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In footnotes or endnotes please cite AIP interviews like this:
Interview of Adriaan Blaauw by David DeVorkin on 1979 August 19,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
For multiple citations, "AIP" is the preferred abbreviation for the location.
Early life and family in Amsterdam; childhood interest in astronomy and telescope-building; undergraduate at Rijksuniversiteit te Leiden (W. deSitter, J. Woltjer), works at Leiden Observatory; growing interest in galactic research (Ejnar Hertzsprung, Jan Oort); contact with others at Leiden (Paul Ehrenfest, Hendrik Kramers). Assistantship at Rijksuniversiteit te Gröningen, 1938; cooperative stellar catalog with Harvard University and Universität Hamburg. Life during the German Occupation, conditions in Leiden and Holland; the Resistance Movement; returns to Leiden, 1945. Begins work on thesis at end of war, continues Jacobus C. Kapteyn's interest in proper motion of helium star (Scorpio-Centaur association); compares Boss Catalog and FK Catalog for systematic errors (Oort). Discussion of postwar developments in time scale problem (Albrecht Unsöld, Victor Ambartsumian). To Yerkes Observatory, 1947; impressions of Yerkes and other American observatories: RR Lyrae variables (Otto Struve), 1947-1948; work on extension of cluster expansion (W. W. Morgan), 1952; work in Kenya on stellar positions (Maarten Schmidt), 1949-1950. Back to Yerkes, 1953-1957 (Bengt Strömgren, Gerard Kuiper, S. Chandrasekhar, A. Hiltner). Directorship of Kapteyn Laboratory, Groningen; organization of the Radio Foundation. Origins and development of European Southern Observatory; five-year term as Director. Views on development of astronomy in Holland (Antoine Pannekoek, Marcel Minnaert, Pieter van Rhijn); radio astronomy.
This interview is taking place on the occasion of the Montreal IAU meeting. Mrs. Blaauw is in the room. Dr. Blaauw, I would like to have some idea of what your early home life was like. Where and when were you born? What were the backgrounds of your mother and father?
I was born in Amsterdam in 1914, April 12. My father was associated with one of the large banks in Amsterdam. He was an accountant. I think that's the name you use also in English, somebody who checks bookkeeping. In fact, he ended up being the head of the large accountants section of that bank which had a very large bureau of accountants. He was, however, the son of a farmer in the part of Holland north of Amsterdam, where all his ancestors had been farmers for many centuries. He was not physically able to be a farmer himself, but he had a very good mind, so he got a very different education. And in this way from the farmer community he emerged into this very different kind of profession. But his brothers remained farmers, so as a youngster, I was still very much in the farming community, so to say, around there. So that was the profession and background of my father.
What was his full name?
His full name was Cornelis. And he was born in 1882. There's not very much to about my mother's background. She came from a family that had lived also in different parts of Holland. She was one of a large family, and perhaps it is interesting to mention that she didn't have a special education, but she spent many years as one who helps to educate children in the large family, as it would be normally in the more wealthy families, where they had somebody to help educate the children.
Not only a tutor but one who would say help the mother in the function of the mother as a housewife; taking care of the children. But what is interesting here perhaps is that was a family that spent most of their life in Indonesia. So the man in the family where she helped was director of a very large establishment in Indonesia, I think plantations and things like that. So she spent many years in Indonesia. Then after returning from there, she married my father. So we of course very much noticed this background. I would almost see this Indonesian environment in her background, things that you hear in her stories. Her father's profession was, I do not know exactly, but I do believe that one of her ancestors was a major in the little village of Monnikendam, one of the interesting little old villages.
How many brothers and sisters did you have and where were you in the family?
One sister older than I am. One brother younger than I am. So I was the middle one.
What have they gone on to do? What are their careers?
We all had our, what you might call in America, high school education, although the high school education at home included more than the American high school. It also included let's say the first one or two years of the American college, up to that level. From that level, you might go to university. Going to university was a rather unusual thing. Going through that high school was not so unusual, although I should say that the percentage of children that went through that high school certainly was lower than the percentage of children that go through an American high school, where almost everybody goes. So all three of us went through that high school, and my sister then took courses at a special school for social care, and she also later went to Indonesia, where she worked with families to improve health care for the children. I think at one time she also had a position with the government, also in that same area of social care. It is difficult to identify these things, which were of such a very different character from what we have in our days. It was in that general direction. My brother studied economy at the University of Amsterdam, and then he ended up as director of a large factory they produce tool and die. He was a director. He is now retired from that, but that was his career. Still very much involved in the management of the general Dutch society of directors of these kinds of factories, taking care of the international contracts.
I would like to have some idea of the nature of your early home life. What did you do for pastimes? What were your hobbies? This would be in the first few years of your schooling.
And by schooling you mean high school?
No, elementary. In other words to the age of about 10, 12. What were you interested in? What did you pass your days doing? Were you outside a lot or inside reading books?
I think I should say both. I know we tended to be outside very much. We lived in Amsterdam, but we lived on the outskirts of Amsterdam, and in fact, the place where I was born is now part of Amsterdam, but at that time, it was still a sort of little village. Only since then has it been incorporated. And I will say, being in that little village, when you were outside the house, you were really very soon in the open air, so to say in the meadows. I know that we loved very much just to go outside, in areas where it looked a little bit still like it was undiscovered territory. It was not a city life. It was much more the life of a small village than life in a city.
What were your specific interests?
Ja, that is perhaps hard to remember. We'd like to read, I know. But just playing outside, or what you call soccer has always been a popular thing in Holland. We would play soccer on the streets, and I would say what I also vividly remember of these early days is that we used to go fairly frequently to these little villages where the ancestors of my father had lived, when we visited my uncles who were farmers to spend a vacation at Easter or a vacation at these farms. They are in that part of Holland where it's very typically Dutch — much water. You do lots of things just by traveling by boat. And that has always left with me a very strong impression of the life on a farm. I would say that has always been something that has given me the feeling that, in a way, I belonged rather to the farmers than to the typical city people.
Did you have any very early reading in science? Was there anything about your being outside that got you interested in nature ?
No. I would not say so. So if you would say, how did you get interested in astronomy, this is something that you might wish to take up now?
If it's an early interest, I would like to identify that. If it happened when you were in school and later, then we'll wait.
I would say my interest in astronomy must have developed from the age of about maybe 13 or 14. Not before. So I would say that when I went to high school, when I was at the age of 12, I do not think that there was any indication yet at that time of my interest in astronomy. It developed after that. Oh, I know, if you ask what sort of professions do you remember as a child thinking about — I remember that I was interested in becoming an engineer of shipbuilding. I know what it came from, because in Amsterdam we, used to go to the harbor. We had all sorts of big ships, we had ports for the whole world and so we used to go there. We would go there on bicycles to see all these ships. I always was much attracted by just being on the water, and I remember that at one time I felt, 'I think I go to high school in Delft and become a ship building engineer.' That was the leading technical high school in Holland at that time. Since then, other technical high schools came into existence but that was the engineering education of a very high level in Holland that we had at that time. So that is one profession that I think I still remember that I was interested in. I do not think that I had ever a very pronounced idea of what I would like to become. On the whole, I would say , we were never much concerned with the question of profession; what will be my way of earning my money.
Why was that?
Why? I think the whole environment was such that you just didn't think about it. You took it for granted that in some way you would earn your money, as everybody earns his money in some way or other. As my father did. He went to his office regularly every morning and came back every night. No, even in my years when I was a student, I think that the nature of the jobs, you would get later — the fact that you would take a job — played a rather insignificant role. That came rather late. But maybe you would like to come back to that later?
Yes, that's all right.
So we are now still in the fairly early years. I think that's all I can say about my interests. Maybe that I some time may have had an interest in becoming a medical doctor, but that was less, I would say.
What was it that began your interest in astronomy when you were in high school?
I think it's a bit difficult to trace. But there are a few moments that still linger in my memory, but it's of course not complete. I do remember, looking backwards, that I think I became aware of the fact that you can learn something about the star and that there exists something like an astronomical observatory — I think I became aware of that by reading an article in a popular ladies' magazine. If I'm not mistaken, there was an article on a Danish or a Swedish observatory in which they spoke about a remarkable young astronomer, and the astronomer must have been Bengt Strömgren. But this is a very vague recollection. But I think that was one of the first times I became aware of the fact that — after all the normal professions, if I might say so — there are other ones that also exist in this world, like an astronomer. But what I know very well is that my interest in astronomy developed very much by reading the popular books of Flammarion, the famous French popularizer of astronomy.
Did you read him in French or in Dutch?
I read him in Dutch. These books were translated into Dutch, very well done, with very good illustrations. They were very stimulating. I'm sure they have played an enormously strong role in creating and developing the interest in astronomy at that time. There were various books by Flammarion translated into Dutch. One was called The Heavens and the Earth. Another was something like The Realm of the Stars. I know I read and re-read these books. There were also a few other books on astronomy, maybe chapters on astronomy in other books for boys, that fascinated rne. But I am sure that these books of Flammarion especially have very strongly influenced me.
What was it about astronomy that fascinated you the most? Do you have any image of particular illustrations out of the books?
No. Maybe I should just simply say that, if you look at the sky at night, you see the moon, you see the stars. You have heard something about these things in these books. You see that there is something very impressive, very mysterious, that there's an enormous space that exists, that makes you wonder, 'what is it?' Then you find from these books that there is very much more to it than you might think at first sight; that there are other worlds, physical worlds; outside the earth. So normally, if you walk outside, you see nature and everything. But even apart from all that, there is still another world which is very much bigger, that most people are not hardly aware of, but that in a way, you should be aware of, even maybe very much more, because it is so much bigger. And why don't we do anything about that? What does it all mean? What is all that? You just want to know and so you get interested. It is, I would say, comparable to people living in one area of the world who then start exploring - as you could still do at that time — part of the earth where nobody has ever been. You have pioneering people who go there to find out what it's all about. It was an extension of exploring the unknown territories on the earth, but one stage further; beyond the earth into space. I am sure my parents encouraged reading the these things. They gave me these books as a birthday present, and certainly, there certainly was encouragement within the family on their part. Also that by that time when I was in high school — I started around the age of 13 or 14 or so — I built my own telescope, in a rather primitive way. So what did you need? You needed lenses and you needed a big tube, and you needed an eye piece at the other end. So I build my own telescope. And my parents of course helped me acquire the lens and things like that, that you need for it. It was a lens of 5 centimeters or so. So I knew what things I needed and my parents helped me to get this lens from an optical shop. I don't remember exactly but I certainly was always in a very encouraging environment. That I should say. Then I built my own telescope. And we were encouraged at school to make things with our hands. I could then exhibit the telescope, with other things that were exhibited by what people did at home. And in this way, the teachers would notice that I was a boy who was interested in astronomy, and they from their side would encourage this. So from many sides, these things sort of came together. The interest which I had was encouraged and supported also by the people in school. Then there was one teacher who was particularly interested in astronomy himself, and who also helped and encouraged me.
Do you recall his name?
That was Dr. L.A. van Wyk. He was a teacher in mathematics.
What was in a high school in Amsterdam?
Which particular high school?
It was "Amsterdam Lyceum." In fact it was a combination of the regular high school where you would get an education that is somewhat fitted to the various professions that you could follow, but which included, apart from Dutch and the languages French, German and English, another sort of high school in Holland where the emphasis was less on preparing for certain professions, but more cultural development. And that included the languages of Greek and Latin. That school tried to combine both. They ended up with those two sorts of educators, but the choice you had to make was made at a much later stage than most children had to make. So you had two years in common between the two. And then, according to the abilities of the children, the choice would be made. It was a very good system . Also they added one year, so that you had more time to do things. And in that school, as a consequence this, they could — apart from the prescribed curriculum — introduce things that were not obligatory, according to law, but very useful. So we had lots of sports — an afternoon for sport and maybe another hour or so sometime — which other schools would not have. We did much in drawing and maybe painting. Much time was spent on that. We had a special teacher for what we call "Handenarteiten". It means, you make things as a hobby .
Yes, crafts, from wood or whatever. I remember at one time, I made a little model of a sailboat.
Your shipbuilding interests?
Well, always the same, shipbuilding and being on the water, it is that same pattern always.
Was this a high school that your parents had to elect to send you to, or was it simply the high school in your area?
No, they elected that. In fact it was far outside the area where we lived. I went on bicycle every morning, some 20 or 25 mlnutes, and back home at the end of the day. So did my brother and sister who also were there.
You all were there.
It was also a somewhat more expensive high school. And it was in a way a financial sacrifice on the part of our parents, that they did send us there. But they did so because the high school almost guaranteed a broader education than the regular high school would have.
I understand that.
I think it was very good. Indeed, by these extra things, we were prepared a little better for general interests than these narrow high schools used to have. It was a very nice spirit in that school also. The director was a man who was a well known person in general education in Holland.
What was his name?
His name was Gunning. He again was the son of another Gunning, of course, who had been a professor in educational theory in university, I believe. So he himself was the descendant of an expert in that field. And it was these experts that at that time tried to create these schools that gave the children more than the somewhat narrow program prescribed by the Dutch law. In Holland that type of high school is a necessary first step before you enter university. You cannot enter university or technical high school without having done the exam at these high schools. But because it is a general law, it also meant that there would be very little room for things that are not relevant to entering the university. And these schools tried to broaden the education, so that there would be other things like sports and crafts and so on. No university would ask you what sports did you do, and crafts. But they would put it in also.
At the time, Holland still was one of the colonial countries in the sense that they had these big colonies in Indonesia. And of course there were colonies in South America. But I think what I would like to mention is that we were also taught in this school (and that did not exist at most other schools) lots of things about these colonies or what were called colonies at that time. But we were taught about these things, certainly not in the spirit of colonization. That same fellow, this Gunning, used to give us, during I think the third and the fourth year, a lecture on the colonies.
So you had classes directly from him?
Ja, I think it was one hour a week. We had different teachers for different subjects. One of these was taught by him. I don't remember the title. He taught us about the old life in these colonies, about the people that lived there. But it was all done in a way which had nothing to do with the idea of colonization. It was very useful to take a large interest in the sort of life of people who were very different from what they were in Holland. I think if I would have gone to Indonesia, which I never did, I probably would have been much better prepared for this than many other people would have been. And it was in that same spirit that we were taught in classes in geography. There was another teacher who taught geography and taught us a lot about people in different parts of the world. I have always kept a very good impression of the way we were prepared for meeting entirely different countries and entirely different type of population later in life. You became aware of the fact that things were very different from what they were in Holland.
What about science courses in this high school?
You mean mathematics and physics?
Well, we had a fairly tight curriculum on mathematics and physics, chemistry.
This was all part of the core curriculum that all high schools had to have?
All those high schools that prepared for university, yes.
I see. So science wasn't considered superfluous in any way?
No. That was an essential part. We did have much mathematics, physics, chemistry, biology, a little geology. But the mathematics and physics and chemistry were main subjects for that sort of education. And then of course there were the languages. But mathematics was something that you would have say six hours per week and then maybe four hours of physics, four hours of chemistry, and the rest would be languages. Of course the language was obligatory, apart from which were German, French and English. We could read well these languages, and we should be able to, in a limited way, express ourselves in these languages. So you were supposed to read at least ten books in each and be able to tell at the examination what was the contents of such a book. And sciences were, I would say, the central, were the core of that education.
That's nice to hear. It explains a few things — why there are so many good Dutch scientists.
It may well be.
Well, you were building a telescope and reading Flammarion through high school. Were there any of your teachers of science or mathematics who specially took interest in your growth of interest in physics, astronomy, science in general? Did you begin to look at astronomy as something that you wanted to be involved with in your university education?
Yes. By the time I did my final exam.
This is the end of high school years?
Yes, that's the end of high school years. It was for me at the age of l8. I knew that what I wanted to study at university was astronomy. That was quite definite.
Did you learn about the applicability of physics and mathematics to astronomy by that time, or was it still merely a descriptive fascination?
Yes, it was.
You hadn't put the physics and math together with it?
No. It was really only at the university that I became aware of the fact that in a way, physics and mathematics are prerequisites for astronomy.
Did you go to Amsterdam?
No. What happened was that I had done my final exam at Amsterdam, and as I told you, my mathematics teacher knew about my interest in astronomy, and had always encouraged it. And by the way, he was the one who at one time, maybe two years before, suggested that I should read the popular books of A.S. Eddington. So I still remember that I read Eddington's Stars and Atoms which was an excellent book which was a popular version of the International Continuation of the Stars that Eddington had written by that time. He knew that book. He told me about it, and I read it in English. I must say I read it also in English because I didn't do so very well in the English courses in school.
No. On the whole I didn't do very well in languages. excellent.
Your English is excellent.
Ja, but at that time I couldn't get interested in doing languages. Especially what I always disliked was that you would get one hour of a language; you would read a book. And then three days later, you would take up the book and read another few pages. But that time you had completely forgotten what you'd learned. It was boring, terribly. But I did get my English then from reading these books that I was interested in. I still have the little notebook in which I then wrote down all the words that I didn't understand in a book like Stars and Atoms of Eddington. I looked the words up in the dictionary. So by the time of my final exam in school, I did not do so poorly in English. The fact that I had a fairly good vocabulary in English was due much more to my reading books on astronomy in English (than those assigned). I don't remember anything of these books that we had to read. They were such a bore really. But I must also say that the extent to which I could do well or not in language depended very much on the kind of teaching. I still know very well the teachers I had. For English, I had a lady teacher, who meant very well but was so terribly dull. And French was difrerent. We had a French teacher who didn't teach me very much, but he would take a book and he would sort of read it for us in French, and it was a little show. German was the one in which I did best. Very simple lady, but she had a way of teaching us languages not by telling you "Now, this word means that, and that and that, " but she always got the word in sentences. And I still know these sentences.
So the way of teaching different languages I experienced at the time could be very different, and the effect would also be very different on what you remember.
I can appreciate that. I've tried a number of languages and they were all very different in the way they were taught to me.
