Background
He was born in Schröttinghausen on March 24, 1893.
(A summing up by one of the greatest of modern astronomers...)
A summing up by one of the greatest of modern astronomers, this book assesses the state of our knowledge of the processes of development in stars and galaxies. The author's historical introduction shows how the modern picture of the universe sprang from the pioneer work of the Hertzsprung-Russell diagram, Shapley's study of globular clusters, and Hubble's attack on the galaxies. The chapters on the classification and observation of galaxies are rich in the experience of a great observer. They lead into a description of Dr. Baade's discovery of the two stellar populations, and of the consequent revision of the period-luminosity relation, which doubled the distance scale of the universe.
https://www.amazon.com/Evolution-Stars-Galaxies-Walter-Baade/dp/0262520338?SubscriptionId=AKIAJRRWTH346WSPOAFQ&tag=prabook-20&linkCode=sp1&camp=2025&creative=165953&creativeASIN=0262520338
He was born in Schröttinghausen on March 24, 1893.
From 1903 to 1912 Baade was a student at the Friedrichs-Gymnasium in Herford. He studied at the University of Münster from 1912 to 1913 and at Göttingen, where he was an assistant to the mathematician Felix Klein from 1913 to 1919.
Shortly after passing his doctoral examination in July 1919 with a sehr gut, he became an assistant at the University of Hamburg's observatory in Bergedorf. There he began systematic observations of comets and asteroids; he reported the discovery of a comet in 1922 and of a minor planet (Hidalgo) in 1920 that turned out to have the largest orbit of any known asteroid.
Inspired by the work of Harlow Shapley at the Mount Wilson Observatory, Baade, almost alone among European astronomers, embarked on an observational program of clusters and variable stars to delineate the structure of the Milky Way.
Many years later, at the Mount Wilson Observatory, he was to use similar isolated variable stars to derive the distance to the center of the Milky Way. His zeal and ability won him a Rockefeller fellowship in 1926, enabling him to visit the large telescopes at Mount Wilson, near Pasadena. Upon his return to Bergedor fin 1927 Baade was promoted to observer, but he failed in his attempt to have the one-meter telescope moved to a more favorable southern location, and when he was offered a staff position at Mount Wilson in 1931, he accepted immediately.
The first problem Baade undertook with the 60-and 100-inch telescopes was the improvement of brightness measurements for faint stars. Like many astronomers of the period before the establishment of photoelectric photometry, Baade was frustrated by the lack of a precise intensity scale. For many years he worked painstakingly with neutral half-filter photographic techniques, but he was not satisfied with the results. When it finally became apparent that photoelectric multipliers could provide the requisite accuracy, he guided several students into critical research problems in this area, never publishing his own laboriously achieved but still imperfect photographic magnitudes. In the 1930's and 1940's Baade's major interest concerned the stellar content of various systems of stars.
During World War II Baade was classed as an enemy alien. (Although he applied for American citizenship, the papers were lost in a move, and with characteristic scorn for bureaucracy, he never completed the naturalization. ) He was nevertheless allowed to observe on Mount Wilson and, aided by the darkened skies associated with the Los Angeles blackout, continued his studies of the hitherto unresolved nuclear regions of the nearby galaxies in Andromeda. By choosing only the best nights, paying fastidious attention to the focus of the 100-inch telescope (which varied with temperature throughout the night), and by using specially sensitized red plates, he finally distinguished individual stars in the center of the Andromeda nebula and its companions. The resolution of these galaxies into stars provided a key to the differing types of components of spiral galaxies on one hand, and elliptical galaxies and globular clusters on the other. Baade conceived of two discrete populations: Type I, characterized by the young, blue stars in the dusty arms of spiral galaxies; and Type II, defined by the older, fainter red stars of ellipticals as well as in the nuclear regions of the spirals.
The concept of stellar populations, although later considerably revised, proved remarkably fertile for the analysis of stellar systems. Using the concept of stellar populations as a guide, Baade predicted the presence of clustertype variable stars in parts of the Andromeda nebula, but they were too faint to be resolved with the 100-inch reflector on Mount Wilson. When the 200-inch Palomar telescope commenced operations in 1948, Baade resumed this research but soon realized (from the newly calibrated brightness of the red giant stars) that the cluster-type variables were still beyond his reach. This fact could be reconciled with other data only by recalibrating the scale of absolute luminosities of the cluster-type and of cepheid variable stars, a step that approximately doubled the accepted distance of virtually all the galaxies including the Andromeda nebula. Announced in 1952 at the International Astronomical Union, this result climaxed Baade's lengthy studies on the contents of stellar systems.
In the 1950's Baade and his longtime collaborator Rudolph Minkowski began a successful survey to identify the strongest radio sources with optical objects. Of particular importance were their identifications of the Cygnus A and Perseus A radio sources as distant galaxies, and Baade's demonstration that the light of the peculiar jet in the galaxy M87 - identified with the radio source Virgo A - is strongly polarized. His detailed study of the polarization in the Crab nebula revealed the intricate structure of the magnetic field and of the synchrotron radiation in an exploded object. Baade published very sparingly, but he freely communicated his results to a steady stream of visitors. In the fall of 1958, after his retirement, he gave a brilliant lecture course at Harvard; published posthumously as Evolution of Stars and Galaxies (1963), it records many of the observations and ideas that he never took time to publish. In 1959 Baade accepted the Gauss professorship in Göttingen, where he died.
(A summing up by one of the greatest of modern astronomers...)
(Lang:- German, Pages 169. Reprinted in 2015 with the help...)
He was a Foreign membership of the Royal Netherlands Academy of Arts and Sciences (1953).
His exuberance, infectious enthusiasm, and delight in practical jokes made him an unforgettable character in the astronomical fraternity.
In 1929 Baade married Hanni Bohlmann, a calculator at the Hamburg Observatory; he later named one of "his" asteroids "Muschi" - the nickname he always used for her.