Oral History Transcript — Dr. Jesse Greenstein
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Jesse Greenstein; July 31, 1974
ABSTRACT: Childhood in New York; high school experience at Horace Mann; Harvard undergraduate at the age of 15. Impressions of ordeal with Harlow Shapley. Depression years in the family business, return to a very changed Harvard in 1934. Thesis work on Interstellar Absorption (Bart Bok), Ph.D. 1937. Postdoc at Yerkes Observatory (Otto Struve) working on Upsilon Sagittarius. Develops the 140-degree camera (the Greenstein-Louis G. Henyey camera); work with Fred Whipple on radio signals from space (Karl Jansky, Grote Reber), Greenstein and Reberís review article on classified radio detection work during World War II. Founding of the Astrophysics Department at Caltech. Radio astronomy in the mid-1950s. Work on white dwarfs from 1957 on. Own accomplishments as scientist and in personal life. Impressions of Martin Schwarzschild, Shapley, Reber, Fred Hoyle. Also prominently mentioned are: Walter Sydney Adams, Lloyd Viel Berkner, John Bolton, Leverett Davis, William Alfred Fowler, Leo Goldberg, Louis Henyey, Fred Hoyle, Edwin Powell Hubble, Milton Lasell Humason, Robert Hutchins, Karl Jansky, Gerard Peter Kuiper, Tom R. Matthews, Robert Reynolds McMath, Donald Howard Menzel, Paul Merrill, Rudolph Leo Bernhard Minkowski, William Wilson Morgan, Guido Munch, Beverly Oke, Donald Osterbrock, Cecilia Payne-Gaposchkin, Harry Hemley Plaskett, Robert Richardson, Allan Sandage, Jan Scheldt, Shklovsky, Charlotte Moore Sitterly, Lyman Spitzer, Edward Teller, Richard Chace Tolman, Robert Julius Trumpler, Merle Antony Tuve, Albrecht Otto Johannes Unsold, Immanuel Velikofsky, Frederick Whipple; Carnegie Institution of Washington, Hale Observatories, Harvard College Observatory, Lick Observatory, McDonald Observatory, McDonald Observatory Nebular spectrograph, National Science Foundation (U.S.), 100-inch Telescope, University of Chicago, and Vista Project.
Wright:This is an interview with Dr. Jesse L. Greenstein at the Greenstein residence at 2057 San Pasqual St. in Pasadena, California, on the 31st of July of 1974 by Paul Wright, on behalf of the Oral History Project at California State University at Fullerton. Dr. Greenstein, would you tell us at length about your childhood and how events influenced your interest in astronomy?
I come from a New York bourgeois family devoted to the business world. I was born in Brooklyn in my grandfatherís house and grew up the first few years under the influence of a large family with which I no longer have any contacts. At the age of three I began to look around my grandfatherís library. My first knowledge of astronomy came from reading and looking at pictures at that time. By the time I was six I remember him buying books for me. He was a very interesting and intelligent man, an immigrant from Russia in 1888, who had completely turned against all his past traditions. He became Americanized; he was quite a scholar in his own way, although a business man. So, I think I was eight, he bought me a three-inch telescope on a brass mounting. It stood on a table. By the time of World War I, even though my parents and I had moved away from there, I remember that I also had a long wave radio transmitting station which, after World War I, was taken off the air by the Brooklyn Navy Yard for causing interference. So, as far back as I can remember, I had an early interest in science in general, astronomy in particular, with no clear idea what it meant, what it was, no idea that it could be a profession. No one in my family was a scholar.
I went later to a prep school in New York and I eventually became a scientist. As far as anybody could see I was the first person to graduate from that school whoíd ever become a scientist, though that changed later. But, in any case, this interest goes back quite a long time, and, I guess, would be traceable to a strange accident. But it also goes back to a strong tradition in Jewish people, even while they no longer in any way conform to the past, that they are interested in all scholarship. They think itís just a different application of the old precepts, live by the book, learn things, and have great respect for Intellect no matter in what useless area. I went to public schools for some years. In New York, at that time, bright children were supposed to skip years ahead in classes. I entered a private school, Horace Mann School for Boys, Fieldston near New York, at eleven, graduated at fifteen and entered Harvard at fifteen. The first organizational activities I remember were from age eight on, at a summer camp in the mountains near New York City I founded what was called the Interesting Topics Club. I remained in it as President and chief lecturer through several summers, with my brass telescope. But it was that kind of early childhood where, with no real push from anybody, I more or less inevitably graduated into a world of thinking of one kind or another. I learned some, perhaps considerable science at Horace Mann. But again, there was no great push.
I continued interest in experiments in physics related to astronomy and spectroscopy. I remember building various gadgets involved with the spectrograph in country houses that we rented in the summer, well before going to college. About 1923 our school radio club erected a giant-antenna and communicated with Australia by voice, which was I think early for radio amateurs. I had an early interest in radio I remember back in summer camp hearing radio stations with an old crystal detector with coils I had wound when I was only nine or ten. Thus, I had an interest in radio at the beginning of radio astronomy in the United States . So I guess you will find most interests go back a long time. It was never clear that I would be a professional or an academic person because nobody in my social class was, at that time, especially in a big city. Other interests: I had an early interest in art which Iíve kept up, and in books. Probably at first I lacked interest in people, which Iíve made up in the last forty years becoming incessantly involved with people. This is about the area you want covered?
Wright:Yes, thatís fine, because I think that covered the area that I really was interested in.
Greenstein:I just wanted to judge the depth and length of answers.
Wright:Just for the record, what High School did you attend?
Greenstein:I went to a private school called Horace Mann School for Boys, which was founded by people from Teacherís College; it was a middle class to wealthy college prep boarding school. It had a day school where you could come there but many boys lived up in Fieldston, a suburb of New York. Itís still a very good school, completely privately supported. In fact, it was a deliberately old-fashioned school, good for me because the New York public school system, though more rigorous than public schools became later, was still not difficult for me. Getting through eight grades by age eleven might so indicate. It was not an altogether good idea to be so young to enter prep school and later college. The work was interesting at prep school because the teachers were really quite good. I had to study Latin hard, which I hadnít taken in elementary school, and I was far behind. As a result of the pressure to excel, I took six years of Latin altogether, there and at Harvard, and one of Greek. It was quite a classical education. They had good chemistry, very good, and a little bit of physics and, of course, mathematics. In general it was a school for people who were going into the business world, who would be supposedly going to good colleges and probably a little bit snobbish, but it matched the background I came from anyway. I learned a lot there.
Wright:What was your familyís reaction to your scientific interest?
Greenstein:Probably mainly disbelief. No one in my family would have thought it the right thing to do, and there as certainly no objection, but it was quite obvious to everybody that I should be a business man, in time. My grandfather died quite young, but he would have probably approved. My father didnít disapprove, just felt it rather odd. They gave me freedom to do anything I liked. It was a world in which, unlike young people now, no one was expected to be independent financially, nor had to. It was expected that I would be supported through college, to do whatever I liked. In a very real sense, Iím deeply indebted to all of them. They didnít object, nor did they refuse to support me, and they had to support me for a helluva long time, eventually.
Wright:Well, during your time there at Horace Mann and then as an undergraduate at Harvard, for the record, what were your impressions of your courses?
They were extremely good. It was very fortunate for me that I went to a very good, rigorous, somewhat old-fashioned school, in the New England prep school tradition, though much newer. For example, Latin, a completely useless subject, I can still read and I could swear. I took a year of conversational Latin, Latin degraded and becoming a Romance language, the Latin of the Early Middle Ages. The teacher in that class threw me out of class almost every other day my first year because I didnít know enough, and was two years behind. The first two forms, equivalent to seventh and eighth grades, I missed. I had to catch up in the first month, which was something of a strain, probably the first I ever had on my intellect. So, I think it was very good. It makes one a little bit competitive, a little bit more modest. I think essentially everything was good. I remember chemistry, which I never took again, a good high school chemistry course. I passed first in New York in the College Entrance Board examination in chemistry that year, almost broke into tears because I didnít get a hundred percent.
I only got ninety-eight point six, or whatever it was, something very high. But not perfect, and therefore disturbing. The whole tradition, though in no way a school for science, was one for rather rigorous education on fundamental classical lines, non-permissive. It had lots of other things I learned, an interest in literature, music and art there. For example, the son of a well known anthologist and poet named Louis Untermeyer was at the school and so we had a good exposure to contemporary American poetry; well-known people came and talked. Eugene OíNeillís son, a translator, I think, later of Greek drama, Eugene OíNeill, Jr., was at the school. So our Drama Club put on some early one-act plays of OíNeill, about 1924; I was stage manager. I generally have a very great respect for schooling as it then was, a great respect for having to work hard. Yet this was done in an atmosphere where probably the main good was what was then called a well-rounded education, in making people well-suited to their ultimate responsibilities in the family banking house, or whatever they were going to be, it was not a school for scholars. Boys who nearly flunked out became business world leaders of the next generation. But it was a thing, you see, which is so dead, except in the few good New England prep schools now, that itís worthwhile remembering that it isnít just an argument between permissiveness and fundamental three ďRsĒ type education.
There was a real value in the classical educational pattern which is now gone. I regret that loss, and I donít regret at all that I went through it. Then also at college, Harvard, 1925-1929, was very different from what it is now. It was at the apex of the Experimental period there in education; there were almost no requirements, you took what you wanted. Although I was always interested in astronomy, and majored in it, I took more courses in English literature. All you needed to get a degree in your specialty was to take four courses in the Four years in that specialty. That was all. There were no undergraduate theses, no formalities at all the first two years I was there. A professor of astronomy who did most of the elementary teaching was off on two eclipse expeditions around the world, so there werenít very many courses given. Yet it was a good education. I learned a little bit of physics, not much mathematics. I took whatever I wanted, I think the minimum requirements specified about eight of the minimum of sixteen courses in four years, but these covered the realm of human knowledge. You could take up to twenty courses if you wanted. In almost every area I had pretty good teachers, probably the weakest being in physics, which was a bit unfortunate. That was a defect at Harvard at the time, partly cured by the fact that M.I.T. had a very bright theorist, John Slater, one of the founders of Quantum Mechanics in the United States, who came over and lectured at Harvard in my senior year. When I asked my advisor whether I should take Quantum Mechanics, which is at the heart of modern physics, he told me that these subjects were coming and going once a year and Quantum Mechanics would be done in a year or two.
Wright:It was a passing fad.
Greenstein:A passing fad, exactly, and I should take instead a really solid course in physics. But it was just a year or two before things changed. I was just there a little too early for modern physics. Never learned Quantum Mechanics in fact, and I had to pick up what I needed much later, when it was a helluva lot harder.
Wright:Harvard had a long established astronomy department, I believe.
Greenstein:Yeah. The first observatory was built in 1843, I believe, by public subscription, and its fifteen-inch telescope was then the largest in the world. The names of the people who led in raising the money are still inscribed on a marble slab still near the old fifteen inch at Harvard. Teaching of astronomy must have gone back very early, because it was needed in New England for navigation purposes. Spherical trigonometry and time-keeping are parts of navigation, and New Englanders were not likely to downgrade something which made for successful whalers and clippers travelling around the Horn. I wish I knew more about that history, but to be quite honest, I donít.
Wright:When did you take your first actual course in astronomy?
Greenstein:Probably in my freshman year, which would have been l925-l926. As I said, Professor Stetson was away for two years, the eclipses were in Indonesia, and there was a substitute. I donít know who that was. I then took whatever they had, for example, positional, practical and orbital. The last year, as a senior, I had my first contacts with the Harvard College Observatory which was about half a mile away, and which was a purely research group. At first there was very little formal graduate work. I think they produced their first modern Ph.D. right after that time, probably 1927-1928. The observatory was run by Harlow Shapley and was a very interesting place. I was especially influenced by a visitor from Canada by the name of Harry Plaskett, son of a well-known astronomer J.S. Plaskett, head of the Dominion Astrophysical Observatory in Victoria, British Columbia. Harry Plaskett was a theorist, who persuaded me that I ought to go to England and do graduate work in theoretical astrophysics, which was probably a fairly good idea. In 1928-1929, summer I believe, I met a famous theorist from England named Milne, who worked both in stellar interiors and stellar atmospheres. He agreed that I could come to work with him at Oxford, which unfortunately never happened. But in any case, the first serious astronomy would have been in my senior year. I did research on a volunteer basis at the Observatory, before 1929, perhaps even the summer of 1928, and I had contact with professional scientists for the first time, still an undergraduate.