Yes. Very much depends on that. So then by the time of my exam, that mathematics teacher knew I was very much interested. I did my exam quite well, at least in the mathematics and physics . I think we had four subjects in mathematics for which you would have to do the exam. Algebra, geometry of the plane, geometry of space, trigonometry, and we had what we called goniometry: angles, sines, cosines, the whole business. Each of them was a written exam of I think three hours and if you did not do well, you would take an oral exam after that. But I got the highest possible grade in all of these four, so in a way, I emerged as a mathematician from all this business. In physics I think I also did fairly well, chemistry not so well and biology not well at all. I couldn't remember all the names of these plants I just didn't like it. They would give you a plant and you would have to take it to pieces, and then you would identify it that way. So by the end you knew the name, but all that was left were little pieces of a flower. I just didn't like that. What I did know was the names of the birds, you see. That I liked. You see these things in nature and it's nice to recognize, etc. But I didn't like this sort of taking things apart. So then as I told you, I did the exam well. I could have gone to the University of Amsterdam for the astronomy courses, and that would have been all right. There was a very good man at Amsterdam. A. Pannekoek was there at that time. But in a way, the Leiden Observatory was also there. It had more fame. There was more staff. William de Sitter was there at that time. And what happened then is that the mathematics teachers took up contact with a professional astronomer who came from Utrecht, but who was a sort of government controller at these high school exams in Amsterdam. And it's through his intermediary, I would almost say, that an interview was arranged for me with de Sitter, who was the director of Leiden at that time.
What was the name of the intermediary?
That was van der Bilt. He was an astronomer at the Utrecht Observatory. And he had his own particular views of the merits of different astronomical institutes in Holland. He didn't think too much of Utrecht itself. That may have had something to do with his personal life. He had a high regard for Pannekoek, but he said that, "With your record of exams, you ought to go to Leiden." So he arranged a visit for me, and I still remember that. I traveled to Leiden and I paid my respects and I visited de Sitter, who was a somewhat elderly man with sort of a fatherly attitude. De Sitter was a very nice person. It was 1932. And de Sitter said to me, "OK, I think you ought to study here at Leiden." Well, that was decided then. That was how I went to Leiden.
Was there a question of financial support?
Well, all the financial support at that time had to come from the parents. Scholarships and things were almost non-existent at the time. And if there would have been something like that, it would have been very complicated, and only for students whose parents really could not afford this at all. But my father could afford to support me financially. So that's what happened.
Right. So you moved to Leiden.
I moved to Leiden. I had a room at Leiden as a student.
A student room.
Did you then have four years of undergraduate work?
No. The arrangement was a very loose one at that time. Normally, you would do your first exam at the university after three years, I would say. Then you would do your second exam I would say after three or four years.
There were several grades. The candidats?
Yes. The first one I mentioned is the candidats, which really is only a sort of conclusion of those first three years but at that time it did not entitle you to anything. It did not entitle you to become a teacher in high school in either mathematics or physics. One thing it did entitle you to do: that was to become a teacher of astronomy. But astronomy was only given at some high schools and not more than an hour a week, so it didn't mean anything. But in a way it was an internal university exam, because then they allow only the people who have done sufficiently well in the first exams to study for the second exam. That is the purpose of the candidats. Or, you could go to another university and they would say, "Oh, I see you have your candidats at Leiden so you can go on, to say, Gronigen....."
You worked through your candidats. Now, at that point, what kind of astronomy had you had? Did you have astronomy courses at that point?
Yes. And in fact in the first year I had an astronomy course from de Sitter himself. He gave the elementary astronomy at Leiden, which is a good thing to remember, because nowadays so many professors that are in research leave the elementary course to other people. But de Sitter gave it himself. He took some pleasure in doing this. It was a very simple course, but it was inspiring. DeSitter was the sort of person who would slowly walk up to the classroom. He had a beard, and he would sort of tell a nice story to these young kids — that's the way he gave his astronomy. The volume of what you would learn was not much, but the way in which it was done was encouraging and aroused an interest in the field .
Was the content similar to his book, the popular book called KOSMOS?
No, it was much much more elementary in astronomy. It was spherical astronomy, and he did a little bit about the Hertzsprung-Russell diagram, and he would tell us about the structure of the Milky Way system and a very little bit about extra-galactic nebulae, a bit about planetary systems, or Keplerian orbits and things like that. There would be some mathematics in it. Certainly he would not avoid mathematics. But it was done on a leisurely basis, that way. That was what I had in my first year. Then in my second year, it was very different.
Again from DeSitter?
No. Then I had lectures from a Dr. J. Woltjer. The father of Ludwig Woltjer. J. Woltjer deserves some description, I would say, and it's good that we have the opportunity, because he was a person who is not referred to very much. But he was an extremely thorough man in his research, and in his preparation for lectures. He was also very demanding of accomplishments by his students. You may know that his main work had been in celestial mechanics. In fact, he got his degree with DeSitter in Celestial Mechanics on the four biggest satellites of Jupiter. That was based on plates that DeSitter had taken when he was an assistant at the Cape Observatory in his early years. A year of observations. And Woltjer measured these things, and did his thesis on it. It was a nice piece of Celestial Mechanics. But Woltjer also got very deeply interested, in his research also, in the internal constitution of the stars, especially from the point of view of Cepheid pulsations. That was the time when Eddington had recently published his book INTERNAL CONSTITUTION OF THE STARS.
Famous book, one of the great books in astronomy. And Woltjer was one of those who studied this very thoroughly, and in fact, there seems to be a review of that book by Woltjer which in itself is a very worthwhile thing to read — the review by Woltjer of Eddington's book. I have seen it, but I do not remember it very well because it was a field that I was not so very much interested in. But I do know that Woltjier did a very thorough work on reviewing that book at the time, when the whole subject was so new.
It wasn't in the BAN?
No. I believe it was in the observatory. But you would have to check this. It may be very interesting from the historical point of view to check this thing.
Certainly reviews of major works are of great interest.
Yes. And my attention was also drawn to this review by Bart Bok, of course, who was older than I, a much more mature student at that time. And he has several times reminded me of the existence of that review. Well, anyhow, this is a little on the side. Then in the second year I had courses from Dr. Woltjier.
Did they include internal constitution?
No. That course was on celestial mechanics. He gave us the course in three parts. The first one was lunar theory. The second one was perturbation theory in general. And the last part was movement of the earth: movement of the rotation axis of the earth with respect to the body of the earth, that sort of thing, means polar wandering. These periodic oscillations of the material body of the earth with respect to its rotation axis as you have in any body that is not a pure sphere. So that is what Woltjier taught us. And at that time, we were a class of I believe eight people. I still remember the class very well.
Who were your classmates? Do you recall any of them? Did they become astronomers too?
There were several who wanted to become astronomers, and some of them have become astronomers. One in that class — but I do not know to what extent they took the exam with Woltjier — was Jule de Kort who was a Jesuit priest who took courses, and he later became associated with the Vatican Observatory for a while. Another one, but I'm not sure, may have been Binnendijk who was the same year as I was at Leiden University, and who, by the way, is here now .
By here, you mean here at the IAU meeting?
Yes. He got a job later in Pennsylvania at the University of Pennsylvania, where he still is now.
There were very few other people. I don't remember. There were also a few who were mathematics students who followed this course. So Woltjier gave that course. It was excellently given, and I still have used these notes, many many years after. What he really did was, especially in this first part, was to develop the lunar theory in a very elementary way. I mean, you could almost have done the whole thing with your high school mathematics. There was nothing about mysterious complicated formulae. It was elaborate, but he sort of led you through the whole thing. At every point he would say, "Now we make this simplification, this approximation, here are these equations to solve it" and so and so — and out would come all these periodic perturbations in the lunar orbit. It was beautifully done. I think it followed more or less what Ponte Coulant has been doing in some of his books.
I'm not familiar with him.
That's my impression, from books that I have seen. Well, that's the way Woltjier worked. But then you had to do the exam for Woltjier. That was a different business from what deSitter had done. The exam for Woltjier's course was oral. We had to go there, and he had plenty of time for eight students, so the minimum amount of time was three afternoons.
Yes. The first afternoon, he checked me on the first part, lunar theory. And I had to think for two or three hours. And after it was over, he said, "You have done very well. Now, day after tomorrow, we continue and take up the second part." So two days later I continued, and I did general perturbation theory: Hamiltonians and Jacobians and all that stuff, and at the end he said, "You have done well. Day after tomorrow, we continue with the third part." Well, by that time, I got a little bit tired out. After the third part he said, "You've done fairly well. Now it's done, finished." But if you had not done well, oh, he would take seven afternoons, until he knew that you knew everything. But by that time, you would also know exactly what you knew.
That was marvelous.
That was marvelous.
Must have taken an enormous amount of energy.
Yes. But it was really very good. So that was what I did on astronomy in my second year. Then after that, I think I followed one of his courses on internal constitution, but I never took an exam on that.
Was that the second year or the third year?
No, that was in the third and the fourth years.
I know the name Woltjier is a very well known one in Holland, as having produced many many very good scientists .
Well, that's very good to know, because these dynastic orders in science are very important to trace.
They do occur sometimes. And this is one of them in the Dutch context, I would say.
Well, we're up to your third year, and I'd like very much to know which courses you took. You mentioned that you had sat in on some courses.
Courses I took in astronomy or in general?
Primarily astronomy and physics now.
Well, for that candidats' exam I did not do more astronomy than this, but it was already quite a bit. But there was no more astronomy for my exam. But I did follow this internal constitution course that Woltjier also gave then, but I never did an exam in this.
Did you have any experience in looking through telescopes or using telescopes then?
Yes. In fact that was somewhat unusual, and that's why I did my candidats fairly late. The point was that already in my second and third year, I started working at the observatory. Normally one would do that only after one had done the candidats. But in some way, I became associated with the older assistants at the observatory.
Who were they?
One of them was A.J. Wesselink whom you may know, from New Haven.
A.J. Wesselink, one of my good friends. There were a few more. One of them died in the war, in a shipwreck in some troop transport. Another one has died also, in Indonesia, in a war. A fourth one has become a teacher. But I was associated with those people already in my early years, and they at one time said, "Why don't you join us in working at the observatory? So I joined them in working at the telescopes. I observed many nights, but was not really an assistant. So I did a lot of real observational work in those first years.
Was this photographic?
Yes, photographic photometry of variable stars. I did all the observing and a bit of measuring of these plates. So in a way that delayed my candidats exam. I don't really exactly remember when I did the candidats. I believe, after four years or so, something like that. It must have been either at the end of 1936 or somewhere around that time. Well, it was around that time.
During that period, deSitter died.
Yes. De Sitter died in 1934 or 1935.
Was it traumatic at the observatory? Were there a lot of difficulties, did work stop for a while?
Of course it was traumatic in the sense that he was still fully in office. He had not retired. But we knew that his health was poor, because deSitter had been suffering from tuberculosis, early in his life. And in fact, I think that was about the time when he was appointed director of the Leiden Observatory. And he had then been in a sanitorium in Switzerland. I know that from that sanitorium, he began to direct the affairs and the reorganization of Leiden Observatory. All his life, and certainly at the time I had known deSitter, he was a man of slow movement. He would never walk quickly. And I understand that was all connected with the fact he had only one lung left. The other lung was entirely out of operation. So he had to do things very carefully.
He was a large man, wasn't he?
He was a tall fellow, yes. But mostly he looked almost fragile, or fragile, maybe that's the word. So that he died fairly early did not come as a surprise to us. But anyway it was a shock, because of course deSitter was a very respected man, and an impressive man, very respected. Of course he had been the central man, I remember, at the IAU assembly in Leiden in 1928. And really, he was a very distinguished fellow in the international astronomical community. And we sensed that as students also. Of course you don't always appreciate it, but you do sense these things. So that was quite a shock, and them he was succeeded as director by Hertzsprung. But it also meant that the field of astronomy represented by deSitter was only partly represented after his death — the field of galactic research. DeSitter knew a lot, and it was continued by Jan Oort. But his cosmological interest was not continued by anybody. And the celestial mechanics that he did a lot on was in a way continued by Woltjier. So that was the situation.
How were your interests developing, as far as specializing in astronomy is concerned, up to the candidats? Were you interested at all in specialization before the candidats?
Yes. My interest before the candidats already went strongly towards matters of galactic research — the structure of the galaxy. And that meant that it was directed much more towards the field of Oort than the field of Hertzsprung. We were involved in observing photometrically variable stars at Leiden, but also we were using plates that Hertzsprung had collected in the Southern Hemisphere. And so he used to give us packages and say, "Now, you do so many variable stars in that field," and so on. That started before my candidats and continued after the candidats.
You had direct contact with Hertzsprung?
Oh, very much, yes.
What was your impression of him on your first contact with him?
Well, I would say, people already had an impression before they ever met him, because he was known as a man of somewhat unusual habits. One was told about this. You know how this is, so at a certain time you meet the fellow and then you say, "Oh, that's so and so ...."
What was he known for?
Hertzsprung was a man for whom only astronomy existed. It was very rare that you could talk to him about matters outside astronomy. His whole life was astronomy. And of course, we knew that his family life had suffered from that very much.
His family did?
Yes, his family life had suffered very much from that. You know, Hertzsprung married one of the daughters of Kapteyn and that marriage sort of broke up.
Did it break up quickly?
No, I do not know. I think it broke up gradually. He never remarried. She did remarry. This daughter of Kapteyn remarried another Dutch professor later.
Were there children?
Yes, there was one daughter. I think she's still alive. She lives in Denmark.
Does she take the Hertzsprung name? Do you know?
Yes. Her first name is Rigel. Rigel Hertzsprung.
Yes . That's the name of a star. It's typically Hertzsprung, he would name his daughter after a star.
So, even during this time, you were being directed somewhat by Hertzsprung, measuring plates, and you knew that your work was going to go in the direction of Oort's interest and deSitter's, in galactic structure?
How did you gain that interest? Because in the courses you mentioned that you took, you didn't explicitly mention galactic structure.
No. I think it must have developed in the course that I took with deSitter in that first year. Ja. Of course, there, after high school, I was confronted for the first time with what astronomy really is. It's very different from being an amateur astronomer, and building a telescope, and looking at the sky and wondering about it . Very different from really hearing, say from deSitter: "astronomy is this and this and this etc." An enormous difference. It still fitted in, but it was so much broader, and you could see where there were interesting things going on. So for some reason, I don't know why, I got mostly interested in matters of galactic structure. Maybe what hd also influenced me was indeed the book of deSitter that appeared around that time. That was KOSMOS, and that was based on a series of lectures that deSitter gave in the United States, I believe at Cambridge. This is a very good book, very nice. And that book went through the whole of the study of the cosmos from the early times, up to and including the time of Kapteyn. DeSitter had been a pupil of Kapteyn, and he presented the whole approach of Kapteyn very well. I think in a way it conveys the admiration for that work that deSitter clearly felt. That again was in line with what he had been doing himself; presenting in his own courses. So then at one stage, when I had already done a good deal of work for Hertzsprung — I guess I had worked on ten variable stars instead of the 25 that he used to give to his students — at that moment I said, after my candidats: I would rather go in the direction of galactic research. We called it statistical astronomy at the time, you see.
Right. And you said this to Hertzsprung?
No. I went to Oort, and I said, "Couldn't I do some work with you, rather than continue what all these people have been doing so far on these variable start?" I remember Oort made some sort of remark in the sense: "Of course, by doing variable stars you contribute your part to astronomy. Every variable star [adds data alone] with everything else." But at the same time, it was clear that he was agreeable to take me as a student. So I really never finished that package of variable stars that Hertzsprung gave me. I think I still have a lot of estimates of variable stars. Once in a while I published some of it . And the way I did it was when there were some pages left open in the B.A.N. [Bulletin of the Astronomical Institute of the Netherlands], the editors asked if anyone had something to put in those pages because that was fairly cheap publishing. And I just pulled out one of these variable stars and polished the thing a little bit and wrote a little article. So in this way I think I have published maybe three of those variable stars that seemed to be the most interesting, as a sort of filler in the B.A.N. That's all I did about it. But from then on, I was associated with Oort and he put me on some first problem, on which I then wrote an article, an article which has never been published, and that was the following. At that time, there were researches done by an American astronomer, possibly R.E. Wilson, who determined the luminosity function of certain spectral types of stars. He determined it by comparing the distribution of proper motions and the radial velocities. The point is, you see, the distribution of proper motions is determined by two things — the distribution of their real velocities, which you get from radial velocities, and the distribution of their distances. And there is an integral equation which you have to solve, then you solve for the distribution of distances. And since you also know the apparent magnitudes of the stars, their distribution of distances is the measure for the distribution of absolute luminosities. Now that's the essential thing.
That's something that, ever since Hertzsprungs time, was of interest.
Since Kapteyn's time. Well, anyhow, what I did was almost repeat work that had been done by this astronomer, from a critical point of view. So I did. Then I showed that really the solutions that he had come up with were not really unique; they were rather ambiguous. You could put in different solutions, and you would still satisfy the observations. And the point he made, this American astronomer, was that you could clearly subdivide these stars into giants and sub-giants and Main Sequence Stars. He said, "You can see that in the results." And I proved, I think, that you could also take much smoother curves, which had a maximum say for the giants and one for the Main Sequence, but let us say entirely without any sub-giants, something like that. And I showed that you could just about satisfy these curves. So I wrote an article. And I showed it to Oort, and for awhile nothing happened. But it turned out that Oort had discussed it with Hertzsprung, and they said, "The article is OK, but it is better not to publish it because, you see, if as a young student you start your first publication by criticizing a well established astronomer, maybe this is not such a wise thing to do." So the article must still be somewhere in the files. And your historical colleagues may sometime find it, I don't know.
Was this standard policy? Could you save it for a while, and publish it later?
No. It was just kept in the file. But it had been a very good exercise for me .
And you must realize, we did not have that urge of publishing soon and much. I mean, what you find recently is such importance to publish, because you can show it to your people, and you can add to your list. That, was something that did not exist at that time. No.
What we call "publish or perish," didn't exist?
No. Not at all. No. Your future would not be determined by your record of articles. It would be determined by what people like Hertzsprung and Oort and de Sitter would think of you, how they would put you in the general scheme, how they would recommend you to other people. And that is in fact, what happened to me also.
At Leiden, did you have any contact with Ehrenfest?
Some, but very little, because Ehrenfest was a theoretical physicist who had succeeded Einstein, and his contacts were mostly with the more advanced students who had already gone through the early years, first years. And Ehrenfest died when I was in my second or third year, I think I was in my second year. Didn't he die in 1933?
Yes, in that time.
I did know his son, Paul Ehrenfest, who also was a physicist, who later died in France, I believe, in a mountain climbing accident. Paul also was a very very congenial, very nice fellow. Ehrenfest was well known, of course. We knew about him. We heard his lectures. But I had no personal contacts with him.
