Baade, Wilhelm Heinrich Walter

(b. Schröttinghausen, Westphalia, Germany, 24 March 1893; d. Bad Salzuflen, Westphalia, Germany, 25 June 1960)

astronomy.

Baade’s father, Konrad, was a schoolteacher; he and his wife, Charlotte Wulfhorst, were Protestants and planned a career in theology for their son. But at the Friedrichs-Gymnasium in Herford, which he attended from 1903 to 1912, Baade decided that astronomy appealed to him more than the church: his choice resulted in a lifetime devoted to telescopic observations that have seldom been equaled, either in technical skill or in theoretical significance.

From the Gymnasium, Baade went briefly to the University of Münster, transferring to Göttingen in the Easter term of 1913. There he remained as a student throughout World War I, gaining competence in the observatory under Leopold Ambronn and serving for three years as assistant to the famous mathematician Felix Klein. Because of his congenitally dislocated hip, Baade was exempt from active military service, but beginning in 1917 had to spend eight hours a day on war work, in an installation for testing airplane models.

Shortly after passing his doctoral examination in July 1919, Baade became scientific assistant to Richard Schorr, director of the University of Hamburg’s observatory at Bergedorf, located about ten miles southeast of the city. His main interest was in astrophysical problems—as shown by his dissertation, written under Johannes Hartmann, on the spectroscopic binary star β Lyrare (1921)—but his job required him to confirm the positions of many comets and asteroids. This he did conscientiously, soon discovering a comet of his own (1923) and providing an explanation for the shape of comets’ tails, published in 1927 with the first of a series of distinguished collaborators—the theoretical physicist Wolfgang Pauli, who was then a Privatdozent at Hamburg. Baade also discovered two remarkable asteroids (1920, 1949): (944) Hidalgo, which recedes farther from the sun than any other asteroid, and (1566) Icarus, noted for its close approaches both to the sun and to the earth, having passed within 4,000,000 miles of us as recently as 14 June 1968.

A meeting with Harlow Shapley in 1920 aroused Baade’s interest in globular star clusters and the pulsating variables they contain. Despite the relatively small size of his telescope, Baade began observing them and in 1926 suggested a way to prove that the radiating surface of such variable stars actually rises and falls. That same year a Rockefeller fellowship enabled him to realize his dream of visiting the big telescopes in California.

Returning to Bergedorf in 1927, Baade was promoted to observer, but got no action on his plea that their 39-inch telescope be moved to a more favorable site. He turned down a job offered him at Jena, because it provided even less in the way of good observing facilities, and became a Privatdozent at Hamburg in 1928. The following year he married Johanna Bohlmann and went to the Philippine Islands to observe a total solar eclipse on 9 May. Clouds covered the sun during the crucial time, but the long sea voyage served to cement his friendship with the Estonian Bernard Voldemar Schmidt. who at Baadeʿs urging designed the optical system used in the Schmidt wide-angle telescopes.

The year 1931 brought Baade an invitation to join the staff at Mt. Wilson Observatory near Pasadena. California; he accepted immediately, resigning his position at Hamburg and moving to the clearer skies and larger instruments in California as to the Promised Land. When his friend Rudolf Minkowski was forced to resign his professorship at Hamburg in 1933, Baade helped him to emigrate, thus enabling the two men to continue in California an already productive collaboration.

Now that Baade had realized his dream of working with the best telescopes in the world, he made the most of it. With Minkowski he continued spectroscopic work begun in Germany (1937), and with Edwin Powell Hubble he studied distant galaxies (1938). His work with Fritz Zwicky on supernovae (1938) led to papers on the Crab Nebula (1942) and on Nova Ophiuchi 1604 (1943).