Wright:Could you give us some impressions of Harlow Shapley?
Well those impressions have evolved as time passed. When I first met him, as an undergraduate, I thought him an absolutely fabulous, charming person, extremely vivid, active, sociable. He used to lead dances at his house Sunday evenings, call the turns or whatever you do for the Virginia reel. Itís turned me off folk dancing ever since. But he was an interesting man, capable of inspiring an incredible degree of devotion among people. On the other hand, now that I begin to think about times past, so long ago, I feel a deep resentment against him which has only grown with time. Part of it goes back to the first research I did. In the year 1929, because I remember other dates now, I did some research on the apparent temperatures of stars as deduced from their colors, using other peopleís published measurements. I discovered that a certain kind of hot star, called B stars, normally blue and hot, from their spectra, were in fact red in two parts of the sky. I thought that possibly their light could have been reddened somehow on passage from the stars to us, in space. But Shapley, many years earlier when he was on the staff at Mt. Wilson, said he had found blue stars in the plane of our Milky Way at great distances, and so he declared space to be quite transparent.
According to his measures, it didnít either dim or redden light. He needed this fact in connection with his work on galaxies later, so he stuck to it, and it was quite wrong, his measured colors were wrong. So, as an undergraduate, I found a dependence of star color-temperature on the region of the sky. We now recognize this easily and from the graphs in my first paper that I ever published, you can see that the distant B stars in the Milky Way were, in fact, reddened. On the other hand, Shapley had said they were not. Therefore, being an obedient undergraduate, I guess, unlike present students, I had to agree with the authority, the great man. So I invented a new mechanism based on a very abstruse theory that the earthís atmosphere changed its transparency as a function of the season of the year, and that the colors of stars observed in the summer Milky Way and in the winter Milky Way were both red because the earthís atmosphere reddened the light more. At this time the new theory of the weather fronts had been developed by a Scandinavian named Rossby at M.I.T. I heard about this, it being a small academic world at that time, and thought that the cold dry weather fronts and the wet weather patterns produced different transparency in the earthís atmosphere. I was too clever, which shows you that it never does you very much good to know too much.
In a sense Shapleyís telling me that space was transparent, which I shouldnít have believed, illustrates a fundamental problem in science, believing what people tell you. Go and find it out for yourself. That same error has persisted in my life and in many other peopleís. Authorities are not always authorities on everything; they often cling to their own mistakes. But Shapley was a remarkable personality, thereís no doubt about it, and had a great deal to do with the growth of astronomy not only at Harvard but in the country. His attitude as a working scientist changed radically with time. My opinion of him kept on dropping, later as a Ph.D. student. It is unfair to forget his early scientific achievements. In any case, he was a charmer; you canít write the history of astronomy in this country without him. Our ideas of the universe come in part from mistakes he made, as well as from fundamental discoveries he made, the eccentric position of our sun in our Milky Way comes from his work hut was misinterpreted. Also for a while he believed galaxies were nearby and contained objects which werenít really stars at all, but that idea vanished rather quickly. As a popularizer of astronomy he had incredible power for a whole generation.
Wright:When you were doing your Masterís in your work at Harvard, what equipment did you use there?
Greenstein:I used published observations when I was an undergraduate. For my Masterís I stayed on another year, 1929-1930, at Harvard, and did theoretical work. As I mentioned, I was supposed to go to England, but had to have my tonsils out, which knocked England out, unfortunately. I never went to work with Milne, and I did more theoretical work for the Masterís, there was no thesis. It was just staying another year, and listened to the observatory staff. In fact, my thesis which was started around 1935 was in part theoretical. I was much more mathematician then than now. I used a telescope at the Harvard Station at a place called Oak Ridge, a little community twenty-five miles from Boston, then in the country. They have a twenty-four inch reflector, a very old-fashioned instrument. So, in connection with the theory of the reddening of light in space, which I obviously stayed in out of disappointment because in between somebody else had discovered it, space produced absorption and reddening. Trumpler of Lick Observatory found it in 1929 and proved it in the very early l930s. When I came back after an episode of family business, I went back into this field in which it was important to develop the theory of absorption and reddening of light by small particles mathematically. I also did experimental work on the law of interstellar reddening using an objective prism in front of the telescope. It produced spectra of very low scale on quite faint stars, and I measured the shape of energy distribution in the spectrum of the reddened B stars compared with unreddened ones. By good luck, it was clear essentially one good month one winter, so I could get enough observing done my first observing.
Wright:This was done about l935-1936 then?
Greenstein:Yes. I was away for four years. I didnít go back to school until the winter of 1934 after I got married, and first did theory, then developed into an observer during that time, 1934-1937. My first work was based on observations published by other people. My thesis observations were really a refinement of the same technique. I had no intention, starting as a junior, to do it again, seven years later, only this time right.
Wright:Now this really doesnít relate to astronomy per se, but what was the social and political atmosphere at Harvard while you were going there?
Greenstein:It had changed enormously. I went there during prosperity, I left during the financial depression of the thirties, and when I came back people had become very socially conscious. It was the time among intellectuals of popularity of orthodox Marxist Communism. Many who had been abstract thinkers were now socially conscious intellectuals. There was discussion of the coming revolution, which never came. The Harvards of my undergraduate and graduate years were different things. The interest, when I was an undergraduate was either in intellectual things, books, art or future professions, law, medicine or business, which were then respectable. In the early thirties, of course, the world had changed, and when I was a graduate student, 1934-1937, people were beginning to feel the importance of politics and Hitler. There were few student activists, individuals, not groups. But Shapley had become interested first in world peace and later in the Soviet Union, and there was a great deal of emphasis on incredible forgotten causes like an ambulance bought for Spain or for Finland when Finland was fighting back the German or the Russian hordes. Of course, a year later, when it was popular to like Russia, we had other things. Political moods began to effect people in the universities. The student revolution thirty odd years later wasnít all that much of a surprise because I do remember a student world in which revolution was at least verbally discussed. Nobody threw bombs, but they talked about it.
Wright:Well, getting back to the depression, I know that you quit school and you worked in your familyís business, in real estate investment.
Wright:Would you care to relate about how this experience might have changed your attitudes, or any changes it might have made in your outlook?
It certainly made an enormous change. One difference I have from most fellow scientists is that early middle class, prosperous background. The other was the fact that there were four miserable years, now that I think of it, that were terrible during the depression in New York, with the closing of the banks, the bankruptcies of businesses, poverty and unemployment of the people, the beginning of Rooseveltís New Deal. The whole U.S. attitude toward society had to change. My attitude changed in that I had some, but not enormous interest in social problems, more importantly I also got a much better feeling for people, for dealing with people, than I would have if it had not happened. I would never have met genuinely poor people. But for a couple of years I collected installment accounts for my fatherís then defunct furniture business and rents from people without money. I even sold leftover materials to department stores, an experience which is good for you, only if you have it once only. I saw people jump out of windows for financial reasons which was rather frightening. I also learned to talk to bankers and to wealthy people, who even then had money and power; I learned to talk to foreign-born people. You get democratized once and for all by a depression in a way that no one now alive can understand in the United States. Europeans are closer to that reality.
People who were through the depression just like the refugees from Hitlerís Germany look at everything in a different way than people who didnít experience it. Just as a vignette, I remember the day Roosevelt officially closed down the banking system of the country. My father was a director of a bank which eventually was closed permanently. The director, and I, and essentially everybody in the financial and business district, went out in the streets. They walked around, they talked, and they ate sandwiches and hot dogs in public. For the first time some people got out of the business world to see that it was, possibly, dead for good, and that they would have to be just people. And it was fun. There was a certain strange abrupt lift in mood. Of course, nothing got better quickly. It got worse for another couple of years, but it was fun in a strange and weird way. By then I was convinced that I wanted to be a professional astronomer, but my family couldnít afford to send me to school and was still used to living pretty well; I stayed on, and made some money. The last year in business I made more money and left business with real estate investments which partially supported me for many years, from the bottom of the depression, 1934. I made more money that year, with almost no income tax, than until a few years ago as a successful professor. So, the depression was bad, and it was terrible, and many people didnít survive, but it made me much more a human being than I would have been. I had a Masterís degree at twenty, could have had a Ph.D. at twenty-two or three, and gone on probably in academic life, and never would have been anything but a professor, and though Iím proud especially to be a professor and proud to be my particular kind, I have other interests. I also learned a little bit about politics out of it.
I kept my strong interest in arts literature first, then visual arts from the times when I wandered New York looking for somebody who had any money to buy a building, which didn't cost much in those days, but in between, Iíd stop off at art galleries. I met the famous photographer Stieglitz, met many modern artists at that time, kept up friendships with a few well-known people now. But thatís a completely different story. Of course, later in the mid-thirties, when I was back at Harvard, we met people from Europe, I mentioned to you Martin Schwarzschild who was a visitor here, and one of the great astronomers of this generation. I remember meeting him at the railroad station in Boston, Shapley told me that this young refugee was coming and his father was Karl Schwarzschild. So I went to meet him. He came from Germany, a little fellow, with a knapsack, and thatís all he had; and of course he had his brains and he was a charming person then. But the Depression and Hitler had a strange effect. Hitler helped the United States win World War II, and sent us the great Hungarians and Germans, and those two things I think were terribly important to the history of people roughly my age. I canít think of it with great gratitude, but you went through it, and got through it and it was good for you.
Wright:Well during your work, your Ph.D. work at Harvard, what professors did you work under, and maybe you could give some impressions of that work.
There had been a great change in astronomy, going on when I was an undergraduate and fully developed by 1934-1938. At Harvard by that time a good number of relatively young people had been brought in by Shapley who proved quite important to the total history of astronomy. The professor I worked with on my thesis was Bart Bok, from Holland who recently retired as professor at the University of Arizona, who in between has been Director of the Observatory of the Australian National University. He was my thesis advisor, interested in the structure of the galaxy. Our view of the galaxy was affected by interstellar absorption, and thatís what I worked on. On the other hand, my thesis was largely theoretical and he was not a theorist. I was influenced by Cecilia Payne, a British theorist, a student of Sir Arthur Eddington, and I got a lot from her. The other very important person was Donald Menzel, who became director of the Harvard Observatory after Shapley who was a purely theoretical person from the University of California, the Lick Observatory.
He was interested in the properties of the sun, of the gases in space, what we call emission nebulae or planetary nebulae, and also in astrophysics, the structure of the atmosphere of the stars, one of the pioneers of that, in, this country I didnít work with Menzel but most theoretical students did. Many of them are now important leaders in the United States. It was a great period at Harvard, and you have to give Shapley credit for bringing in such people. Students of Bok and Menzel for many years dominated astronomy. It stayed as one of the leading graduate schools until World War II. The most interesting change possibly at Harvard was that it had serious summer lectures by visitors. They brought in lots of Europeans; very famous European astronomers, during these Harvard summer schools when I was a graduate student. I met Jan Oort, who discovered the rotation of our Milky Way, and Pannekoek, also from Holland, expert on the solar atmosphere and quite a good theorist. I met H.P. Robertson, then of Princeton, later at Cal Tech, a great relativity expert who became one of my best friends, and Otto Struve, Director of Yerkes Observatory, with whom I later worked. The summer courses were really attended by visitors from all over the country, and lectures by visitors were, in fact, a great institution at Harvard. The Harvard Graduate School was a place that formed American astronomy almost completely for a generation from Iíd say the mid-thirties until the war began. Of course then it was cut off like everything else. After Iíd left Harvard I went back, in fact, for one more summer in 1939. The last possible year, the last year people came from Europe. It was a sad ending.
Wright:Do you have any anecdotes you would care to relate about your work with Bok or any of these other individuals youíve mentioned?
Greenstein:Oh, no. That would go on forever.
Wright:Some of them maybe stick out in your mind prominently?
Bok was a wonderful guy. I didnít stay in or appreciate his type of work at all but later I did enjoy working with him. He was a wonderful person; he made it a career to rescue almost certain failures among the students whom he turned into successes. He was a very jolly guy; he told me many things, one of which I would like to keep alive. He said, ďYou know,Ē he said ďĎwhen you lecture about anything, if you canít say it in ten minutes, itís not worth saying. If you canít say it in five minutes, itís not important.Ē He said, ďWhen you give a lecture, you get up to the board, you face the audience and you tell them what youíre going to say, then you say it, and when youíre finished you told them what youíve said so it has structure, form, and anyway, people are stupid so it takes at least three times for them to hear anything. And say it quickly so you have this formal structure, and also speak loud.Ē He spoke loudly. So do I, so Iím clearly influenced by him but he had a very non mathematical and non modern way of looking at things. A classic Dutch, stellar statistical point of view which I didnít pursue any length of time, in fact. And he had people who counted stars; after a guy had counted one million stars, he would get a small ceremony and maybe a cup of tea, and at two million heíd get a cookie also, or something like that.