Did you have any contacts with Kramers?
Yes, with Kramers. After my candidats, I took courses in mathematics and physics, theoretical physics, because courses in astronomy were not very much, since there were very few formal courses. Hertzsprung gave a course, and deSitter wasn't there any more. Oort gave courses in galactic structure: galactic dynamics. I followed those but I also took courses in physics with Kramers, and in mathematics with several mathematics teachers. But then in 1938, there was an opening in the assistantship at the Kapteyn Laboratory at Groningen. The assistant had gone. I still remember that was at the first IAU assembly that I ever attended, that was in Stockholm, 1938. Yes. We were then not really staff members, but as young students, sort of junior invited participants of the sort that you have now. And it was more sort of "sneaking in" there and listening than being a part of the delegation you see.
This was your first IAU?
Ja. And as I say, I was still really as a student, not at all having finished my studies. If you were like that in Holland, you got a little bit of money from some foundation then in Holland so we could make the trip. It was during that assembly that at one moment, P.J. van Rhijn came to me, who was the director at Groningen, and said to me "Now, the assistantship at my laboratory is vacant, would you be interested in coming to Groningen and becoming assistant there?"
He certainly must have heard about you?
He must have done it at the advice of Oort, you see. It had nothing to do with my showing him a paper I had published. Simply Oort or maybe Hertzsprung had told van Rhijn or van Rhijn must have asked, "Do you have a fellow for the place?" Well, they had plenty at Leiden, because there was no other prospect of getting paid or getting a job. So I was very pleased with this possibility at Groningen. It didn't pay very much. Still my parents had to give me some financial support.
But had you completed your doctoral?
No. I had not. But I had done practical work at Leiden Observatory. And van Rhijn didn't mind. So from September, 1938, I became an assistant at the Groningen Observatory. But as I said, I had not done my doctoral exam by that time, but I had taken the courses of Oort and of Hertzsprung and these physics courses that I mentioned. So I still had to do a number of my "tentamens". We have tentamens, you know. That means you do an exam on each of those subjects. It's a sort of tentative exam. They were like what I did with Woltjier. I had three afternoons before my candidats. That is what we call a tentamen, you see. It was an examination, but it is not the final exam. So I did the examinations on those courses with Oort, and I think Hertzsprung, and I still had to do some with Kramers because I had theoretical physic from Kramers, all my theoretical physics. So in that way I knew Kramers fairly well. I had to do five exams in theoretical physics. I did not do any in mathematics . But I preferred to do it all in physics . I liked that much more. The exams with Kramers were in atomic physic, one in quantum physics, one in what he called point mechanics, and there was one in mechanics of solid bodies, and one in quantum statistics. They all went very nice, I would say. The atomic physics and the quantum mechanics. I did with the book that Kramers had written. You may know that Kramers had written a book in two parts.
I'm not familiar with it but I'm aware that he did.
Excellent books. They are known much too little. They are not really textbooks in the modern sense but they are very good books. And I did my point mechanics from his course. So then there were two left. One was quantum statistics, and the other solid body mechanics. For quantum statistics, I came to Kramers and said, "Now, I want to do my quantum statistics, but since I am at Groningen now I haven,t been able to follow those courses. What shall we do?" Well, Kramers said, "I just received a book," (it was a big book) written by Sommerfeld and Waldman," — Waldman of the people who has become rather famous nowadays. And Sommerfeld of course was a great man in physics, and they together had written a book on quantum statistics. And Kramers told to me, "You read that book for me, and the exam I take with you is what you tell me what is in the book." So, I studied that book. It was very nice . Really it was a very good book. And I did that exam. He seemed to be satisfied .
So, you were in Groningen.
Ye. I did all this in my evening hour, you see.
So I did all this in my evening hours at Groningen. As assistant, I had my hand full during the day at the laboratory. But let me just finish about these tentamens. In the fifth one, I still had to do my solids. But then Kramers said, "Well, you are now sufficiently advanced, I just grant you that whole thing." I didn't have to do anything any more. That was Kramers. Oh yes, I must say, he gave me one other thing. He gave me for a reading assignment, an article by a fellow Herbert Jehle. And, that was about the planetary system orbits where Jehle had developed a theory in which he looked at the planetary system in the way Bohr looked at the atom, in quantized orbits. And Kramers said to me, "Is this a genius, or just the opposite? Or a kook?" I must say, Jehle is still alive. I met him, not so long ago, a few year go, and I believe he has done very good things in physics, so don,t think that he is a kook. Not at all. But he had written this article which was entirely very much out of the ordinary sort of thing. And Kramers said, "What about this article?" And I remember reading it and discussing it with Kramers, and while there were some interesting suggestions in it, we didn't; go any further on that.
Was it based somehow on Bode's Law?
Yes, it had something in it, but Bode's law is only a description. It's a formula to find out where the planet is. You put it in the formula, you can find out. It doesn't say anything of why it is like that. So, you might say Bode's law is a formula and maybe give a try to put it in a broader context. But that thing was soon forgotten. It's the sort of thing that Kramers used to do, you see. He had a very wide interest. He would notice this and this is the way he would sort of convey it to the students also.
That's quite interesting, yes. That's good to know.
So then I went to Groningen. But that was a very different life, because an assistant at the Kapteyn Laboratory, you had the full time task of supervising what the staff of the laboratory was doing. That started in 1938. At that time, there was a director, van Rhijn. There was one assistant, and that was me. And there was staff of some five or six whom we called "Reckoners". Now, if you translated the word, it would be computer, but of course you must not think of someone as computers then. They were people whose profession was to do the computation.
We had the same term in the United States and in England. In fact it was an official rating for a person in government service.
I see. It's the same thing. Well, what these people did was all work on the large Durehmusterung routine programs that the Institute did. They have published at Groningen tremendous catalogues of proper motions, of photometry, of thousands and of stars. And it was the task of the assistant to supervise the daily work of the computer staff. van Rhijn himself would spend only part of his time on that, and the other part he would spend on preparing for his lectures and doing some research on his own, for which he sometimes included one of those computers, or he would compute himself and so he was a little bit detached from that. But as an assistant, you had to supervise these computers. Certainly in the beginning that took me the whole day. So all the time I had for preparing for my exam was in the evening.
You were living alone at Groningen?
And how long a period was it during which you were an assistant and studying for your doctorandus?
I went to Groningen in September, 1938, and I did my doctoral exam in 1941 I believe. Not later than 1941. In 1940 the war began, in May, 1940, and then, it was a question of, can you still do your final exam without submitting to the requirement of the Germans? And I think I did it not long before the Leiden University closed as a sort of protest. I did it at Leiden, but it was something I had to do in my spare time. We married after I had done my doctoral, and we married in September, 1941. I must have done my doctoral maybe in the Spring of 1941, something like that, you see. So altogether it took a very long time because I entered university ln 1932. I did the doctoral in 1941. But I did all kinds of jobs in between, and the candidats was late, because I was already in on the observing staff before my candidats, which was very unusual, and I had this assistant job which was I would say very demanding, from the time I was at the Kapteyn Laboratory. I would say, in my career, these dates of exams have become more dates of when it was possible to do this, than that the jobs were defined by the exams, you see. In a way these things run parallel to each other. The real exam had very little a direct influence on the career itself. Of course in a way they were a necessary condition, but more to the extent that the people would say "Well, he seems to be doing well in exams, and the formal exam will come some time," than that they would say, "Now he has done the exams so now he is entitled to so and so." That was the way thing went at that time.
Let me go back just a second to the 1938 IAU. You mentioned that you did attend some sessions and you met van Rhijn. Do you recall any vivid memories of those sessions?
I do recall still some of that. I recall sessions —- let me say that that had an a attendance of maybe to or three hundred people. So, it was not too difficult to identify people. I met Annie Cannon, van Maanan, J. Sahilt, the one who was at New York, you remember?
There was, W. Luyten. All these are Dutch names. You know your countrymen in some way, not that I was particularly associated with them. There was Shapley. H. Shapley must have been there. There was Bertil Lindblaad.
What sessions did you attend?
Oh, I attended the sessions that had to do with galactic structure, and maybe with proper motions and photometry, that sort of thing. Not so much the sections on the planetary system, or fundamental system etc. Maybe the extra-galactic session also, I think, but that was not so very much at that time. I remember that even at the extra-galactic session they spoke about galactic nebulae also.
You remember them using that term?
Well, one thing I remember, that there was an extra-galactic session. And of course Hubble was one of the people that were still prominent, and somebody started to talk about Hubble's nebula. But Hubble's nebula is a reflection of varying density, just a galactic nebula and has nothing to do with extra-galactic. Strange loose connection existed at these meetings. I remember a boat trip that we made in these isles there on the coast of Stockholm, sitting there with Shalit and discussing with Shalit a paper he had published on inbound and outbound orbits of stars, and I asked him what he meant by that. And Shalit gave a reply, and I think he was more interested by the scenery than by the articles. He spoke to me about how beautiful these isles were, all that sort of thing. That's what I remember of Shalit . And I remember of Annie Cannon that we were at the big closing dinner in the beautiful city hall of Stockholm. I still have a photograph of that, very impressive. They have this big city hall within which there is what they called the Blue Room, a beautiful thing. At the dinner I was sitting at a table with Annie Cannon. Annie Cannon used to be surrounded by a sort of cloud of young Harvard astronomers, of my age at that time, you see. So these young girl and boys sort of gathered around. She was always in the midst of something like that . I was also at that table, so Annie Cannon was sitting there with these young Harvard people, and one fellow that was sitting there was the Swedish astronomer who had worked on interstellar absorption, rather well known at that time for that work. Well we all were sitting at the table, so in that way I got a glimpse of who Annie Cannon was, and how she was sitting. These are some memories of that meeting, but that meeting took place 41 years ago.
Let's talk about Groningen up to the war, and how you met your wife.
I met my wife at Leiden, because she also was a student, in pharmacy. We met in the student association.
: So you met while you were working for the candidats? Before you went to Groningen?
Then you maintained contact when you went to Groningen.
But you were separated, over that period of time? Was that typical, nothing unusual?
Nothing unusual. No. Then she got a job an "apotoken" or pharmacist in Groningen. Of course she'd been looking for a job there, while I was an assistant there. And then after a while we married at Groningen. So I was at Groningen alone the first part of the assistantship, about three years. And we married after I had done this doctoral exam. It was still so at that time that you would not easily marry if you did not have some sort of security. Now, I did have a job, but in a way this doctoral exam was the exam that would entitle you to teaching jobs, and would be a necessary condition for really going on in the university. So you would say, "Well I take up the responsibility of a marriage, by the time I have that more solid base for being certain about my future."
Well, at that time, of course, there was the Occupation.
Yes. That had started in May, 1940.
This was already months after that. Did you know that after your exam, after your doctoral, you were going to be able to remain at Groningen?
Let me tell you how that was. The Kapteyn Laboratory at Groningen was engaged in the big project of routine measurements and once in a while it produced a catalogue number so and so — two, three, four volumes — in that big series. That was a series that was done in collaboration with Harvard University and with the Hamburg Observatory. And the idea was that Hamburg would determine spectral classification for these stars, and we at Groningen measured the apparent magnitudes for these stars. We measured them on plates that we got from Harvard, which were taken at Harvard. On the Harvard side, these things were initiated by Bart Bok, who was at Harvard then, and who had been a pupil of van Rhijn and got his degree with van Rhijn also.
What was Hamburg's association?
Hamburg's association was simply this. Much of the work of the Kapteyn Laboratory at that time was still an implementation of the large program that had been set up in time of Kapteyn. So Kapteyn had said "in order to find out about the structure of the galactic system, you have to get all the data in a number of selected areas in the sky," and that was an enormous program.
That was the "plan of selected areas."
Yes . And so what we did was collect for these selected areas spectral types and magnitudes. And this particular program worked on the Northern selected areas, and the Hamburg observatory, because they had a good telescope with an objective prism, would determine the spectra, and Groningen would measure the magnitudes. We would put these things together, and an enormous amount of interchecking had to be done, of course, between those two.
So you used plates from both Harvard and Hamburg?
No, we used plates from Harvard for measuring the apparent magnitude. Hamburg took its own plates, with spectra, to determine the spectral classifications. We would make sure that at that position, there was the same star for which we measured a magnitude. And Hamburg at that position on the plate had the spectrum which it classified. Then we put the two things together. You say, "Star number" so that we have now sort of checked that it is the same, has that magnitude, that spectral classification, that's what we list. That's the way it went. So there was much communication between Hamburg and Groningen at that time .
Who at Hamburg primarily?
That might have been Schwassmann, but I'm not sure. It was something with "assmann." I would have to look into these because a whole series of catalogues has been published, and the whole series is called the "Bergedorfer Spectral Durchmuterung," because the Hamburg Observatory is at Bergedorf, near Hamburg, and they did the final printing. It was a wrong title because "Bergedorfer Spectral Durchmuterung" suggests that it was primarily a German publication. But I am sure that at least 70 percent of the work was done at Groningen. I mean, it's a much more elaborate piece than the spectral classification.
What happened after the Occupation? Did this activity continue?
Yes, it continued. But it could still continue especially after we were occupied. We were in a way in a postal service that covered Germany you see. So letters could go hack and forth between Holland and Germany. And you would not write about things for which it would not be necessary, but that sort of scientific communication went on. So we would send lists to the Bergedorf Observatory, and they would check, and they would give us data, etc. So it went on like that for a while.
How did you feel about that?
Well, I think we separated work on the scientific project: a list of stars with their magnitude and the spectra. We separated it entirely from the fact that you had to do with Germans. At the same time there was opposition to German military forces during the Occupation. That went along simultaneously with doing the scientific work and it became difficult only at a later stage. We did not say "In principle we do not work on this because the fellow with whom we work has now become part of the enemy world." That was not the way things were done. And I would say, nobody has ever thought about it like that. Also in Holland nobody would say, "How can you work with the Germans on this?" You would oppose any relation to the Germans that would be interpreted as supporting them. But it is difficult to see this in retrospect.
You treated the German astronomers as astronomers. Not as part of the war.
Yes. Now, I must say, the only one I had to deal with was the director of that place. Much of the correspondence of course went with him and van Rhijn. But only in a very formal way, because they would respect each other as "scientists colleagues". They would have no justification at all for the Occupation of the Netherlands by Germany. Van Rhijn was strongly opposed to what the Germans did in Holland. He would scold them and gave absolutely no trace of any agreement or support, nothing of the kind. He would do what he could to support any underground opposition. But at the same time, there was this colleague at the other end of whom you had no reason at all to think that he would be involved in supporting the German Army occupying us, and only wishing to get this job done. For instance, would he be one of the fellows who would say "Heil Hitler" or not? Van Rhijn told me that at one time he had noted that Schwassmann had said "Heil Hitler" to another German an he said, "Why do you do that? How can you justify that?" That was the sort of relation that existed. It was in that context that I, as an assistant, supervised this measurement at the laboratory. But then after awhile, van Rhijn fell ill. He got tuberculosis, and he spent a long time in a sanitorium in Holland. Also many of our computing staff had to leave, because some of them were in the army, and the army of course was then soon [incarcerated]. Anyhow, thesc people regularly disappeared from the place where they worked since they had been in the army. There came a time when the Germans became more and more severe with the Dutch, and they would just pick up people from the street and send them to Germany, just to get rid of them.
To work in factories?
Ja, but also to get rid of these unpleasant Dutchmen who wanted to oppose them and obstruct them wherever they could. So especially the people who had been in Army service in Holland felt that it would be safer to disappear. And they did. At least two of them disappeared from the staff. And there was another one who couldn't cope with the mental stress of that time. In fact one of them committed suicide, all unpleasant things. And there may have been another one who just stayed away. I don't know whether I was at the laboratory all the time. But the intensity of the work went down very much. I remember that at one time, van Rhijn was in the hospital, and I was called to appear before the German substitute major mayor of Groningen at that time. And he said to me, "I have heard from Germany that you have this collaboration, but when I asked about it in Germany, I was told that very very little progress has been made lately. What about it? And I think I must have told him, "Well, under the present circumstances, the director is ill in hospital and most of our people have disappeared, so what can you expect, Sir?" And of course I did it because I had started working on my thesis at the time, which is a very different subject. So he interviewed me on this, and I thought "Well, what can you expect under the present circumstances?" And he just said, "Well, goodbye," and I said, "Goodbye," and that was it. I never heard anything about it any more.
So he didn't press the matter?
Did you feel you were in any personal danger?
Everybody felt personal danger all the time. It was a sort of a standard circumstance under which you lived. Well, later they put me in prison for a while, but it was for very different reasons.
What was that for?
Oh, it was a story in itself. But let me just continue the business about the Laboratory. In the later years of the war, the production was almost nil on that joint project. I think during the last 2 years of the war, there was no communication at all any more with the Bergedorrer Observatory. So, the work just stagnated.
There certainly wasn't any communication with Harvard during that time.
No, not at all.
Did you receive any of the Astronomical Newsletter that Bok was involved in sending?
Ja. We received some of that. But I do not remember whether that was during the war, or whether it was right after the war. I may still have these things. But I am not sure.
You must have maintained contact with Leiden?
Yes. The contacts within Holland with the different observatories were maintained, very much. So I had contact with Leiden. We had contact with Utrecht and other places, as far as we could, we had an annual gathering of astronomers in Holland, what we called an Astronomer's Conference. It was really a getting together of the professors with all the students that in some way were interested in astronomy, even second and third year students. We had a three day conference at one of the holiday resorts somewhere in the center of Holland. You would all get together, and they would talk about astronomy, and there would be some lecture, and they would make music together, and they would go hiking. It was very pleasant. And the inspiring man in this was especially Minnaert. The astronomer from Utrecht. Wonderful fellow. He inspired this. He started this. This is one thing that I know went on during the war year, maybe not to the end, but I believe still in 1942 we did still have that, you see. So the contacts between Dutch astronomers were continued up to perhaps, I think, a year before the end of the war. Then there was a breakdown of communication in September, 1944, when there had been a transport strike in Holland, just to oppose the Germans. It was a rather effective, but it also meant that to go from Groningen to Leiden was a very difficult thing. If at all possible, we would go to our parents in Amsterdam. It was the last time, that was impossible. We were really cut off. And after this, food became scarce, in what we called the Hunger Winter. That was the winter from 1944 to 1945, when food was so scarce, especially in the west of Holland, that these people began to starve. One of the things that we did at Groningen at the time was to organize shipments of food from Groningen to the Leiden Observatory. We were still better off as to food than these big cities in the west of Holland. And I remember one time, we even organized quite a shipment, there was something like six or ten barrels of sauerkraut. That was something you could buy and preserve, and so we sent six of these barrels to Leiden Observatory. We sent a chest of potatoes, and we put in something else, but that was stolen on the way, and we sent meat. It was a silly situation. What you did is, you would send all this stuff secretly. We wee forbidden to send food.
