Allen Sandage Biography

Emily Gaubatz

Mr. Percival

Astronomy

21 May 2012

Allen Sandage

            Sandage graduated from the University of Illinois in 1948 and got a PhD from Caltech in 1953. He was one of the first in that university to graduate from the astronomy program. Walter Baade was his teacher. Sandage worked at Mount Wilson with Hubble.

In 1950 Baade had discovered that Hubble’s estimate of the distance to the Andromeda Galaxy, 700,000 light years, was half too small, based on the identification of Cepheid variables in Andromeda. After Hubble passed away in 1953, Sandage continued his research. In 1958 he won the American Astronomical Society’s Warner Prize for outstanding achievement. He studied the physics and evolution of stars, allowing him to develop a method for aging stars that have left the main sequence of the Hertzsprung–Russell diagram. At the award ceremony for the Warner prize he released his latest work. He had recalculated Hubble’s measurements using the Hale telescope and found several miscalculations in the distance to other galaxies. Hubble had misidentified several objects in distant galaxies as supergiant stars, when really they were globular clusters, because of this Hubble’s distance guage was off. The Andromeda Galaxy was actually million light years away. The Virgo Cluster was also discovered to be fifty million light years away, not seven million.

Sandage’s findings changed the universe. He made it bigger. Sandage helped prove how large the universe is and pointed out that it was expanding.

Sandage came up with a new Hubble’s constant for universe expansion at 75 kilometers per second per megaparsec. Today’s best measurement is 71 kilometers per second per megaparsec, very close to Sandage’s estimate. From this constant he estimated the universe to be around 15 billion years old, close to today’s 13.7 billion years.

Later Sandage worked with the Hubble Space Telescope and discovered sunburst activity and black hole jets in the galaxy M82. He published the Hubble Atlas of Galaxies in 1961. He published over 500 scientific papers in his life. His last one was on RR Lyrae variable stars.