Menzel, whom I worked less with, and certainly interested me a lot more because he started, in this country at least, much of modern theoretical astrophysics which I have used for a long time. Although Iím an observer, I have always mixed theory and observation. I learned that from him. But other things I learned were that important things in life were often hobbies. As an example, seeing Donald Menzel playing ping-pong with one of his brightest pupils, Leo Goldberg, former Director of the Kitt Peak National Observatory and perhaps the leading organizer and planner, as well as a good scientist, the two of them fiendishly scowling at this one-inch ping-pong ball, slamming it at each other as if they could kill each other, or watching them play bridge late at night with every card clearly in their memory and every mistake forever engraved on it, you just learned that life requires a certain degree of competitiveness. A pretty important thing to realize. I had myself learned a lot of this the harder way, in the business world, too. Donald Menzel taught me another extracurricular thing in that area.
He had a cottage out near the observing station which turned into an absolute mud puddle in mid-summer with green algae and filthy brown water. I rented the cottageís cottage the first summer I was a graduate student and without my wife. This little shack was on the Menzel puddle, where Goldberg and I and another guy lived out there and bathed in a trickle of water that came over a little dam, to keep cool and to wash off the poison ivy from our legs because the outhouse was surrounded by poison ivy. We did our own cooking with steaks that cost twenty-five cents a pound. They played bridge and ping-pong with Donald until two or three in the morning, got up again to work. With Menzelís insights into theory, though not the deepest were very broad, and he had influence on things I later did. There were essential divisions and strains within the observatory staff. Shapley had his elderly ladies working for twenty-two hundred dollars a year, counting or measuring galaxies, or cepheids; there was Menzel who taught modern astrophysics, there was Bok who taught stellar statistics and structure of galaxy. These were modern subjects at the time, and they have been important since. It was a vivid place and stayed that way for quite a few years after I left.
Wright:Do you have any anecdotes about your lab work while you were there at Harvard?
Greenstein:Humph! Observing astronomy is a weird thing, there is almost no occupation which is more physically unpleasant than working at night, all night, so I remember mostly how bad weather was and how the few times it was clear it was cold as the devil -- clear and cold go together in New England. And youíd work very long nights and then you had to drive back because there was nowhere to sleep there over night, and Iíd be anxious to get back. There was another observer working on another telescope whom I will call the vulgar Bulgar, not to insult any living Bulgarians, nor dead. The vulgar Bulgar would insist at dawn on frying ham and eggs, and as blue smoke filled the tiny little galley, the sun was rising, and I wanted to go to sleep. It was just sabotage, itís the only word for it, though it had not yet been invented. I could have killed him after a while. But observing is very hard work. You never really get so that you can say that itís joyful, and I never got so I could particularly sleep after that, but it was worth doing because you learn in the process, even though it was a rather elementary kind of observing, even for those times. You learn quickly how hard it is to get a fact. People think that the mad scientist looks through the big eye, and comes out shouting to the reporters, ďEureka,Ē or whatever. A single fact involves a tedious, incredibly long, difficult process in astronomy. You fight sleep, the tendency to make mistakes, to get hysteria, and Iíve been doing it essentially since that time. Probably I have observed twenty or thirty nights a year, on the average. Maybe in the early years, forty or fifty nights, now that I think of it. I can just tell you it is one lump of beauty mixed with lots of incredible boredom and discomfort.
Wright:I found a paper that was published, soon after you received your Ph.D. on the temperature of extragalactic nebulae and the redshift correction, and you indicated that it seems improbable that the effect of the redshift on the apparent magnitudes of the nebulae found by Hubble could be interpreted either as a velocity or a non-velocity shift. Would you care to comment on your perception of this paper at the time you wrote it?
Itís a long time ago, I guess youíd have to have a long background to understand. That paper was written after Iíd gone to the Yerkes Observatory and after Otto Struve suggested a new instrument to myself and another young recent Ph.D., Louis Henyey. The question was what the most efficient possible astronomical spectrograph, a sort of midnight question, what would you do to make the best one? So we dreamed up a new scheme which turned out in fact to be good. We had it built within a few weeks at Yerkes, out of existing optical parts; later we took it down to the McDonald Observatory, in west Texas. It was called the nebular spectrograph. We could study the spectra of gaseous emission nebulae. It lead to the discovery of ionized hydrogen (H II) regions. What you asked me about was the spectrum of the Andromeda Nebula, M31, which was done so as to get the light emitted over a wide range of wave lengths. Based on measures on stars, of known absolute brightness, I could study M31. I found that the Andromeda nebula was much redder than Hubble had assumed in interpreting the velocity-distance relation while working on the cosmological problems. Since this nebular spectrograph was efficient far into the ultraviolet, I derived the flux of the typical galaxy in the far violet.
Now when a galaxy is red shifted, Itís that ultra violet light that appears in the normal wavelength region. This had the following significance. If the nebula is faint in the violet when itís red shifted, it will appear to us to be much fainter than if it had high energy in the ultra violet. If it had a flat spectrum at all wavelengths, the shift would not change the energy received, except for relativistic effects. But in the interpretation of red shifts, there are three corrections needed. One is that each photon is decreased in energy because it is shifted to lower frequency. Energy is the quantum constant times the frequency. So at lower frequency, each photon is less energetic. Next the number of photons arising per second is reduced, and finally if the spectrum is not flat, there were fewer photons in the ultraviolet. Well, I was a young scientist in those days, only the second year after my Ph.D., and here I was attacking a very important paper by Hubble and Tolman. Tolman was a good theorist in relativity, he also wrote the famous textbook on thermodynamics, which you may have seen as a student of chemistry. As a theoretical person he helped Hubble interpret not only the red shift-brightness relation but Hubbleís counts of the nebulae at faint apparent magnitude. This went much fainter than his redshift measures could go, and based on that Hubble had gotten not only a velocity distance relation but a certain aspect of cosmology, the deceleration of the expansion, which is still under discussion. My work showed that there was a big error in a certain coefficient, which measures the correction to the brightness caused by the redshift, the K-correction. Hubble had adopted a high temperature, but I measured it to be lower than he thought. I remember the first time I ever met Hubble. After my paper had been published I had sent him a reprint. He looked at me with absolutely no expression and said, ďWe know at Mount Wilson that the distribution of energy in the galaxies is so and so.Ē This rather upset me, but on the other hand, by that time I had begun to realize that if an expert tells you something it is not necessarily right, no matter how great he is. This attitude I have treasured ever since.
Now I am the old S.O.B. I have to be careful how I talk to young people because of that, or I, like Hubble, Iíll be wrong. This same study of the ultraviolet distribution in galaxies has been done again, by Code at Mt. Wilson and by Whitford, who was Director of the Lick Observatory. Even when Hubble and Tolman first worked they had allowed as a possibility that the redshifts were not of cosmological origin. Then the correction to the brightness produced by a given redshift is different. With a 10% redshift there will be a 20% difference beyond the inverse-square law. If it is a non-cosmological redshift, it is only 10%. Now the point is that much else was wrong, though nobody knew it at the time. Fundamentally, one error was that the brightness of the galaxies was wrongly estimated. There was an error in the brightness scale for faint stars and galaxies that has made a big correction to Hubbleís early work. So that many of the observations had been wrong that had been used in the very good papers by Hubble and Tolman. The fact is that what I found made them impossible to interpret; later when the true brightness and true scale of the universe were derived, most of these discrepancies disappeared. So all I had done was ďdrive a coffin nail,Ē though it wasnít in the right problem. The answer wasnít discovered until about seventeen years later. By the way, the rate of expansion of the universe in the 1930s was supposed to be 500 Km/sec./million parsecs and now it is about 50 or 60 Km/sec./million parsecs.
Wright:About the time you were at Harvard, somewhat earlier, Hubble determined the distance of the Cepheid variables in M 31. Strong evidence of the galaxies existed outside the Milky Way. Was this theory conceptually accepted by your professors?
Greenstein:By the time I went back it was accepted. Shapleyís earlier mistakes had been discretely buried, because Hubble had completely proved the universality of the period-luminosity relationship.
Wright:In 1929, Hubble formulated the relationship between the distance and the recessional velocities, and then in 1934 he showed that the distant galaxies are uniformly distributed to the limit of what could be observed. How were these works perceived by you and your professors?
Greenstein:Well at first as the God given truth, and certainly I learned that when I was at Harvard. The question brought up about this so-called K correction, which I worked on much later, made the galaxies very non uniform. In fact, if the counts that Hubble had made were right, and my work was right, which it was, and the Hubble-Tolman paper was right, then the density of galaxies increased enormously when they were more distant. Iíd made them appear intrinsically fainter and therefore they disappeared essentially very rapidly. Therefore, if you see a lot, you have to assume many more at great distances. So this issue has been fought over. But nevertheless, if you asked me the picture of the universe I got, it certainly was the expanding universe with uniform density and a very large Hubble constant, so-called, five hundred odd kilometers a second/mega parsec, I mentioned. This is what we got educated on. When Sandage began to work, he was among the first students here when I started the department, that was the number, five hundred; it shrank. As somebody put it, between 1948 and 1958 the universe got ten times bigger. In other words, it expanded at ten times the velocity of light, from being half a billion light years across to five billion, with just a stroke of the pen. So thereís been a lot of change from the original Hubble picture, but conceptually itís the same. The big outline is still the same, and we hope correct.
Wright:You mentioned Trumpler, I think, before, then in 1930 he showed that from data on galactic star clusters that interstellar absorption existed. Did this work influence your later work on the selective absorption based on spectroscopy?
Greenstein:Oh yes. Actually it was a terribly significant thing. He found it from different methods than reddening, but rather from the changing apparent size of the galactic clusters. It was so important to change the size of our Milky Way from a few thousand light years to a hundred thousand light years the minute you knew absorption was important. Having a more theoretical point of view then, than I do now, I started from a theory of small dust particles. Thatís why I worked on it. It had a great deal to do with Bokís work on the structure of the Milky Way. Thatís why, in fact thatís how in a sense I got to work with him, Trumplerís was a completely clear proof. I remember the day that that paper reached Harvard. People ran around the hails whispering to each other, and got more or less ill because I realized that I had said it a year and a half ago. My attitude towards Shapley is colored by events of forty-six years ago, 1928. Bad for me as an oral historian, I am too involved. Trumplerís work, heís a much forgotten astronomers in many areas was extremely important. He never published most of his results, unfortunately, but did publish that, and it made all the difference,
Wright:How did you perceive the field of spectroscopy and stellar evolution prior to your decision to concentrate your efforts in the field?
Well I remember I was scared to the devil of it; the area connected with gaseous nebulae that Menzel worked on was perfectly straight forward and was growing rapidly when I was a graduate student the second time. On the other hand, stars and the sun were terribly complicated, and theory was much more primitive, although there was a rapid development in the mid thirties. Eddington and Milne had laid the groundwork for it; Pannekoek, whose name I mentioned; the German Albrecht Unsold; and Henry Norris Russell, American, had founded the spectroscopy of the sun on good grounds. In 1938 in the summer school, Rupert Wildt from Yale, of German background, had brought over from physical chemistry the concept of the negative hydrogen ion. I heard the first lectures about that soon after his discovery of its importance in astronomy, and that changed stellar spectroscopy. Previously there had been quite a mysterious discrepancy. The sun, for example, was supposed to have a composition which would make it about one-half heavy elements, and the other half hydrogen and helium.