So this was all against the rules?
Yes. But we could send a big chest that was full of wheat but we would put on it "Astronomical Instruments." "Be Careful, Don't Open," that sort of thing.
— Don't expose them to the light. —
Yes. That was delivered at Leiden Observatory. So they made the bread out of it and things. And the same with the sauerkraut, you put on it, "Astronomical Instrumentation, Don't Put Upside Down," and all that sort of thing. It got there.
Did you organize this or van Rhijn?
No, vanRhijn was in the hospital. So the two of us organized it .
You two did . That's marvelous.
And our neighbor did.
And our neighbor. Of course, you had help from people who could get the food. I mean, all these things were done in collaboration with all kinds of groups. That was almost evident. It was the one way you could do these things; at that time. So that was the sort of contact we could have. And we could telephone. I believe -
And I think, because of the pharmacy, if there was something wrong with the recipe, we need the telephones. So we kept the telephone quite a long time.
Yes, that was an advantage.
That was good, then you could call Leiden.
Yes. But there was not much contact. You see also, in Leiden, most of the people had dispersed. They were also afraid of being taken away and maybe sent to Germany. So the staff was diluted very much, and the activity was low, so there was not much reason left for communication, apart from getting something to eat. At that stage that was the dominating need of people — how to survive. Especially in the west of Holland. How to survive, how to get something how to eat wood for the stoves, and all this sort of thing. People were making their meals on improvised stones. They had invented very small stoves that you put on top of a normal stove, and you put in a little bit of charcoal, and it would just give enough heat to cook a meal. People were very inventive, you know. People get very inventive in times like that.
Well, and they ate tulips.
Oh, tulip bulbs were eaten, yes. It was horrible.
They're pretty to look at.
I think their ration for bread was about like this, [hold out hand] for a week.
One slice for a week?
If you could get it.
Yes. So you see, the immediate need for surviving, for heating, for eating dominated life, I would say certainly for the last year, and you can imagine, under those circumstances, scientific production fails to zero.
In 1944 you wrote a paper on proper motions of B type stars which came out in February. I have a copy of it here. This was the type of thing that one would expect you would be able to do during the war when nothing else was possible, the comparison of catalogues.
Yes. Indeed, yes that's right.
So you were able to maintain, on a very low basis, some activity.
I'm interested, how long was van Rhijn in the hospital? Did he survive the hospital and come back?
Ja, he came back, but when did he go to hospital? I think must have been ill already in 1943 I think, maybe some two years before the end of the war. And at that time, I began to work on what would become my thesis. And that maybe leads also up to this thing . Van Rhijn at one stage had said to me, "Now, apart from all the supervising what the computers do, of course you should also take up something for your thesis work."
So he was aware of course that you were to advance.
Yes. Van Rhijn was a very nice fellow. He's been given much too little attention in historical surveys, so maybe you would like to learn a little more about van Rhijn? But what happened was that van Rhijn of course was very much a follower of Kapteyn. And what he at one stage told me to do, at least to look into, was the following: At that time, there had appeared the catalogue of proper motion of Benjamin Boss. Not Louis Boss. Louis Boss was his father, but there was Benjamin Boss, his son, and Benjamin Boss had compiled the catalogue in four or five volumes. One introductory volume and four volumes, each with six hours of right ascension. And in it were 33,342 stars. And I've always thought that it was a mistake of Benjamin Boss that he put in these nine additional stars. If he had just taken out nine stars of the lowest accuracy, it would have been 33,333. Wonderful number, right? 33,333. So why did Benjamin put in these stars? [Laughter] So, well. That catalogue had appeared around 1935, I think. Now, that is one thing. Among the main works of Kapteyn was his investigation of the proper motions of what Kapteyn called the helium stars. What we call the O and B stars. That has been one of the major Kapteyn sidelines. This work of Kapteyn I believe dates from around 1917. It was published in two articles in the ASTROPHYSICAL JOURNAL which you'll also find in the reprints of the publications of the Mt. Wilson Observatory. These publications were reprints of the ASTROPHYSICAL JOURNAL and there are two thick articles in that, and I think they are Mt. Wilson publications, numbers 147 and 80 or so.
That can be found .
And they are of course mentioned in my thesis. There's no problem at all. Well, in those publications, Kapteyn had investigated the proper motions of the bright O and B stars. And that led to very interesting conclusions about their common motion, and he used that again for determining luminosities. It fitted into the general pattern. So when that catalogue had appeared of Benjamin Boss, with new proper motions, then van Rhijn, knowing about this work of Kapteyn, said, "Now, what about you trying to do this work of Kapteyn now in the light of this new material, which is so much more accurate and so much more extensive?"
So that was van Rhijn's suggestion to you?
Van Rhijn's suggestion, yes. I then looked into this in my spare time. And that led to what became my thesis, which dealt with the Scorpio Centaurus association, which was still called a cluster at that time, but which is the main body of helium stars in the Southern Hemisphere, and in which these properties of the proper motions that Kapteyn had noted now became much more apparent, much better defined, because of the higher accuracy of that material. So it turned out that looking into this indeed was a lucky choice. It proved that you could see that something interesting could be gotten out of that . I continued working on that, and van Rhijn and I intended First to do the whole sky, but I found that by concentrating on the problem of the Southern one, where you could identify the structure in these early type stars, that had its own properties, its own role in the galaxy, then I decided that I would make that particular section the subject of my thesis. So I worked on that and it was done mostly during the later year of the war. I remember my typing this thing in the evenings at home on one of the old fashioned typewriters. Page after page, and I did it over and again, and during the time I would do some computing, etc). So from then on it was a single man's job. There was no van Rhijn to talk to, nobody else, and I did the whole thing practically unaccompanied.
This is resulting publication: No. 52 of Groningen?
That's right, yes. That is at the same as my thesis.
It is quite long.
Oh, some 140 pages or something, isn't it? Ja. Somebody has once used a remarkable word for that. Because I think year later, decades or so, there was again a publication on this subject by I think D.H.P. Jones from England, and he says something in the introduction of the "so and so work of Blaauw on this". Well, the word doesn't come back to me.
Now the other paper in 1944, I can explain now, the one that you referred to earlier, that wa published during the war. You must see in the context of that thesis work.
I appreciate that, yes.
You see, what happened was the following. In dealing with these proper motions in the Bos catalogue, I hit on certain systematic effects, which would seem to indicate that if you would take them for real motions, that there were unexplainable systematic streaming of these stars in certain parts of the sky. And it seemed odd. So I looked into the problem. I looked into the problem of the systematic effects in the catalogue of Boss. And about that time, A. Kopff's publications appeared. He was a well known German astronomer. And he is the one who was an expert on fundamental catalogues. You know, the establishment of fundamental catalogues of stellar positions and proper motions has been a very strong German tradition for many years. It goes back to the early times when there was the German Auwers, who made a catalogue. And then as a second installment, there was made a fundamental catalogue that they called Fundamental Katalog, the FK. And then a second one was made. Every time they included the more recent meridian observations, that is to say every 10 years, to improve these positions to get better proper motions. This gets closer to what you consider as a basic reference system of the positions of the stars in the sky. So, by that time — that must have been around the 1930's early forties — they had established the third installment of the FK series, and systematic as the Germans are, the first one was called FK-1 and then FK-2, FK-3. So by the time FK-3 had appeared, containing maybe a thousand stars that represented a system of positions and proper motions, but quite apart from that, Benjamin Boss had made his own catalogue, which in itself represented a system. And that meant that you could take the list of stars in the list of Kopff in the FK-3, and you could take the same stars in the catalogue of Boss and you could see whether the same thing came out of it. I found that there were differences, systematic differences. In certain parts of the sky, all the proper motions in one component let us say in declination, would be systematically different from what you would expect from Kopff's catalogue. Clearly there were systematic effects. And they would of course effect this study that I was doing on these B stars. That is one piece of information. The other one is that about that time, Oort was also working on these problems. Oort at that time, in the war years, was separated from Leiden Observatory, and he lived somewhere in the center of Holland. This was also one of these moves where people get away from the place because it wasn't safe to work any more if you were at an Institute. At least for Leiden Observatory at that time, it was better to stay away.
Wasn't he especially active in the Resistance?
Not that I know of. I just can't say much about it, I don't know. You see, the problem with the Resistance is that the people who did really very valiant important work, you hear very little about. So, if you don't know whether he did Resistance work, he may not have done any, he may have done a lot. And I would say in general that the people who became so well known about their Resistance work were really on the fringe. They maybe made more fuss about it and were afraid to be forgotten. I don't know. It was extremely complicated to evaluate what people have been doing during the war, you see.
I appreciate that, yes.
It's hardly possible to evaluate that. Of course you hear that some people had been killed by the Germans because they did things. Those you know. But for those it was too late.
Were there any astronomers involved?
Not that I know. I do know not of astronomers in Holland who had been killed by the Germans. We do of course know that Minnaret was taken as a hostage, in the early stage, and he was hostaged in one of these hostage centers in the southern part of Holland, but he survived. I just cannot say any more about Oort. I never discussed it with him. But I do know that Oort used that time while he was sitting quietly at a place where he would not be disturbed, to write a book on galactic astronomy. But book has never appeared. What happened was typical. Oort had a list of chapters, and one of the first chapters was basic data, and among that was the fundamental system of positions and proper motions.
I see what happened.
So, Oort got interested. Oort looked into that, got interested in it, and started work on the same question of which is better, the FK-3 system of the Germans, or the system of Benjamin Boss, which we call the GC system? That means General Catalogue. As I said, the FK was the outgrowth of the old Auwers catalogue, rooted very deeply in the German tradition of making accurate observations of stellar positions. It's a very thorough German subject and still is. Walter Fricke, who is director of the Heldelberg Institute, is still working on FK-5, you see.
Is he here at the meeting?
He's here, Ja. I had a chat with him yesterday.
He's working on FK-5?
Yes, I believe, or FK- 4 or 6. No, 4 ha appeared. Maybe he is already thinking about 6. So, Oort was working on that, and remarkably I sort of independently worked on that. Contacts at the time were already so slight that I did not know that he worked on that. And it was only just before I sent the thing to the printer, I think, that I had contact with Oort at one of these Dutch reunions, where everybody tried to get together, and I spoke about this. I had opportunity to show him the manuscript. And I know it very much has influenced his view on that problem. I think he came to just the opposite conclusion that I had come to. But he changed it, because he found out that I was right. So there was this remarkable instance of independent work, but we had an entirely different way of reasoning. Mine was much more pragmatic.
I'm interested in that.
I wanted to ask you about the philosophy you'd use in comparing fundamental data and system. I have had the impression that you were very much interested in understanding the nature of techniques, from your chapters in STARS AND STELLAR SYSTEMS that you later wrote. I'd like to have some background on that: the pragmatic approach that you developed.
On this particular subject that we spoke about, this question of which this question the two systems is the better one?
This is what you spoke about to Oort at the meeting.
Yes. Oort's approaoh his been that he looked into how Kopff did it, and how did Boss do it.
Asking, how they did it?
Yes. And in fact, what it means is that you make a sort of average of lot of data, and you see whether they have taken into account all kinds of sources for systematic errors and you try to think, which can they be? Is the flexure of the telescope? Is it the refraction of the earth's atmosphere? That sort of thing. And then you evaluate it and you ask yourself: would I have done things the same way? That is the way Oort went about it, and he came to the conclusion that he thought that the GC probably would be better than the FK. My approach was a different one. I said, "Let us see what come out of it." And I said that, "If I use the proper motions in the system of the FK-3, then these B stars seem to behave in a way that does not look implausible. This was contrary to what I found if I took the system of Boss; the GC. What do I see then? These B stars, especially the fainter ones, are at large distance and they all are fairly strongly concentrated towards the galactic plane. So what you see in the sky is a sort of narrow strip along the Milky Way equator. If I now apply these proper motions in the system of the GC, what do I see? I see for instance in the Southern Hemisphere that at certain points, it looks like all these stars move away from the galactic equator in a fashion that seems to contradict the fact that now they are also so nicely aligned along the galactic equator in a fashion that seems to contradict the fact that now they are also so nicely aligned along the galactic equator, which would suggest a systematic motion for which I have no understanding, and which might tend to deform that pattern. But moreover, these systematic motions seem to be preferably along the line of increasing declination. That seems very unnatural.
Yes, there's no reason why you'd expect it.
What might it mean? It might mean that these proper motions are affected by a systematic error that we have put in which makes it seem as if they move in those directions. But that would not be a real motion. So I said, "If I now look at the differences between the two catalogues, it would seem that in the FK-4 system, the pattern is compatible with what we expect for these stars Whereas for the GC system, something is added which is very suggestive of an error that the compiler of the catalogue has made."
Well, I worked that out of course in terms of strict formulation, and set up formulae for that, and introduced such things as systematic errors which depend on declination and on right ascension. I did it separately for systematic errors in the component in right ascension and the component in declination. I knew that these two components may be affected by causes of error which are entirely independent. That much of course, I had to put in my knowledge of the whole technique that is behind this. My conclusion was that, knowing what kind of errors there can be, seeing what the result is, I concluded that indeed, these errors, especially in the proper motions and declinations, have entered somewhere, but they have entered in the procedure. Much more in the procedure that was followed by Benjamin Boss than in the procedure that was followed by Kopff. So it is a semi-pragmatic way of saying which of the two is the best. Now, that work of course was later followed up by work of H.R. Morgan of the Naval Observatory, whom I have known and discussed these things with. He worked it out later in a new system that was called the N-30. He and Oort wrote an article about these things. In that article of Morgan and Oort, Oort discussed that was essentially in this chapter that he wrote during the war. That article, which may have appeared in maybe 1947 or so has, in a way digested all the things that Oort did during the war on that subject together with the new information of H.R. Morgan, the knowledge of what it would mean for practical applications. That,s a very nice article. They confirmed that the one system is better than the other; what sort of systematic relation must be applied; and what does it all mean for precessional constant and all that sort of thing. So you see, this was an article that has grown through many developments, that artlcle of Oort,s by Oort and Morgan.
This is after he saw your work, he and Morgan?
Ja. We saw that work of each other already during the war. So, I then proceeded using my approach in the thesis work. I would have to check that, but I think I did. But you see how it is. One article appeared before the end of the war, and the thesis of course appeared later .
Right. In your thesis, you worked on determining the age of the Scorpio-Centaurus cluster as it was called then. Of course you indicated that there was also the question of the reality of the cluster at that time, but that if it was a cluster, there was a disruption age, was it, of between 1010 and 1011 years?
I think I concluded there that one could understand the present cluster — especially its shape and the orientation — if one would assume that it had originated in originally much smaller clusters. But by some perturbation in the gravitational field, it would have been disrupted, and elongated. And the elongation would be determined by the general galactic field of force. So then you can then explain it on the basis of the computation of these orbits. And that,s done in the thesis. And I left in the thesis the question unanswered concerning that earlier stage. So I said, "If you assume that you start from the small volume in which these stars are, and you introduce that sort of perturbation, then you can explain the present object, and you can indicate a time scale during which that perturbation has worked."
I think I came to a time scale of something like 6x107 years or so, a time scale of let us say 60 million years. That is what I arrived at. And I should say that the whole idea of looking at these disturbing effects in the galaxy was inspired by the work of Bertil Lindblad. Lindblad has done important pioneering work, as you know, in galactic dynamics. In his attempts to explain spiral structures he studied the structures that you would get in the galaxy if you have a group of stars that is disrupted and therefore tends to spread out along certain lines. And these lines then of course, you tend to interpret in terms of spiral structure . We now know that that is not the explanation of spiral structure. In fact, it would lead to a rather different pattern. But all the same, in the context of that problem, Lindblad had developed this theory of the individual orbits in stellar system. And I took that thing up and tried to work it out in order to explain remarkable structure of the Scorpio-Centaurus cluster. But I left the problem unanswered of what, came before. One must remember or realize that, at that time, if we spoke about ages of stars or of the solar system, we always spoke in terms of 109 years — it might be several times 109 year. We knew at that time that that was an age that was acceptable for the galaxy. We knew that ages of let us say 1013 or so were not acceptable. But also, and I think we should realize that, speaking about ages of stars very much younger than that did not happen at the time.
This is what I'm interested in.
You see, the idea that there would be very different ages of the stars, very different from the age of the solar system, came up only about that same time.
But you weren't aware of it?
Well, we became a little bit aware of it, I would say, but that was after my thesis. You see, my thesis was written during the war years, and published afterward. But right after the way it was difficult to get something published. There was no paper, for instance. There were no printing facilities. They had been dismantled. They had been destroyed in the war. Everything had to be set up again. And you will see, if you put all the Groningen publications together in a volume, and you look at it from the side, you will see there is about a one centimeter thick layer of very dark paper. That is the poor paper that we had about a year after the war, and that was the only paper that was available to print my thesis on, you see. And it later became better and better and it became whiter and whiter. [Laughter]
I was just going to make that comment, because to find your paper, I found the bound volumes of the Groningen publications, and of course they did get much thinner and the paper was very brown.
Oh yes. It's typical. So you see, what is in that paper is work that was done during the war.
But after the war, of course, we could read other things again. There were really two things that appeared. One was worlc by Unsold. I'm not quite sure but I think it was Unsold who pointed out that if you look at the most massive stars, and you take the amount of radiation they put out, and you take into account what we then knew about energy production by transformation of hydrogen into helium — that is another thing that was developed only at those times by the nuclear physicists. That was all new at the time. It didn't exist yet at the beginning of the war, you see — if you took that into account, then you come to the conclusion that these stars of large masses, say 10 solar mass, could not have existed for that long time of 109 years. So I think it was Unsold who said we would then have to conclude that these things have existed only for 107 year or so, 10 million year. These remarks were not made in the context of galactic studies, but more from the point of view of the astrophysicist who studies the structure of individual stars. But that was one remark that was so to say injected into the literature, that maybe was not given too much attention. But after all, Unsold's papers are papers that you are supposed to read. I mean, an author of that standing, you would also naturally say: "Well let's see, what does he say in that article?" And it was about at the same time that we became aware of the work of Ambartsumian.
