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Interview of Robert W. Noyes by David DeVorkin on 2007 December 5, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/38095
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In this interview Robert Noyes discusses topics such as: his family background; undergraduate at Haverford College; graduate work at California Institute of Technology (Caltech); Frank Press and geophysics; Fay Ajzenberg Selov; Robert Leighton as his advior in graduate school; Mt. Wilson Observatory; Smithsonian Astrophysical Observatory (SAO); Leo Goldberg; Chuck Whitney; astronomy; solar satellite project; helioseismology; Tim Brown; Dave Charbonneau; Ed Reeves; Bill Parkinson; George Withbroe; Andrea Dupree; Martin Huber; John Raymond; Peter Foukal; Jacques Beckers; Frank Low; Sacramento Peak Observatory; Orbiting Solar Observatories (OSO); Fred Whipple; space solar physics.
This is an interview with Dr. Robert Noyes, we’re in his office at the Center for Astrophysics in Cambridge, the date is December 5, 2007, and, auspices are the Smithsonian.
I’d like to start out just by getting a sense of who you are; where you came from; where you were born; what kind of a family you were born into; what your mother and father did?
I was born in 1934, in Massachusetts, but at a very early age I moved with our family to Mountain Lakes, New Jersey where my father was an electronic engineer at Aircraft Radio Corporation in neighboring Boonton, NJ. I graduated from Mountain Lakes High School in 1953, and then went to Haverford College, which is a small Quaker-oriented college in the suburbs of Philadelphia.
Let’s move back. Give me your father’s full name and your mother’s full name.
My father’s name was Atherton Noyes Jr. My mother’s name was Barbara Wilson Noyes.
Wilson was her maiden name?
How many generations had they been here in the United States?
For many generations. Both sides of the family can trace their roots back to the 18th century. In fact, my mother enjoyed relating a no doubt apocryphal story that during the Salem witch trials one of her ancestors was condemned as a witch, by a judge who turned out to be one of my father’s ancestors
Now, your father was an engineer? Is that correct?
Yes. He was an electronic engineer.
Was he college-trained?
Yes. He graduated from Harvard in 1926, and later received a ScD degree from there.
And your mother?
She graduated from Olivet College, in Olivet, Michigan. After she married at age twenty-two or so she became a housewife raising us four children.
Where are you in the order?
I’m the second from the eldest. I have an older brother and also two younger sisters.
And, what did they go on doing in life?
My brother worked for the State Department for some years before retiring. He now lives in Maine. The elder of my two sisters lives in Arlington, Massachusetts, and professionally has taught French at a local high school. My younger sister received a Ph.D. in oceanography and has done research and teaching where she lives in Maine.
What was your mother’s interest, when she was in school? Did she major in anything that she carried with her as an interest?
She would probably have described herself as a home maker, but she had strong interests in children in general. She taught Kindergarten, and ran a pre-school program.
Did she teach before she was married?
No, after she was married.
How would you describe your early home life?
I suppose it was fairly normal. But my father had a strong interest in math and science, and I was led to take after him. As I mentioned, he received a Doctor of Science degree from Harvard, working with Professor George Washington Pierce in the Physics Department. But long before that he had become very interested in the new phenomenon of radio, and was one of the country’s first radio hams around 1920 or thereabouts. He used to use that to communicate with folks all over the world. One summer he worked as a counselor at a summer camp where he was the official ham radio operator — a very advanced activity at that point early in the 20th century. His interests in radio led him first to a position at the new General Radio Company, and around 1936 he moved on to Aircraft Radio Corporation in New Jersey as I mentioned earlier.
Did he include you in his ham activities, or your older brother, or both of you equally?
No. By the time we arrived he’d given up his amateur stuff. But, I think his continuing technical and scientific interests were a formative influence on me. I developed a natural interest in math and science, which he actively encouraged. It turns out that I was a strong student, consistently near the top of my class, which understandably pleased my parents.
Did your brother excel academically as well?
Perhaps not so much, but he excelled in other ways. He was the athlete of the family, while I was the “nerd”, as he sometimes put it.
What kind of books and magazines were around the house? What kind of magazines did your parents subscribe to?
We subscribed to typical middle-class magazines like Time, Life, The National Geographic.
Did you have encyclopedias at home?
Was religion part of your life?
Yes, but not a central part. Our family attended the Mountain Lakes Community Church, which is a Protestant Christian church which most of my schoolmates also attended. We went to church almost every Sunday, but as I said this it was not a dominant feature of my life.
How would you describe the economic position of your family, as you were growing up?
I would say upper middle class. I think our family was rather typical of families in Mountain Lakes, which I also would describe as an upper middle class town.
Do you have any memories of World War II? And, how would you characterize that in terms of your upbringing in your life?
I remember Pearl Harbor day vividly. And let’s see, that would have been just before my seventh birthday. And, I certainly remember the following four years in various ways, including rationing, buying savings bonds, even collecting fireflies to support the war effort in some obscure way. I remember more, of course, towards the end of the war. In 1944 when I was going on ten, I went to summer camp, and I remember lots of discussion of the war because there were lots of headlines then. And I vividly remember VJ Day in the summer of ‘45.
Did the fact that your father was working in aircraft radio technologies, were you aware of that and did you appreciate that?
I was aware of it, but somehow I made no connection between that and the war, and if there were any war applications of his work, I was unaware of them. He never mentioned anything about the military. In fact I’m not sure whether he was actively developing instrumentation for specific military purposes. He was doing more basic R&D I would say, for how radios could be used in aircraft navigation.
Any teachers that stand out as being influential in directing your interests in your life?
I excelled in math and science and therefore those teachers I remember well. I got strong reinforcement from my high school math teacher. But I don’t think it was my math or science teacher who pointed me in the direction of math and science; rather that was something I had a natural inclination for. And, I’m sure at some level I was seeking approval from my father. I certainly enjoyed being able to achieve things that surprised and pleased him. I’m sure that he was pleased that I seemed to be following in his footsteps.
He was able to give you feedback that was positive?
Yes, he was. I can remember a specific instance. I had received a book about mathematics and I read a lot about it, and I remember once in school, perhaps in eighth grade, we were discussing complex numbers and actually the teacher was showing me how to plot complex numbers on a rectangular grid, real on the horizontal axis and imaginary on the vertical axis, and showing how you can add two complex numbers together by combining their vectors of angle and position. I went home to my father and told him what I had learned and I remember him being extremely impressed. He said he might have learned about that only in the university. I remember that explicitly because he didn’t shower people with praise easily. It was rare that he would make a recognition of that sort.
Was your mother supportive of these interests?
Yes. She had little interest in mathematics or science, but I think my success in that area gave her pleasure. As I said, I was close to the top of my class throughout school and college and I think that made her pleased.
Did you continue to go to public school throughout this time?
Yes. I attended the Mountain Lakes public schools from kindergarten through high school graduation, after which I went directly to Haverford College in 1953.
Now, how did you come to choose Haverford?
Well, I applied to Harvard College, which was my father’s alma mater, and visited it and liked it. But at the last minute a friend of the family, who had a Quaker background, said, “You know, Harvard is a great institution but it’s huge and it’s very anonymous, and you ought to consider this small Quaker college at Haverford, which is also excellent, and will give much more personal attention.” So, I went and I interviewed there, as well as at Swarthmore, which is somewhat similar and a little larger. I liked both of them very much. I think my final choice hinged on a relatively minor point, which was that Haverford offered me a modest scholarship. I’d never been offered a scholarship in my life and I thought that was pretty neat. So, that tipped the balance to Haverford. It was a close decision at the time. Afterwards, I was very pleased I had done that.
Did your parents enter into the decision at all?
No, not really. I think my father would have been delighted if I’d gone to Harvard which was his alma mater. And, I don’t know if he was surprised that after having been accepted at Harvard, I turned it down. I suppose that doesn’t happen very often these days.
What about your specific interests and hobbies?
Well, one interest, which has been important throughout my life, is music. I started taking piano lessons, at my mother’s instigation, at age six in kindergarten, and I continued doing that all the way through high school. I also was prevailed upon, because I knew how to read music and how to count time, to take up violin when they needed a violin in the grade school orchestra. So in addition to my piano lessons I began studying the violin; and I continued with violin studies throughout high school, and even throughout college. I’ve continued to play both the violin and the piano ever since, although I must confess I am really not very good on the violin and never will be. The piano remains my major instrument. In fact, two years ago I began to seriously study the piano again and I’m now taking piano lessons.