The sudden discovery of H minus as we called it, the negative ion of hydrogen, as a source of opacity, suddenly dropped the metals from that important position to less than one percent by weight of the material of the sunís atmosphere, and thatís true. That happened in 1938, an important discovery. Struve came and spoke and I met him. Eventually he invited me to come for my post Doctoral Fellowship to Yerkes. He was a spectroscopist and he scared me. Everything about it was scary. With the nebular spectrograph I began to work in it and suddenly found it was fascinating. Then Struve said, in a conversation, he was a really great leader that way, ďYou know, Jesse, you ought to work on a certain star, Upsilon Sagittarius. It is really a fascinating star.Ē In a certain sense I made a living for five or six years out of that one star and it is still a fascinating, not understood star. Itís the first star in which you could clearly demonstrate an enormous difference in chemical composition from the sun. It had almost no hydrogen. It was made largely of helium, and had much too much nitrogen and neon. Itís still a mystery in many ways. Itís a super, super giant, highly luminous star in a binary system which emits too much infrared light and doesnít have any hydrogen. But it was the first star ever analyzed that had a different composition, and I started that area of spectroscopy in the late thirties. It continued when McDonaldís Observatory big reflector was built, and that became a revolutionary period, unfortunately, just a year or so before the war broke out, hut it proved to be something I liked to do ever since. The changes of composition proved to make sense from nuclear physics.
Wright:You mentioned that Otto Struve was instrumental in having you come to Yerkes. I assume you worked with the forty-inch refractor?
Greenstein:Yeh, a classic instrument.
Wright:Who were some of the other members of the staff at Yerkes at that time?
Well, Yerkes, thatís a very interesting question. Observatories, scientific groups, are like, I guess species, biological species. They have a time when they flower, and a time when a new rival comes up and takes over and the first dies off. At that time Yerkesí great strength which Stuve had achieved was that it was populated by some of the very best scientists, many of them European. He had brought over from Europe just about the cream of the people whom he could get. The famous names at Yerkes I guess, in addition to Struve, were Chandrasekhar, the distinguished theoretician who dominated many areas of theoretical astrophysics for generations. Gerard Kuiper, who was a planetary expert but at that time was interested in intrinsically faint stars, so-called M dwarfs and the white dwarfs, which I later took over. W.W. Morgan, who invented modern accurate techniques of classifying stars on a very small scale, from spectra a few millimeters long.
You could recognize the temperature, intrinsic luminosity and peculiar compositions, and this really artistic multi-dimensional classification was being invented, was on-going at that time. Letís see, and then van Biesbroeck, who measured stars, a field which has been neglected. He eventually died recently at the age of ninety-nine, observing almost to the day before he died. Letís see, Henyey, who was a young theorist and a real mathematical wizard with whom I worked on the nebular spectrograph, on the theory of dust clouds, and many other areas. Henyey later went to Berkeley and developed the present computer techniques for stellar interiors and evolution. He became head of Berkeleyís computing center at Livermore. That was a classified facility; the big computer which he used for stellar evolution was out there, and Henyey worked with them. And another thing Struve did was bring from Europe many visitors, one of whom, Polydor Swings from Belgium, was a world expert on cometary spectra and on molecules in stars. Another German, Karl Wurm, worked on spectra of gaseous nebulae and the theory of atomic structure relevant to the production of spectra, in gas clouds. Later there was Beugt Stromgren, a leading theorist. Iím sure Iím forgetting some of the most important people, but that group of Struve, Chandrasekhar, Kuiper, Morgan, certainly was about the best. Soon the leadership in astrophysics was clearly centered at Yerkes during the very fortunate period that I was there.
During that time the Mt. Wilson people had the hundred inch and the sixty inch. So they had a bigger telescope than Yerkes which had the eighty-two inch in Texas to operate. But unfortunately, the Mt. Wilson group hadnít done as much innovation and there were no theorists in these areas. Although they did important spectroscopic observation, they did almost nothing about quantitative interpretation. Yet simultaneously stellar atmospheres and gaseous nebular theory were well developed, so one could begin to do quantitative analysis of stars and gas clouds, and that was never done in the thirties and early forties at Mt. Wilson. It has become a great thing here and everywhere since. But because of this largely European influence and the good theorists that Struve kept bringing in, plus observations first with the forty inch, a primitive telescope of the l890s, still used by Morgan almost exclusively for his classification work. Then Yerkes had the use the McDonald eighty-two inch of the University of Texas. Texas didnít then have an astronomer. I think the Provost of Texas at that time, who had been the Provost at Chicago and Texas, called Hutchins at the University of Chicago and said, ďWhat about doing something about our new multi-million dollar gift for a big telescope.Ē Hutchins asked Struve, who took over leadership and arranged that Yerkes would supervise the building of the McDonald telescope, which was done, and use it, and eventually Texas would develop its own staff over a period of over twenty years. Now it has an excellent and very large staff, but for that twenty years or so the McDonald telescope was certainly the most modern telescope and provided Yerkes a great opportunity. Not as big as the hundred inch, it had a lot of important stuff on it. Balances began shifting, the astrophysicists who used to go to Harvard came to Yerkes, and thus each place shifts. If youíre interested in the sociology of dominant scientific groups youíd wonder when we in Pasadena are to be knocked off our perch, and by whom.
Wright:Do you have any idea how Struve came to select Mt. Locke in Texas for the location of the McDonald?
Greenstein:I donít know too much about that. That happened before I arrived.
Wright:That had already been settled?
Greenstein:Well, yeah. The telescope went into operation in 1939, by which time I became a faculty member at the University of Chicago and Yerkes. Before that Iíd been a postdoctoral fellow of the National Research Council, and I got on the faculty when the telescope just began working in 1939. My guess is that it was a constraint that it be in Texas; it had to be on a mountain, and it had to be away from the wet air of east and central Texas. The Pecos Mountains are among the highest in Texas, theyíre relatively well situated. It has a poor summer climate, only because of mountain thunderstorms, but otherwise itís got a reasonably good location. Fortunately, itís still probably the darkest observatory in the continental United States, because there are no big cities anywhere near, and so it stayed a competitive instrument. It was named after Struve some years ago they got a hundred and seven inch from the Space Agency, and so itís a very important place. I know nothing of its earliest history however.
Wright:Could you compare the seeing conditions of McDonald with the Williams Bay location of Yerkes, being close to Milwaukee and Chicago?
Greenstein:Oh well, I donít think the cities affected Yerkes because all its equipment was still on a relatively ďprimitiveĒ side. It didnít matter if it was near a city almost, but Yerkes is in the continental weather pattern, which means that itís cloudy almost all the time if it isnít snowing or raining. It had about probably a hundred good nights a year, while McDonald with maybe two hundred and thirty or forty, just a guess, was infinitely better. Seeing is different from transparency. Seeing is the turbulence and the seeing at McDonald is only average, probably not greatly different from that at Yerkes. When itís clear at Yerkes you can have terrible seeing if itís a very bad cold snap or sometimes moderately good seeing. McDonald has often dreadful seeing due to a certain weather condition in Texas called the ďnortheasterĒ or ďnortherĒ where a very cold wind blows across the plains, and the images of the stars go away, even though itís completely clear. Both are inferior to Arizona or to the west coast observatories. McDonald was fairly good, and I imagine they must have made some kind of reasonably good search.
Wright:From an operational and optical standpoint, how would you characterize the McDonald telescope?
Greenstein:Very good. Very good. Itís one of the first modern telescopes. The optical instruments on it were extremely good. Thatís why we did really very well for quite a few years at McDonald, both on gaseous nebulae, peculiar or faint stars or high-dispersion spectra of stars on which I worked. It had quite decent equipment, and after the war, by the time I was leaving, it already had some of the first infrared equipment which Kuiper had gotten because he knew of military developments at the end of World War II. At that time Kuiper began working on the planets with infrared. So it stayed modern pretty well through the 1950s, and has started in quite well again recently.
Wright:Could you tell us how and why you and Henyey developed the hundred and forty degree camera thatís been used for photographing the Milky Way.
You know too much. Thatís come from a military requirement. I stayed at Yerkes through the war, working for the National Research Council on optical designs for the military. I turned out more and more practical and Henyey more and more theoretical as time went by. I would gather ideas of what was needed, such as tank and antitank gun sights, bomb sights, submarine periscopes, searchlights and testing equipment. Henyey would go home to think it over, and come back with a lot of equations, and then weíd go to our desk calculators and work for weeks, even months. We had a little shop building one of-a-kind military prototypes. That went on for I guess four years. The wide-field camera started as a device the Navy wanted to use as a projector for simulated air plane attacks on, say, a big bomber like the B-29, to train gunners to track them. They had used a thing called the Waller Trainer, which consisted of seven movie projectors and seven screens.
They would photograph models in a true trajectory. Then the gunner would shoot his make-believe machine gun, which projected an invisible beam of light. If he was pointed at the right place to hit it, it would score for him. This awkward thing which existed as a building, I think, one of a kind, somewhere on the east coast, had been developed by the Navy Bureau of Special Devices. We replaced it with a one projector, which could double as a camera. Unfortunately for us the war ended, although we built five of them, I think. Two went to an Air Force museum and we liberated a couple for astronomy, and I think those were the ones used for pictures youíve seen. The Russians, by the way, invented an all sky camera which was much worse for auroral photography. Incidentally, this whole development was the predecessor of the wide screen Cinerama or Todd AO process. The Todd American Optical thing was, in fact, a lineal descendant of our military device, improved on by a guy at the University of Rochester. After the war he turned it into a camera with a lens in front of it, and ours was a camera with a mirror in front of it. I can give you one true anecdote you didnít ask for. When I told my son, then, I think, five years old, that Hopalong Cassidy had called me up about some wide-screen process which he might buy to develop it for commercial purposes, my son said, ďDad, I didnít think that an important man like Hopalong Cassidy would call you up.Ē
Greenstein:Thatís unfortunately a true story. In any case, Henyey and I did a lot of that kind of thing. That particular camera is in fact about the ultimate, about an F-1 camera which can cover all of the sky.
Wright:After World War II, your interest appears to have shifted to radio astronomy. What were the circumstances that you came to work with one of the pioneers of radio astronomy, Grote Reber?
About 1936 I got interested in an even more pioneering radio astronomer, the man who first found radio signals from space, Jansky. I was working with a young professor at Harvard named Fred Whipple. He and I developed a theory to explain Janskyís work. But it proved to be incorrect. What we did was right, but it couldnít explain the strength of Janskyís signals. When I was a boy I used to live on the Jersey seacoast in the summers and Iíd see these radio transmitters that belonged to the Bell Telephone System and R.C.A., I guess, near the coast of New Jersey. So being a radio amateur I stayed interested. Then during the last years of the war I met Grote Reber, unmarried and living with his mother in a town sixty miles south of Yerkes. He came to the attention of Chandrasekhar, who was editor of the Astrophysical Journal, because he sent in a paper. Nobody had ever heard of him, but he claimed detection of radio signals from the center of our Milky Way at a hundred and sixty megacycles frequency, about five times Janskyís frequency. I heard about it and I immediately realized that if Reber was correct and Jansky was correct, it was absolutely impossible to explain Janskyís signals by the method which he and I tried ten years earlier. It was obvious that there was a genuine mystery. Chandrasekhar was worried as to whether Reberís paper was telling the truth or whether he had, in fact, turned a knob behind his receiver. How could he be a scientist without a B.S. degree? Kuiper, whom I mentioned had been working during the war on radar and radar countermeasures, was supposedly our ďelectronics wizardĒ at Yerkes. Kuiper visited Reber, I did not, at first. He came back convinced that Reber was telling the truth, that he was a sincere observer, even if not academically literate. He was certainly a good engineer.
When later I met Reber we got friendly. When Reber developed an even higher frequency receiver, and with the same radio antenna found the signals at five hundred megacycles, it became clear that whatever else you could say about radio signals, they were what we now call of non- thermal origin. They could not he produced by any object which radiates its heat at a temperature. Nor could they be produced by antennae radiating on other worlds, for example, thought of, much later, in connection with the pulsars. They were natural. They came from the center of the Milky Way and elsewhere in the Milky Way and they were non-thermal. Nobody had a theory until about 1951, I think, when a Soviet astronomer, Shklovsky, said they were from high energy electrons in magnetic fields, which proved clearly correct. But at Yerkes, since Reber was nearby, we were conscious of radio astronomy, and I was interested in it, having earlier failed thoroughly. Henyey and I and Keenan, a staff member in spectroscopy, wrote another paper, which also failed to explain the radio signals as coming from an optically thin thermal plasma at ten thousand degrees such as we know exists in gaseous nebulae. The trouble with the spectrum of the radio radiation in space is that the higher the frequency, the lower the temperature required. At the low frequencies with which Jansky had observed it had been above a million degrees signal, and at Reber frequencies it was in the thirty to hundred thousand degree range. It just didnít make any sense at all, but Janskyís observations and Reberís, together, were explained by Shklovsky, a Russian, by this non-thermal method. It gives a spectrum which decreases in brightness from low frequencies to high with a power law.