When the United States entered World War II, Baade was classified as an enemy alien, but this favored rather than hampered his astronomical career: with many astronomers engaged in war work, and the lights of Los Angeles dimmed to protect coastal shipping, Baade had increased access to the telescopes and the added advantage of darker skies. Under these favorable circumstances he was able to photograph stars in the hitherto unresolved inner portions of the Andromeda galaxy, M31, and in both of its satellite galaxies, M32 and NGC205 (1944). This achievement was both technically difficult—thought, indeed to be unattainable with the 100-inch telescope he used—and theoretically significant, because the brightest stars in the nucleus of M31 turned out to be red—not blue, as in the surrounding spiral arms. Baade realized he was dealing with two different stellar populations, which he called Type I (found in dusty regions, brightest stars blue) and Type II (found in dust-free regions, brightest stars red).

At a ceremony dedicating the 200-inch Palomar telescope on 1 July 1948, Baade outlined the ways he thought this great new instrument should be used to explore the universe. He suggested that since distance measurements depend critically on a reliable standard sequence of stellar magnitudes, the first thing to do was to replace the North Polar Sequence with a better one based on photoelectric techniques. His concern with distance criteria soon had spectacular results in another way, when he looked for cluster-type variables in the Andromeda galaxy. At the accepted distance of 750,000 light-years, these stars should have appeared in photographs taken with the 200-inch telescope; when they did not, Baade reasoned correctly that the galaxy was more distant than had previously been thought. Announced in 1952 at the Rome meeting of the International Astronomical Union, this conclusion cleared up several inconsistencies, but also essentially doubled the size of the universe. At a symposium on stellar evolution held during that same meeting, Baade presented colormagnitude diagrams for star clusters that his young collaborators Halton C. Arp, William A. Baum, and Allan R. Sandage had just completed, in support of his theory that Type I stars are younger—on a cosmological time scale—than Type II stars. This was an oversimplification, as suggested by Boris V. Kukarkin during the ensuing discussion, but it represented a major step toward today’s understanding of the life cycles of stars.

Baade left his mark on yet another aspect of astronomy when he identified, in photographs he had taken with the 200-inch telescope, several objects first detected by radiotelescopes (1954). One of them, the radio source Cygnus A, had a twinned appearance: Baade correctly placed it far outside our galaxy—which seemed unbelievable—but his conclusion, based on theoretical work done in 1950 with Lyman Spitzer, Jr., that it represented two galaxies in collision, has not stood the test of time. In a final contribution to the understanding of objects later called quasars, Baade showed that a jet issuing from the galaxy M87 emitted strongly polarized light (1956).

Upon his retirement in 1958 Baade gave a series of lectures at Harvard University (published as Evolution of Stars and Galaxies), and then spent six months in Australia, where he used the 74-inch telescope at Mt. Stromlo near Canberra, before returning to Göttingen as Gauss professor. An operation on his hip and six months’ convalescence in bed preceded his death from respiratory failure. Much of his work remained unpublished—in some cases because he was dissatisfied with it, in others because he preferred active research to the tedious job of writing about it—but of what did appear, the British astronomer Fred Hoyle has commented: “Almost every one of Baade’s papers turned out to have far-reaching consequences.”

Considering his accomplishments, Baade received few honors during his lifetime. He was awarded the Gold Medal of the Royal Astronomical Society in 1954, for his observational work on galactic and extragalactic objects, and in 1955 received the Bruce Medal of the Astronomical Society of the Pacific. He was a member of the American Philosophical Society, and of scientific academies in Amsterdam, Göttingen, Lund, Munich, and Mainz.