On expanding associations?
Yes. What I had done in my thesis, where I had indicated a time scale of 50 or 60 million years for these B stars, plus this information from this astrophysical nature, seemed to indicate that you need not worry too much about the problem of what a group of stars had been doing before, because you might say, "Well, it originated at that time. " And I still remember that in 1947 I gave a colloquium at Harvard on that thesis work. It was before the Ambartsumian epoch, I must point that out. I said then that we can explain this structure of the Scorpio-Centaurus group by assuming that it has started by disrupting from a small volume. And coming from a small volume into the galactic gravitation or field of force, it will then have this structure in 60 million years. Shapley was there, and Shapley said, "What about before that time?" I said then, in the light of Unsold's remark, "Well, maybe we have to assume that these stars originated at that time, because that would seem to be the age that you would assume for these stars." And Shapley said: "Well, that is one way out of the question."
While we didn't continue the discussion, I had the impression that he didn't really appreciate that sort of solution very much; that he thought it was sort of ducking the problem. I only mention it because clearly, the idea that you could speak about stars having been formed 60 million years ago, instead of 1,000 million years ago was not yet generally accepted by astronomers. That, just began to emerge then at that time. The idea that there would be stars around a thousand times younger than the sun was not common property among astronomers at the time. Not at all. We had always been thinking in terms of: "well, all stars are about the age of the sun, 109 years or 4 x 109 years. The age of the whole universe, after all, is something like that, from the Hubble expansion — the sun gives the same figure — well, then probably everything in the universe has that age." But to say then that there are stars that are a thousand times younger, that was something that required time to penetrate in our minds.
Baade's 1944 paper on the populations didn't indicate this, it indicated that there were two relative ages, it didn't really tell you there were very young stars.
Doesn't say much about the ages.
So now I see why that wouldn't have been a crucial paper for you.
No. It was an interesting paper, but it was not crucial for this.
Exactly. You certainly continued on after the war, working on the expansion of associations.
I'd like to know what kind of reorganization took place at Groningen after the war, after the Occupation. What was your position? Did you know what your future would be like? Especially how did you come to go to the United States?
Well, Groningen and I had written my thesis, and the war ended in April, 1945. And at that time at Leiden, certain positions could be filled again and of course Oort knew about the work I had been doing. At least he knew shortly after the war, and he had visited us in 1944 at Groningen, coming from where he had been hiding, making a trip to Groningen, etc. I don't know exactly. But anyhow, soon after the war was ended, Oort asked me whether I would be interested in taking on a job at Leiden Observatory on the staff. That would be a much more interesting job than I had at Groningen, so, I think we then said OK, and went back to Leiden. Then, I took the job in October 1945, half a year after the end of the war. We were just beginning to reorganize what we'd do, to settle again, to establish ourselves again.
How did you feel about this, Mrs. Blaauw ? You had your continuing job as a pharmacist. Mrs B: This was just to be able to live without support from the parents.
I see. Mrs B: It was a very small pharmacy, and didn't come out to much. And then when we went to Leiden, I had to continue of course and try to sell it. It wasn't possible to sell it, because there was not enough money coming out for the family to live on. So it was divided in between the two next pharmacists. It was sold, but they took each a part of that. So I was able to follow him.
It was no great problem really. And the position at Leiden was very attractive, because it was one of the permanent staff positions.
Oh yes, certainly.
We had great difficulty in finding a house at Leiden. So there was a period in which I stayed with relatives. And the family stayed at Groningen. I would corne home to Groningen once every week or two weeks.
Because I still had my pharmacy to take care of.
And I had two small children at that time.
So it was a bit difficult, but all these things were overcome. And then we found a house, a very small house at Leiden. And not so long afterwards, we could live in one of the big houses that were part of Leiden Observatory, so we very easily settled in Leiden again. After all, we had done our studying there, so we knew the place very well. And at Groningen then, my position was taken by a colleague who had been with them named Plaut. I don't know if you want to talk about Plaut too. Maybe we can do it separately. A very fine colleague who then got that position and continued the work I had been doing there. So we went baak to Leiden, and then in a way I continued work on these problems. But I then became a lecturer in 1948. I think one would call it compared to an associate professor in this country.
You mentioned you were at Harvard in 1947.
How did you manage to travel there? Was there a specific purpose?
Oh, it was like this. Right after the war, we had had a visit from Otto Struve at Leiden. Otto Struve was one of the leading astronomers in the world at that time, leading both by his research (he was an enormously active fellow) but also leading in the sense that he knew the astronomical world. He was of Russian origin, had found his position in the United States, was very respected all over the world and well known. He made a tour to Europe at that time, and on that that occasion, it developed in talks at Leiden that I might go to his observatory — the Yerkes Observatory, for a while. And so I went there in 1947, to work with him on a project that, I must say, I did not find a particularly interesting, but it was a way of getting some experience somewhere else. And it was more or less in the general tradition of the work of the Leiden Observatory. So I worked with Struve from the middle of 1947 till early 1948 on the problem of the radial velocity variations of RR Lyrae.
That's quite different.
Yes, it was completely different. But of course I had seen so much of variable star work at Leiden that I was rather familiar with the work, and I could appreciate the significance of that problem on the whole. So I worked with Struve on measurements of radial velocities of RR Lyrae on plates he had taken.
You were just finishing talking about working on RR Lyrae with Struve.
Did you have any choice in this? Or were you interested in trying other things?
Well, you see, I might say I didn't have much choice in it. It was an opportunity to work at Yerkes Observatory for eight months or so. And during that time at Yerkes, I was alone. My wife and the children stayed at home. I had been away for nine months, and I should perhaps say right away that at that time we were expecting our third child, and when I came home, she was six month old and that was the first time I saw her. That was the way we did things at that time. You were glad to have an opportunity to travel to the other continent. It meant rather a burden on the wife and the children, and you accepted that you would see your third child only months after he had been born for the first time. But did not say, "Oh, but I cannot go away from my family for so long," as some of these youngsters nowadays say. There are people now that you say, "Now, you go for an observing spell of six weeks to so and so,"(and they may say, "Oh, but do you really imagine I could go away from my family for that long? My wife wouldn't allow me." These silly ideas — you didn't have them at the time. You take your possibilities. You take what is possible and you wouid be happy to have the opportunity, and you would go there on a very small amount of money.
You must have lived at Yerkes.
I lived at Yerkes. And that time at Yerkes, was a great time for Yerkes Observatory. It was a time when there were many prominent, excellent people there. Just to mention a few, of course, there was Chandrasekhar, there was Struve himself, there was Kuiper. During the time I was there, for many of the months Stromgren was there as a visiting professor.
Yes, he had come back. He was there in the thirties.
Yes, but he came there again as a visiting one. There was G. Herzberg, who also gave a lecture now, whom I also know from that time who was working on molecular problems. That was only a temporary stay. But they were all there, you know. There was Bill Morgan.
Herzberg was only there temporarily?
But Struve made tremendous efforts to build up instrumentation for him in the basement, spectroscopic instrumentation.
Do you know whether Struve was trying to keep Herzberg?
Oh, he must have tried to do it. That is what it was. Oh, undoubtedly. Undoubtedly yes. Well, there was, I think, Bill Morgan. There was Al Hiltner. Lots of people, you know. But especially, there were many brilliant students. It was the time when you had students, not only the very young students that just had graduated, but many people who came back from Army service. They had been through the war. They had been in Army service in different parts of the world, maybe at the age of 25, 26, 27. They took up studies. But they were anxious to study hard, to get somewhere, not what you have in young students enjoying life of a little bit in other ways. It was very serious business for these people, and there were brilliant people among them. I don't remember all the names, but it is a fact that of that age category, many have become prominent astronomers in the United States. I know many of these names. I was there in 1947 through 1948, and again in 1952 and then from 1953 on. So sometimes I don't remember exactly whether a fellow was there in 1947 or whether he was there in 1952. But for instance, names that I do remember, of those early times, were my fellows in the next office, Art Code. I think, what's his name, was in medicine, was there. Art Code was there. Don Osterbrock was there. Guido Münch was one of the students. Nancy Roman was there, she was a young student and Ann Underhill was there as a young student. Billy Beidelman was a young student. But they were the younger category, and not so much some of this more senior category. Marshall Wrubel was there, a very gifted student. You know he died a number of years ago. Well, this is just a few names. There were many more. And it was this very good staff of people, with excellent lectures; lectures of Chandresekhar, of Strömgrur, of all these people that meant very much. And this very good generation of students, that made Yerkes Observatory an outstanding place in those years.
It was also a period of reorganization of the observatory.
Well, of course it was very much Otto Struve who did all this. He was very powerful in reorganizing the place. It was the center of the editorial management of the ASTROPHYSICAL JOURNAL, which Chandra did, having taken over from Struve who did it in earlier years. It was also the time when Yerkes Observatory implemented the collaboration with the University of Texas in the use of the McDonald Observatory.
Certainly. Well actually Struve was the director.
Yes. He was the director there. And I went with Struve observing at McDonald also, once or twice. And so it was a very lively and very inspiring place at that time.
The first time you went you worked with Struve directly on the RR Lyraes?
Did you do any work with Morgan on galactic structure? Because he of course was also interested in early type stars.
Ja, a little bit but there was not much time left on this project with Struve. You see, what we had to do was measure I believe some three or four hundred radial velocity plates that Struve had taken. And we agreed that I would do half and Struve would do half.
That's fair enough.
And probably I did 60 percent and Struve did 40 percent, but Struve still managed to do that, with all the other things he had to do. I did a lot of the reduction of the measurements and I drafted the paper on this and I finished it after I was back at Leiden. That stuff has all been published. We found certain beat period that we knew in RR Lyrae. We could recognize them in the radial velocities also. So in itself, the work was quite all right. It was not in my field. But altogether the total experience of working at Yerkes, meeting all these people, and being in this entirely new world, for a young Dutch astronomer was valuable. The fact that it was not exactly in the field I had been working with did not mean so much. The other things all together count much more than that it happened to be making something that I have not continued working in.
Where did you stay? Did you stay at the observatory?
Oh yes. I had a room in the Battleship. Do you know Yerkes Observatory?
Yes. I worked there.
You know the attic. It has all these round windows, and that is why we call it the battleship. I had a room there, with many other students. I lived there because I got a small salary from Yerkes Observatory and I saved as much as I could to buy things to send to Holland because at that time in Holland you couldn't get anything. So I sent material to make dresses, little things for the children, all sorts of things, you see. We all did that. All the Europeans did that. You know who even did it? Our old Chinese astronomers Chang who is here now. He is the leader of this Chinese delegation. He was also at Yerkes at that time. He was older. He had been there before. And one time I had the office next to him. That's why I know him so many years, you see. And I know he also bought things and sent them home. So you would live on a minimum. We did not have to pay for these beds in the Battleship, and it was only in the last month that I then took a room in the student dormitory section of the van Biesbroeck House. That was a relief, I can tell you, because that summer in that attic was so terribly hot.
I spent two weeks there.
The coolest place in the observatory was in the basement and that's where I had my office. So it was better in the office than in the bedroom. We had our meals at Biesbroeck. All our meals we had at the van Biesbroeck Dormitory. That was very pleasant. They were a delightful couple, you know. They were so good to all the students. That was a very fine contribution. It made a big difference when you've got a household that will take you in. They did a wonderful job.
And you mentioned that during this period, you also spent time at Harvard?
Well, you know how it is. You give a colloquium here and there and I visited Harvard, and of course that was because Bart Bok was there and you know how Bart Bok is. You go there and he is kind to everybody and makes you feel at home. And in that context, I gave a lecture at Harvard, a colloquium. Then of course I spoke about the work I had been doing in Holland.
Did you go any other places in the United States?
Oh, ja, I have been so many places in the course of the years. Certainly, one place where I would go was to Sproul Observatory. That was to visit P. van de Kamp and L. Bineindrick at the University of Pennsylvania. Mrs. B.: You were in California at the time that I sent you a telegram that the baby was born.
Ja, I made a trip to California. Oh, I have been many many places. But that was, you see, because I went with Struve to Texas. And being in Texas, I thought, I am so close to California, let's go there. So I could go there. I took the Greyhound bus and visited people. So I have in the course of those years visited many places.
Well, I'm interested only if you have recollections of specific instances where you discussed your research or gained new ideas in talking to people.
It happened at many places. I went to Mt. Wilson. But I think I talked there only with R.E. Wilson or O.C. Wilson. There were several Wilsons at Mt. Wilson.
O.C. Wilson is the spectroscopist.
Ja, but I must have talked with R.E. Wilson. But I do not remember much of that I must say. I have been at Lick and I remember my talking to G. Neubauer, but these things are sort of a chapter apart.
I was getting an impression of the way they work. Of course, I have been to Indiana, visiting Frank Edmundson's place, and Cleveland where there was Nassau and his collaborators. I've been several times there. Oh, I must have been at New Haven, where Wesselink was, and Brower at that time.
Wesselink was not there that early. He came later.
Yes, he was in South Africa at that time. But I was at New Haven I think. So, I do not remember well when I was where. But I have been at very many places in the United States in the course of the years. You see, I was in the United States in 1947, 1948 and I again was at Yerkes, as an associate, invited as a visiting professor or whatever it was, in 1952. For five months.
That's a very important time. It was just the period when spiral structure was becoming identified. Morgan was very much in the middle of all this. I would like to know very much, since you collaborated with him, what your recollections are of that time.
1952. I was indeed there because I was then fully involved again in working on early type stars.
That must have been the incentive for asking me back. And I had before that done the work on expanding associations in Perseus.
Maybe we should take that up first because in a way that followed up on what I had done in my thesis. But not only that. It was also much inspired by what I mentioned earlier — Unsold's introduction of the astrophysical notion of limited ages and by the fact that by then, we were aware of the work of Ambartsumian. The work of Ambartsumian was published in the last years of the war but it was communicated to us after the war, in some difficult papers. The papers were all in Russian and it was difficult to locate them and you had to find somebody to translate the business. And I remember, there was at one time a very good translation of these works by a French astronomer, who made them better available to us. It was Kourganoff, a Russian name but a French astronomer.
I thought he was Russian.
No, Kourganoff was in France. Maybe he was born Russian but he was in France at that time. He had done a lot for making the Western World know what the Russian astronomers had done.
I recall he wrote a text on radiative transfer.
I believe he is in Paris now. But he may be retired. But he was also one of those people who helped very much. So Ambartsumian's papers became known to us, and I studied those.
Were these translated by Kourganoff and then published?
Well, several things happened. They were translated by Kourganoff, mimeographed and distributed to several observatories. Not very good appearance. But at least you would know what was going on, and Kourganoff would have his own comments. At the same time, these things were translated at Leiden by one of our staff members. That was Miss Pelz and now is Mrs. Van Herk, an astronomer, who had also been an assistant to de Sitter, by the way, a lady. And she knew Russian and she also translated several of these papers because there was a whole series of papers which overlap. So you tried to do what you could to read all this stuff. And so I took up reading these things, I would say rather independently from other things I had come to. I noted that there was something in these papers that we really had to be aware of. Then I saw Ambartsumian's suggestion in which he said, "We do observe that there are these groups, and they are not gravitationally bound, so what must we conclude? We can only conclude that they have originated from something smaller, that they are in a state of dispersion and that they have a limited age." And he came to ages of the order 107 years. That was around 1948 - 1949. Now you see how that fitted in with what I told you earlier, about these astrophysically limited ages and what I had found myself on the Scorpio-Centaurus Cluster. It all indicated that in this group of stars, you should think of ages of 107 or several times 107 years, rather than 109 years which we still adopted for almost the whole population of the galaxy. So then I said,"(Now, at one time I studied another group of stars." It is at the end of that paper on the proper motions that you have there.
In 1944, "Moving clusters of early type stars in Perseus."?
Yes, exactly. I had studied that thing earlier. But at the time I had only pointed out that there is this cluster that nobody had recognized and we had better look at it. But I couldn't quite understand it. Then after the Ambartsumian paper, it came back to me that I had looked at this cluster and that should be one of those that should be fairly young and could I indeed see the expansion that Ambartsumian predicted? So, I took that cluster. I had meanwhile this new knowledge about how to improve these proper motions because of all these studies with FK-3 and G.C. So I made a new determination of the motions in the cluster, because I felt at home in that world of meridian astronomy and fundamental astronomy which is a world in itself. And I did the job myself and I looked for Ambartsumian's expansion, and really it came out that way. I found an age of a few million years which in a way confirmed Ambartsumian's prediction. Ambartsumian had never really taken a cluster and said, "(now, I take the motions in the thing and see, it does expand." He had only predicted that it ought to expand, because of those general considerations. And I thought it worthwhile to take it up, because I thought I had the observational data, and of course it fitted with what I had done earlier. So this work emerged from all kinds of thoughts and data becoming available at that time. I wrote that paper on the expansion of the group in Perseus, and having done that, I then asked myself: "Now, if you have a group that expands this way — and we found an age of several, I think, 1.3 million years or so, it was very young — it's still a bit puzzling, but OK, let's leave it for the moment." Then, I asked: "What will be the future of such a group? If it does disperse, what will it look like in ten million years?" The B stars will still be B stars, and if you have an expanding group in the gravitational field of the galaxy, what is it going to do? And of course I had touched that problem in my thesis already. But now I worked it out in more detail, so I said: "let the group expand, then see what the shape will be and the orientation in the course of time." And that led to a way of explaining the Scorpio-Centasurus structure that I had found earlier .
But now it could be put in a much more satisfactory context. And that question that Shapley once asked was finally answered where I said, "well, we have to assume that it is only created at that time —" but which you could not put in the astronomical thought of that time; at least to him that seemed strange. Years later I could have given him the complete reply to that question, you see.
Did you ever do that?
No. I think I never saw Shapley again.
So this work had been done by the time of my second visit to Yerkes in 1952. Then at Yerkes I got Bill Morgan's up to date spectral classifications, and then we did several things. One thing was that I asked: "We have now shown this to be the case for the Perseus association, are there more cases?" And with the classifications Bill Morgan had, and with my background in this field, and with more photometric data, we could locate another group that seemed to behave in a similar way. That is a group in Lacerta. And there's a paper by Bill Morgan and myself on that subject.
Right . This is in the Apj in 1953?
