Walter Baade: A Life in Astrophysics

By Donald E. Osterbrock

Although less well known outside the field than Edwin Hubble, Walter Baade was arguably the most influential observational astronomer of the twentieth century. Written by a fellow astronomer deeply familiar with Baade and his work, this is the first biography of this major figure in American astronomy. In it, Donald Osterbrock suggests that Baade's greatest contribution to astrophysics was not, as is often contended, his revision of Hubble's distance and age scales for the universe. Rather, it was his discovery of two distinct stellar populations: old and young stars. This discovery opened wide the previously marginal fields of stellar and galactic evolution--research areas that would be among the most fertile and exciting in all of astrophysics for decades to come.


Baade was born, educated, and gained his early research experience in Germany. He came to the United States in 1931 as a staff member of Mount Wilson Observatory, which housed the world's largest telescope. There, he pioneered research on supernovae. With the 100-inch telescope, he studied globular clusters and the structure of the Milky Way, every step leading him closer to the population concept he discovered during the wartime years, when the skies of southern California were briefly darkened. Most Mount Wilson astronomers were working on weapons-development crash programs devoted to bringing Baade's native country to its knees, while he, formally an enemy alien in their midst, was confined to Los Angeles County but had almost unlimited use of the most powerful telescope in the world.


After his great discovery, Baade continued his research with the new 200-inch telescope at Palomar. Always respected and well liked, he became even more famous among astronomers as they shifted their research to the fields he had opened. Publicity-shy and seemingly unconcerned with publication, however, Baade's celebrity remained largely within the field. This accomplished biography at last introduces Baade--and his important work--to a wider public, including the newest generation of skywatchers.

• Language: English
• Publisher: Princeton University Press
• Release date: Jan 12, 2021
• ISBN: 9780691223285

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WALTER BAADE

Walter Baade

A LIFE IN ASTROPHYSICS

Donald E. Osterbrock

PRINCETON UNIVERSITY PRESS

PRINCETON AND OXFORD

Copyright © 2001 by Princeton University Press

Published by Princeton University Press, 41 William Street,

Princeton, New Jersey 08540

In the United Kingdom: Princeton University Press, 3 Market Place,

Woodstock, Oxfordshire OX20 1SY

All Rights Reserved

British Library Cataloging-in-Publication Data is available

Library of Congress Cataloging-in-Publication Data

Osterbrock, Donald E.

Walter Baade : A life in astrophysics / Donald E. Osterbrock.

p. cm.

Includes bibliographical references and index.

ISBN 0-691-04936-X

eISBN 978-0-691-22328-5

1. Baade, Walter, 1893–1960. 2. Astrophysicists—

United States—Biography. I. Baade, Walter, 1893–1960. II. Title.

QB460.72.B22 O77 2001

523.01′092—dc21

[B] 2001021129

www.pup.princeton.edu

R0

    CONTENTS    

PREFACE   vii

1.The Preparation: Göttingen and Hamburg, 1893–1927   1

2.The Path toward the Two Populations: Hamburg, 1927–1931   25

3.Before the War: Mount Wilson, 1931–1938   49

4.War and a Great Discovery: Mount Wilson, 1939–1947   82

5.Young Stars and Old: Palomar and Princeton, 1948–1953   112

6.Radio Astronomy and the Size of the Universe: Palomar and Pasadena, 1948–1958   147

