Wilhelm Heinrich Walter Baade (March 24, 1893 - June 25, 1960) was a German astronomer who immigrated to the USA in 1931.
Along with Fritz Zwicky, he proposed that supernovas 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, and identified the Crab Nebula as the remnant of the supernova of the year 1054, and 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.
He won the Bruce Medal in 1955, and the Henry Norris Russell Lectureship of the American Astronomical Society in 1958.
Walter Baade: A Life in Astrophysics, Donald E. Osterbrock, ISBN 0-691-04936-X
Asteroids discovered: 10 930 Westphalia March 10, 1920
934 Thuringia August 15, 1920
944 Hidalgo October 31, 1920
966 Muschi November 9 1921
967 Helionape November 9 1921
1036 Ganymed October 23, 1924
1103 Sequoia November 9 1928
1566 Icarus June 27, 1949
5656 Oldfield October 8 1920
7448 1948 AA January 14, 1948