Yes, pretty much so.
Who are some of your favorite composers?
Well, in the last couple of years I’ve been working on a Beethoven sonata, Chopin, Brahms, Bach. But also I worked hard on George Gershwin’s Rhapsody in Blue, and recently played it in a performance.
Do you play with other people in chamber music?
Yes, I do. I’m, in fact, playing chamber music tonight with a group. As I said, I’m not very good at the violin, but together we have a lot of fun. I really enjoy playing chamber music because I enjoy the communal aspect of making music. I’ve also played in various symphony orchestras, starting with the Mountain Lakes Symphony while in high school. While in graduate school at Caltech I played in the Pasadena Civic Symphony. And recently, I have played in the Cambridge Symphony Orchestra.
That’s the mark of a real enthusiast, and a certain amount of talent too.
Well, as I said I’m not very good on the violin. When I play in these orchestras I play a second violin and I don’t play very well. I enjoy it though. I’m better on the piano.
Okay. Your mother played, you said? Or, did anybody else in the family play?
Nobody else really played. I think my brother was also led to a piano at roughly the same age but that did not take. At least one of my sisters took piano lessons but I don’t believe that lasted long.
You said you excelled in math and science? Was there a point that you can point to, possibly a teacher or some other influence, that caused you to start thinking of what part of math and science you might want to have a role in, or whether you started thinking about it at all at this time as being your life work?
Not because of any math or science teacher, but one other aspect of my growing up led in a round-about way to where I am. When I was in eighth grade I had a very good school friend who was interested in collecting minerals. And, I don’t know how I linked up with him, but I became interested in that. Three or four times his mother would take us to the Natural History Museum in New York City to and view their fantastic mineral collection, and then buy a specimen or two at the Gift Shop. Also, we would go out also on weekends, usually driven by one of our two mothers, to various collecting sites in New Jersey and collect them. For example, there’s a particular site in the town of Franklin, New Jersey that was sort of the Mecca for us. Franklin is the center of a small mining district where zinc ores are mined. Franklin’s suite of zinc minerals and other exotic species is unique and world-famous. Some of them exhibit fantastic colors under an ultraviolet light, which causes them to fluoresce. Particularly beautiful are rocks containing a variety of calcite which fluoresces bright red, which occurs together with a zinc mineral called willemite, which fluoresces bright green. We would go to the mine tailings in Franklin at nighttime with a portable UV light and shine it on the tailings, and these specimens of calcite and willemite would light up red and green like little Christmas trees. Another beautiful mineral found there is Franklinite, which is named after the town, and which occurs in beautiful octahedral crystals that are found no place else in the world. So, that boyhood experience got a lifelong interest in mineralogy going. I remember that in my high school sophomore year we were asked to write essays in our English class what we wanted to do for a career. And I thought, “Gee, minerals are neat. I think I’m going to become a mining engineer.” And so I wrote a paper on becoming a mining engineer, which convinced me I didn’t want to be a mining engineer. The actual realities of mining engineering were not really very interesting to me, like how you build tunnels in such a way they don’t cave in on you and this kind of thing.
You investigated what it took to be a mining engineer, and decided against it?
That’s right. However, I was still keenly interested in minerals. This interest remained strong when I went off to Haverford College, but I realized it was just a hobby, and so I put that interest on the back burner for a time. I took an introductory physics course, in which I met a number of other fellows who were also very much interested in physics, and the upshot is that I ended up majoring in physics, with a minor in music. And, this led me to go on to graduate school in physics. I have to confess that my decision to go on to grad school in physics was not driven by a strong passion for scientific research, but more because this was a well-travelled path by others before me, and I was clearly good at it. However, to return to my interests in mineralogy for a moment, in my senior year at Haverford I took a course in geology, actually at Bryn Mawr because Haverford did not have a geology department. This I found quite interesting, building upon my hobby of mineral collecting but greatly expanding on it, and I began to think about perhaps studying geophysics in graduate school. Also in my senior year at Haverford, I decided to take an introductory survey course in astronomy just for fun, and this I suppose also opened my eyes to the breadth of possibilities in physics-related research.
At Haverford, was this course given by Louis Green?
Yes. Louis Green was in fact one of my Haverford professors I remember best. Aside from the elementary astronomy course, I took from him a quantum mechanics course for physics majors. And he and his wife Elizabeth took a number of the physics majors under their wing, entertaining us at home.
In any case, I decided to go on to graduate school in physics without thinking very deeply about what my focus would be, I decided to apply to Caltech simply because of its reputation of being one of the best places in the world to do physics, and because it was clear across the country in a place I had never visited. So, I applied there and got in. I also applied and was accepted for graduate school at Harvard, but in the end I chose Caltech. Then, when I got to Caltech I thought, “Well, I’m interested in both physics and geology, so let’s go find out about geophysics.” So I enrolled in a seminar in geophysics during my first year in addition to basic graduate-level physics courses, and I also went to the Seismology Laboratory, which was run by Frank Press at the time, to see if there was an opportunity to participate in a research project to get my feet wet in that area. And Press did indeed assign me a small research project. He was interested in constructing a 2-dimensional physical model of the interior of the earth, through which he could pass acoustic waves that might mimic actual seismic waves in the real Earth. The model was made of a flat disk of aluminum, but modified so that at every radius in the disk the sound speed was proportional to the sound speed at the corresponding radius in the real Earth. The sound speed was to be adjusted by using a lathe to carve away part of the thickness of the disk at each radius, and then my assignment was to pour epoxy into the disk where material had been carved away, after which the disk was to be re-machined to uniform thickness — but now at each radius the disk was composed of part aluminum and part epoxy in a ratio such that the mean sound speed at that radius was proportional to the modeled sound speed within the Earth. Then the idea was to put a transducer at one point on the edge to generate earthquake-like impulses, and receptors at other positions around the circumference to detect the waves after travel times that bore some resemblance to what is observed in actual earthquakes. My main job in this was to oversee the cutting of the disk, the pouring of the epoxy, and the final shaping of the disk. I guess Frank Press felt that I ought to learn how to get my hands dirty if I was going to be a physicist or a geophysicist of any stripe.
So, was this your first extensive laboratory experience?
That was my first real laboratory experience, although in retrospect it was not very extensive, and never led anywhere.
So, back at Haverford you must have taken laboratory physics, but it was all cut and dry?
Well, I did a senior research project at Haverford for which I decided, again because of my interest in mineralogy, to investigate x-ray diffraction patterns of crystals. This also was not a great project. I remember that the chairman of the Physics Department there, Aaron Lemonick, invested a couple of thousand dollars on my behalf in purchasing an X-ray diffraction apparatus, and I pulverized various materials and recorded their X-ray diffraction patterns, then wrote out a paper describing what I found. But, it certainly wasn’t original research. It was just sort of top-level exploration of how the apparatus worked and how one could identify substances through their diffraction patterns. In fact, I remember there was a visiting faculty member to Haverford at the time, Fay Ajzenberg-Selov, who read my senior thesis. I met her the next year at Caltech, and she said, “Oh yes, you’re the guy who wrote this undergraduate thesis on x-ray diffraction.” And I replied, because I thought it appropriate to sound modest, “Yes. It wasn’t much of a job.” And she said, “I totally agree. It was not much of a thesis.” So, that put me in my place, which was appropriate.
Was that comment a serious one, or were you very self-assured during this time that you were…
I was pretty self-assured. I made that comment fully expecting her to say, “On the contrary, it was a fine thesis.” But she was very straightforward in telling me what she actually thought. And, she was right, as I said.
But the main thing that happened at Caltech that steered me in along the circuitous route to where I am now; was that like all incoming students, I was required to be a graduate teaching assistant. And that’s where I met Robert Leighton, because I was assigned to be a lab assistant in his freshman physics course.
Let’s, let’s try to get a year frame for this. What years are we talking?
I guess this would have been spring of 1958, the spring term of my first year in graduate school.
Leighton was the formative figure in my professional life. Initially I just knew him as a really excellent teacher, because I sat in on many of the lectures in an undergraduate physics course he taught, and he was also an excellent teacher in the lab and supportive of my work as a teaching fellow. So, I really liked being with him. But, I was still planning to be a geophysicist.