7.Telling the Good News: America and Europe, 1953–1959   177

8.The Finale and After: Australia and Göttingen, 1959–1960   200

ABBREVIATIONS   229

NOTES   233

BIBLIOGRAPHY   259

INDEX   261

    PREFACE    

WALTER BAADE was the great observational astronomer of the middle years of the twentieth century. Edwin Hubble was much better known to the general public, probably deservedly so, for his discovery of the expansion of the universe and his confirmation of the fact that our Galaxy is but one of myriads of roughly similar star systems, spread through space as far as we can see with our largest telescopes. Baade, much more voluble with other astronomers but much more publicity-shy with reporters, writers, and broadcasters, discovered the two stellar populations which turned out to be young stars and old, and thus opened up the fields of stellar evolution, star formation, and the evolution of galaxies which have contributed so much of our present knowledge of the universe. These fields provide the tools that astronomers use today, to push that knowledge out in space and back in time. Baade’s research achievements have recently been recognized most appropriately by the Carnegie Institution of Washington, which operated Mount Wilson and Palomar Observatories in Southern California, where both Hubble and Baade made their great discoveries. The CIW president announced that its new 6.5-meter (260-inch) state-of-the-art reflecting telescope, nearing completion in the Chilean Andes as I began this preface, would be named the Walter Baade Telescope. This new research instrument in the mountains has now joined the Edwin Hubble Space Telescope in space in helping to acquire the quantitative, factual knowledge that will still further extend our understanding of the universe and its evolution.

Certainly Baade deserves a biography of his own. As a research astronomer turned historian of astronomy I have long wished to provide it. This book is the result. My aim in writing it is to present the known facts of Baade’s life and scientific career in interesting and readable form, and to let the reader draw his or her own conclusions about him and the astronomers and astrophysicists with whom he interacted. I have tried to guess at Baade’s thinking from my knowledge of him and of the astronomy of his time, but I have been wary of vast generalizations. Of course Baade’s biography includes the astronomical setting in which he worked. It was very different from today, with many fewer astronomers and only a handful of important research institutions. There were no telescopes in space, no ultraviolet or X-ray astronomy, very little infrared, and until the end of Baade’s career no radio astronomy. The ground-based telescopes were smaller, but Baade’s Mount Wilson and Palomar Observatories had all the biggest ones. He and his fellow staff members were an elite group; only they had access to the 100-inch and later the 200-inch reflectors on a regular, continuing basis. There were no national observatories except the specialized Naval Observatory, and no federal funding until just at the end of Baade’s career. All these aspects of the astronomy of his era I have tried to weave in throughout the book.

As a graduate student at Yerkes Observatory of the University of Chicago half a century ago, I learned from several teachers, especially Thornton Page, William W. Morgan, Otto Struve, Bengt Strömgren, Gerard P. Kuiper, and William P. Bidelman, about Baade’s recent research accomplishments, and especially of the importance of the populations concept to all branches of stellar and galactic research. I first heard Baade lecture in 1950, at the dedication of the new Heber D. Curtis Schmidt telescope of the University of Michigan, and was entranced by his personality, his way of speaking, and his many new (to me) insights on galaxies and the stars they contain. As a postdoc at Princeton in 1952–53 I worked closely with Martin Schwarzschild; both he and Lyman Spitzer, Jr., the observatory director whom I also came to know very well, were unstinting in their praise of Baade. Following that year at Princeton, in 1953 I participated in the month-long summer school (or workshop, as we would call it today) on astrophysics at Ann Arbor, in which Baade was one of the main lecturers. It was a wonderful experience for me, and for all the other postdocs, graduate students, and young faculty members who were there. All of us were inspired by Baade, and many of the participants became outstanding research astronomers and astrophysicists who treasured the insights they had gained from him.

That summer of 1953 I was on my way west to California, where as an instructor and then an assistant professor at the California Institute of Technology and a staff member of Mount Wilson and Palomar Observatories I saw Baade frequently for five years. He taught me to take direct photographic plates with the 100-inch and 200-inch telescopes and discussed my research with me frequently, even after I became a nebular spectroscopist. Baade’s knowledge, experience, and ideas covered a wide range of astrophysics, and he was always affable, lively, and stimulating. I had a number of long conversations with him, mostly about astronomy, spiced with stories he told me about himself and other astronomers. My last personal contact with Baade was at the American Astronomical Society meeting in Madison, Wisconsin, June 29–July 3, 1958. I had just resigned my position at Caltech to take up a new one at the University of Wisconsin, and Baade was there to give the Henry Norris Russell Lecture of the society as he retired from the CIW research staff. He, Albert E. Whitford (who was leaving the University of Wisconsin to become director of Lick Observatory in California), and I were all in the lounge of Baade’s motel near the campus at midnight on June 30, exchanging toasts with good Wisconsin beer (Baade’s phrase) as our jobs changed.