Ja . And from that time date also, we did some other work on fast moving early type stars. Or was that a later stage? No, that was a later stage, I think. Anyhow we explored the motions and distributions of early type stars, and since I was there only a limited time, I couldn't do so very much. I gave some lectures and I went to McDonald. But in connection with what you said about the time of the spiral structure: indeed, as I looked at the individual clusters, Morgan was mainly interested in the large scale distribution of the early type stars.
Right. But was he building his chart on his wall at the time you were there?
Yes. There was that great chart. Wasn't that the time when he collaborated with Whitford perhaps?
I know he collaborated with Nassau during that time. Whitford also?
Ja, Whitford. And somebody else. Maybe Hintner?
That was a very poignant time.
Ja, that was a very exciting time, because Morgan had developed his spectral classification system, and surveys were also being made or rather large programs of photometric and spectroscopic work on early type stars. And people who were participating in that included Whitford and possibly Code. And of course they used objective prism classifications that they had from Nassau. One would have to check in the literature. What resulted was that Morgan took more and more data on spectral classification on photometry. He did his own spectral classification mainly with the telescope at Yerkes, which was the 40-inch, and later he did it also with the 80-inch at McDonald. And he had these made and once in a while for the group he would have a distance from the sun. He also knew the direction and so he would put that on that map, which was a sort of map of the galaxy. And gradually something emerged that became more or less a spiral structure.
Were you there as he was realizing this?
Yes. The thing was gradually growing, you see. And I would say that that was really the first discovery of spiral structure in our galaxy. It was around 1952.
Now, as you were there, were you also aware of the general surveys that were being made by radio back in Holland?
Did you discuss these surveys with Morgan?
Not so very much, because there was, as far as I remember, much publicity had been given to these surveys in Holland. And I could only confirm these things. I mean, the papers were known. But I really believe that one should say that the discovery that there is spiral structure in our galaxy was first, I really think first, from the plots of Morgan. The identification of spiral structure from radio work was a next thing. That is my recollection. Maybe strange, I don't know it exactly, but I really believe that the discovery of the spiral structure in our galaxy came first from the work of Morgan.
I believe the first that was actually published was the radio work. Morgan's work was of course announced at an AAS meeting, and then just a mention of it was made in SKY AND TELESCOPE, but the actual publication didn't come for awhile.
That is true. And in SKY AND TELESCOPE, I believe, is a photograph of that board that he had, where you'd see these things pinpointed on it with the sun in the middle and with the spiral structure appearing. But I would say that the awareness of the astronomical world — that we do have spiral structure in our galaxy — came in the first instance from that work of Morgan, than from the radio work. And wasn't there a paper on this problem by Morgan, Sharpless and Osterbrock which I believe presents this in a more complete way in 1953 perhaps? Well, that did not come as a new unexpected thing, because this work of Morgan had become known. Among astronomers in general, I would say.
Sure. You saw it building in his office.
Yes, I saw it building in his off ice, and it did not come to me as something like confirming what we had found from radio astronomy. Radio astronomy gave us a spiral pattern for a very large section of the galaxy, reaching out to very large distances. Morgan's work was confined to an environment of not more than say 3 kiloparsecs from the sun perhaps, you see. It was that small section. And the radio work did incorporate that section for which Morgan had outlined that piece of spiral structure. So I would say the merit of radio astronomy has been to tell us that the large scale structure in neutral hydrogen in our galaxy is spiral structure. But the fact that there was spiral structure in our galaxy, I would say comes first of all from what Morgan had done. It was not a great surprise to find spiral structure from the radio work, because at that time we knew from the Morgan work that this structure existed in or neighborhood, up to a few kiloparsecs. And therefore you would surmise that it might extend also beyond this. You see, that is in my recollection the sequence of discoveries of becoming aware of things .
Yes. I would like to know if you were there through the AAS meetings in Cleveland where Morgan announced his work?
I must admit that I don't know. In any case, you see, my becoming acquainted with the spiral structure did not happen at such a meeting. It just happened because I was at Yerkes and saw these things developing.
What I'm trying to recreate here is a feeling for how Morgan managed his day to day and week to week work on this. Was it something which he was driving at, working at intensely? Was it something he was getting very excited about? How would you typify the way that he worked on the problem, adding to the board?
Well, let me say it all took place in the context of his assembling more and more accurate spectral classifications, which he did himself, and combining them with more and more photometry. He had his program of collecting improved MK classifications, that is to say for all the bright stars in the bright star catalogue.
Yes. I know the techniques. I mean, as a person, how was he taking all of this?
Well, I will come to that. So I would say that in his regular work, this was what he would do. But in the course of it, these data became available, and the pattern emerged. And I think one can say that he himself was very excited about it. Not excited in the sense of going out and telling everybody, but excited in the sense that he felt that he himself had discovered something very fundamental. And I think he even was emotionally much affected by it . Of course, he was a person who always worked in a certain, I would not say isolation, but rather individualistic approach to things. He liked to work in his own world. His office, everything neatly arranged, his own darkroom at the observatory, which should not be used by other people — although there were students and others who would use other darkrooms and leave them in awful chaos. He wished all that protected. He had his own darkroom. He would work fairly cleanly, I would say, on these things. But he would not speak about these things so very much. But certainly with people like Stromgren, I would say he would Stromgren was director in 1952 at Yerkes, you see. It had changed. And I guess his contacts [were close] with people like J. Nassau and W. Baade, who was a very lively element in astronomy at that time. It is perhaps a bit difficult to see how much this discovery contributed to the somewhat special place that Morgan had in the staff at Yerkes. You might ask, if he had not discovered the spiral structure, how different would it have been? Maybe not so very different. But it added the emotional element of: "now I have discovered something very important." I think the discovery affected him very much. I'm pretty sure it did. Yes.
We're moving into the 1950's. You are beginning to do work on photoelectric photometry.
Ja, but I should perhaps say that in the year 1950 I did something entirely out of order in the sequence. I spent half a year in Kenya.
Kenya, Africa? What were you doing there?
Now, I went there at the end of 1949, I think that's what happened. I spent five months in Kenya, and that was for the following reasons. I have mentioned before this f fundamental problem of stellar positions. And now, the greatest difficulty in it is to get the positions in declination without systematic error. If you look into the systematic error, it's always the error in declination. That is introduced by the fact that it's a normal meridian telescope, you observe the star's position, the declination, and there is an error due to the flexure of the telescope, in the vertical sense, and to the fact that there is atmospheric refraction. Early ln the century, people had realized that you can eliminate both these things if you do the observation from a point on the equator. You go to the earth's equator, and you see where on the horizon that a star rises and where does it set. Since you are on the equator, the star rises vertically and sets vertically at various azimuth angles. But if you are on the equator, then the azimuth of setting and rising is the declination, or the double declination, or 2 times 90 degrees minus the declination, however you want. But it is fixed only by the declination. And this vertical flexure error of your telescope and refraction is eliminated, because there it is only in right ascension. So what do you do? You go to the equator and measure where a star rises, where it sets, and you measure the angle, and you have the declination. Very simple. There was an expedition around 1930 from Leiden Observatory, where two people did this, and that expedition was repeated in 1950 or 1949. That was under the leadership of van Herk who is now retired, an astronomer of Leiden Observatory. He went with an associate, and he set up the whole thing. But Oort needed somebody to be a liaison between what was going on there, and the problem of reductions had to be done at Leiden Observatory. So, after they had established themselves there, and of course with all kinds of financial difficulties that you have in such a case, I took it upon myself to do the supervision of that work at Leiden. But I started by joining them for five months in Kenya.
They were down there for a much longer time?
For three years. Yes. So, I was there, and participated in the observing, and I saw how everything worked, and it was a very interesting time. It was also a hard time. We were at the observatory at an elevation of 3000 meters, 9000 feet. You couldn't walk hard. You would be out of breath after a few seconds. That was the effect it had. And it was terribly cold at night. There would be clear skies sometimes, cold humid winds, so you would observe for four hours and then there would be a change of the crew. But in this way I thoroughly got acquainted with the instruments.
What kinds of instruments were they?
Well, something like a theodolite. A theodolite is a thing which you rotate around a vertical axis. A theodolite is a telescope of about two feet or three feet focal length. That scans the horizon. We put it a few degrees above the horizon. You have to make corrections and all that sort of thing. But the principal idea was that telescope would scan the horizon and see the stars setting there and rising there, and you would measure that angle and the time, etc. So I spent those five months there, and of course I saw a little bit of Africa also at that time. I had a wonderful trip, when I went home. I went through almost untouched parts of Africa, which you could still do at that time. I had been a little bit involved after that with the further reduction of the material. That has all been published by van Herk. It is mostly his work. I think my contribution is only mentioned by him in the introduction, on observations, and Oort has some friendly words about my participation in the introduction of the whole book.
Did you find the skies very nice there?
No. But it's remarkable, there's practically no place on the equator of the earth which is good for an observatory. It's always cloudy, cloudy.
A lot of wind?
Yes, a lot of wind, and cloudy, and poor seeing from that.
Too bad. I'd like to see if there was an early developing interest in establishing a major laboratory, because we eventually will talk about the ESO.
Oh yes. No, it had nothing to do with the ESO down there at that time. Well, it was a bit adventurous also, and I do like that, so I did not decline the suggestion that I would be involved in this. You may be interested to know that after I had left, we felt that there should be an additional assistant at Kenya to help van Herk, and first we sent out a fellow from Amsterdam for half a year, and then we sent out for at least a year Maarten Schmidt, who's now director of Hale Observatories. He must have spent more than a year, I think.
He was a student of Oort.
This must have been before his thesis.
Yes, that's right. He was a very young student.
That is right. Well, had an interesting apprenticeship then.
Ja, ja, oh, ja . He also liked this. He had the same attitude of "Oh, let's go and see the country." Yes.
Well, let's move on through the fifties, and get some idea of your research and how your position changed at Leiden, and how you saw the development of astronomy, especially in your field.
Well, when I came back from the States first, in 1948, I made a lecturer. I don't know whether I have mentioned that. In 1962 I was in the States again and Stromgren who was the director of Yerkes asked me whether I would like to join the staff of Yerkes as a professor.
Was that a difficult decision to make?
Well, not so very difficult. I knew Yerkes very well from the times I had spent there, altogether more than a year. I knew the people. I knew Stromgren. I knew the staff. I knew what we had at Leiden Observatory and of course I had at Leiden a very good position as a lecturer. But I think we felt that I was young enough still to broaden the base for my whole career. And I think we said; "well, we go to Yerkes for three years in any case, and we see what we do next." That sort of attitude. I was convinced that I could do good work. It was a nice place to live. And I didn't look too far in the future.
You were facing this question before, when we declined it. For that time. You were asked already. And we were not ready.
That was before Stromgren's time?
It was at a time we were at Leiden and you were there, you came home.
Oh, I had been asked for other positions. I had been asked once for the directorship of the Bloemfontein Observatory. But declined.
What was your answer to Stromgren? I'm not aware of this. Did you go?
Well, Stromgren approached me in 1952. I was at Yerkes. I said I'd like to think it over. Then after a while, I think when I was back in Holland, I said, "yes, I'd like to do that."
I didn't realize that. So you spent how much time at Yerkes?
Well, then, I took the job at Yerkes in 1953, and I was four years at Yerkes. And for all practical purposes we had just emigrated from Holland to the United States. It was not with the idea to stay a few years and go back. We went with the idea we may well stay the rest of our lives in the United States.
Which house did you live in there? Can you identify it?
Yes. Very well. Do you know the von Biesbroeck House, or what was that house?
I believe so. It was down closer to the avenue.
A big house. We lived in what they used to call the Glass House . That is a house just opposite the corner of the van Biesbroeck House. In fact it was the property of van Biesbroeck. It may be still known by that name.
I don't remember.
Ja, ja. Sure. I recently had a photograph of it that one of our friends took. So I was on the staff of Yerkes Observatory for four years.
You taught there?
Yes, I taught. I did the teaching in Yerkes and in Chicago. We had graduate students and undergraduates. Undergraduate courses were at Chicago, and the graduate courses were at the observatory. Of course, the graduate students would come to Yerkes.
So, I was on the staff there, and Bengt Stromgren was director, Gerard Kuiper was there, and Chandra, Morgan, and Hiltner were there. There were very fine visitors, many of them. It was a lively time, ja, and of course I taught at Chicago and would go there once every two weeks for lecturing. So I got to know also a bit the University of Chicago, which of course had very fine people at the time. It was the time still of Fermi. Fermi died in the course of those years. Well, Urey was around, with his lunar theories, and all of those people.
Of course, it explains so many of these papers in the fifties. You worked with Hiltner. You worked with H. L. Johnson.
Yes, that was all from there. Yes. And I worked with Morgan, and it was at that time that I wrote a paper on the nearby early type stars. It was published in 1956, I think, and it has a number of things which one could later continue research.
So in those years we were at Yerkes. In 1956, van Rhijn's position at Groningen became vacant: the professorship, and the directorate of the Kapteyn Laboratory. And they asked me whether I would be interested in succeeding him in that position. We thought it over, and we were very much in doubt whether we wanted to do this.
That would have been quite a change from Yerkes
Yes, it would be. So I said, "Well, certainly I want to stay at Yerkes till somewhere in 1957."
That was to complete research that you'd been working on?
Yes. It was to complete things I had been working on, and also because we were not quite sure that we wanted to go back to Holland. We had gone to the United States, as I said, more or less as emigrants from Holland, and we liked it very much there. Where we lived at William's Bay was a very pleasant place and we had very nice friends there. The educational situation for the children was not bad. It was a good school. Or course, we did realize that the time would come when the children would have to go to school to other places, and we felt somewhat less certain about this. It is something to see children educated in a country rather different from the one of your own background.
You wished them to be educated back at home in the Netherlands?
No, I would not say so. I think we all felt that the possibilities for the future of children in Holland were rather limited. Possibly you could say the environment was fairly safe. It did not have the extremes to which children might go in the United States. But on the other hand, the possibilities of development, for different sorts of futures, also the less strict and the wider range of possibilities of American universities, were all things that I think we had the feeling that — as seen from the child's future — there were so many more possibilities in the United States than in Holland. So there was certainly not a feeling that we wanted our children educated in the country where were came from. However, you might judge it differently than what you could in Holland. So I would say that the future of our children was not a motive at all for going back to Holland. It was rather thinking about the country, the United States has so much more future for its people. Ever so much more. A fellow who really wants to make his future can do it so much better in the United States than in the European countries and Holland, where many things are so restricted. As an example, in United States you can enter the university no matter what you have done before. You enter, and you have to prove yourself. You have to work hard, but if you do, you get through. You may be a housewife 30 years old and have never had any education, but you can register in college and if you work hard enough, you get through. But in Holland, they will ask you if you "did that exam in high school." And if you can't show that paper, you just are eliminated. You can't make it at all. You can now if you make an enormous effort and you do all sorts of exams first, you see. They are more concerned in Holland that you have a certificate in something.
They do not ask: "are you willing to work 20 hours a day and put all your effort in it?" that is much more the attitude in the United States. It depends on yourself, what you want and how much guts you have to get there. And in Holland, it's so much more traditional and all built in, you see. So for children, I think we would rather think that maybe the future might be better, wider, in the United States than in Holland. On the other hand, I felt attracted to the job in Holland, and there was a circumstance — the general situation at Yerkes that had developed at that time. You may remember, that was the time when Kuiper was building up his interests in having his own laboratory there.
It was the beginning of the Lunar and Planetary Laboratory that time in Arizona. That was one thing . In the same way, we realized that the new center for astronomy was to be in one of the states with excellent climate. There are as might soon become the center for astronomy rather than the places where it was done up to that time. The McDonald Observatory, which had been an affiliate of Yerkes Observatory, was already becoming more and more independent. So you saw Kuiper going this way and other people, A. Meinel, H. Abt were drawn in that direction. That was one element.
The National Observatory was being planned during those years.
AURA was being planned during those days. We heard about all those expeditions of Helmut Abt, Meinel and others. So you see, things were being developed. But it meant that members of the Yerkes staff became involved and disappeared in those directions. Meinel soon left Yerkes went to Arizona. Abt went that way. There was Harold Johnson, whom I haven't mentioned yet, who was at Yerkes in 1952. He left and went I think also to Arizona.
There were also difficulties amongst the Yerkes staff itself.
Ja. I will come to that also. Let us just follow them.
Stromgren stayed for awhile. Chandra of course was drawn more and more to the Chicago campus rather than to Yerkes Observatory. Chandra always had his relations with the physicists there, with Fermi especially. Chandra of course had a deep interest in developments ln physics, and at one stage decided that he would live in Chicago. And he moved to Chicago, I think, in the time when we were still there, or soon afterwards. You saw all these things coming. It was clear that the Stromgrens would leave.
The Stromgrens were leaving and there was a question about the directorship of Yerkes.
Ja. So Stromgren was offered the position at the Institute of Advanced Studies at Princeton.
That, of course, was a wonderful thing in a way, in that it was the position of Einstein. And to have for the first time an astronomer appointed there, an astronomer of that distinction and standing Bengt Stromgren, was in a way a great thing. But it of course meant a loss of Yerkes. So we saw that the staff of Yerkes was dispersing in all directions, and there were certain international frictions that helped loosen up the place. But this was accelerated in a way by such things as Stromgren being offered that position as the developments in Arizona.
What were some of the differences? I understand that Kuiper and Johnson had differences primarily. But I may be wrong.
No, that is not what I remember as being prominent in any way. I think that one can say that the philosophy of management, as Chandra saw it and as Stromgren saw it, was very different. They had a very different idea about how to run an observatory like Yerkes. And this was combined with Chandra's view that the input of physics into astronomy had to be much stronger and had to be oriented much more to the campus of the University of Chicago than Yerkes which is a wonderful place for weekends, but does not have the intensity of the exchange of ideas with the physicists that you have at a place like Chicago, which was a very good place of course. Consider the things that were happening in nuclear physics, think of Murray Gel Mann and R. Feynman. It was a time when they became important. So there were differences. I think that was one of the differences I could mention. Maybe there were differences with Al Hiltner also. Al Hiltner had his own views of how an observatory should be run, and that caused a split. Al Hiltner soon afterwards went to Ann Arbor, Michigan.
I don't think that the idea Gerard Kuiper going to set up his own laboratory was very involved at that time, because he became the director at Yerkes, didn't he?
