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Walter Baade
Walter-Baade Astronom.jpg
Born (1893-03-24)March 24, 1893
Schröttinghausen, German Empire
Died June 25, 1960(1960-06-25) (aged 67)
Nationality German
Citizenship German
Alma mater University of Göttingen
Known for Coined the term "supernova" and "neutron star" with Fritz Zwicky
Awards Bruce Medal 1955
Scientific career
Fields Astronomy
Institutions Hamburg-Bergedorf Observatory, Mt. Wilson, Palomar Observatory
Doctoral students Halton Arp
Allan Sandage

Wilhelm Heinrich Walter Baade (March 24, 1893 – June 25, 1960) was a German astronomer who worked in the United States from 1931 to 1959.


Son of a teacher, Baade finished school in 1912. He then studied maths, physics and astronomy at the universities of Münster and Göttingen. After receiving his PhD in 1919, Baade worked at Hamburg Observatory at Bergedorf from 1919 to 1931. There in 1920 he discovered 944 Hidalgo, the first of a class of minor planets now called Centaurs which cross the orbits of giant planets.

He worked at Mount Wilson Observatory from 1931 to 1958. There, during World War II, he took advantage of wartime blackout conditions (which reduced light pollution), to resolve stars in the center of the Andromeda Galaxy for the first time. These observations led him to define distinct "populations" for stars (Population I and Population II). The same observations led him to discover that there are two types of Cepheid variable stars. Using this discovery he recalculated the size of the known universe, doubling the previous calculation made by Hubble in 1929. He announced this finding to considerable astonishment at the 1952 meeting of the International Astronomical Union in Rome.

Together with Fritz Zwicky, he identified supernovae as a new category of astronomical objects. Zwicky and he also proposed the existence of neutron stars, and suggested supernovae might create them.

Beginning in 1952, he and Rudolph Minkowski identified the optical counterparts of various radio sources, including Cygnus A. He discovered 10 asteroids, including 944 Hidalgo, which has a long orbital period, and the Apollo-class 1566 Icarus, the perihelion of which is closer than that of Mercury, and the Amor-type 1036 Ganymed.


Asteroids discovered: 10 
930 Westphalia March 10, 1920
934 Thüringia 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 Pöllath January 14, 1948


  • Foreign membership of the Royal Netherlands Academy of Arts and Sciences (1953)
  • 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
  • The crater Baade on the Moon
  • Vallis Baade, a vallis (valley) on the Moon
  • One of the two Magellan telescopes
  • The asteroid 966 Muschi, after his wife's nickname
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