So, in addition to my brief adventure with creating a two-dimensional seismic model of the earth for Frank Press, I took a course in geophysics, in the spring of ‘58. One of the topics discussed had to do with internal magnetic fields of the Earth and planets. I learned a little bit about the theories of a magnetic dynamo within the Earth and other planets. This seemed an interesting topic to pursue, but I didn’t know of any research projects going on at Caltech in that area. However, just at that time I discovered that Bob Leighton had just started a project to research magnetic fields on the sun. I thought, “It’s not magnetic fields in the earth, but solar magnetic fields sound interesting too.” But probably the more important reason is that, as I mentioned, I had I really liked being a TA for Leighton, so I got a summer job as a research student, working with him on studying magnetic fields on the sun. And, that’s how it all started.
Very interesting. Now the person who was doing planetary interiors, was that Wasserberg?
Well, the course I mentioned was a seminar, involving several faculty. It may have been led by Wasserberg; I don’t remember for sure.
Bob Leighton was interested in planetary work as well, and instrumentation. I’m curious about the solar work, though. I mean, of course solar magnetism was something that was very important in the history of Caltech, going all the way back to Hale.
Yes indeed, Hale’s influence was very evident at Caltech, and particularly so on Mt. Wilson, where I ended up doing the bulk of my graduate work with Leighton. I think Leighton approached his work on the sun from an instrumental physicist’s perspective: he thought up better and more imaginative ways to make astronomical observations than others had tried before, and he was able to use them to push scientific investigations to a new level. I could spend hours talking about Leighton’s science and I don’t know whether it’s helpful or not, but I could certainly tell you a few highlights.
Certainly want to know more about Leighton. I did have a chance to interview him many years ago, in the ‘70s. But I’d love your perspective.
Let me just start. So, I began working with Leighton partly because he was interested in solar magnetic fields. That interest started well before I met him — he started out as a cosmic ray physicist, by the way.
Yes. And with Anderson, I think.
Actually, Leighton was amazingly talented in instrumentation, and able to apply it in novel ways to astronomical problems. I got the feeling that he figured out clever instrumental approaches first, and then found the perfect application. He once told me that if you could develop a new instrumental capability and apply it to a given scientific area, you’re almost sure to find something interesting. One of the most important things that Leighton ever told me, by the way, which has stayed with me all my life, was “Science is where you find it,” by which he meant that a good scientist is not wedded to a particular field all his life. He goes where the action is, and that’s what he always did. He may have started in cosmic ray physics, but he also had an interest in astronomy. Somewhat before I met him, he thought that he might be able to improve on the astronomical images that could be obtained from telescopes like the 60-inch and 100-inch telescope Mt. Wilson. So he developed an optical image stabilizer, which corrected for telescope guiding and tracking errors. He put this on the 60-inch telescope and proceeded to take the world’s best photographs of Mars. They were so good that a few years later, it became very important at JPL and their Planetary Sciences Program at NASA.
He took motion pictures, color motion pictures of the planets in rotation.
Yes. And I think they were better than any obtained before that time.
I remember seeing them as a kid. They were phenomenal, for the time.
Anyway, Leighton was interested in high-resolution images, not only of the planets, and of course he was familiar with the images of the surface of the sun, showing the solar granulation but rather blurred out by the atmospheric seeing just the way planetary images are. So he went up to the 60-foot solar tower and took 35 mm time-lapse photographs of the granulation, then selected out the very best frames, and measured the mean sizes of the granules by a clever analog autocorrelation technique. This technique involved superimposing two film images of the granulation and passing light through them, then seeing how the total amount of light passing through the film changed as he displaced the two film strips relative to each other. This was well before the days of digital computers, and Leighton was basically using an analog approach to calculate an autocorrelation function, which a computer can do trivially today. He also estimated the mean lifetime of solar granules in the same way, by measuring the correlation between pairs of images separated by different times. And by developing this analysis technique, Leighton was able to determine for the first time some interesting aspects of the physics of solar granules.
Now, this is ‘58, ‘59?
This would have been in 1957, which was just before I arrived at Caltech. His paper on this is 1957, PASP 69, 497.
When I arrived on the scene, Leighton had just developed a new technique to measure magnetic fields on the sun. He knew from Hale’s work that in the presence of a longitudinal magnetic field the Zeeman effect causes a tiny red or blue shift of magnetically-sensitive spectral lines, which can be seen if one uses a circular polarization analyzer to separate out light of right or left circular polarization. Hale had used the Zeeman effect to find that magnetic fields in sunspots were as large as several thousand gauss. But now Leighton realized that he might be able to detect much weaker magnetic fields if he used Hale’s original spectroheliograph, which he rebuilt for the purpose, to record two simultaneous spectroheliograms in the wing of a magnetically-sensitive spectral line, one in right-hand and one in left-hand circular polarization. He did this by introducing a beam splitter just before the entrance slit of the spectroheliograph, which made two identical images of the sun side by side along the slit, and then he used polarizing optics to pass right-hand circular polarized light to one image and left-hand to the other. With this set-up he would make two simultaneous spectroheliograms of a magnetically-sensitive spectral line, which were identical in every way except for where there was a magnetic field. But wherever there was a magnetic field with a component in the line of sight, then the right-circularly polarized light in one image would be shifted very slightly toward the red, say, and in the other left-circularly polarized image it would be shifted slightly toward the blue. Leighton then positioned the exit slit of the spectroheliograph about halfway up the violet wing of the magnetically-sensitive spectral line, so that wherever there was a magnetic field the dark center of the line was shifted toward the red in one image and that image became a little brighter; and in the other image where the line was shifted toward the violet, that image became a little darker. So the images were identical in every way except where there was a magnetic field, and in those places the difference in intensity between them reflected the strength of the field. Then Leighton would take the pair of photographic plates to his home darkroom and make a contact print of one of them to unity contrast, so that when he laid the positive contact print on its own negative original, every feature cancelled out and all you saw was uniform grey. But when he positioned the contact print on top of the other image, every feature that was exactly the same cancelled out as before, but features that were opposite in the two images were re-enforced. So this cancelled out everything except the effects of the magnetic fields, which were doubled. And what resulted was a photograph of the magnetic field structures of the sun in magnetically active areas. This is all written up in a paper of his in 1959 (APJ 130,366); I participated modestly in this during the fall of 1958, helping with some of the data reductions.
This was my first introduction to real research. This paper showed for the first time that the sun’s magnetic field away from sunspots is highly structured and most importantly that it is extremely well correlated with heating in the overlying chromosphere, as shown by brightening of the Ca+ H and K lines. I think this was a really important result for solar physics, and I was pleased to be part of it even if my own role was quite minor.
Not everything I did with Leighton led to important new results. One thing he wanted to do was to extend his work on the granulation patterns to obtain very high resolution images in three colors, not just one. In this way he hoped to get a better handle on the temperature variations in the granulation. And in addition, he wanted to photograph the entire solar disk, not just the small fraction of it that he could image with the 35 mm camera in his 1957 paper. Now the solar image at the Mt. Wilson 60-foot tower is about 7 inches across, so Leighton went down to C&H Surplus and picked up some World War II surplus aerial cameras that have a seven-inch aperture. Then the challenge was how to make a focal plane shutter that could open and close in 1/1000 second over that huge aperture. We did this by making a set of three concentric rotating disks with slightly different rotation speeds, each of which had an opening shaped like a piece of pie, and for which the narrowest opening rotated its own width in about 1/1000 second. The three openings came into alignment about once every 10 seconds, at which time the narrowest opening swept across the field exposing each part of the film for 1/1000 second. In addition, because the objective lens of the 60-foot tower was chromatic, so that the focal length depended on color, we had to move the massive focal plane shutter mechanism and the camera back and forth by several inches to be in focus for each of the three colors.
So, when I worked for Leighton that first summer one of my jobs was to design and build this camera, which was frankly a bit of a Rube Goldberg contraption. The first thing Leighton did, by the way, after I joined him, was instruct me to go off and take a shop course, which I did so I learned how to use basic machine tools.
The three colors was to measure the temperature using a Planck curve kind of?