The exponent of that power law frequency decrease, which was really well established by these early observations, Shklovsky used to show that it was the same power law spectrum that you have for cosmic ray protons. He required, in facts that there were cosmic ray electrons in space, never detected before. There was a sudden explosion of ideas concerning whatís really modern plasma physics in space, magnetic fields, containing and accelerating particles. This was an enormous revolution. it made radio astronomy such an exciting new tool that one of the first things that happened when I came here was the conclusion that we just must have a good radio observatory in this country. We didnít at the time, although Jansky had found radio signals twenty-two years earlier. In 1954 we had a conference to see whether radio astronomy was ďrespectable science.Ē That was organized through DuBridge, then President of Cal Tech, and me, because we wanted to know whether it was worth our while to build a radio observatory. Thatís how chancy it seemed then. In the 1946 period some were not sure whether Reber was a crank or not. In 1947 Reber and I wrote a long article reviewing the then previously classified work on radio detections during the war, on the sun, and the galaxies, and published it in an English journal. Most of the work had been done in England, Australia, a little in the United States.
Wright:Could you tell a little bit about the equipment that Reber was using?
Greenstein:Reber had built a wooden frame in his motherís back yard, and then he built a parabola which I think was about thirty feet in diameter. There was a receiver detection unit at the focus of the parabola. He could only turn it north-south, to a certain angle from the horizon, and let the sky move by. He would then record signal strength as a function of time on a moving chart galvanometer. Reber, being a radio engineer, working with some company, Admiral radio I think it was, had known about these high frequency detection methods in radar for military purpose, and had ďliberated,Ē whether legally or illegally I don't know the first high-frequency tubes for radar receivers that he could get. This made it possible for him to detect weak signals; thirty footís a pretty good size for the frequency used. Not being able to turn it to follow meant that he could only observe a short time on any one object, hut by letting time pass and doing it another day and another day, and by tilting it, he could map the sky. The whole thing came out on a paper chart recorder, rather well, considering that it was completely his own, built and paid for it by himself.
Wright:Do you have any more original reminiscences of Reber?
Greenstein:Oh an absolutely original person, with no respect for theory or academic life, he was a bachelor, I guess still is, very individualistic -- typical American inventor. If heíd had commercial sense, heíd have been rich at something, but he liked to putter and he was free to do so. When we worked together for a bit, he knew everything that was going on in radio astronomy. Thatís how we got to write this first postwar article in an English magazine on the subject. He was sufficiently a ďlone wolfĒ that he couldnít work, really, with any of the later developers of large instruments and observatories. He had to work on his own, and so he eventually made the wrong choice. He decided that radio astronomy should be done, as he put it, ďwhere the power is,Ē at low frequency. Unfortunately, thereís no high directivity possible at these low frequencies. Heís tried to measure the lowest possible frequency radiations that can only rarely get through the earthís ionosphere. He chose to go to New Zealand with a very low frequency receiver to get signals coming in at the south geomagnetic pole, which is near there. Itís had little scientific impact, more curiosity value. Heís had various other quite original ideas, but he couldnít work with a group like the National Radio Observatory. Theyíve got his antenna there on exhibit, and thereís a lectureship on radio astronomy once a year to the best contribution in the field in this country called the Reber Lecture, and so forth. Unfortunately, he dropped out of leadership in planning radio astronomy early, when it was beginning to boom in the United States. Itís good to be a ďlone wolf,Ē but not for too long, especially when a thing becomes a success. Everybody gets into it, with millions of dollars, and big staffs.
Wright:In 1948 you were selected by Cal Tech to be a professor and to found their Astrophysics department. Can you describe your feelings on your selection in the light of the Rockefeller Foundation designation of Cal Tech to operate the soon to be dedicated two hundred inch at Palomar?
Greenstein:Well, I was flattered to hell, to put it mildly. I had just refused an offer to go to another major place -- I guess we shouldnít mention it -- eventually to become its director. They asked me again ten years ago. I was flattered then, and I am now. I felt terribly pleased. We had spent eleven years at Yerkes. Having come from a New York background, also my wifeís background, eleven years in a small town in the Midwest I guess were enough, but to come here seemed a great opportunity. Bob Robertson, a Relativity expert, was here and he had something to do with it. He invited me to come see, and I loved the idea and the opportunity and I leapt into it with great pleasure. Further, of course, after the war I had been changing, getting back to science from this military type thing. Life had moved in such a way that I was looking for some completely new thing to do. I didnít want to do gaseous nebulae and interstellar matter anymore. I needed to do more spectroscopy at Mt. Wilson which was then running and had a very good spectrograph. There was the further opportunity that Palomar had essentially no staff, just one person, Fritz Zwicky. So there was the whole question of the staff that would be built up for Palomar and I as a teacher didnít feel terribly qualified. On the other hand it sounded like it would be good fun too, so we came. There was very little question about that. I would say in all honesty Iím almost certain I was second choice, and the first choice was certainly obvious, but he wouldnít come, so I was delighted to be asked to be second. It was good enough.
Wright:Would you care to relate some anecdotes on the success or possibly failures in connection with managing the Astronomy department at Cal Tech?
Greenstein:Well that would take too long.
Wright:Maybe some outstanding ones.
That whole area is a very full and fascinating one. First of all, for a year or two I was the only person here giving any formal instruction. Although by then I was much more experimentally than theoretically inclined, youíre not a great theorist for a very long time in astronomy. I had done my work, my thesis, mathematically really twenty years before, so as a mathematician I left something to be desired. So having to teach some pretty bright students, some of whom have succeeded, both stellar interiors and stellar atmospheres, I was not often very far ahead of the students. One of the more flattering things is that Allan Sandage every now and then tells me how frightened he was of me as a teacher. I was scared of him, and also scared of most other people. I was also scared of the fact that if I ran out of material on the particular aspect of the convergents of solutions in matching stellar-interior models in one lecture, I couldnít be sure I could go on beyond that point, because I was learning as I went. I had never done stellar-interior evolutions. Next, I knew absolutely nothing about nuclear physics when I came here, but I learned, although I didnít know any quantum mechanics. I enjoyed studying low energy nuclear physics for three years, which I did, and applied it, although it was pretty traumatic since Iíd never heard of it when an undergraduate at Harvard since there was no such thing.
Nuclear energy levels exist, like atomic ones, and there are problems of the structure of nuclear energy levels that are important to stellar interiors, to the origin of chemical elements, which are similar to vibrational rotational structures of a molecule, Different selection rules and different quantum numbers are involved. Well, going through all of that and keeping ahead of the boys, and also nuclear synthesis, which had come along as a possibility, and nuclear energy sources, which were beginning to be understood, meant that teaching here was trouble. First of all we had three students, I think, the first year. One of them was Sandage, another was Helmut Apt, second in charge at Kitt Peak, the editor of the Astrophysical Journal now, so it wasnít an easy year. Neither for the boys was it easy, and they all had problems. They were all out of the military, you see, and they were older and it was a little hard to get accustomed to the tough life they were facing at Cal Tech. We expected and got a lot from them. The problems of getting staff were very interesting, because we had to have a staff that would he capable of using Palomar which became fully operational in three or four years.
They had to help design instruments, and thatís something I knew nothing about. Ií did know many young people all over the country, and that was a plus for me, and I had complete support from Cal Tech administration and from the physicists. The place was much smaller, more informal, anxious to help astronomy grow. I would say until oh, seven or eight years ago, I never asked for anything seriously at Cal Tech that I didnít get in the way of appointments, money, and so forth. Palomar instrumentation had been pretty well designed, and was being built under the supervision of Bowen, who had been a Cal Tech professor originally in cosmic rays. He resigned as professor at Cal Tech and became director of both places, Mount Wilson and Palomar, and I reported to him and also to the Dean of the Faculty. Bowen gave me further freedom with appointments. For teaching, the Mt. Wilson staff, who worked for the Carnegie Institution of Washington, did some teaching, informally, about one term a person every few years. But there were enough of them that the first few years of teaching here was strengthened by older scientists from Mt. Wilson. Many had never taught in their life, and since there were only three to six students, in the second year, it wasnít all that difficult. It got a little difficult planning for the next year, when we ran out of people who had never tried it, because those who tried it didnít want to repeat, but all in all I think the first few years were excellent for students, some of whom are now great men. They were really pretty well treated, and learned a lot, as I was learning a lot. People became gradually very good; I would imagine, though I wouldnít want to hear their version of it, that it wasnít as traumatic altogether as it seemed at the time. I had seen hysteria, people promising to leave tomorrow, couldnít stand it, in almost all cases we made it and it was fun. You know itís so easy when you have everything either on your side or soon to be. I can imagine how hard it would be to do the same thing in a second-rate institution on a downhill slide. I never had to run a rescue operation. I think Iíve been every place at or near the best times; if you like the mood of failure, I can imagine it, but Iíve never really had it. We had personal failures, you know. We had one guy come who left after about two months and is now a vice president of Bausch and Lomb. He said, ďIf this is science, I donít want to be a scientist,Ē then left, and heís probably right. Yet the advantages were great.
Students who could work on experimental things, could work with the older people from Mt. Wilson, leading astronomers of the world, specifically Walter Baade, in Sandageís case, and a couple of others. In spectroscopy they learned all the theory they needed from me, and from Santa Barbara Street, Carnegie spectroscopists, who were getting old at the time, but who knew a lot. The hundred inch with its Coudť spectrograph was very good. We were weak in the beginning in electronic astronomy, which is now a dominant activity as you know. That was one area where our students for some years were probably not as well treated, either in learning or having things to use. Nobody on the staff did electronics at first. We gradually improved until now weíre up at a level where itís almost too hard to use the stuff. Really, itís almost impossible, and so I would just say in resume, we could add staff members and did, at a rate such that in perhaps six years we had as good a hunch of professors who knew modern areas of theory and who were skilled observers rind who knew what they waited built in the way of auxiliary equipment, that by 1956, at the latest, we were about as good as we were ever going to get. I hope we get better as time goes on but the first few years went very well, although they were harrowing, because I was so damned alone, and I was learning. In 1951 I worked with one of the Cal Tech professors on my last major contribution to the theory of interstellar matter, the origin of stellar polarization, and by 1951 I was making observations on rare elements in stars which were connected with the origin of the elements in stars, so in three years I went through two major personal scientific revolutions. It was not exactly an easy life, but a little later more people came in and it became easy. Eventually the department was rated best in the country.
Wright:You continued your interest in radio astronomy in the early fifties and worked with Minkowski on discrete sources of very high energy outputs. How was this work accepted by the rest of the astronomical community, and how did you perceive its importance at the time, to astronomy?
Well, weíd gotten a radio observatory started by the simple subterfuge of borrowing somebody from Australia. He began building, with Office of Naval Research support, a radio observatory, and he was the guy who first, working in Australia, had identified a galaxy as a radio source. Minkowski got the spectrum of that galaxy, and it had some interesting features, and since Minkowski was non-theoretical, and I was still relatively theoretical, we worked together on that and other radio galaxies. As more were detected, Minkowski would identify them. Minkowski and Baade worked together a lot on identification. Minkowski got spectra and in some cases I did the theory. At this time, radio astronomy was just exploding all over the place and was a very competitive field, but the only place that did any identifications of distant sources was Mt. Wilson - Palomar observatories. Minkowski did photography, which I never did. He would have to start, often, with bad positions, find a strange galaxy, which turned out to be the radio source. That would give the distance from the redshift if you believed in the redshift -- and at that time everybody did -- so the great problem was applying Shklovskyís theory of this High Energy Electrons in Magnetic Fields. It was clear by 1955, so he and I wrote a paper on this subject, and we went to an International meeting in Manchester, England, 1955. It was at the very beginning of the horror of the problems that radio astronomy was going to give us. The energies involved were too large to be explained, their origin was unknown. Had I known how awful it was, I might not have stayed with it, but it was fun.