BIBLIOGRAPHY

1. Original Works. Baade’s dissertation, “Bahnbestimmung des spektroskopischen Doppelsterns β Lyrae nach Spectrogrammen von Prof. Hartmann,” was presented at Göttingen 3 Aug. 1921. Works cited above are “Über die Möglichkeit, die Pulsationstheorie der δ CepheiVeränderlichen zu prüfen,” in Astronomische Nachrichten, 228 (1926), 359–362; “Über den auf die Teilchen in den Kometenschweifen ausgeübten Strahlungsdruck,” in Die Naturwissenschaften, 15 (1927), 49–51, written with W. Pauli, Jr.; “The Trapezium Cluster of the Orion Nebula” and “Spectrophotometric Investigations of Some O- and B-type Stars Connected With the Orion Nebula,” in Astrophysical Journal,86 (1937), 119–122 and 123–135, both written with R. Minkowski; “The New Stellar Systems in Sculptor and Fornax,” in Publications of the Astronomical Society of the Pacific, 51 (1938), 40–44, written with E. Hubble; “Photographic Light Curves of the Two Supernovae in IC4182 and NGC1003” in Astrophysical Journal, 88 (1938), 411–421, written with F. Zwicky; “The Crab Nebula,” ibid., 96 (1942), 188–198; “Nova Ophiuchi of 1604 as a Supernova,” ibid., 97 (1943), 119–127; “The Resolution of Messier 32, NGC205, and the Central Region of the Andromeda Nebula,” ibid., 100 (1944), 137–146; “A Program of Extragalactic Research for the 200-inch Hale Telescope,” in Publications of the Astronomical Society of the Pacific, 60 (1948), 230–234; “Stellar Populations and Collisions of Galaxies,” in Astrophysical Journal, 113 (1950), 413–418, written with L. Spitzer. Jr.; “Basic Facts on Stellar Evolution,” in Transaction of the International Astronomical Union VIII (Cambridge, 1954), pp. 682–688 (discussion on pp. 688–689); “Identification of the Radio Sources in Cassiopeia, Cygnus A, and Puppis A,” and “On the Identification of Radio Sources,” in Astrophysical Journal, 119 (1954), 206–214, and 215–231, both written with R. Minkowksi; “Polarization in the Jet of Messier 87,” ibid., 123 (1956), 550–551 and Evolution of Stars and Galaxies (Cambridge, Mass., 1963), ed. by Cecilia Payne-Gaposhkin from tape recordings of Baade’s lectures at Harvard in 1958.

A list that includes seventy-three papers by Baade and ninety short communications is appended to Heckmann’s obituary notice (see below); references to Baade’s book (mentioned above) and several other contributions to symposia can be found in Poggendorff, VIIb (1967), 166. Baade’s notebooks and other unpublished material are divided between the Mt. Wilson-Palomar Observatories and the Leiden Observatory.

II. Secondary Literature. The citation delivered by John Jackson when Baade received (in absentia) the Gold Medal of the Royal Astronomical Society was printed in Monthly Notices of the Royal Astronomical Society (London), 114 (1954), 370–383; the one by Olin Chaddock Wilson that accompanied the Bruce Medal appeared in Publications of the Astronomical Society of the Pacific, 67 (1955), 57–61, and includes a portrait. Obituary notices on Baade include those by Fred Hoyle, in Nature, 187 (1960), 1075; Erich Schoenberg, in Bayerische Akadenue der Wissenschaften, Jahrbuch 1960. pp. 177–181. plus a portrait facing p. 184; Otto Hermann Leopold Heckmann, in Mitteilungen der Astronomischen Gesellschaft [Hamburg] 1960 (1961), 5–11, with Portrait and list of publications; Allan R. Sandage, in Quarterly Journal of the Royal Astronomical Society, 2 (1961), 118–121; and Halton C. Arp, in Journal of the Royal Astronomical Society of Canada, 55 (1961), 113–116.

The role Baade played in the early days of quasar research is described in Ivor Robinson, Alfred Schild, and E. L. Schücking, eds., Quasi-Stellar Sources and Gravitational Collapse (Chicago, 1965), pp. xi-xiv; and an essay on Baade’s life and works by a longtime associate, Robert S. Richardson, constitutes ch. 16 (pp. 260–294) of Richard-son’s The Star Lovers (New York, 1967).

Further accounts of Baade’s work are Fred Hoyle, “Report of the Meeting of Commission 28,” in Transactions of the International Astronomical Union VIII (Cambridge, 1954), pp. 397–399; Hermann Kobold, “Komet 1922c (Baade),” in Astronomische Nachrichten, 217 (1923), cols. 175–176, and an unsigned report on Planet 1920 HZ [later named Hidalgo], in Nature, 106 (1920), 482; and R. S. Richardson, “A New Asteroid With Smallest Known Distance” [Icarus], in Publications of the Astronomical Society of the Pacific, 61 (1949), 162–165.

Sally H. Dieke