Yes. But I think the thing that really motivated Leighton was the fun of doing it, and being able to get very high-resolution images of the entire solar disk at reasonably rapid cadence to take advantage of good seeing. I think he hoped to end up with the world’s best very high resolution images of the sun.
Did you get granulation?
Oh yes. I presume the pictures still exist. There should be several rolls of film of this aerial camera seven-inch-wide film showing images of the sun in some vault someplace at Caltech. They’re not very useful. No one will ever look at them because it’s been superseded by far better pictures.
Did you end up publishing?
No. We didn’t end up publishing. And it never would have been worth publishing simply because we got some pretty pictures.
Oh, that’s why I didn’t find any of this.
By the way, another problem I haven’t mentioned was how to develop a seven-inch-wide, very long film-strip. We bought this film, but had no easy way to process it once exposed.
Aerial camera film?
That’s right. But you can’t go down to your local photo shop and say, “Please develop this 100-foot long strip of 7-inch wide film.” You could cut it up into little pieces and develop it that way, but Leighton wanted to develop the whole roll so as not to cut into the individual images. So, we needed a developing tank that would develop the whole strip, and he asked me to build that. And so, I built this Rube Goldberg film processing machine, and I must say that it’s amazing that it actually worked. It was about four feet long and four feet tall. For the purpose I learned how to use the carpentry shop, and I made this box out of wood, which I covered with fiberglass to make it liquid impervious. You threaded about a 20-foot leader strip into the box through many rollers, and then put on a light-tight top and flipped a switch on the drive motor. The film would be pulled over the first roller and down into a pre-wash tank, and then into the developing tank in which we had loaded developing chemicals, and loop through that tank long enough to complete the developing process; then it would come up and around and down into another chamber holding a stop bath, then into a wash bath, and finally into a heating area to dry the film. After that it would come out the other end and be spooled onto a take-up reel. And so, I would load this thing up, put on the light-tight cover, turn it on and it would go through the whole developing process and out would come the developed film. It worked beautifully. I would never have had the courage to build this thing, but Leighton said, “Well, it should be straightforward”, and so I built it following his ideas, and it worked just fine.
Another project Leighton undertook at the time was to follow up on Dicke’s claim from observations at Princeton that he had detected the oblateness of the sun, at a level that showed Einstein’s theory of general relativity to be wrong. And so, Leighton built a fancy gadget that he mounted at the sixty-foot solar telescope to measure how circular was the seven-inch image of the sun. The device had a pair of rotating photocells, which rotated perhaps at 100 rpm around the limb of the solar image, and which would yield a periodic signal if the sun’s limb were not perfectly circular. Leighton spent a fair amount of time on that and eventually, I guess, gave it up as a lost cause because he never could get the sensitivity to the level of precision required to check Dicke’s claim. In any case, nothing ever came of it; but to me it nicely illustrated Leighton’s inventiveness.
Now, you were also taking courses at Caltech, right? You were a first-year and second-year?
My first year was largely devoted to courses, plus assisting in Leighton’s lab; I got directly involved in research in my second year.
And, at some point in here you must have started thinking about what it is you’re going to do with your scientific life?
Actually, I was very much in an exploratory mode, but my initial encounter with Leighton began bending me toward making observations and ultimately to my thesis work in observational solar research. And so, when Leighton offered to have me continue helping him with his research, I eagerly signed on, starting in the fall of 1958, with helping with the magnetic field paper I told you about a few minutes ago. And the first new project I got involved with was a direct outgrowth of that work.
Leighton had modified Hale’s original spectroheliograph at the 60-foot telescope to incorporate a beam-splitter to make two identical images, then used polarizing optics to bring out the magnetic signal in opposite senses on the two images. So now he decided to use this approach to look at velocity fields — that is, Doppler shifts of spectral lines that should be produced by the rising and falling granules on the sun. He hoped to measure the speeds of up-flowing and down-flowing granules, following up on his studies of the granulation that I mentioned earlier. By then these Doppler shifts had already well-observed by others, from photographic spectra of the surface of the sun which showed “wiggly lines” along the one dimensional slit of a spectrograph due to the granulation. But Leighton wanted to get a two-dimensional image of the velocity field in the granulation. So, he modified Hale’s spectroheliograph in yet another way, by introducing two glass blocks into the spectroheliograph just beneath the exit slit, one for each of the pair of images that was created by the beam splitter he had built for the magnetic study. Of course he removed the polarizing optics he had used for the magnetic study. But then, by rotating the blocks in opposite directions, he could position the spectrum going through the exit slit to be on the red wing of the line for one image, and on the blue wing for the other one. So the result was two spectroheliograms, made simultaneously and identical in every way except that now wherever there was a Doppler shift — for example making the dark center of the line shift toward the red, the spectroheliogram recorded on the red wing of the line would be a little darker, and likewise the one recorded in the blue wing would be a little brighter. All the other brightness patterns on the image, for example due to temperature changes in the solar photosphere, would be the same for both images. Then, by subtracting the two images photographically, the opposite brightness changes signals due to the Doppler shifts of spectral lines were accentuated and the much larger signals that were the same on both images disappeared. So the result was a “Doppler Image”, or “Dopplergram”, i.e. a picture of the velocity field of the sun, where brighter areas showed where material was rising and darker ones where it was falling. And interestingly enough, you could see rising and falling elements in the Doppler plates, but they seemed somewhat larger in size than the solar granules which, being about 1 arc second in size, were about at the limit of resolution of the spectroheliograph due to its 1 arc second slitwidth. This could have been the first clue that something very interesting was going on, but I at least didn’t pick up on it.
Was this your first experience under Leighton with what I would regard as moderately sophisticated manipulation of optical designs and that sort of thing?
This was. Yes.
And you were looking at a lot of components layered on top of one another and making them all work?
Okay. And that interested you?
It interested me very much. Like the magnetic measurements he had made before, Leighton’s approach beautifully illustrated the value of making differential measurements, designed so as to pull the small signal you are interested in out of a very much larger field of variation that you are not interested in. I thought this was enormously clever. So the next thing that Leighton did was to say, “Okay, let’s find out how the velocity changes over time.” And this was instigated in part because of his studies of granulation. The prevailing notion at that time was that the solar granulation was the top of Benard Convection, convection cells coming up and turning over, with a lifetime of about eight minutes, after which the pattern would be different because granulation is just a stochastic convective phenomenon. After a few minutes a given granule would disappear, and other new granules would appear. Leighton wanted to investigate the lifetime of the solar granulation in detail, I think because he had a deep-seated notion that their motions had to do with creating and destroying magnetic fields and making the solar cycle. So, I think already he was motivated by looking for the big picture of solar magnetism.
So Leighton decided to record pairs of Doppler images of the sun’s velocity field, just like those I described a moment ago, but that differed from each other only in the time when they were exposed, so that when they were subtracted photographically, the brightness of features seen would be proportional, not to the velocity, but rather to the velocity difference, or how much the velocity had changed in the intervening time. So we made two Doppler scans, the first going in one direction over the sun, and immediately afterward we’d move the plate to a new unexposed part of the emulsion and start a second scan going in the opposite direction. Now it took perhaps five minutes for the spectroheliograph to scan in one direction over a patch of the solar surface, and then another five minutes to scan back to the starting place. This means the time difference between when the same piece of the sun was recorded would be nearly zero at the end of the image where the slit was when we ended the first exposure and started the second scan in the opposite direction, and that time difference would increase linearly along the plate to the location of the end of the second exposure, which was the same as the point where the exposure started about 10 minutes earlier. Then, when these two images were subtracted photographically to make what we called a “Doppler Difference” plate, there should be no Doppler difference signal at the end where we turned the scan around, and at the other end we should have an image of the change in velocity over the 10 minutes of the complete scan.
That is ingenious. I mean, from an optical/mechanical manipulation standpoint of all of these steps and everything.
It certainly was. Now Leighton, and I, fully expected that we would see a pattern showing no Doppler difference features at the end of the plate where the time difference was nearly zero; but as we scanned down the plate so that the time difference increased up to around ten minutes, we should see more and more velocity difference signal as the granulation, with its around 8-minute lifetime, changed and lost coherence. If we took a scan over a longer time baseline, say 20 minutes, we should see the velocity field become more and more uncorrelated as the time difference increased, reflecting the disappearance of old granules and the appearance of new ones uncorrelated with what went before. Boy, were we ever wrong!