I was stunned at the news of Baade’s death in 1960; I had imagined that he would live many more years, and that we would meet again somewhere. After his posthumous book, Evolution of Stars and Galaxies, edited by Cecilia Payne-Gaposchkin, came out in 1963, I used it for twenty-odd years as a supplementary text in graduate courses on galactic structure and stellar populations at Wisconsin and at the University of California, Santa Cruz.

Thus I knew Baade well. This book is not based on what he told me, however, although I believe that I understand him better from my contacts with him. Baade was famous for, in the words of Whitford, never letting a few facts get in the way of a good story. The facts of his life and career are in his published scientific papers, his book, his correspondence, and his working papers, including notes and reading manuscripts for lectures and talks. Baade saved little of his correspondence and copies of only a few of his own most important letters, but by the time of his retirement he had accumulated more than thirty boxes of working notes on stars, novae, supernovae, Cepheid variables, radio sources, peculiar nebulae, galactic and globular clusters, galaxies, clusters of galaxies, selected areas, and measurements of all of these. He also saved the manuscript or notes for practically every colloquium, journal club report, invited paper, lecture, or series of lectures he gave. This material is preserved at the Huntington Library in San Marino, California, as part of its magnificent Mount Wilson Observatory Collection. I am most grateful to Ronald Brashear and Dan Lewis, successively curators in charge of this collection, for the help they gave me in using it. I am also grateful to the Huntington Library for awarding me a Mayer Fellowship, which made it possible for me to spend a full month there in 1993, examining these materials. I have returned many times since to work further with them.

The most fruitful sources of Baade letters are other archives, at research institutions and universities where his correspondents’ papers have been preserved. I am especially grateful for help from Dorothy Schaumberg of our own Mary Lea Shane Archives of the Lick Observatory, Judith A. Bausch (Yerkes Observatory Archives), Clark Elliott (Harvard University Archives), Bernard Schermetzler (University of Wisconsin Archives), and several other archivists who are named below.

Baade was born and educated in Germany; he lived there until he was thirty-eight years old and always remained a German at heart and by citizenship. His student days at Göttingen University ended just after World War I, and he carried out some of his most significant research in America during World War II. Thus conditions in Germany, Hitlerism, Nazis, and two great wars in which he was on the losing side, though he lived and worked in the United States for twenty-seven years, are all parts of his story. I am exceedingly grateful to Jochen Schramm, both for his excellent book Sterne über Hamburg: Die Geschichte der Astronomie in Hamburg, which tells, with many excellent illustrations, the complete story of the observatory where Baade worked from 1919 to 1931, and for sending me copies of all of the correspondence with him that is in the files there. These include a set of personal letters between Baade and Richard Schorr, the observatory director who first hired him, and who tried to lure him back from America to be his successor. Dr. Schramm tracked down these letters himself and generously shared them with me. I am also grateful to Theodor Schmidt-Kaler, who has written and published two most interesting articles on Baade and his teachers in Germany, and who has kindly sent me much important information about Baade’s family, which he learned through his own research in Germany. Hilmar Duerbeck and Dieter Reimers were also especially helpful with photographs and information from Germany.

Thanks to my family heritage (all German), my high-school teachers, and the University of Chicago language examinations, I can read German fairly well (especially if some of the long words are astronomical), so most of the translations are my own. However, for expert help with the more difficult (to me) passages I am most grateful to Peter Bodenheimer, Andreas Burkert, Alfred Gautschy, Wolfgang Hillebrandt, Wilhelm Kley, and Harold Yorke.

