Walter Baade

German astronomer who discovered stellar populations and significantly refined the cosmic distance scale. His work with Fritz Zwicky led to the prediction of neutron stars.

Biography

Born in 1893 in Schröttinghausen, Germany. He studied at the University of Göttingen, receiving his doctorate in 1919. He worked at the Hamburg Observatory, then emigrated to the USA in 1931 and began working at the Mount Wilson Observatory. During the war, he was a German citizen, which restricted his movements but allowed him to observe extensively during blackouts. It was then that he discovered stellar populations. Later he worked at the Palomar Observatory. He received the Catherine Bruce Medal and other awards.

Key discoveries

The concept of two stellar populations (I and II) in 1944
which explained differences in stellar composition and galaxy evolution
revision of the distance to the Andromeda Galaxy
which doubled the size of the known Universe
together with Zwicky, proposed the neutron star hypothesis in 1934
development of the Baade-Wesselink method for determining the radii of variable stars.

💡 During World War II, Baade observed stars at night in blacked-out Los Angeles, which allowed him to resolve the central part of the Andromeda Galaxy into stars for the first time. He meticulously verified every hypothesis and once said that he triple-checked his calculations before believing in the doubling of the size of the Universe.

Quote: "Stars are like people: they are born, age, and die, but through them we can read the history of the entire Galaxy."

Biography

Key discoveries

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