Maarten Schmidt came here a couple of years later hut itís interesting that he never worked on the radio sources when first here, as a postdoctoral fellow, because others, like Minkowski and Baade, were doing it. I think that we were lucky at first; the dimension of the theoretical problem -- where is all that energy coming from -- was what was involved with. From then on the improvement in radio techniques, especially of positions which in part depended on our own Owens Valley Radio Observatory interferometer, which Bolton developed. Students went into radio astronomy, some from engineering, many from physics. We began to have people doing theses when we couldnít make up an examination committee -- literally true -- because we had so few scientists involved. We didnít have a professor on the radio staff yet, because Bolton was an engineer in background, and there wasnít in America a qualified radio astronomer! They didnít exist, but they do now. We trained first experimentalists people who now are running radio astronomy around the country. The theoretical parts were more or less invented by the students as they did their theses. It was a very rapid period of growth. Soon after this we got into the twenty-one centimeter line which gave a distance scale to hydrogen clouds within our own Milky Way, from the rotation of the Galaxy. This was Maarten Schmidtís thesis! This is a scientific revolution with little or no professorial part in it. The research went on, the kids did it themselves and developed the theory and interpretation themselves. We were not very heavy on the theory unfortunately, in interpreting the radio sources at first. In their location we were leaders and thus we did moderately well for quite a few years.
Wright:About this same time you seem to have shifted your interest, or your attention to spectra studies of planetary nebulae and the relative size of the neutral hydrogen as compared with negative hydrogen regions. Were there any particular reasons for your change of interest or your going into this area?
Greenstein:Well it was one which was very short lived. I was somewhat interested in a similar area. I can tell you one anecdote since you donít want everything serious. On that thing I published a paper with another astronomer at another institution which to my pleasure is so absolutely wrong that it is funny. I can see pretty clearly now. It is the most completely circular piece of reasoning in the whole body of my science. If the universe didnít exist it would still be funny because, in fact, it was just a silly bit of poor logic, and I think, though I worked on the central stars you know, you can get a certain sensitivity to what you donít want to work on [laugh] anymore. I havenít worked on that since. [laugh] Lyman Spitzer and I did an interesting -- my one quantum mechanical job of my whole career. We did a job on the so-called two photon emission where an atom when itís stuck at a certain level doesnít know what to do and it canít get out of it except by emitting two photons that add up to the energy it has got to get rid of instead of one, because itís not allowed to emit one. Thatís relevant to the same nebular problem. This whole area is important, hut not one I contributed to in the long run, the question of the cooling of gas in space when made to shine by high energy particles or by ultraviolet photons. I just got in and out of that area very quickly. I was really turning much more toward the composition studies and their interpretation about the time. Maybe thatís my excuse for having made this one beautiful error. Well, maybe there are other errors in my work, but thereís none which is so clearly zero as that.
Wright:Well, in early periods in your career -- you have been interested in the polarization of light by dust grains. Do you recall how you came to be interested in this aspect of astronomy? Thatís going back, many years.
Yes, quite a while. Well actually what happened is an example of how new science really gets done. Chandrasekhar, who has been a great theoretician, had solved a problem on the light emitted from a star if the opacity of the starís atmosphere was completely by free electrons. The result was a prediction that in a very hot star, the light would he slightly polarized. Then two different groups of people moved, by advances in photoelectric technology, this was a long time ago, one group at the U.S. Naval Observatory, John Hull, the other from Yerkes, named Hiltner, working at McDonald, both found polarization to exist in hot stars. This sounded great except it was about ten times as large as Chandrasekhar predicted, and really had nothing to do with the stars, but originated in interstellar space. Two people independently, Hiltner and Hull, found this from just an experimental improvement, from the high accuracy of polarization measurement. Well, since Iíd done theory, I wanted to see whether it could be explained another way, that is, by interstellar matter. Lyman Spitzer of Princeton, a very distinguished theorist, decided to apply the growing knowledge, pretty generally accepted, that there was some magnetic field in space. This knowledge really predates Shklovskyís use of fields in radio astronomy.
This was from cosmic rays not moving in straight lines, but being deflected by magnetic fields in space. Enrico Fermi had worked out a theory for acceleration of cosmic rays by magnetic fields in space. If there were fields, and Fermi had made an estimate of their size, could we explain polarization? It turned out that Spitzerís theory had neglected an important aspect of dust particle dynamics. He said that the little dust particles were like compass needles oriented by the magnetic fields. While thatís true, it turns out his theory orients them in a wrong direction. In fact, a physics professor, Leverett Davis, an expert on the mechanics of rigid bodies, and I collaborated, with Davis carrying most of the mathematical analysis, which was very difficult. We developed, in 1951, a theory which I think is still correct. We used magnetic fields in which the particles have to spin, because they are always colliding with atoms. They spin up to very high speeds, 1010 cycles or so a second. It is like the molecular rotation in a gas. So we have to orient a rotating particle, not a stationary one. Davis and I worked out the theory, using paramagnetic relaxation with resistive losses, part of solid state physics, plus the dynamics of rigid bodies on which Leverett Davis was an expert. The question of paramagnetic losses in a spinning body is recent physics, and together we worked on that, and I worked out the theory of the polarization fraction produced if you could line up spinning bodies with their long axis perpendicular to the magnetic line of force, which is what happens in the paramagnetic relaxation process. Just as of this year it is possible that a new, more correct explanation has been arrived at by Purcell, a physicist at Harvard. Because his interesting process, while fundamentally the same, involves the particle being non-uniform, it doesnít have to be a needle, just a dirty, mucked-up thing.
Oddly enough that works better than spinning needles because it takes a much smaller magnetic field. Davis and I needed a magnetic field almost ten times larger than Fermi needed to accelerate or trap cosmic rays, and larger than radio astronomers found by direct observation. Our radio astronomers tried to find magnetic fields in space but they couldnít, and they were down by the time they gave up to one-tenth of what we had required to align the particles. The fields have been found since, but are small. Something is still wrong with the theory and itís an open question for over twenty years. But, to have a theory right for twenty-three years is almost a worldís record about a thing as obscure as this. Spitzer added parts to it later in which he used paramagnetic resonance of ferromagnetic materials. The first explanations of the amount of cosmic ray electron energies and magnetic fields in radio sources were incorrect. They evolved from Minkowskiís and Baadeís showing that the galaxies associated with radio galaxies were hot, had too much emission-line energy, compared to ordinary galaxies. They blamed the energy on collisions because the galaxies looked funny; that theory is incorrect. Itís almost certainly an internal explosion which throws out very high energy particles with magnetic fields, just blasts them out at near the speed of light from the explosion. When we first found these things, we didnít know that, and only later was it realized when we knew the enormous energies required that even two galaxies colliding wouldnít produce enough power. This long duration question of how big the magnetic fields are is very important. If they were as high as the original theory required for the alignment of Spitzerís particles, there would be enough power because he required a thousand times bigger magnetic field, which is a million times bigger energy. Well, okay, but itís not that way and so because of these strange radio galaxies, and even the fact that our own galaxy is emitting too much radio waves, which we knew from 1937 on, really, we were left with the fact that there had to be some unknown energy producing process. Now itís almost always blamed or collapse of a relativistic body into a super large black hole or something, millions of solar masses colliding into each other and falling into a hole. Not external collision, an internal collapse. Well, all of this hangs together and so the viability of the scientific field is when new discoveries are still made in it, and new areas keep opening up, when new things have to be explained. This is still going on in this area. I think it will for a long time.
Wright:Your wide breadth of interests were proven when you engaged in some solar work. Do you recall how you came to work with Martin Schwarzschild and Robert Richardson on the abundance of carbon 13 on the sun?
Greenstein:Thatís directly from problems of the source of stellar energy because as the result of the energy released from the center of sun or stars, you predict that the composition of the center changes, depending on whether a reaction rate is fast or slow. If fast, the element will be consumed. If the reaction rate is slow, the element will last a long time under nuclear bombardment. Laboratory nuclear cross-sections predicted that there would be a lot of carbon 13, specifically from the work of Willie Fowler who is head of the Kellogg Radiation Lab of Low Energy Nuclear Physics. Well, they improved nuclear reaction rates to a point that you had to believe them, and there was this prediction that there ought to be a lot of carbon 13. Certain stars were known to have a lot of carbon 13. So we looked at the high resolution solar spectrum and couldnít find carbon l3. I think it has now been found in the spectrum of the carbon monoxide molecule in far infrared. We looked in the violet, where there were no detectable traces, only an upper limit. Many years later I looked in the spectra of a comet and found some carbon 13, in about the same amount as the sun. The surface layers of the sun can only give us upper limits, and this started a train of thought. Maybe you never see stuff from the center of the sun at the surface. To test this out I did later work with other people on other elements in the sun, the sun being by far the best star to observe at very high detail, because itís so bright.
Wright:In conversations with Robert Richardson, he characterized his solar work as not being of very much significance. Perhaps this is more a reflection on Richardsonís personality, but I believe that learning as much about the sun is really a first step in learning about stellar evolution. Would you care to comment on this?
Well, your statement that learning about the sun is the first step is correct. Learning about the details of solar activity has yet not had great importance to stellar evolution. It ultimately will, but the surface of the sun is dominated by the magnetic fields, by the flares, by the prominences, and those are, unfortunately, red herrings. Theyíre so complicated. Itís worse than, but like, meteorology in that thereís no guiding principle that makes it possible for us to tell how weather patterns will move on earth. No, itís not quite that bad in the sun now, hut itís almost that bad. As you look in the far ultraviolet and x-rays, the sun gets even weirder and even more exciting. Itís more dominated by the magnetic field and by the very hot regions, and this tells us a lot about the sun and also about other stars, but unfortunately for ordinary evolution it makes no difference at all. The total effect of all this magnetic activity at the surface is not profound. It is only superficial. It may have something to do with weather on the earth for example. Thatís one reason itís been studied. Predicting flares has some importance, but there is a kind of lack of direct involvement with other areas.
Explaining the behavior of charged particles in magnetic fields by observing the solar envelope is important for plasma physics, I donít understand Richardsonís remark, but as you say it may be personal. Solar physics is now very active. It is somewhat detached from the main body of astrophysics and only recently have astronomers found evidence for similar phenomena on a greater scale on other stars. An astronomer on Santa Barbara Street, Olin Wilson, has been studying stars over some seven or eight years, and finding that certain stars have solar cycles, and that they have variable chromospheres. The outer layer of the sun is a chromosphere. His stars have chromospheres, and these vary in time more or less as in the sun, like the sun spot cycle, only a stary cycle instead, but this is still, as I said, important but not central, whereas magnetic fields in space are, terribly central, very important parts of astronomy and high-energy cosmic ray physics. I donít like his remark, but I donít blame him for feeling that way. I wouldnít have put it quite so harshly.
Wright:Do you have any anecdotes you might care to relate about your work or relationship with Martin Schwarzschild?
Greenstein:Our relationship has been most valuable. You have to meet him yourself to know why thereís nobody in the world like him. Heís terribly bright and terribly careful, and I would say winning a fight with Martin Schwarzschild would be a very great triumph for almost anybody, at any time. Heís extremely vigorous though he is nearly my age, a genius. He says he has a bad memory, but I donít believe it. No, I guess I happen to like him too much that I wouldnít dare say anything funny. Thatís an experience youíve got to get on tape. You can tell him that.
Wright:O.K! Among your more important contributions to stellar evolution since 1957 must be your work on white dwarfs and other subluminous stars. How and why did your interest go in this direction?
Recently I just have been using the same silly joke, ďI guess Iím getting old,Ē but I wasnít all that old in 1957. I think I like problems which suit what I can do, that nobody else can, based on available experimental equipment and technological advances. There must be an important theoretical component, that is, I donít like merely discovery or cataloguing as much as something which illuminates an interesting theoretical question. Perhaps the one part of stellar interior theory which is absolutely certain, and has been for forty years, was developed by Chandrasekhar when he was a student at Cambridge in England, the theory of degenerate matter, very high density matter such as occur in white dwarfs. Well, Chandra developed the theory which at first was arguable, he had a big argument with Eddington, who was his teacher and they parted company on it after Chandra was right. Thereís a major prediction called the mass-radius relation, which says if the starís sufficiently dense, the larger its mass the smaller it gets. Beyond a certain mass, which Chandra determined from theory, without present knowledge, around 1.4 or 1.3 times the mass of the sun, the star cannot exist. On the basis of that theory at least, it cannot be a white dwarf. It would shrink to a point; we would now say it would become a neutron star. Chandraís was pre-neutron star theory, before knowledge of the existence of neutrons, in fact. Well anyway, that theory is fundamentally correct.