OK, I’ll bite. What did you see?
Well, I remember vividly that key moment in my scientific life, when Leighton came back from over the weekend. He had taken a few Doppler Difference spectroheliograms home to work on in his home darkroom. He came up to the 60-foot solar tower on Mt. Wilson where I was already setting up for making observations, and he said to me, “Bob, I’ve found your thesis project!” I said, “What do you mean?” And he said, I don’t remember his exact words but it was something like, “It’s not true that the solar velocities lose coherence over a time of 8 minutes or so, like the granulation. Of course there is no signal at the end of the plate where the scan turned around and the time difference was almost zero. And, as you look down the plate away from that end, the time difference gets larger, and as you’d expect the velocity difference also grows larger and larger. But only until you get to the place where the time difference is about 2 1/2 minutes; then, as you look further down the plate, the velocity difference starts to decrease again, so that when you get to the place where the time difference is about 5 minutes, the velocity difference gets very small again. And this is happening all over the sun.” In other words, and these were his exact words, I recall, “I can guarantee that if a piece of the sun is moving upward at a given moment, then 2 1/2 minutes later it will be moving downward, and 5 minutes later it will be moving upward again.”
So, it’s repeating itself?
It’s repeating itself. Put another way, each point on the sun is oscillating up and down, with a period of around 5 minutes.
No wonder this paper is highly cited. I mean, this is the origin of what all sorts of people are doing these days, or trying to do, with the oscillations. Is that, is that a fair statement?
Yes, I think it’s fair to say that this discovery marked the birth of helioseismology.
As a parentheticcal comment I might say that it took me a while to be convinced of what was so obvious to Leighton, because this was totally unexpected. And indeed a few days later I was worried that something was wrong. Leighton and I went off to breakfast at the Monastery at Mt. Wilson, and while we were at breakfast, we left a chart recorder running to record the light intensity when the spectrograph was positioned on the wing of a sharp solar spectral line, in order to test the wavelength stability of the spectroheliograph. And when we came back after breakfast, the chart record showed that the spectral line was moving back and forth with a period near five minutes, albeit a very small amplitude. We had taken the big objective lens of the 60-foot tower telescope out of the beam, so we were looking at raw un-imaged sunlight, but here was this unexplained apparent Doppler shift anyway. I thought maybe the 5-minute oscillation might be something in the Earth’s atmosphere, but Leighton pointed out that of course it had to be on the sun since the imaged velocity differences showed all the details of the velocity images themselves which we had been carefully investigating. But I was still skeptical enough to go up to the spectroheliograph one evening and monitor the position of the zero order image of the exit slit in the spectroheliograph when a bare light bulb was placed over the entrance slit, and sure enough, it was oscillating back and forth with a period of about 5 minutes. When I told Leighton he immediately realized that what was happening must be a sloshing of the cold air in the vertical pit that houses the 13-foot long spectroheliograph instrument, and that sloshing acted as a wedge prism to shift the spectral lines a tiny bit. It was just coincidence that the period of the sloshing was near five minutes. Fortunately the amplitude of this instrumental effect was completely negligible compared to the solar signal we were recording. Nevertheless, Leighton devised a cardboard baffle which we put into the spectroheliograph pit, and that fixed the problem.
So, you got rid of the instrumental effect?
Yeah. And in any case the instrumental effect was tiny compared to the solar effect. And, it is really not very interesting compared to the real discovery. So my apologies for the digression.
No, it’s marvelous stuff, because Leighton is extremely important, and it shows how your career was propelled by this experience with him. I’ve always imagined him to be extremely creative, extremely inventive, but I’ve never experienced it like you’ve just shown it to me.
I think the story of that amazing time at the 60-foot solar tower is incomplete without mentioning the other big discovery that came out of it, namely the discovery and characterization of the solar supergranulation, which became the thesis project of George Simon.
I was going to ask you about George Simon.
Well, Doppler plates not only showed the small-scale velocity field, which we initially thought was due to overturning solar convective elements but later turned out to be largely the 5-minute oscillations modes, but they also showed a larger-scale field of mainly horizontal velocities. Rather than having time scales near 5 minutes, these flows persist for many hours and appear to be the upwelling and spreading out of very large convective cells, some 30,000 km across, which we called “supergranules”. George selected as his thesis topic to explore and characterize them. It turns out that they are a vital component of the dynamics of the solar convection zone. One very important aspect that George worked on in detail was the close relation between the boundaries of the supergranules and the magnetic field pattern in the solar photosphere. That pattern is shown not only by magnetic maps of the photosphere, but very strikingly, by the pattern of emission in the ionized calcium line, which reflects the heating of the low chromosphere. So it appears that the horizontal flows of supergranules sweep the magnetic fields into their boundaries, where the magnetic fields become concentrated and then are instrumental in guiding energy from the convection zone up into the chromosphere, producing chromospheric heating and hence the emission in the ionized calcium lines. This is all very complex, and I think it is fair to say that the detailed origins of the supergranules that orchestrate the whole thing are still not fully resolved, but the discovery of the supergranules at Mt. Wilson during the time we’re talking about had a really enormous impact on solar physics. The main characteristics of the supergranulation were presented also in the Leighton, Noyes, and Simon paper, plus a follow-on paper by Simon and Leighton (Simon and Leighton, 1964, “Velocity Fields in the Solar Atmosphere. III. Large-Scale Motions, the Chromospheric Network, and Magnetic Fields,” APJ 140, 1120).
Let’s switch gears and talk about how you got to the Smithsonian. Was that your first postdoctoral position?
Yes, that was my first one, and in fact my only one, since I never left SAO. I suppose I started out as a typical postdoc, in that the first thing I did was to write a follow-on paper to the initial Leighton, Noyes, and Simon paper; this described a number of details of my thesis work on the observations of the 5-minute oscillations.
1963, APJ 138, 631: Velocity Fields: Solar Atmosphere II. You were thinking, at some point, about a career?
To tell you the truth, I was having fun and not really thinking very hard about my ultimate career. You know, those were very different times from today, in the very early 1960’s. Jobs for newly-minted physics students were very plentiful, and frankly I was not worried about a career path. I certainly wasn’t looking for job security or anything like that. Back in those days career options were plentiful. I remember in my last year of Caltech being courted by all sorts of companies that wanted to hire me or in fact, any graduate from Caltech with a physics degree. They used to come courting me weekly and they would take me out and feed me fancy lunches and tell me how great it would be if I came to work with them. I recall one day Leighton said to me “Would you kindly tell these folks, who keep trying to recruit you, to lay off me? Because, they come to you and then they come to me as your advisor and they want to take me out to lunch too, and I don’t have the time.” Very different from today!
Did they come in their sports cars?
I don’t recall.
That’s what they used to do at UCLA.
I do remember one time a recruiter took me to lunch at a dimly-lit steakhouse not far from Caltech and tried to ply me with martinis. It was really awful.
My god. Was this from the aerospace industry in the area?
It could have been. I did briefly flirt with General Atomic down in La Jolla, who were thinking about building a rocket ship propelled by nuclear explosions, and I guess they thought a physicist from Caltech could help. But I considered many possibilities. I was curious where plasma physics was going so I interviewed at Princeton’s Plasma Physics Lab. It looked as if space research was an interesting new direction so I had an interview with John Lindsay at Goddard Space Flight Center. Finally, because my folks lived in Concord, MA, I visited nearby Sperry-Rand to find about their plasma physics program. And in that visit I also dropped in to SAO, because I had heard about a scientist there named Charles Whitney, who had written a theoretical paper about waves in the solar atmosphere [Whitney, C. 1958, Smithsonian Contr Ap 2, 365] that seemed quite relevant to our observations at Mt. Wilson. So I met and had a good chat with Chuck Whitney.
And, in short, SAO seemed like a really interesting place, for two reasons. First of all, Chuck was very interested in what I’d been writing my thesis on; and secondly, down the hall was a scientist I’d never heard of called Leo Goldberg, who was starting a program to study the Sun from space.
You’d never heard of him?