My friends Allan Sandage and Halton Arp, Baade’s two Ph.D. thesis students at Caltech, were most helpful with their thoughts, memories, and other informative material. Albert E. Whitford, in many personal discussions, and the late Martin Schwarzschild and Lyman Spitzer, Jr., in their letters, provided extremely important information from their personal knowledge of Baade. Owen Gingerich, whom I first met as a fellow participant in that 1953 summer school, and who has selflessly encouraged my historical endeavors in later years, very kindly made available to me copies of letters which the late Cecilia Payne-Gaposchkin had given him from her scientific correspondence with Baade.

Spencer Weart informed me of the microfilm at the the Niels Bohr Library of the American Institute of Physics containing some of the correspondence between Baade and Jan H. Oort, and made it possible for me to use it. Adriaan Blaauw and J. K. Katgert-Merkelijn arranged for me to obtain copies of all the other surviving letters between Baade and Oort from the University of Leiden Library. W. Butler Burton was most helpful in sending me several photographs of Baade from the Leiden Observatory. To all of them I am most grateful.

Others who have helped with notes, letters, photographs, and other material include Horace W. Babcock, Roger Bell, Ray Bowers, Arthur D. Code, George V. Coyne, S. J., David DeVorkin, Richard D. Dreiser, Ronald D. Ekers, Michael Feast, Roy H. Garstang, Karl Grandin, Janice Goldblum, Dorrit Hoffleit, Karl Hufbauer, I. Khan, Tom Kinman, Helen Knudsen, Douglas N. C. Lin, Sabino Maffeo, S.J., Tina McDowell, Jeremy R. Mould, Joseph F. Mulligan, Leos Ondra, Roswitha Rahmy, Kenneth W. Rose, Walter L. Sanders, Maarten Schmidt, Irwin I. Shapiro, Maxine F. Singer, Don C. Skemer, Tom Steman, William G. Tifft, George Wallerstein, John Whiteoak, Lo Woltjer, and the late Hendrik C. van de Hulst.

Finally, let me say that I have used the English-language names of cities and regions in Germany, such as Munich and Westphalia. I have generally used the names of people that they used themselves in adult life, such as Walter Baade (though he was probably christened Walther, the accepted German spelling at the time of his birth) and Cecilia Payne-Gaposchkin. Rudolph Minkowski spelled his first name Rudolf before he emigrated to the United States, but I have used Rudolph throughout the book. Johanna Baade was the name of Walter’s wife, and her nickname, which she evidently used with her friends in Germany, was Hanni, more or less the equivalent of Jo in English. But Baade, at least in his later life in America, called her Muschi, equivalent perhaps to Kitty or Cozy, and most of his American friends who knew them well also called her by that name. Hence I have used that name throughout almost all of the book, although in fact she signed her letters in English to important contemporaries such as Oort and Ira S. Bowen as Hanni Baade, especially after her husband’s death.

This book is based on a series of three long articles, published in four installments in the Journal for the History of Astronomy in the years 1995 through 1998. I have rewritten them carefully, including substantial amounts of additional material.¹ I am most grateful to Michael Hoskin, editor of JHA, for his excellent editorial assistance with the original articles and for his kind permission to draw on them freely for this book. All the photographs are reproduced with the permission of the institutions, observatories, and individuals credited, for which I am most grateful.

WALTER BAADE

    1    

The Preparation

GÖTTINGEN AND HAMBURG,

1893–1927

Introduction

Walter Baade was one of the great astronomers of the twentieth century. He opened up the fields of study of stellar and galactic evolution that have made up so much of astronomy in our time, but which were sterile and unproductive before his discovery of the two stellar populations, young stars and old. Baade was lucky in being the right man in the right place at the right time, but he was also able to seize the situation and make the most of it in a way that none of his contemporaries could.