Well, but you could already see these interests developing. It is true that Kuiper took over the directorship after Stromgren, that is true, but not for very long. Two years only, you see. But maybe one should say that Struve was able to keep the thing together. And you must remember, Struve left to accept the directorship of Berkeley, and later went to the National Radio Astronomy Observatory.
And while people have sometimes said that you can have at an opera only one prima donna, and a lot of good players, but you cannot have six prima donnas. It doesn't last for long, unless you have one person who very strongly keeps it together. And maybe one should say that there were all these prima donnas, but not one who kept the whole thing together strongly enough, by one common motivation, you see. I think one should look at it in that way. Maybe not the fact that there were frictions. There are frictions almost everywhere. I don't know of any observatory where there have not been frictions. But maybe it was asking too much for a group of prominent people to be working in a place that in itself, by its isolation, demands much more of the qualities of harmony of people than if you had that somewhere in the environment of a big university, you see.
I can appreciate that.
I think that's the way one should look upon it .
All right. In that environment, you made a decision.
Yes. It was in that general environment that we then decided that we go back to Holland and accept that position at Groningen.
Did you make an agreement with Groningen on the basis of changing the philosophy of astronomy there, to change it more towards specific work, to build up the department rather than catalogue work?
Ja . Well, the catalogue work had been practically finished by that time. On the other hand, radio astronomy was developing in Holland. There was the Dwingeloo Radio Observatory that was dedicated in 1956. I was still away then. It really opened the future for participation in that work. So then when I went back to Holland, I said of course, "Now, this place has to be, in a way, rebuilt, modernized, and we want to participate in the radio work." And that was agreed upon, because the radio work in Holland is organized in the context of a general foundation that includes in principle all the universities and institutes, you see. Not just Leiden but everything.
Did you have anything to do with setting up that original institute?
The foundation? Ja, I had something to do with that. In fact, I was secretary of the foundation for quite a number of years. Soon after I came back to Holland I was secretary of it. And of course, I saw the development of radio astronomy in Holland in the very early years. I did not participate in that very much. That was Oort, and a few engineers, and H. van de Halst but no so very much. At Leiden in the early years, there was division of tasks. Oort was much involved in radio things and much excited by it. I kept more to the things that I have mentioned already.
But were you changing over more to radio work when you went back?
You just wanted to support it.
I wanted to support it, and we created a division for radio astronomy at the Kapteyn Laboratory. That was done by hiring an associate — van Woerden — who later became a lecturer in radio astronomy. These were the early steps that led to the important role that the Kapteyn Laboratory now plays in radio astronomy. There are some excellent people there: there's von Ellen, von Ekers, von Woerden himself, Miller Goss and quite a list of people who are doing very well. I would say radio astronomy in Holland has two components, at least, in galactic and extra galactic work: one at Groningen and one at Leiden. I would say they are about equal components now, but supplementing each other very well. In a way it is one large institute. So the Groningen Institute has developed very much in this direction. When I started this work at Groningen, there was still the director position and one assistant and one scientific officer at a level in between. And in those years we have been able to add more and more staff so that ten years later, it must have had a staff of 25. We started out with just a few. But you see, the times were favorable in 1957 and in the early sixties. And we also built an optical observatory outside Groningen, the Roden Observatory. So the main developments were, apart from continuing on galactic research in the classical sense, a division for radio astronomy, mostly with van Woerden as the one in charge, and at the same time, the building of an optical observatory with a telescope of 24-inch, outside Groningen. That was done mainly by Borgman. Those two men were first made lecturers in astronomy, and later, Borgman was made the professor of observational astronomy, and then later the staff grew and grew.
Were you responsible for gathering funds?
It was not so much at the time a matter of gathering funds, but convincing the university that this was a place to develop. So annually you would say, "I propose that so many positions of this kind are added." And it would go through the university administration, maybe to the ministry, and they would say yes, or no, but in this case they may have said yes. I was responsible for planning this new observatory in Roden, which meant that you had to submit a proposal for building it, and determining the best telescope. That would go through the university administration. They would find support at the ministry. It would come back, and it would be tested several places. So in a way, the funding was not something that I was directly involved in. I was involved in the planning, in saying "It will cost so much. It's up to you gentlemen to see how you will finance it, between the university and the ministry." But there are all these special channels. It was not funded through any agency outside the government, you see. It was not funding through something like NSF. All within the university center. An integral part of the university, an integral part of the faculty of sciences.
I see. So you don't make individual requests to outside funds. You go through your university.
And they make the contacts with the ministry.
Yes. The Ministry of Sciences. There are things outside the university, like this radio foundation is outside.
Yes, all right.
But then you have to have a special national center. But this could all be done within the university. As I said, the times were favorable. There was sufficient money, so a good proposal had a good chance of being granted.
I follow that.
That's the way things developed .
You continued to work on your research during the sixties on kinematics, early type stars, and I see some articles later in the sixties on intermediate velocity features and local hydrogen layers, so you did do some radio work.
Yes, I did participate in the radio work also. At Groningen. Ja, ja. And what we did is the following. Of course, 21 centimeter line work was the main theme for radio astronomy in Holland. They had built an excellent receiver for this, and we had a division of work where Leiden would continue doing the large scale features in 21 centimeter distribution, and we at Groningen would look more at the small scale distribution of hydrogen, the cloud formation, for instance. And then that means also that you direct the observations more to the higher galactic latitudes, than in the plane. So Leiden worked in the plane, large scale features. We, the intermediate and high latitudes, and the small scale structures. And that led to publications on, say, the number of clouds, the volume of space, the velocity distribution of interstellar clouds, and the evenness or unevenness of the distribution of clouds in high galactic latitudes. There was a paper at one time in which we pointed out that in certain directions, there seems to be a hole, and then we also started looking at the clouds of higher velocities, and you see a sort of relation between these two things, so that was the sort of national division that we introduced in the radio work.
The way it was divided up.
That allows you to actually use the radio facility for long periods of time independently of the other institutions, because you were looking at different parts of the sky?
Well, you see, in the context of that institution of the Radio Foundation, there's a program committee, and programs are proposed, and they divide the time. And in the context of that time division, you would find a natural distribution of time to Groningen and to Leiden.
So you have two institutional members, and it seems to be very different then from the way the NRAO was set up in the United States, where you do have institutional members, but they don't necessarily have institutional projects. Individual scientists have individual projects.
Let's see, as to institutional members, in Holland of course we also have Utrecht. But it is more solar physics. It is not so much in stellar work. Amsterdam, a little bit. But in effect it's mostly Leiden and Groningen.
I'm just trying to understand the difference.
Ja. Well, you might say that projects are proposed by individuals. But before an individual proposes a project, it has been looked at within his institute. It emerges from the work done at the institute, and of course, if people are working on problems of clouds, interstellar cloud formation, distribution of clouds, cloud velocities, etc., the next proposal in that field would fit within the whole thing, and the computer facilities and the whole way of thinking about the problems would fit in. There would be sometimes proposals to do something entirely different. And these would not be excluded. In fact, Groningen has developed a strong interest in extragalactic radio astronomy. You might say that the radio astronomy of the nearer galaxies is done very much at Groningen now, whereas Leiden is involved in some nearby extragalactic work, but puts the emphasis more on the cosmological aspects.
Counts of faint radio sources, properties of typical radio galaxies. So Leiden does more the distant things, Groningen more the nearby things. But it's very much an overlap. And there is always a very good consultation and very good planning for research distribution. This is a continuation of an interview with Dr. Blaauw. This is now August 21st. We are in his office, the office of the president of the International Astronomical Union at the Montreal meeting. Should we begin by discussing the origins of ESO?
Yes. It all started during a stay of Walter Baade at Leiden Observatory early in 1953. Walter Baade was visiting, and of course discussed all kinds of things with the astronomers, including the general level and the future of European astronomy. And it was Baade who said, I think it came up in a discussion with Oort: "If you European astronomers really want to reach a level of performance comparable to that of the United States, especially in the Californian observatories, then you ought to join forces and have one big telescope that you can pay for really only if you put together your financial resources and your resources of astronomers and technicians." I remember that Oort came to me, rather excited, in my office. My office at the Leiden Observatory was just across the hall from Oort's. And Oort came to me and said, "Baade says we should do so and so, and wouldn't that be a good idea?" And of course we all said that it was a good idea. And soon after that, Oort convened a number of leading astronomers from European countries, and I could try to remember the names, although I am not quite sure of it, but I think they included B. Lindblad from Sweden; O. Heckmann from Germany; A. Danjon from France. There was Bourgoin from Belgium, and I believe H. Spencer-Jones from England. I'm not sure about this in the annual reports of the European Southern Observatory. I should also mention that there is a book by Heckmann, I don't remember the title, but it is a book that he published about a year ago. It is sort of reminiscences of an astronomer. He deals with cosmology, with the history of ESO, with all sorts of things that he has been acquainted with in the course of his career as an astronomer. So that was the beginning. And discussions were continued. Then I must say that I left Holland later in 1953 to take my job in the United States "Yerkes". I think I left in September or so. So I heard rather little about this project during the years I was in the United States. And when I returned in late 1957, I found that really very little progress had been made. And the reason was, of course, that at the time it was still too very difficult to acquire the necessary funds. But then gradually it was taken up again, and one of the first things we then decided to do was what you have to do in such a case: you approach the governments. You see how such an international organization has to be organized, as to statutes, bylaws, and all that sorts of things. These things required processing through the government levels and especially through the ministries of foreign affairs, because it is at that level that you make the international convention. All that took an awfully long time. But meanwhile we started doing some site testing in what we then thought would be the most likely place for erecting the observatory, and that was South Africa. At that time one knew very little or nothing about the qualities of the sites in South America. There was very much experience with the sites in South Africa because there were a number of observatories there. We also had our relations with the astronomers down there. So it was not difficult to organize a site testing expedition, extending the information on these sites that were available to the South African astronomers .
Was there any official connection with any of the South African observatories or countries?
Well, there were connections in the sense that they knew what we were doing, and they would be our hosts when we were there for site testing. The Union Observatory in Johannesburg, and the Cape Observatory near Cape Town were very collaborative, I would say. And I remember very well when I had to go there that we stayed at the Cape Observatory, where Dr. and Mrs. Stoy were our hosts, and did everything they could to help us. And at Johannesburg it was Dr. Finsen of the Union observatory. But they could not participate in the project because they had their own establishments already, and they wanted first of all to promote the further work of their own observatories. So we worked independently, but with very good help on their part. So there were a number of site testing expeditions, and I was involved in those in the sense that I did some supervision of that work, helping organize it, although the real observers had their own program. They stayed there for a year or longer. I was a sort of liaison between them, and things going on in Europe.
Did the British still support the South African venture?
No. Let me put it this way. We were testing these sites, but parallel to that there was still this negotiation going on between the governments, and the money that was made available for the site testing was not yet money from the new organizations, but money made available by the Science Foundation in the Netherlands, by the Science Foundation in Germany. So it was individual organizations that made it available, anticipating that eventually this would become of course a task of the organization itself. So parallel to the site testing, there was the negotiation between the governments, and that was very difficult, because this idea had to compete with projects that were being taken up on a national basis. I particularly mention that in France, they also had the idea to have a large national telescope, which now after many many years sort of has resulted in their share in the Canadian-French-Hawaii project. That is something that has a long long history. We had the impression that they first wanted to secure the funds for the national telescope, and if that would be safe, then they would go on with the European venture. Now things have changed a little bit later. For the British it was different. In the beginning there was much support of Spencer-Jones. Later, Spencer-Jones was succeeded by Sir Richard Woolley who, or course, had been director of the Stromio Observatory in Australia before he was appointed as Astronomer-Royal. He had a strong liking for doing things on a Commonwealth basis. So he was much more inclined to develop the British project in collaboration with the Australians than with the European partners. We sometimes had the feeling that the British could have done both, considering their size, their national income, and the size of their astronomy program. But that's not the way it went. The balance went in the way that they preferred to do things on a Commonwealth basis, and that has resulted in the Anglo-Australian Telescope. So once the decision was made for the Anglo-Australian Telescope, their participation in the European Southern Observatory was out. And from then on, they did not participate any more in our meetings.
Was this very much Woolley's decision?
Yes, I would say so. Of course I do not have insight into their internal matters. But to the outside world it was very much Woolley's decision.
So then negotiations went on, and I believe it was only in 1963 or that the international convention was signed, many years after the beginning of the whole business. That convention included five countries, four or five. I believe Belgium was the fifth to join after four had done it already, and later on, Denmark also joined, which means that the six are Sweden, Denmark, the Netherlands, Belgium, West Germany and France.
Was the site testing taking place still in South Africa?
In South Africa until in the early sixties where it was found that there were outstanding sites in South America. And that was mainly due to site testing done by the United States astronomers. They were also looking for a Southern site, which eventually resulted in Cerro Tololo Observatory. And in that process it became clear that the sites were comparable if not much better than those in South Africa. I believe the American efforts go back to the investigations by the American Air Force about qualities of the climate in South America. I am not very much acquainted with that, but there was something of a very old origin of this whole thing.
But was there any feeling about the political climate, the political stability of Chile or of South Africa?
Well, I would say that the political aspects of South Africa were not very pronounced at that time. The emphasis on their favor of apartheid and other countries being opposed to that, at that time, was not yet a matter so such disputed as it became later. Chile at that time was considered as an example of how stable a country in South America could be. It was considered the most stable of all the South American states. In a way maybe also a rather democratic government. So, politically, there wasn't the least doubt as to Chile being suitable. Now, I should say that considerations about political aspects have never played a role of any significance in the decisions made on where to put the site. That is just a fact. I mean, it was not because people said, "no, we don't want to do with politics, or so." The quality of the site was so much a dominant element in the whole thing that you would say, "if that is the best site, then that is where we ought to go. There may be other considerations. There may be considerations taken into account by certain government officials etc. But we astronomers think that that's where it ought to be." And I would say, the opinion of the astronomers has been accepted almost unchallenged.
So in the government in the Netherlands had nothing to say about shifting the site from South Africa to Chile?
No, nothing. Certainly not. Not in the other countries either, because at that time, when that decision was made — and I believe that must have been around 1964 — we saw indeed these South American sites are superior to all we have found in South Africa. By that time, that became more and more clear. And I should say, when the Americans found this, we still made about half a year of site testing in South America, on comparable sites, with the same instrumentation we had been using in South Africa, just to make sure that if you used the same instruments, you got indeed a better result than we had in South Africa. After that it turned out also with our instruments that it was superior. Then the decision was taken fairly quickly by this organization to establish the observatory in South America. And at that time, I believe there was a government under the leadership of Allesandre, I think he was then the premier of Chile. And that was a government that was almost like the European governments, as to stability and such things. Then a convention was made with the Ministry of Foreign Affairs of Chile, and from then on, well we went ahead with establishing the observatory in Chile.
Did you purchase land or lease land from Chile?
No, we purchased land. So there was a lot of site testing and then exploring which sites might be available. And it ended up with the purchase of a very large area of territory that was the property of the government of Chile and an adjacent site was purchased from an individual owner. I believe it must have been one-fourth or so of the total area that we finally obtained. And we did then obtain a total area of about 625 square kilometers, a very large area. And that is still the area that is the property of ESO at this moment.
And what questions in ESO took place as to what type of telescope, what type of instrumentation to have ?
Oh, very early in the whole history of defining the project, it was said that what we need is a telescope of about 3 meters, and we need a Schmidt telescope , and we need some smaller telescopes, auxiliary instruments, and an instrument for stellar positions, — something like a meridian telescope. And the main telescope, the 3-meter; was the size of the Lick Telescope, which had been just recently completed. So we thought, a 200-inch was too big; too big a step from the modest telescopes that Europe had. However, a 120-inch is probably just right for us. So in the convention, you will find the 3-meter telescope. Later it was found, also at the advice of the Lick people, that since in such a telescope you have to have the observer in the prime focus cage, and it's all just a little bit too narrow to work comfortably. So the size of the telescope was increased 3-1/2 meters, and eventually it became 3.6 meters. So the real size is a bit larger than what the convention had specified.
How was the funding spilt up between the different nations? Did each take an equal share or?
No. The shares are divided exactly proportional to the national income of the participating countries. So every three years we revise the division. We look at the national incomes. We look at the budget, the total contribution, and your contribution. That is split into parts proportional to the national income as it is then.
Does that have anything to do with the accessibility of the telescope to different nations?
No. From the beginning we separated entirely how the contributions are divided, and how we divide the time. And it's only very seldom that it has been said, "After all, this country pays so much, so much more or so much less than the others, therefore it should have more or less time than it has had so far." The division of time has been done 99 percent on the basis of the quality of the proposal. But it has also turned out that if you make statistics after a number of years, and you average out over all these years, then you have something which is very close to the percentage of financial contribution. Just because that has been the experience, we have now made it a point of looking at what the financial contribution distribution is.
Has that ever disappointed anyone seriously, or has it been minor? Has there ever been any serious rift in this organization?
No. Never. Of course it has had difficulties, and they are difficulties that all these kinds of organizations have. One has been to just get the money, you have to persuade six governments that you need it. That's a complicated affair so we have to plan long in advance. They want to know three years ahead how much do we think we would need. But that is not so bad. It forces you to do your planning yourself on a long time scale, and that is only to the good of the organization. One difficulty that we have had was just the lack of experience of European astronomers in building a very large instrument has meant that the largest telescope was the last to be completed, and in the early years was grossly under estimated. It started out by giving this project to an engineering bureau in Germany. This was because in the first year, Heckmann was director of the observatory, but that engineering bureau worked with a staff of only six people or so. It was just impossible to do the job that way and there was a very drastic change in the setup in 1970. We really said, "Now the big telescope has to be done. Otherwise we will never do it."
That's when you began.
Ja. So when I became director following Heckmann, all the small or most of the small telescopes had been completed. The buildings on the mountain had been completed. What was not finished yet was the Schmidt telescope, and what had hardly begun was the very big telescope.
Did you have the mirror by that time?
No, but the mirror has never been a difficulty. In fact our mirror was ready two years before it could be put into the telescope .
OK, because I know historically with the 200-inch it was the mirror that was the big problem.
No. Not in our case. So, my first jobs were to have the Schmidt telescope completed, and that was a bit difficult because it was in the hands of a very able German engineer However, he was a fellow who did not want to have any contract. He considered that as a sort of insult, that there would be a contract stating what the obligations. His attitude was: "It was sort of gentleman's agreement, I build a very good telescope for you, you must have confidence in me."
Could you name him?
