Along with Fritz Zwicky, he proposed that supernovae could create neutron stars.
He took advantage of wartime blackout conditions during World War II, which reduced light pollution at Mount Wilson Observatory, to resolve stars in the center of the Andromeda galaxy for the first time, which led him to define distinct "populations" for stars (Population I and Population II).
He discovered that there are two types of Cepheid variable stars, together with Fritz Zwicky identified supernovae as a new category of astronomical objects (W. Baade, F. Zwicky, 1934, "On Super-Novae". Proceedings of the National Academy of Sciences of the United States of America, 254-259.) and proposed the existence of neutron stars. He also identified the optical counterparts of various radio sources.
He discovered 10 asteroids, including notably 944 Hidalgo (long orbital period) and the Apollo-class asteroid 1566 Icarus (whose perihelion is closer than that of Mercury) and the Amor asteroid 1036 Ganymed.
* Gold Medal of the Royal Astronomical Society (1954)
* Bruce Medal (1955)
* Henry Norris Russell Lectureship of the American Astronomical Society (1958)
Named after him
* Asteroid 1501 Baade
* Baade crater on the Moon
* Vallis Baade, a vallis (valley) on the Moon
* One of the two Magellan telescopes
* Baade's Window, an area relatively free of dust near the Galactic Center in Sagittarius
* The asteroid 966 Muschi
* Osterbrock, Donald E.. Walter Baade: A Life in Astrophysics. ISBN 0-691-04936-X.
* Dieke, Sally H. (1970). "Baade, Wilhelm Heinrich Walter". Dictionary of Scientific Biography 1. New York: Charles Scribner's Sons. 352-354. ISBN 0684101149.
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