Walter Baade

Walter Baade , 1893-1960, German-born American astronomer. From 1919 to 1931 he was on the staff of the Hamburg observatory; from 1931 to 1958, at the Mt. Wilson observatory. Baade studied the Andromeda Galaxy, M31, and other spiral galaxies and presented evidence for the existence of two different stellar populations , the younger Population I, and the older Population II. From these data he inferred that similar spiral patterns could be found in the Milky Way. Perhaps his most important contribution came in 1952 from observations of Cepheid variables in nearby galaxies through the 200-in. reflecting telescope at the Palomar Observatory; he calculated that it was necessary to double the cosmic-distance scale, i.e., the distances between external galaxies and the Milky Way . With Fritz Zwicky and Rudolf Minkowski he distinguished two types of supernova based on their spectra and on their maximum absolute magnitudes. In 1949 he discovered Icarus, an asteroid whose orbit takes it close to Earth.

Bibliography: See W. Baade, Evolution of Stars and Galaxies (1963).

Baade, Walter (1893–1960) US astronomer, b. Germany. From Mount Wilson Observatory, in the 1943 wartime blackout, he observed individual stars in the Andromeda Galaxy and distinguished the younger, bluer Population I stars from the older, redder Population II stars. He went on to improve the use of Cepheid variable stars as distance indicators, and showed that the universe was older and larger than had been thought.

Baade, Walter( Wilhelm Heinrich Baade) (1893–1960)German‐Americanastronomer. In 1944 he identified two different populations of stars in the Galaxy, and found that both contained Cepheid variables. Moreover, each population of Cepheids had its own period–luminosity law. In 1952 he began to search for Cepheids in the Andromeda Galaxy, M31, but found none, even though they should have been luminous enough to be visible; he reasoned that M31 was over twice as distant as had been thought, which made the Universe both larger and older than had been believed. Baade collaborated with R. L. B.Minkowski on identifying radio sources, and with Minkowski and F.Zwicky on supernovae. He also discovered ten asteroids, including Hidalgo and Icarus.