Well, I guess I had heard the name, but that was it. In a minute I’ll tell you how little I knew about astronomy. But in any case Chuck said, “Go talk to Leo,” and I did, and learned about this project he had to launch rockets to look at the sun. And, I thought, “That sounds interesting.” The upshot was that I thought about for a day and then told Chuck, “Yes, I’d be very interested and can we talk about a job?” At the time I thought of this as simply a next step; I certainly wasn’t thinking it might be where I would be forever. But somewhere in making my choice was my realization that this could lead to a permanent position in the federal civil service, which was extremely attractive, even in those days where opportunities were all over the place.
Did you get any advice from Leighton?
Uh… not really. I think Leighton believed in following his own intuition, and was not one to give lots of advice. But let me just tell you the other thing I was going to say about my astronomy background.
I had essentially zero background in astronomy, and having been a physics major at Haverford and then a graduate student in the Caltech physics department, I never took a serious course in astronomy. For example, I didn’t even understand at the beginning of my work with Leighton such elementary facts as why the sun is darker at its limb. I think Leighton was also on a bit of a learning curve; I recall he and I both sat in on a course at Caltech taught on elementary stellar atmospheres; I think it was taught by Grant Athay, visiting from the University of Colorado. In any case, after the discovery of the 5-minute oscillations came out, Leighton was asked to give colloquia at various places. He came to me one day and said “You know, I had the most amazing experience last week. I was invited to give a colloquium and I drove over to this place in New Mexico. High on top of a mountain in New Mexico there’s an observatory called Sacramento Peak Observatory, and you know what? There’s a bunch of guys there and they’re all studying the sun.”
No? He’s kidding?
I don’t think so. I suppose Leighton had previously known about Sac Peak, but I think he’d never been there before, and I had never heard of the place even though I was near the end of my thesis work on one of the most important discoveries in solar physics. I was really coming at astronomy brand new, and this helps to explain why I didn’t know about Leo Goldberg. But anyway, that’s how I ended up at SAO. When I came I supposed I might stay for a year or two and then see what happened next. In other words I didn’t have the sense that “solar research is my life’s work,” or anything like that. I could easily imagine I might later decide to move on to Sperry-Rand to do plasma physics, or something else.
Leighton was working with Gerry Neugebauer also at that time, when the graduate students were building a sixty-two inch infrared dish?
Yes, I think this work began just as I was finishing up at Caltech. I’m not sure what inspired him to enter the field of infrared astronomy, but I suspect it in part it was that he saw infrared as a wave of the future in research, and maybe in part that he thought of a neat new technical approach — including spinning the infrared mirrors you just mentioned. Anyway, for one reason or another, he got interested in spinning mirrors for infrared telescopes. And he thought of this really cool way of creating parabolic mirrors, really cheaply, by spinning a cast containing liquid epoxy while it hardened. As for the sixty-two inches, I remember kidding Leighton by asking “Did you want it to be sixty-two inches so when they put it on Mt. Wilson it’s the second biggest telescope on the mountain, bigger than the sixty inch?” But Leighton replied, “No, it’s just that this was the largest size that would fit through the door of the shop.” But then as you know, he went on and he built these much larger mirrors.
You know that story?
Well, I don’t know too much about them, but these huge mirrors that could be taken apart, metal mirrors.
That’s right. I was sort of disappointed when I heard about that because I thought that spun technology was so cool, but he abandoned that technology when he found a better approach for making much larger mirrors needed for sub-millimeter astronomy.
They were huge. He was even talking, at one point, about them being deployable, the kinds of things that could be flown.
Yeah? Okay. I can believe that.
Okay. So, you came here, you got in contact with Goldberg and he started talking to you about rocket instrumentation or satellite instrumentation, or both? Who else were you talking with here? You said it was Chuck Whitney?
I got the feeling when I came that the Solar Satellite Project at Harvard was quite distinct from the activities at SAO. Harvard College Observatory and the Smithsonian Astrophysical Observatory seemed like quasi-different institutions, although sharing the same building. Goldberg had plans afoot to launch rockets to look at the sun in the ultraviolet and when I expressed interest he said, “Why don’t you join us?” So although I was a new Smithsonian employee, I became heavily engaged with the Harvard Solar Satellite Project. In retrospect, this seems a little weird, being paid by SAO to work on a Harvard project. But there seemed to be no objections. I felt that my job as a new Smithsonian scientist was just to do the best science that I could, and I didn’t worry much about institutional affiliations. Nor, it seemed, did those to whom I reported. At that time, there was none of the administrative supervisory framework there is now at SAO, like performance plans and the like.
So to get back to the Solar Satellite Project, I arrived in the fall of 1962, just in time for the first rocket launch of a prototype solar ultraviolet spectrometer, and I went out with Leo Goldberg, Ed Reeves, Bill Parkinson, and a number of project engineers to White Sands. Since I had just arrived, I went along sort of as a tourist. But I remained with the Solar Satellite Project throughout the series of Orbiting Solar Satellites, and then continued through the ATM Mission on Skylab and beyond. So I was very deeply involved in this way with solar research up to the late ‘80s. But, throughout my time at SAO I’ve changed the focus of my research greatly, and currently I’m not doing any solar research. Right now I’m doing extra-solar planets.
Well, that’s certainly a hot topic.
That transition occurred more than ten years ago.
Are you using transit techniques?
Where are you doing that?
Well, I am currently working with Gaspar Bakos, who is an outstanding postdoctoral fellow here at CFA and who has built a collection of completely automated 4-inch aperture telescopes based in Hawaii and in Arizona, to monitor the skies for transiting planets. But that’s not the way my exoplanet work started.
How did it start?
Well, I had renewed my interest in helioseismology, I suppose in the mid-1970’s, because of all the extraordinary science that was coming out of studies of the p-mode oscillations of the sun now that they were understood to be global modes that could tell us about the structure of the solar interior. And, I felt a certain satisfaction in having been part of their original discovery. I began to wonder if we could do the same thing with other stars; that is find the stellar analog of the 5-minute oscillations and learn about the interior of stars. I had a good friend, Tim Brown at the High Altitude Observatory, who is a cracker-jack instrumentalist as well as a cracker-jack scientist. He was also interested in the same problem. With Tim, and also Ron Gilliland who was then also at HAO, and Larry Ramsey at Penn State who had built a fiber-optic echelle, or FOE, spectrograph at Kitt Peak, we gave it a try studying the star Procyon. Things looked promising, although the signals we were seeing were barely above the noise level. But it occurred to us we might build a dedicated spectrograph for this purpose and install it at SAO’s 60-inch telescope on Mt. Hopkins, where we hoped to get lots of observing time. So we did, and called the instrument the Advanced Fiber Optic Echelle, or AFOE. By the way, in this development Pete Nisenson and Sylvain Korzennik at SAO played a very major role. Unfortunately the instrument and telescope combination wasn’t sensitive enough to convincingly detect the p-modes, even in a bright star like Procyon. For stars like the sun the radial velocity signal, averaged over the stellar surface, was only about a meter per second or so, and we just didn’t have the sensitivity. But, around then people were intensifying the search for a possible planet orbiting another star using radial velocity studies, and there you would expect the radial velocity wobble of a star like the sun due to a planet like Jupiter to be around 10 meters per second. This seemed like something the AFOE could have a chance at. So we began looking for this as well. And that’s how it started.
And what happened? Did you have any luck?
Well, we didn’t and we did. We began amassing data on the night-to-night variation of the velocities of a few dozen stars. One of them happened to be 51 Peg. I was at a conference in Florence in the summer of 1995, and it was there that Michel Mayor announced the discovery of the planet orbiting 51 Peg, which was the first exoplanet. Michel was kind enough to tell me the name of the star the night before he publicly announced it, and so that early the next morning, while it was the middle of the night at Mt. Hopkins, I called to the 60-inch telescope there to tell the news to Tim Brown, who was observing with the AFOE at the time, and Tim said, “I just finished an observation of that star five minutes ago!” For this was one of the stars that seemed to us to be showing something interesting. After Michel Mayor and Didier Queloz gave their earth-shaking announcement the following day, we went back into our data and saw it matched their results perfectly. But they got there first.
How did it feel to come in second in such a landmark discovery?
Well, we recognized that all the credit for this epochal discovery certainly belonged to Michel and Didier, and appropriately so, for they had been monitoring this star for months before it even made it on our observing list. Still, it was fun to be associated even in a tiny way with this landmark discovery. And it helped convince us to push on with our own program, which ultimately did detect several planets of our own.