Baade was a unique person, a great scientist who was also a warm, friendly human being; a German who was widely admired, loved, and respected in America, which had twice fought bloody wars with his country; a very good teacher who claimed he did not like to teach; a research scientist who was not a professor but who left a generation of astronomers he had advised and inspired behind him. Widely considered only an observational astronomer, he had in fact had an excellent training in astrophysics and collaborated in research with astrophysicists all his life. His aim was to understand the universe, and he took us far along the path toward it.

Baade’s great discovery of the two stellar populations did not come to him out of the blue at Mount Wilson Observatory in the mountains of Southern California in 1944. His whole life was a preparation for it; the discovery was the culmination of his career, begun twenty-five years earlier, as an observational astronomer who sought physical understanding. A little, undated notebook he started as a young scientific assistant at the Hamburg Observatory, probably in 1921, bears the title Stellar Evolution. What it actually contains are charts and reductions of variable star measurements in the globular cluster M 53 and references to papers on the spectra of nebulae, including not only gaseous nebulae but also galaxies like M 31. But this is in fact the path he followed to open up the whole field of stellar evolution.

When Baade gave his first, big, post–World War II invited paper on the two stellar populations, at the American Astronomical Society meeting held at Perkins Observatory in Ohio in 1947, he began by reviewing the steps which led to the recognition of two distinct types of stellar population. What I want to show is that this conception emerged gradually during the last 25 years.¹ That quarter of a century began in Germany, where Baade was born, educated, and trained in research, and where he began his own work on variable stars, globular clusters, local-group galaxies, and distant clusters of galaxies. Hence Baade’s preparation, mostly in Germany but including one year spent in the United States on a Rockefeller Fellowship, up to the time he left his native country to take a permanent position on the Mount Wilson Observatory staff, was a very important part of his scientific career.

Early Life and Education

Walter Baade was born in Schröttinghausen, a small town in Westphalia, in northwestern Germany in 1893, early in the reign of the young Emperor Wilhelm II. Otto von Bismarck had resigned the prime ministry just three years before Baade’s birth. The little baby was christened, in the German Lutheran custom of those days, with a long string of names, Wilhelm Heinrich Walter Baade, but as an adult he was always known simply as Walter Baade. His father, Konrad, was a schoolteacher and later principal, whose first two wives had died childless. He and his third wife, Charlotte (née Wulfhorst) had four children. Walter was the oldest, then his brother Martin, and then two sisters, Katherine (Käthe) and Elisabeth (Betti). The future astronomer received an excellent classical education in Schröttinghausen and at the Gymnasium in Herford, a larger city where his family moved when he was ten. Besides French and English, he studied Latin, Greek, and Hebrew; in later life he liked to say that his parents raised him to become a theologian, but in fact he received very good training in mathematics and science as well. Baade began to show an interest in astronomy at about the age of fourteen.

In 1912, when he was nineteen, Baade entered the nearby University of Münster for one year, and then transferred to Göttingen in 1913. It was the Harvard of Germany, with a tradition in astronomy going back to Carl Friedrich Gauss, and in his first year there Baade attended the noted mathematician David Hilbert’s lectures on mechanics, actually more like a course on differential equations.² Baade had been born with a congenital hip defect, which made him walk with a pronounced limp and prevented him from running. It saved him from field service in the German army in World War I, and perhaps saved his life.³

At Göttingen Baade, an excellent student, took courses in astronomy, mathematics, physics, and geophysics. His teachers included Johannes Hartmann and Leopold Ambronn in astronomy, Hilbert and Felix Klein in mathematics, and Emil Wiechert in geophysics, all of them famous in their fields. Baade worked for Klein as his assistant, and during the war also spent two years in the army auxiliary service at Ludwig Prandtl’s Institute for Experimental Aerodynamics in Göttingen, while continuing as a part-time astronomy student. Although Hartmann had been a pioneer in photographic astronomical spectroscopy at Potsdam, he was in his sixties when Baade began his graduate work, and Ambronn had devoted his entire career to visual positional measurements. Göttingen Observatory’s equipment was obsolete, and Baade learned to observe visually with transit instruments and a heliometer, but had no opportunity to use even a moderately large telescope or to take direct photographs or spectrograms of stars.

