Eggen,
Donald Lynden-Bell and Sandage, first describing the collapse of a proto-galactic gas cloud into our present Milky Way Galaxy. He later defended the paper in 1990. In his 1961 paper "The Ability of the 200-inch Telescope to Discriminate Between Selected World Models," he suggested that the future of observational cosmology would be the search for two parameters: the
Hubble constant H0 and the
deceleration parameter q0. This paper influenced observational cosmology for at least three decades as it carefully specified the types of observational tests that could be performed with a large telescope. He also published two atlases of galaxies, in 1961 and 1981, based on the
Hubble classification scheme. In 1962 Sandage studied the possibility of directly measuring the temporal variation of the redshift of extra-galactic sources. This analysis became known as the "Sandage–Loeb test". Sandage discovered jets erupting from the core of the so-called
Cigar Galaxy. These must have been caused by massive explosions in the core, and they have apparently been occurring for at least 1.5 million years. Sandage was a prolific researcher; during his career he published more than 500 papers. Until his death he continued to be an active researcher at the
Carnegie Observatories, still publishing several papers a year. ==Personal life==