Great! But what about the transiting planets you mentioned?
Well, of course everyone realized that with an orbital period of only about 4 days, planets like 51 Peg’s had to orbit very close to their parent stars, and so there was about a 10 percent chance that they would pass in front of the stars in their orbits, and reveal their physical size by the amount of light they blocked during the transits. So like many other folks I got interested in transit studies, and I sent our Harvard grad student, Dave Charbonneau, to work with Tim Brown at HAO to undertake transit studies with Tim’s little transit telescope; and Dave and Tim made history by discovering the first transiting planet, orbiting the star HD209458. (To be fair, another group independently saw the transit signal in exactly the same star, and both results were published side by side.) Then finally, when Gaspar Bakos came to SAO shortly after that, he quickly got caught up in this great new research area and turned his automated telescope system to search for transiting exoplanets, with enormous success over the past several years.
That’s quite a story. But now let’s go back to your coming here back in 1962 and then your deciding to stay here. How did that happen?
Oh, it happened because I think I got caught up and excited by the Solar Satellite Project. I found that really exciting; it seemed like the wave of the future in solar research. I did continue trying to do some work on the five-minute oscillations. As I said, the first thing I did when I came to SAO was to write up my thesis work for publication. But then my focus shifted rather rapidly into space research. And so I was not part of the realization that unfolded over the next several years; that the 5-minute oscillations were really due to the global wave modes inside the Sun, which has revolutionized solar science.
Okay. Getting back to solar space science, by 1964 you have a paper with Parkinson, Reeves, and Leo Goldberg, and yourself, “Preliminary Results From a Rocket Flight of the Harvard OSO-B Spectrometer” [Astronomical Journal, Vol. 69, p. 140 (1964)] So, this was a preparatory flight, I take it?
Yes. The purpose was to verify the performance of the OSO B flight instrument, which was designed to image the Sun in spectral lines from 500 to 1300 Angstroms. This was an essential first step toward the actual OSO-B mission, which was to be launched a year or so later.
What was your role on the team? Or did you even see it as a team effort?
It was a team effort but I was new, and initially I was a relatively minor player on the team. I had no part in actually physically developing the various instruments as they evolved through the program, but I did play a role in helping decide on basic instrument parameters, like spatial resolution and spectral range and resolution, and for the ATM mission on Skylab, helping determine the optimum combination of wavelength positions for its seven detectors. This was in collaboration over the years with many scientists who were associated with the Solar Satellite Project, including Ed Reeves, Bill Parkinson, George Withbroe, Andrea Dupree, Martin Huber, John Raymond, Peter Foukal, and a number of others.
So, your experience with Leighton then did not propel you into an instrumentation career?
No, working with Leighton did not propel me into instrumentation, but it did give me very much an observational, rather than a theoretical approach to astronomy. And maybe it was Leighton’s example that led me to jump into new areas if I saw there was interesting science there. I remember he once said that if you ever find yourself measuring something to the third decimal place it’s time to move on. So, when I came to SAO I saw the Solar Satellite Project as a great new scientific opportunity. But I continued with ground based optical solar observations as well. I worked with Jacques Beckers at Sac Peak on spectroscopic observations of the jets at the solar limb called spicules, which we studied using a special purpose optical beam-splitter inspired somewhat by Leighton’s beam splitter at the Mt. Wilson spectroheliograph, except that we configured it to take spectra at two heights above the limb simultaneously. This work also involved my first Harvard graduate student, Jay Pasachoff, who worked on these data as part of his doctoral thesis. And, then I got interested in the possibilities of infrared solar observations, and this led me into a pretty extensive foray into solar infrared astronomy. I decided I’d like to measure the intensity of the solar limb in the infrared — to measure the brightening expected at the extreme limb because of the temperature rise into the chromosphere. So, working with Jacques Beckers again, and with the help of Frank Low at the University of Arizona, we carried out observations of the limb of the Sun at the 20-microns in the infrared, using Frank’s bolometer. We used a telescope at Mt. Lemmon in Arizona for this, but covered its aperture with black polyethelene so as not to fry the optics when we pointed it at the Sun. It worked beautifully, except that we couldn’t get enough angular resolution in the infrared to rule out the predicted brightening at the extreme limb. So then Jacques and I decided to try similar observations during the 1966 eclipse in Peru. The actual eclipse observation was a bit of a cliff-hanger, as such observations often are, but in the end we got useful results — still no limb brightening, even with the increased resolution afforded by the moon’s limb crossing the Sun’s. The results helped refine the description of the vertical temperature profile in the solar atmosphere, showing that the solar temperature minimum occurred higher in the atmosphere than previously thought. And then, in 1972 I began working with grad student Donald Hall looking at the solar near infrared spectrum using the infrared spectrograph at the Kitt Peak Observatory solar telescope. Don wrote his thesis on this work, which included a beautiful atlas of infrared spectral lines seen in sunspots. With Don I also carried out observations of the infrared CO lines, which showed beautifully the thermal response to the 5-minute oscillations we had found a decade earlier in visible light at Mt. Wilson. And, a couple of years later I worked with Giovanni Fazio on the development and initial flights of the SAO 102-cm balloon-borne infrared telescope, which used a bolometer of Frank Low’s, and mapped the Orion nebula and other H 2 regions at a wavelength of 69 microns.[Fazio, et al, “A balloon-borne 1 meter telescope for far-infrared astronomy,” NASA. Ames Res. Center Telescope Systems for Balloon-Borne Res. p 38-50 (SEE N75-12735 03-74)].
In recent years I have moved almost entirely into the field of extra-solar planet research, as I’ve already mentioned. But I’ve already spent too much time in a long-winded answer to your question about the influence of Bob Leighton on my scientific career. In summary I really do think his philosophy that science is where you find it inspired me to move around quite a bit in the topics I worked on. I did make a few sorties in the direction of developing innovative instrumentation as Leighton did, but I think I recognized intuitively that I have nothing like his talent in that area. As an aside, one student of Leighton who does have that talent is Alan Title, and he has made enormous contributions to solar physics as a result. I may have had some success in interpreting and understanding data, but my efforts to develop or use new instrumentation have either not gone very far, or when they’ve been successful it’s because I collaborated with others who have substantially more instrumental talent.
I should also say that in the 1960’s and 1970’s, all the time I was exploring these other aspects I remained closely involved with the Solar Satellite project, which was producing wonderful new data on the structure of the solar atmosphere as seen in the extreme ultraviolet part of the spectrum.
Now, when you say “solar satellite,” what satellite are you actually referring to?
Well, there was a series of satellites, Orbiting Solar Observatories. The Harvard experiment on these satellites consisted of a spectrometer that could either scan the extreme ultraviolet spectrum of the sun between about 300 and 1400 Angstroms, or could pick a wavelength in that region and make a map of the distribution of emission over the solar disk. These instruments were developed by the Solar Satellite project, under Leo’s direction but with Ed Reeves and Bill Parkinson overseeing the detailed implementation by the engineering group. The first OSO Harvard was involved with was OSO-2, but our experiment failed at turn-on because of a short circuit in the instrument electronics. The second, OSO-4, was launched in 1967 and worked very well for about five weeks before failing, but during that time we made the first detailed maps of the structures in the solar chromosphere and corona, with about one arcminute resolution. Then in 1969 we flew a successor experiment on OSO-6, which worked for many months and yielded a wealth of data on solar phenomena in the extreme ultraviolet including flares, prominences, and so on. And finally we got, as you know, the wonderful data from the ATM mission on Skylab later on.
As you moved through the ‘60s here, how did your responsibilities or activities change within this group of solar workers? Were you always Smithsonian or did you have a Harvard appointment?
The second year I was here, in 1963, I was asked to teach an introductory graduate astronomy course, which I did. This was a challenge, since as I just told you a few minutes ago, I knew nothing about astronomy.
Yes. Well, maybe that’s how you learn?