Except for the fact that it was correct, that a few white dwarfs were recognized, at the time, 1930s, nothing was known about white dwarfs except that they existed. Kuiper who was at Yerkes had worked a bit on this area but then dropped it in favor of planets. Oh, well, I should say, Minkowski had looked at spectra of one white dwarf which had unidentifiable features in it, and this star had what they now call Minkowski bands, still not identified. It was proved just three years ago to have an enormous magnetic field, now estimated about fifty million gauss. The earth has a half a gauss, so it makes you think. Well, nobody knew this in 1957, hut it was clear that it was time somebody did something about white dwarfs. Here we had the biggest telescope. I had the use of a spectrograph which was really designed for the redshift of galaxies which gave very low dispersion spectra of faint objects. So I started using it on white dwarfs, I think in 1952, just a little bit. At first almost everything I did was silly and wrong, and a lot of it didnít get published anyway. I looked at the star that had the Minkowski bands, I could not identify them either. I published a paper on that in 1957 with Harlow Shapleyís daughter, Mildred Shapley Matthews, who worked for me. We just published a map of these bands. Nobody had ever done it. I went on with other kinds of white dwarfs, found other strange ones. It really involved the planed use of a large telescope with very efficient equipment for the first time really to explore these very faint stars. Nobody else really did anything on stars with the two hundred inch prime focus nebular spectrograph. This just gradually got obsessive beginning around 1963. We had on our staff a man named Eggen who was recently Director of the Australian National Observatory, who worked with me, a classical stellar astronomer.
He measured the colors and brightness and I the spectra. Iím now using a very modern piece of equipment, you should be aware of it, a thirty-two channel spectrometer. We measure the brightness at thirty-two wave lengths simultaneously, and can scan, move from the end of one channel to the other. You can get complete spectral coverage at moderately low resolution, my major enterprise right now. The trouble was that these objects are so faint that I had to give up working with the Coudť spectrograph which can be used when the moon is up. I began to compete for galaxy observer time, which is bad because I donít get much. I could get twice as much if I would stay with the Coudť, but Iím a competitor with the redshift people. Quasars and galaxies have to be measured when the moonlight isnít too bright. My poor program on these midgets is not all that high priority, but I like it; we now have even more efficient electronic equipment. But it has a theoretical facet to it which is even more exciting. Now I have roughly four hundred white dwarfs with observed spectra, when I started there were probably half a dozen observed spectroscopically. The real thing is my having enough time, enough leisure, and not too much competition so I can accumulate data. You can really learn things like cosmic times of evolution. White dwarfs have no energy sources except their own heat. If they had nuclear sources they would explode. Theyíre s dense that reaction rates in hydrogen would be 1012 times the sun. When a white dwarf is first formed it has a temperature of a hundred million degrees, which with any nuclear fuel would mean an explosive reaction.
So, what they have is heat they are born with and they merely cool off. What Iíve been trying to find is really now answers to two questions. What are they made of? We can observe their surfaces and find that some of them have hydrogen, many of them have helium, some of them carbon, some of them have unknown composition. We still have the Minkowski bands to explain. The other question is how many are there of a given temperature at their surface, which means essentially how many are there of a given brightness because theyíre all about the same size, about as big as the earth, and they all weigh the same amount, about seven tenths as much as the sun. They all have a mean density of about a million grams per cubic centimeter, hut they have different surface temperatures, and so what Iíve been trying to do is get the temperatures for a large number, and then count how many there are. When we started we knew something as follows: that most of them were very white, i.e. very blue, i.e. very hot, but there were a few that were cool. Fortunately there are a few cool white dwarfs so near the sun that they are apparently bright though intrinsically faint. These were the cool ones, and a few of these had been known, in fact, three.
We probably knew something about maybe twenty white dwarfs, from color and proximity to the sun. Now we know how many there are at different temperatures, and Iíve been especially trying to reach the very cool faint ones to find out how many there are. You canít call them ďwhiteĒ dwarfs if theyíre red, and the cool ones are red. Some are cooler than the sunÖ We call them red degenerates and white degenerates or blue degenerates or hot degenerates or cool degenerates. Degenerate meaning degenerate matter at this high density. The interesting thing is that what this reflects on is how hot they are in the center because thatís where all their heat comes from. They radiate at the surface and what Iím really involved now with is if there are as few red degenerates as I seem to be able to find. Where are they? Did they never get created from the cooling of the hot ones, or is there some mystery? The mystery is now I think resolved. It is an obscure point in the specific heats of solids at very low temperature. Have you heard of whatís called the Debye temperature?
Wright:Yes, we talked about it in chemistry.
It occurs usually on Earth at below twenty degrees Kelvin, I think, for solids. Well, it turns out that a white dwarf reaches its Debye temperature at about four million degrees Kelvin because of the high density. What happens is the electrons are degenerate, no longer free. The ions can oscillate around their equilibrium position, and thatís heat, but if the oscillation energy is below a certain quantum level, the ion canít oscillate, it canít occupy an excited state. Itís then at zero temperature effectively. It has no heat content that it can get rid of, and that is what happens to these poor stars below about four million degrees interior temperature, they are not only frozen solid, but theyíre solids below absolute zero effectively, as far as available heat. So they then cool so rapidly they vanish; my current major interest is to establish this. Itís a theory developed by various theoretical physicists, and itís related to the same problem in neutron stars which, as you heard, are solids, super solids, at l015 grams/cc. These white dwarfs, only 106 gram/cc. And so this is one of the justifications for having done all that work in discovery of new white dwarfs, on the temperature determination, composition determination, that I think we now have a completely new theory to apply. That is solid state theory, and that at an extreme equivalent to near absolute zero.
So this is the way it started, 1957. I guess I was working on white dwarfs because so little was known. Now I think we have whole new mysteries connected with cooling rates, and the most exciting mystery is completely new, that is magnetic fields exist in the white dwarfs which were found, beginning with Minkowskiís star, and where Iím trying to finish a paper, racing other people, on all knowledge available on the spectra of the stars with intense magnetic fields, which range from a few million to probably fifty million gauss at the surface. A discovery Iíve recently made is that an abnormally high fraction of the magnetized white dwarfs are very cool, as compared to the normal degenerates where about eighty percent are very hot and only a few are known to be cool. They are about fifty-fifty, cool and hot, where I break the sample at eight thousand degrees surface temperature. Half of the known magnetic stars are below eight thousand, and only the one-fifth of the known degenerate stars are below eight thousand. This cooling business seems to me o be involved somewhere. Iím trying to observe all circularly polarized, of these stars. Iím trying to observe their spectrum, and only one has hydrogen, one has carbon and hydrogen in its surface. Others have either no lines or unidentifiable broad bands, and all of them have these broad bands of different wave lengths. Exactly like what happened with the quasars while I was working on it, we used to sit around for two years making jokes about how each quasar had a different set of lines, hut the answer was simple. They were at the wrong wave lengths.
They were a perfectly reasonable lines only they were not at the right place, shifted. Now this may be a similar thing, a magnetic shift of the line spectrum which can also broaden the lines, and in the one star with hydrogen you see the Zeeman splitting due to the intense field, making the line into a triple. This is also not published, a discovery by somebody else. So itís a fascinating business. You start on something because you have a technological possibility and a theoretical question, end up with a whole new set of technological things being done, and a whole new set of theories being tested. Weíre not even bothering about testing the theory of degenerate matter. Miss Trimble and I measured a lot of redshifts in white dwarfs due to gravity. Einstein predicted this gravitational redshift, and itís certainly true. This shows what the mass is. But this is all in the past. I wouldnít touch another thing connected with that.
Wright:Since 1961, youíve shown an interest in the nuclear nucleo-synthesis of elements in the solar system. Why did your interest go in this direction?
That was one mistake also. Thereís nothing wrong with the theory there, but it was a mistake I ever worked on it. That comes from nucleo-synthesis in stars. I would say that the exciting thing that was found about nucleo-synthesis in stars, that it largely worked, that you could explain the composition of the universe and of the sun and everything, but a few of the things required a very peculiar extra process whose nature is still not certain, or whether it really occurs. So what happened was that in the famous paper by Burbidge, Burbidge, Fowler and Hoyle of 1957, they put in a thing called the X process, the unknown, to produce a large number of the chemical elements found in stars and on Earth. Particularly the fact that I had found some lithium and beryllium in the sun, right after I worked with Richardson I worked with others on those problems, suggested that although the nucleo-synthesis in the interior destroyed certain of these elements, they never got to the surface.
Thatís why we never saw carbon 13, which should have been a third of carbon 12 at the surface. But how come thereís any lithium and beryllium left? How come lithium was depleted from the terrestrial abundance by a factor of a hundred? Yet other stars were found by some of my students and others later to have a hundred times as much lithium as the earth. What happened? So it was then assumed that the process, unknown process, probably involved high energy particles bombarding heavy nuclei and breaking them up into fragments which were in fact lithium and beryllium and a few other elements. Well, this is still ďiffyĒ, and in a very ďiffyĒ theory by Fowler, myself and Hoyle, we decided to employ the idea of a super intense cosmic ray bombardment during the formation of the solid bodies in the solar system, planets, not in the sun but in the gas that formed the planets. Very intense production of cosmic ray particles occurred due to contraction of this gas which contained magnetic fields and generated cosmic rays. It was a pretty ďiffyĒ theory. It may even be true. Parts of it I think may be applicable to supernova conditions, parts of it may be applicable to peculiar stars which have intense fields like magnetic ďAĒ stars. These are not degenerate.
Theyíre main sequence stars. Whether itís true about the earth and sun I doubt, but it is actively worked on. The main importance really is from a stellar evolution point of view that if you could prove that the matter on the surface of the stars never had been until the late stage of evolution mixed in with the interior, then a lot of things we know about the origin of the elements can be understood. This is true in certain areas of evolution, as Schwarzschild invented in the red giant evolutionary stage, separation between the core and the surface has to be pretty complete and in the late stages theyíre sort of violent events and thatís non explosive ones through which things mix up, so you see products of evolution. The sun has not been in it yet. Itís only when itís a red giant. There are red giants with peculiar composition. So this is part of this theory, and as I said, I view it a pretty ďiffyĒ part, can we skip it?
Wright:Okay. Youíve worked and I believe you continue to work with Hoyle on a number of projects. Would you care to give some impressions of him? I understand he is quite an interesting person.
Greenstein:Well, heís a great guy. You might get him some time. Heíll he here next winter.
Yeh. Still doing it. Now letís see. I brought Fred to the department as a visiting professor I think in 1952 for the first time. He had a very interesting theoretical problem in stellar evolution, the generation of energy when star runs out of hydrogen at the core, and he lectured on this, and the low energy nuclear physicists were challenged by him to find a certain nuclear reaction which he said had to occur because carbon, which is the product, exists in nature in large amounts, and in great excess in certain stars. They found it, and so from then on Hoyle and Fowler worked together. I did not. After a few years they had become very much involved with the technical problems of reaction rates, especially during the late stages of evolution. Hoyle and I have actually worked very little together, though I listen to him with great pleasure, but Fowler and he put together the theory of chemical evolution, theory of stellar explosions, the super-nova theory and recently quite speculative things on super massive stars. I didnít stay with this. Thereís a limit as to how many new fields I could get into and that one went off without me, though Iíd been involved in it from 1951 on.
Iíve done a lot of experimental work, however, on stars in connection with it. Letís see, in 1957-1967 roughly, I had a large program of what we called the ďabundance projectĒ of young visitors. Hoyle came on that a few times and a lot of the others were spectroscopists and theorists and this was supported by the Federal Government. Those monies stopped and I stopped working in that area, and also I stopped work anyway on high dispersion spectra which this involved which had provided a lot of the evidence on the chemical composition of stars. Oh I worked on the theory of super novae for a while. I thought I had a process which Fowler and Hoyle hadnít thought of, which explained the peculiar composition of super novae but that is either wrong or irrelevant, which often happens with theories. Iíve really tried recently to stay away from it because Iíve got my own runaway specialty of degenerate stars, which others will have to explain in the future, and Iíve having my fun on it. Hoyle is an incredible person. Heís bright. He tries anything. He would never have said what I just said. Whatever the problem is, heíll try. He tends to try and learn what experimenters have found and explain it, sometimes prematurely, sometimes incorrectly. Heís said in print that if a theorist makes ten theories, and if ore is right, heís done his duty. I think he should publish once every few years a list of the nine theories which are incorrect, but he doesnít, and this is a difficultÖ but heís so terribly bright, and heís so original. Right now I regret that heís gone off on the theory of the variation of natural constants in explaining the redshift, which I think is mad but on the other hand he probably thinks Iím conservative, so we donít agree. Did you ask Sandage that question?