That was Stravinsky. He was the one who also built the Schmidt telescope for the Hamburg Observatory, a very capable engineer, but as I say, with a lot of queer attitudes about how you deal with a project like this.
Did he ever have a contract?
No. I have never succeeded in having him sign one. But we pushed the thing so much from day to day and said, "What has been done now" that in this way, we have succeeded in realizing the thing. And I must say it was at one moment that we said, "OK, now, you deliver this thing and we will do the rest." And soon after that, Stravinsky died. A few senior astronomers were then involved. And then at a certain point, they gave the whole project into the hands of one of the staff members of the ESO Observatory — Dr. Andre Muller. And he did a very good job in getting the telescope completed and making it operational. But it was still a long long story, to start from where it was left by Stravinsky, to a really working status. Well, this seemed the best way to realize the thing because, it was already fairly advanced by the time I became director. Heckmann had very much confidence in this man, understandably because he had done very well under Heckmann's direction at the Hamburg Observatory. But the biggest problem was that this engineering bureau also had been in charge of the big telescope. And because they were really much too small for that, very little had been done. So the participating countries said, "Now, this telescope must be realized now. We must go ahead with it." And we felt that we needed the help of a large scientific institute or projects that had experience in building large instruments. I explored several possibilities. I explored, for instance, possible help from the European Space Research Organization. I explored possible help from large industries that had been making optical instruments. And one thing I explored, and that is what indeed brought the pursuit further, was collaboration with CERN, that ss the European Organization for Nuclear Research. CERN was established near Geneva. It's a very large effort. At that time they had some 4000 people working there and I think they still have, making big accelerators , one after the other one, always thinking about the new generation of instruments, dealing with instrumental problems which are very much of the same kind as ours and which require the same expertise as building a very good modern telescope. We found the director, who was at that time Gregory, and his associates very collaborative and very much willing to collaborate with us. And we also found that this idea was strongly favored by the governments of our countries. That is because the whole setup of CERN was very similar to the setup of the European Southern Observatory. The text of the international convention, the way their council works, their finance committee, all these sorts of things were similar. So they felt that if we would use the same framework, that would make it much easier for the government people to understand how to finance this thing, and we would have the same people in the board, in the council. We made an agreement and then it went very very fast. Before I became director, the council had asked me to draft a new way of realizing the big telescope. So I said, "You have to do it in collaboration with a certain institute." We took up the negotiation with some early in 1970. I believe that the contract was signed in May. It all went very quickly even though many governments were involved. At the time CERN had some barracks and buildings that could be used and, in fact, in September some of our people were at work in those barracks. It went quickly only because CERN itself was interested in establishing it. So we established the group of ESO people in their own housing. This was the technical division. It grew quickly and established new expertise. We could also get people from CERN appointed temporarily on our staff with the assurance that they could go back. CERN helped us on all these things. There were so many people at CERN, so you could just ask them for people on a day to day basis when they were needed. It was an excellent arrangement. I would say it was one of the best examples of collaboration between two scientific organizations in instrumental affairs. It should be followed by others too because there are so many cases where new project staff do not have the experience required that could better be done within the environment of a larger organization that does have the expertise. It's like putting a plant in a very fertile soil. If it's dry soil, you have to put everything in to make it grow. So that all went very well, the big telescope was realized and it has now been in operation for some time.
Can you give me some sort of brief idea bout the spirit of ESO, and if there is any connection between the spirit of ESO and the spirit of the Common Market, or something of that sort?
I would say the spirit of ESO has always been one already noticeable in the very early days, where it was a group of European leading astronomers who got together and said, "We must do this thing jointly". The European Common Market has, I would say, never been mentioned in serious connection with ESO. Maybe one should rather say, that doing things jointly, or making Europe joint as one would say, is something that we did almost automatically in those early days. We felt that you had to pool all your resources in order to get something done. And maybe it is better to say that we were just little pioneers in this idea which was taken up later on a bigger scale by the politicians in the European economy. To us it just came naturally that you had to do things that way and we still feel that way.
There have been a number of different directors at ESO?
The director at ESO is a very simple series. It started out with Otto Heckmann who became a director I think in 1963. It was then the convention had been signed. Then they had to say, OK, now we need a director, etc. you see. Heckmann was director until 1970.
Then you were director.
I was director for five years, until 1975. Again in the tradition of CERN also, we appointed our director for five years. And normally would then choose another director after five years. That was the general idea that you can have directors from different participating countries, and everybody has his share in time. I was followed by L. Woltjier. But in this case then the council also asked me whether I wished to stay after five years. At that time I thought I would better not do so. It was a very challenging job, I must say, very interesting, but also physically very demanding, with all the traveling back and forth between Europe and Chile, and sometimes the tension of working with different governments and different opinions, and sort of finding your way — on the ore hand the organization, on the other hand the governments —although I must say that on the whole, I found it very interesting.
The tensions were typical, the kinds of things that you might expect?
Well, you might say, the tensions that exist politically between some of these countries. And you could even say there's still something between Germany and France, etc. That will have to die out, although it is so much better now than in the past. These tensions you would notice also in council meetings. You had sometimes the feeling that if one of them proposed something, then the other one would look at that more critically than if it had been proposed by one of the other countries. Politicians are trained to have a rather reluctant attitude towards certain other parties. Well, that was apparent sometimes. And then as director you had to reconcile that in a kind of way that was acceptable to all of them, and sees what was the optimal thing that you can realize under those special conditions. Well, that's what I call certain tensions. But as I say also it was a challenge, this whole thing. But I decided that I would rather not continue, because I felt that carrying this project further would require a strong person, physically, someone up to the rather fatiguing way of life that it entailed, and I was very very happy that we found Woltjier willing to succeed me. Of course in a way it was difficult, because again that was another fellow of Dutch origin. You like to distribute things, but we decided that Woltjier was the best candidate, and the council decided, first of all Woltjier was the best candidate, and only secondly they thought of nationality. So we had Woltjier, and in this case the council decided again to ask him whether he would continue, and he did decide that he will continue beyond his first five years. So ESO has had only three directors.
The sense of cooperation also extends to the new journal, ASTRONOMY AND ASTROPHYSICS.
Well, we can talk about it now, but perhaps I should say right from the beginning, this has been separate, in principle entirely independent of the ESO. It is sometimes identified with the ESO, but essentially it's entirely independent. The the story there that in the same spirit in Europe we would rather do things together than doing everything on an individual national basis, we decided that: "if I say we, the number of astronomers involved, who I would not mention now by names" "We have a number of journals. We have national journals in astronomy in Holland and France and other countries. Really we again must do something jointly in order to raise the level of quality of what we publish." It was an effort to improve on the quality and to promote the best dissemination of astronomical literature. So the idea came, shouldn't we have a joint journal for Europe?" Ideally you might say we ought to have a journal for the whole world. But of course we have the ASTROPHYSICAL JOURNAL, that's the leading Journal. We have the ASTRONOMICAL JOURNAL, it still exists, and the MONTHLY NOTICES, which is more British or maybe United Kingdom or Commonwealth, whatever you call it, you know what the nature is. Then it was decided to have a European journal, and this developed entirely independently of ESO. By 1968 a group of people was formed who had decided: indeed, we are willing to join. Our people at home agreed that the existing journals should merge into one common thing. That was already a very big decision for some journals that had existed for many many years. ASTRONOMISCHE NACHRICTEN had existed for many years, the Annales d'Astrophysique for many years, the BULLETIN ASTRONOMIQUE in France also. I believe it had existed for 100 years already. And in Holland it was the BAN. That we also were willing to merge.
The interesting thing about the BAN is, the philosophy of the A&A Journal seems to be a repeat of the philosophy of the BAN in 1920 when it was formed.
Yes, you could say In Holland, first the institutes had journals. Then you had the BAN as a national journal. And the next step was to have a journal on the European basis. In a way, the same thing happened in France. They had their institute publications. Then they created the Annales d'Astrophsique, a general French journal, and again the next step was to merge — the same thing as with the BAN.
Which nation was most in favor of this amalgamation of journals?
I would say the negotiations, or the thoughts were mainly in the beginning between people in Holland and in France and in Denmark. I would say they were instrumental in the first steps.
You were involved, for Holland?
No, I was not personally so much involved. I knew about this and I helped in a way, but for instance in Holland the person who had done a lot about this was Stuart Potash, who was also one of the first editors of the journal. In France I would say especially J.L. Steinberg of Meudon, and I know in Denmark, one who has promoted the idea very much was Anders Reiz, of Copenhagen Observatory. He has promoted this idea for many many years. So then we got together and we said: "OK, now, we know what we want. We need two things. We need a contract with the publisher. And we need a board of people to make sure that insofar as these are contracts with the government, the people on that board can have the support at home. They can solicit subsidies from the government for running the editorial offices." And that's where ESO came in. I was at that moment director of ESO or almost director of ESO, because that was in 1968. You see, in 1968, I didn't tell you, but I had been scientific director of ESO for two years before I became general director. So I was scientific director under the directorship of Otto Heckmann, and that was on a 50 percent time basis, in 1963 and 1969. So I was much involved in ESO. I saw that I would become director in 1970, I knew it in 1969. In 1968 we created this board of directors for the journal, independently, and then we said, "Now, we have to have a contract with a publisher. We cannot conclude a contract. We have no legal status." And having a legal status as an international organization is a terribly complicated affair. You have to go through all the rigmarole of having the approval of all the ministries of foreign affairs, and doing all that with the already eight or nine countries that were involved then seemed too much. So we said, "We'll ask ESO to conclude this contract." And that was especially easy because I, as prospective ESO director, could agree to that. So in this way, ESO expressed itself to be willing to do this for us. Of course it did not have a financial risk of its own. And that's what was done. So the first contract was signed between ESO and Springer-Verlag, the publisher. It was signed by Otto Heckmann, after I had arranged these things. Of course Heckmann was willing to do that. Then the contract and the rules according to which we worked also said that there should be a board of directors with delegates from the countries on it. And there should be one delegate from ESO because of the role which ESO played in helping out in the concluding of the contract, and supervising the financial administration. For that you need an expert.
So I offered to do all these things through ESO. And then they made me also chairman of the board. So I have been a chairman of the board right from the beginning, from the creation of the board, I think in 1968. All through the time I was director of ESO also. But you see, basically the two things are entirely separate .
I see that now.
It is just the role that ESO played in helping out, and being the natural agency, because it also is a realization of European collaboration in astronomy. But as soon as we have to rewrite a new contract, the board looks into it and at a certain moment asks ESO for help.
What about the choice of format, style, and the language you use?
Well, of course, you look into these things as editors and you compare with other journals. The allowed languages were English, French and German and still are. But the percentage of French and German is maybe 2 or 3 percent. It plays no role. Very exceptional.
That's interesting. Because I found it very interesting that the BAN was in English.
Well of course, as a Dutch journal, you realize that if you want to be read in other countries, you had better not publish in Dutch.
Right. That's a very good description of the European journal, and the relation was just a parallel course with the ESO.
Yes, and one should never forget that there are countries participating in the Journal which are not members of ESO. For instance, Switzerland participates, Greece participates, Italy participates, Norway participates. None of these is a member of ESO. But they do accept the ESO role in this whole thing.
I see. Well, we have the final area that I would like you to discuss. That is your view of the general development of astronomy in Holland in the past 50 years.
Yes. Of course, normally one speaks about the developments in Holland, and one sees that there was a sort of revival of astronomy in Holland which started at the end of the last century with Kapteyn — who was a very very well known astronomer, known all over the world. And I think we should not say too much about that, because that can be found from other places. The important thing is that Kapteyn had a number of pupils, followers, and among those de Sitter was one of his first assistants. There was also van Rhijn, who became his successor at the laboratory at Groningen. There were other people associated with him, especially Czernike who was a physicist, and who got the Nobel Prize in physics, maybe some ten years ago. He was a very ingenious fellow. He was the one who designed the phase contrast microscope. I don't know what you call the thing. That has played a very big role in medical applications.
Was van Mauner a student of Kapteyn's?
I believe, Ja. But I want to mention that we had this school of Kapteyn producing de Sitter, producing van Rhijn. We had Pannekoek in Amsterdam somewhat later who was a very well known astrophysicist , a very capable man who did very many different things and all very well.
I've heard that he never was able to really build up a large department at Amsterdam.
No. This is true. At one time, when de Sitter was building up the staff for the reorganized Leiden Observatory, in the early 1900's he attracted Hertzsprur. He also wanted Pannekoek, I have been told. Yes. However, the government did not appoint Pannekoek because Pannekoek had very strong political views, and was in a way a political agitator, and they didn't want that. But then Pannekoek later was appointed the first professor of astronomy at the University of Amsterdam. That's why he created his institute.
I see. He actually worked on similar topics to Hertzsprung. In different directions.
Ja, but Pannekoek did quite different things. He worked on the distribution of the intensity of light in the Milky Way. He worked on stellar spectra and abundance determination. He was one of the first who did very solid work on abundance determination. Pannekoek also, apart from his political views, did political studies. I believe he was really one of the people who knew the philosophical background of many different political views. But also he was an excellent historian of astronomy. He has written a book on the history of astronomy, which is a marvel.
It's amazing how he saw so many different things so well.
I've used that book.
Well, that was Pannekoek, who in a way developed somewhat independently, from the 1920's. Then in Utrecht, you have the school in which Minnaert started to play an important role, from about maybe about 1930 or so.
Solar physics, because Minnaert was a biologist originally.
I didn't know that .
He was interested I believe in the influence of radiation on plants. You would have to check this, but he comes from that area, and then was so involved and fascinated with solar research that through solar research, he became an astronomer and director of the Utrecht Institute.
I didn't realize that.
Oh, Minnaert was also one of the very remarkable people, and one of these people worth, so to say, a biographical study.
Also a very charming fellow, a very modest man also. For me, one of the people I have always admired most. One could talk very much about him but it maybe more interesting to see the main lines at Groningen was van Rhijn, who followed very much in the course set by Kapteyn, and who had been director of the laboratory for many years there, from 1922 to 1957. And in that time, he accomplished a very large amount of, you might call it routine works. But it is a very thorough compilation of photometry and proper motions in the selected areas and also work on such problems as luminosity functions. And the best data that we have now in my feeling, the most thorough data is the determination of luminosity function by van Rhijn. Of course we have parallel to that the work of J. Luyten. But I would say that if you really want to see exactly how the luminosity function data is now determined, you have to go back to the work of van Rhijn. That's an enormous job, and goes back to the early work by Kapteyn, step by step by step. I mention that because nowadays, the luminosity function plays such an important role in studies of stellar formation. The luminosity function means, in a way, that you have information on the mass distribution of the stars, and that means that you have information on the mass distribution at the time of their formation. So basically, what did develop out of this very fundamental piece of information, goes back to the work that van Rhijn did. I think sometimes people don't realize that it was such an important part in the whole development . And I mention this because, as you probably know, when all these people write biographies they make a list of very well known astronomers, and my feeling is that van Rhijn ought to be put in there, and he will have to be put in, you see.
Do you feel in popular histories, that Pannekoek's politics somehow could have affected some of the portraits of astronomers that he discussed in his book? Or do you feel it's quite objective?
Ja, I would think so, ja. Pannekoek was too much a scientist, with the conscience of a scientist, to do anything that would be subjective rather than a scientific account.
Well, you're giving me a view of pretty much optical Dutch astronomy, up to the war, and we know of course that radio astronomy became extraordinarily important after the war. Did you want to discuss that?
Well, we can follow the main line for this. Of course, radio astronomy was in a way picked up during the war years, or right after. I would say it is to the merit of Oort that he realized the enormous importance of the first articles on the subject. There was an article by Grote Reber, under the title of "Cosmic Static" in the ASTROPHYSICAL JOURNAL, which most people would have considered something weird. They just wouldn't know what to make of it, and would skip it in their reading. But it is typical of Oort that he saw this and realized that here was something very important, that could be very important, and he followed it and we needn't go into the detail of how radio astronomy itself developed at that time. He then had the idea that, whereas this Cosmic Static was a sort of general broadened radio emission, as it would be termed nowadays, he realized that it would be tremendously important if there was radio emission in a very narrow spectral line. And that's how he came to suggest that it would be so important to find out whether perhaps the interstellar matter would have radiation in a narrow spectral line, and as far as I remember, he then suggested to van de Hulst, who was a brilliant young student working at Leiden: "Now, can't you find out whether there is an emission in the radio region from interstellar matter?" And van de Hulst took it up and this led to the prediction of the 21-centimeter line. And of course, that being established, the prediction being made, the next step was to see whether it really was there. Then, you know the whole history. In fact, there were three discoveries made of the 21-centimeter line. One was made in Holland. One was in the United States. I think one was made in Australia. In rapid succession. The Dutch efforts had some difficulties. At one time, when they had already developed a laboratory for this, there was a fire in the laboratory, and everything had to be started from scratch again.
When was that, 1949?
Well, in those early years, but those dates I don't remember very well.
You mean, they probably could have had the detection before Ewen and Purcell?
I would say, they might have had before. Ewen and Purcell had it, and before the Australians had it, but that's just speculating.
Sure, I appreciate that.
The facts are that they found it in fairly rapid succession. And then of course, since that was successful, and since that was the kind of astronomy that we could do in Holland just as well as somewhere else, in contrast to optical astronomy, very much effort was put into developing an astronomical observatory for this radio emission, and that led first to observation at Kootwijk, soon after at the Dwingeloo Observatory. Dwingeloo was dedicated in the year 1956.
Where was the first observatory?
In Kootwijk. It was in fact a station belonging to the postal service in Holland, a section that had something to do with radio communication. And they still had a telescope there that could be used by astronomers. In that corner things started to develop. But then the Dwingeloo telescope was put in a new place, and it was dedicated in 1956. It was one year before I returned to Holland.
So I saw something happening there in my country on the other side of the ocean. So that was en route, so to say and producing interesting things. Then the next step was the enlargement that led to the Westerbork Center. In all these accounts as I give them, there's a selection of topics. One makes an unconscious selection of things. Many things have happened that, if you think about it and you read about it again, you say, "oh, ja, but I should have mentioned that also." In a way, it is unbalanced. So in that way it is rather personal.
Well, that's what we're hoping to get — personal reflections.
Ja, but I would say, if I would have prepared an account, it might have looked more complete.
Well, we're happier this way.
Of course, I could go on for days and talk about these things.
Well, thank you very much for the time you've given me.