In 1916 he began his astrophysical thesis on the spectrum and orbit of β Lyrae, a bright eclipsing and spectroscopic binary, under Hartmann. Baade measured, reduced, and analyzed the spectroscopic plates of it which his professor had taken at Potsdam years earlier. There were twenty-six spectrograms in all, covering the years from 1900 to 1909, but concentrated especially in the autumn of 1908. Baade learned all the necessary measuring techniques, using a high-powered microscope mounted with a hand-operated, precision screw-driven moving stage as a measuring machine to identify and determine the stellar and comparison lines’ positions on each plate. The next step was to make the long numerical computations necessary to derive the observed stellar lines’ wavelengths, and from their minute differences from their known rest (laboratory) wavelengths to compute the radial velocity of the star or stars. Then he could move on to interpreting their meaning. Baade’s progress was slow, because of his duties for Klein and Prandtl, and Hartmann by now was devoting most of his time to teaching, lecturing, and writing on the history of astronomy. In 1919 he became dean of the faculty and head of its mathematical and scientific division, especially demanding administrative posts in that chaotic postwar year, and had little time to guide his student’s work.

Baade’s main results were to confirm in large part the results Ralph H. Curtiss had found on β Lyrae from his own similar spectroscopic observations, obtained at Allegheny Observatory in America. He had taken most of his spectrograms in 1907, but in contrast to Hartmann had worked them up and published his paper quickly. According to both Curtiss’s and Baade’s papers, β Lyrae consists of two stars, a brighter B5 one with a strong-emission line spectrum associated with it, and only much weaker absorption lines, and a fainter B8 star, with strong, easily measurable absorption lines. Baade, like Curtiss, derived the period and orbit of the B8 star about the center of mass of the system. This again involved long, complicated numerical calculations, using well-known but sophisticated formulae and fitting procedures. The two astronomers’ results for these orbital parameters were very similar. But Baade, examining the lines’ appearances carefully and how they varied through the period, was able to prove that the weak B5 metallic absorption lines had the same radial velocities as the hydrogen and helium emission line, but varied differently in strength from them. This meant that the source of the emission lines moved with the B5 star and was bound to it, but was not centered on it, because these lines were partially eclipsed by the B8 star at a different phase from the B5 continuum and absorption lines. Baade thus proved that one of Curtiss’s two possible interpretations (that the B8 star was in orbit about a postulated much more massive gas cloud which surrounded the B5 star) was untenable. The alternative, that the B8 star was in orbit about the B5, led to reasonable masses for the two stars. But Baade’s interpretation left the question of just where the source of the emission lines is located with respect to the B5 star unanswered. He could not interpret this puzzle then; β Lyrae remained an object of intense study for more than fifty more years as the solution was worked out by numerous astronomers using bigger and better telescopes, spectrographs, computers, and theories.

Baade finished his thesis and received his Ph.D. in the summer of 1919, nine months after the Armistice which marked the defeat of Germany and the end of World War I. He clearly had not gained much inspiration from Hartmann and Ambronn, but had learned many techniques from them, and above all had proved to himself that he liked research and could work hard at it and get results, even from old data. His thesis was not published in full, and remained unknown to most later researchers. It fulfilled the formal requirements for the degree, but the main new ground it broke was in asking questions that he could not answer with only the spectrograms Hartmann had taken more than a decade earlier.⁴ Baade’s degree really meant that his professors knew that they had taught him all they could, that the war was over, and that he was ready for a research career. Evidently he had been doing a lot of reading on his own, including copies of whatever journals reached Göttingen from America, for he knew about some of the research that was going on with the big telescopes there. This independence, self-reliance, and absolute dedication to research were to prove to be three of Baade’s strongest characteristics throughout his life.