Greenstein:I would not like to know his answer.
Wright:Well, maybe not quite in those terms, but sort of leads into my next question about in the early sixties you became interested along with Maarten Schmidt in quasi stellar objects, and why did your interest go in this direction?
The thing is very odd in this way, I guess my interest came from the challenge to a spectroscopist, if guys who worked on a problem from the beginning are bright and they couldnít identify anything, therefore I felt I had to. I might add that Schmidt was by then on our faculty, working on galaxies, radio galaxies. The quasars were identified with optical objects by Sandage and Matthews, who thought they were stars. The theory I will not tell you about on super novae also depended on the quasars being the relics of super novae, objects of peculiar compositions not redshifts. Sandage got some spectra with this nebular spectrograph of 3C48 and it had some rather clear features in it he couldnít identify, so he told me about it, so I took a spectrum, have I got it the other way around? I forget which way it was now. I took a spectra of 3C48 which Sandage had identified, and I couldnít recognize anything, and Sandage took more, and couldnít recognize anything.
We discussed this, no dice, no explanation. Sandage and Schmidt then, I think independently, kept on identifying quasar stellar objects with radio sources, that sources of radio noise which looked like points in optical photos, but couldnít identify any lines because every object had different lines. Thatís this incredible paradox of why you donít make discoveries. If every object has different lines, either objects are either all completely crazy, different from each other, hopelessly, or thereís something wrong with your statement ďevery object has different lines.Ē Every object has lines in different places. Had we ever said that I betcha people would have said, ďOh, of course. The lines donít belong where we see Ďem.Ē But we didnít. So for about a year and a half when Sandage and Matthews were writing, we kept having luncheon conversations about these spectra and making silly jokes. I couldnít identify the lines, but I had my secret way of identifying the lines in 3C48 with certain peculiar elements which will go secret because itís wrong and unpublished. Along came Schmidt with 3C273 and the minute Schmidt told me about it I immediately knew what was wrong with 3C48, I had the redshift in less than fifteen seconds. Because I had actually even mentioned that the lines could be well known lines at wavelengths wrong by thirty-seven percent. So the minute he showed me 3C273, that same minute I said thirty-seven percent about 3C48. Well, from then on all hell broke loose, everybody identified all their spectra with different redshifts in other objects. Matthews, Tom Matthews a radio astronomer, and I identified the lines of 3C48 the same day and published a paper in the same number of Nature on the redshifts, and Sandage and Matthews put a correction as a footnote in their paper on radio stars, saying the stellar objects are not stars, but are redshifted radio sources. From then on the subject ran away from anybody, it went on so fast.
I never worked on it after that except to explain with Maarten Schmidt as much as we could of the composition, density, temperature of these two objects, and I dropped the subject. It would have been an absolutely impossible situation to compete with my own young associates and once the idea came, the identifications became trivial. Bowen, the director at Santa Barbara Street, made a list of all possible lines, and interestingly enough a former staff member, Osterbrock, now Director at Lick, but then at Wisconsin, had proposed a set of lecture notes discussing the lines that might exist in the ultraviolet. He ultimately published a paper as the result of some student work looking up the literature of all the ultraviolet lines you would see in gaseous or planetary nebula if you could see them from space in the ultraviolet. Well that list and Bowenís list explained all the lines that people had on their plates, and all the quasars with different redshifts. Disastrous business, to be stuck for a year and a half by one silly preconception that wave length means anything.
Wright:Well, I have to ask you this question. What is your interpretation of the current controversy regarding these objects?
Greenstein:Iím exhausted, I couldnít care less. I think the redshifts are genuine. I have severe doubts about intrinsic redshifts. I would think that it would be very exciting if astronomers could find the clear proof of an object with an intrinsic redshift, provide a theory that would explain it. Not, in other words, special ad hoc theories. That would be about as exciting as the discovery of the expansion of the universe, therefore I must remain somewhat neutral. I think that it is cosmological. I would be, in fact, somewhat distressed if it were not cosmological, but from the point of view of astronomy in the larger sense, I would think it would give us an opportunity as big as we had when Hubble realized that there was a velocity redshift relation. I hope it doesnít go that way from a selfish point of view because, in a sense, the redshift has been the philosophical center of astronomy for the public, and weíre going to have a hell of a time explaining it away, unless we had, at the same time, the explanation of it as a new kind of fundamental theory, just as fundamental as General Relativity. If we donít come up with that, weíve really had it from the publicís point of view. I think we would he badly off, but this is an extraneous consideration. It doesnít make any difference to me. There are plenty of people to whom it makes an enormous difference. You canít ask that of everybody.
Wright:Since 1970 your interest has apparently shifted to the supermetalicity of main sequence stars. How did you become interested in this area of spectroscopy?
Well no, it hasnít shifted. It was the last thing I ever did in straightforward composition of stars, and I think I wish I had never done it. Itís not a terribly productive area. The trouble is itís led to innumerable controversies which could have been avoided if people said what they really thought. In the general picture of the evolution ofí the galaxy, the one thing weíre sure of is that the oldest stars were very metal poor. However, within a half a billion years they had about the same composition as the sun, which was formed six billion years after that. This is something of a mystery. Therefore, people began looking for some evidence of a growth in metalicity, this one percent or one and a half percent metal composition, change from the oldest of what we call the disc population stars, to the sun, to the youngest stars, four and a half billion years younger than the sun, and the trouble is that the changes in composition, called super-metalicity, are very marginal. Itís at most a factor of two or three, and the errors in the composition determination are at best about fifty percent. So itís only two or three times an error. And then it is not a general composition change. It was a terrible word to use. What it is apparently is a change specifically in certain chemical elements, and there is even difficult theoretical discussion as to whether itís even required there.
I think the general consensus is that two or three chemical elements, specifically sodium and magnesium, are up in abundance compared to hydrogen by a factor of two or three in the most metal rich stars, and that other chemical elements like iron, which is more abundant, may be up by only fifty percent. Silicon may be up by fifty percent to a hundred percent, almost a factor of two. The whole word super-metalicity was unfortunate. I didnít invent it, I collaborated with two groups of people. I again, in a certain sense, donít feel that this was a terribly important contribution because itís just a kind of a red herring. The real mystery of compositions is in how the metals changed from a one hundredth of a percent, 0.01%, to one percent in the half billion years. That is a mystery. Beyond that the metals changed a little bit and it is details of the changes weíre arguing about. Some say it happened almost instantaneously, and that itíd change with place of origin, that the stars farmed far from the plane of our Milky Way are the ones with low abundance of heavy elements, and those stars nearby have all about the same. And Iíd say thatís an equally acceptable generalization. The trouble is you donít want generalities, you want to be terribly specific. There are certain stars where itís clear that the surface composition is enriched in certain elements, mainly the rare earths, by factors of hundreds to millions. Thereís one star recently found with boron on it, never found in the sun. Many stars have been found with lithium a. hundred times too abundant.
So that there are changes is clear, but it may be that these occur during the star formation period. That was this paper by Fowler, Greenstein, Hoyle on Solar System Formation of Lithium Beryllium and Boron. It may be that some stars have a composition anomaly of enormous amount, because their planets concentrate heavy elements, solids, and fall in. If the planetary system loads the surface, and if the surface never mixes with the interior, which is this deep theory which I mentioned earlier, then these stars will he super metal rich as long as thereís no mixing. If you dropped Jupiter in the Sun and if Jupiter has iron and silica in it, itíll double the iron, silica content of the outer layer of the sun, but if that mixes with the interior of the sun, itíll then drop to a one percent change in this one percent, therefore, nothing. So this is the kind of speculation weíre in now. If the subject were better defined I could explain this better, instead I am giving a history of contemporary astrophysics, so letís go on.
Wright:During your career, you have already mentioned that your participation in a number of groups such as National Science Foundation, committees to guide the government in spending on Astronomy. The recent so-called Greenstein report for, in a sense, to set priorities for funding of various astronomical projects including the Large Space Telescope. I would assume that youíve seen the recent article in the Los Angeles Times. According to this you have written to Congress to reinstate the telescope. Were you reported accurately in this article?
In the article, yes. By Congress, no. [laugh] Thatís the trouble. No, Iíve been an adviser to government, since 1952 in one area or the other. First in military, Air Force, Space Agency, Science Foundation the year it started, National Aeronautics and Space Administration when it started. The Large Space Telescope was a dream beginning about 1963-1966. A committee headed by a physicist Norman Ramsey made recommendations and various studies of the problem. I was involved in the Astronomy Missions Board, and a commission headed by Roger Heyns who had been President of the University of California. We felt that the long term, long range instrument in space was the Large Space Telescope. The main advocates are Lyman Spitzer, whom I mentioned several times, central in the history in astronomy recently, and Martin Schwarzschild. The trouble was in 1971 that we were advisory in this report to the space agency as well as N.S.F., and unfortunately the space agency plans when we were working on this had put the Large Space Telescope into about 1985, and therefore had nothing to do with the ten year program for priorities in astronomy. I guess if we had been politically very wise, we would have worded everything with more this and maybeís. I could write a short prediction of how to spend one-half billion dollars over ten years. A problem is that you write for an audience of congressmen and especially the congressional staff. Congressional committees have good staffs, very intelligent men. The budget people, OMB now, the Office of the Management of Budget. The budget bureau have very bright young guys and they havenít time to learn everything when theyíre spending hundreds of millions of dollars.
They want a broad brush and they donít want too many hedges, and they want the scientists to take responsibility in setting this comes first and donít do that, and you canít do science that way because science is an organic, living breathing thing that changes from, it seems to me, from month to month, so whatís important? Any plan is always wrong, especially a ten year plan, yet if we donít do it, some bright young kid who works on a congressional committee whoís had training in law and economics is going to decide, and heís going to decide wrong, so we tried, and now weíre getting slapped for it. Thatís life, and I donít know what to tell you. Iím very enthusiastic about the Large Space Telescope. I think, however, almost everything we said in two volumes about it is correct, if read carefully, but they donít read it carefully. They read the list of four priority things, and if they would do all of those they wouldnít do the Large Space Telescope, but theyíre not going to do all of those. Theyíre only going to do the few things theyíve chosen. Theyíve chosen three out of the four, but theyíve omitted the thing I felt was most important, so I canít tell you how to live with the government. Nobody can. The problem of how to give scientific advice to the government, or to anybody with money, or how to plan the future of science is insoluble. I know that. But we do our best, and get some things. You canít win them all.
Wright:You have many accomplishments that you can justifiably feel proud of. Would you care to relate which of your accomplishments give the most pride?
First the people who learned something from me, one way or another learned something at Cal Tech, learned something working in Mt. Wilson and Palomar. The only thing you can really be proud of. Thereís that. Next Iíve led a perfectly reasonable personal life. Iím happy. Thatís the next thing. In science, I guess my own individual research, one of the most exciting things to me, itís always what Iíve done last or what Iím doing now. So I really canít grade them, and I have written three hundred and eight papers, I think, and I canít remember them at all. Youíve touched on a lot of them which Iíve forgotten. I forget things for a long time which I need to remember. I guess itís one general pattern I have been continuing to do new things, through my present age, which is pretty good to have done. Iíve not stayed in the same field very long ever, Iíve learned many new things continuously and am learning. Iíve learned new technologies. Iíve been in three very fine institutions, all of them very good at the time, and maybe all of them are gonna be good again. Iíve been involved with Harvard a lot administratively. I was on their Board, and it was fun. Iíve met a lot of interesting people that way, so I guess Iím fond of that.
Iím very fond of Cal Tech, proud of having been here that long. Iím proud of half a dozen major areas, the theory of nuclear synthesis, itís obvious I feel very excited -- my long connection with interstellar matter is dead ten or fifteen years, so I canít claim very much excitement about that -- and composition of stars as connected with nucleosynthesis. Then recently these very dense stars, the white dwarfs, another thing we havenít touched on the whole area of the late stages of evolution -- pre-white dwarfs -- which are not in the bibliography because they havenít been published, but made sort of major new insights into what kinds of stars exist before they get to be a white dwarf. Iíve brought up the complete new theoretical parts unexplained puzzle on the dying stages of the pre-white dwarf stars. Theseíll be very important soon, but theyíre not yet. So, you can say that Iíve been in half a dozen different areas; the cooling of the degenerate stars will keep pace with my aging, so weíve got a few years yet to study and explain it.