The following April, less than a year after Baade’s degree was granted, Harlow Shapley and Heber D. Curtis held their Great Debate, actually a pair of lectures, in Washington before the assembled members of the National Academy of Sciences. Curtis upheld his view that the spiral nebulae were really island universes or star systems, while Shapley maintained that they were indeed nebulae. He was wrong, and Curtis was right. Understanding the structure and makeup of island universes, which we call galaxies today, was to be Baade’s life work.⁵

Hamburg Observatory

In 1919 Mount Wilson was the most famous observatory in the world. Its 60-inch reflector had begun work in 1908. An outstanding staff, directed by George Ellery Hale and headed by Walter S. Adams, had begun making brilliant discoveries on the astrophysical nature of stars. In 1919 the 100-inch went into operation, the largest telescope in the world (which the 60-inch had been until 1917). Baade, who was especially interested in astrophysics and in stellar spectroscopy, wanted to go to Mount Wilson immediately, to do research with the 100-inch as an unpaid volunteer assistant, more or less the equivalent of a modern postdoc. This is just what Henri Chrétien had done in 1909–10, with the 60-inch, under the sponsorship of Nice Observatory. However, Baade’s professors advised him that such a program would be quite impossible for a German citizen less than a year after the Armistice. The twenty-six-year-old new Ph.D. would have to get a job in his own, defeated country.

He had heard through his friend Heinrich Rauschelbach, a fellow 1919 Göttingen Ph.D., of an opening for an assistant at Hamburg Observatory, and wrote to its director, Richard Schorr, to apply for the job. Baade’s teachers, Ambronn and Hartmann, recommended him strongly to Schorr, emphasizing his thorough training in classical astronomy and his strong interest in astrophysics. Baade was clever and industrious, very apt and thorough, and a very pleasant and amiable person (a recurring description of him all his life). At the end of his paean of praise for Baade, Hartmann advised Schorr to grab him. The Hamburg director did so, and Baade started work on October 1, 1919.⁶ Edwin Hubble, who had completed his Ph.D. thesis on faint nebulae (mostly galaxies) at the University of Chicago in 1917, then served as an infantry officer in the American Expeditionary Forces in France, had begun working at Mount Wilson just a month earlier.⁷

The Hamburg Observatory was actually located in Bergedorf, a village outside the smoke and the worst of the light pollution of the big port city. With his job, Baade was assigned a two-room apartment at the observatory where he was required to live; Rauschelbach had not been hired because he was married and all the apartments in the observatory dwelling were for single men only. Thus did Baade qualify for his first observatory position! Luckily for Rauschelbach, who had been much more interested in measuring positions of the moon and planets than Baade, and in making time determinations with a meridian circle, there was also an opening for an astronomer in the Time Service of the German Naval Observatory at Hamburg, so he got a job too.⁸

Schorr, then forty-eight years old, had been the director of Hamburg Observatory since 1902. He was not famous for any research he had done, but he had earned his Ph.D. at Munich under a great teacher of the previous generation, Hugo von Seeliger. Schorr, a short figure, always erect and well dressed, concentrated on keeping on good terms with the rich Hamburg merchants and the important local and national officials who controlled his institute’s budget. Its main instrument was its 1-meter (40-inch) reflector, the largest telescope in Germany. Baade, young and eager, intelligent and quick to learn, soon made himself a master observer. Schorr, who had supposedly been using the telescope himself, was busy and greatly occupied by his administrative tasks. In 1920 he turned all the observing with the reflector over to Baade.⁹ The young Ph.D. was patient and skillful in guiding the long photographic exposures, yielding the accurate positions of comets and asteroids which Schorr, a classical astronomer, considered the most important work in his observatory. But Baade, reading the Astrophysical Journal and the Mount Wilson Observatory Contributions, was much more interested in variable stars, globular clusters, and other astrophysical research he could do by direct photography.

One minor project Schorr assigned to Baade was to take a few exposures of the variable star SS Cancri, which Kasimir Graff, a senior Hamburg astronomer, was observing visually with the great 60-cm (24-inch) refractor of the observatory. His long series of measured magnitudes determined