I guess so. But, I don’t think I gave the greatest course, as a result. But I got through it, and I think the students learned something. In any case this involved an appointment as a Lecturer in the Astronomy Department, which I maintained for some years. Jumping ahead, when Leo left HCO the Solar Satellite Project was very important here. It was important scientifically of course, but also as a practical matter it was quite large and brought in substantial overhead to HCO. Leo left to take up an appointment as Director of Kitt Peak, but for a while he maintained his role as professor at Harvard and as principal investigator of Harvard’s ATM experiment on Skylab. But, when he decided to leave permanently he had to give up his professorship. So the Harvard astronomy department decided to find a new professor to replace him. They did a nation-wide search and somehow they came up with me, right in their backyard. So, I was appointed a professor in the department in 1973.
But, by then you were already Associate Director?
I actually became associate director just after I became a Professor.
July of ‘73. That’s when it was announced. CFA the reformulation.
Yes, I became a Professor in the department in July of ‘73.
I want to carry you back a little bit. I mean, this is a huge time jump up into the ‘70s. But, how aware were you of the complexities of the governance and operation of the Harvard/Smithsonian relationship between Goldberg and Whipple? In the ‘60s when you came.
Well, when I arrived in the fall of 1962, I had no idea about any of those complexities.
When did you become aware?
When I got to know Leo a little better he let down his guard about a few things, and I heard second-hand about conflicts within the organization. One memory I have is that Leo told me he had been trying to get a Harvard telescope in Hawaii, but that Don Menzel, who was HCO Director, had some independent discussions with the Harvard Provost that somehow more or less scotched the deal. I didn’t then and still don’t know the details. Perhaps you do.
I’m trying to learn more about it. That was when there was a big problem also with the Observatory Council and Menzel. And, I don’t know exactly what it was for, but it was one of Menzel’s programs that the council wouldn’t support. But, that was before you got here. Maybe ‘64 or ‘65.
Well, as I said, I was on the premises as early as 1962 and so was here at the time you mention, but I was not aware of these discussions. But I do remember a time later on, after the 60-inch telescope was placed on Mt Hopkins, when Leo spoke to me and he was boiling mad because he had heard, second hand, about a deal that Fred Whipple had made with Aden Meinel at University of Arizona. Meinel had acquired six 72-inch telescope mirrors, and Meinel and Whipple had made plans to put them together into a large SAO-Arizona multi-mirror telescope on Mt. Hopkins. The thing is Whipple hadn’t bothered even to inform Leo about this. As I said, Leo was boiling mad. He said to me, “What if somebody comes up to me and says, ‘Tell me, what do you think of Whipple’s new telescope initiative?’ I would have to say, ‘I’ve never heard of it.’” He was really angry that Whipple didn’t clue him in as to what was going on. I’m sure you must know this story from other perspectives?
Yes. Leo Goldberg has indicated that in his oral history. I interviewed him, and Spencer Weart interviewed him in the ‘70s and ‘80s. But, we’re trying to fill in that history, because it’s very complex. There were a number of observatory proposals and some consortia proposals as well. And meanwhile, Whipple was moving on with his own consortium, which ended up with the MMT. Who knew what and why and how is a difficult thing to sort out and whether it’s even important that they knew it or not. But what I think is important for me to better appreciate is the degree of contact you felt you had with Smithsonian and Smithsonian programs generally at your level of work. Did you feel as if there were a lot of strangers in the house here that you had no idea what they were doing or did you have a pretty good idea what everybody was doing?
Well, I had a rough idea what most people were doing, but the place did seem full of people who didn’t interact much scientifically. The combined SAO and HCO was a huge place with lots of different areas.
Well, for instance, the satellite tracking people. There were quite a few of them around. There was a whole…
Well, I and most of the scientific staff were at 60 Garden. They were down at 185 Alewife, which was pretty removed. I didn’t see much of them.
Oh, that’s true. The Computation Center was there. So you had very little contact with any of them?
That’s right. My main contact with the Satellite Tracking folks was during a short time in 1966 when they supported the eclipse experiment I mentioned, which we took to Peru and set up on the Altiplano not far from the SAO satellite tracking station in Arequipa. The satellite tracking folks provided critical support to all the logistics of the expedition. I built this with Jacques Beckers at Sac Peak. I got enormous support from Chuck Lundquist and Tillinghast in building this thing. They gave me a pot of money and they good engineering services. Chuck came and said, “Yeah, you got the money, go for it.”
Moving into this period of reorganization when clearly Leo Goldberg and Fred Whipple were not communicating, which is generally what the record said, there was an OMB audit of the Smithsonian in 1970. They asked: “Is the SAO a proper Smithsonian organization or should it maybe better be part of NSF?” That sort of thing. And, OMB did a study of that.
At the time I was totally unaware of that.
Okay. Then, there was a series of visiting committees where a number of people testified, and I think you were one of the ones who did testify about the relationship between Smithsonian and Harvard?
And when would this have been?
This would have been ‘70 to ‘71.
So, at that point I was not yet on the faculty at Harvard. I was not an Associate Director either, because CFA didn’t yet exist.
Right. Were you paid by the Smithsonian?
Yes, I was always paid primarily by the Smithsonian. Later, as a Harvard professor, I received a token salary support from Harvard, but it was only a few thousand dollars. I’ve never had a significant Harvard salary.
Did you ever feel like a second-class citizen?
No. I had no gripes. I got the support I wanted. I was given complete freedom academically. I could do what I want. Nobody told me what science to pursue. Never did I feel like a second-class citizen. In fact, I think a tenured civil service job at SAO is very much a first-class appointment.
So, would you characterize this saying you had no role to play in the reorganization? The creation of the CFA.
No, I was not consulted. And, I didn’t expect I should have been. At the time I didn’t feel part of the management in any sense. I was basically an independent scientist who had this nice research job. I got to do what I wanted; I got paid well. I had complete academic freedom so that basically I could write my own ticket. I felt that was really neat. I sensed that this was a very desirable position compared to most positions.
So you were, you were happy as a clam, basically?
Then, then in the time frame that led up to the July ‘73 period when the Center for Astrophysics was formally announced — actually, people were discussing it in late ‘72. That’s when George Field sent this proposal around. And, I don’t know if that rings a bell at all?
I think I have seen this document, but probably not at the time. I think I may have seen it later. For example, as recently as a couple years ago, I believe, this surfaced in the context of the discussion of Irwin Shapiro’s Parity Plan.
I have the document here of the original Ad Hoc Committee on the Relations Between Smithsonian Astrophysical/Harvard College Observatory and the Department of Astronomy. And, indeed, you were not one of the people who gave testimony. Those included Alexander Dalgarno, David Layzer, John Danziger, John Wood, Ed Lilley, Gene Avrett, Charles Lundquist, and three Harvard graduate students in their last year.
Do you happen to have their names, just out of curiosity?
Catherine Cezarski, Eric Chipman, and Jeffrey Hoffman.
This took place — this was a meeting on January 22 and 23, 1971. Dean John Dunlop was acting as chairman for the Harvard side, and Undersecretary James Bradley was representing Secretary Ripley. They had this committee. The committee was Greenstein, Kuiper, Purcell, Salpeter, Simpson, and Lyman Spitzer. So, I take it you just were not, you weren’t involved?
I wasn’t involved. But I’m not surprised that some of my cohorts, such as Gene Avrett, were. I presume that the committee wanted to get representative SAO and HCO scientists from different areas of the two Observatories, they could have picked Gene, or me, or Owen Gingerich, or any of a number of others, and they picked Gene.
Were you in the same group as Owen? Owen was doing stellar atmospheres.
I guess you are referring to the Stellar Atmospheres group led by Chuck Whitney. And, that would be a reasonable expectation since it was Chuck who hired me. The Stellar Atmospheres group consisted of Chuck, Gene Averett, George Rybicki, Owen Gingerich, Steve Strom, Wolfgang Kalkofen, and perhaps one or two others. But this was much less formal than the scientific divisions that were created later when CFA was formed. The emphasis of the group was on calculating theoretical radiative transfer models of stellar atmospheres, including the solar atmosphere. But this was not at all my area of expertise or interest. My background was more oriented toward observations and their interpretation, as I’ve already described in some detail. I had spoken to Chuck about my observational work with Leighton on the velocities in the solar atmosphere, and so he knew what he was getting. So I believe he hired me without any expectation that I would change course and do theoretical radiative transfer calculations of stellar atmospheres.
Because they were doing abundances, cross sections, that kind of stuff?
Right. And also, perhaps because I very quickly become focused on the extreme ultraviolet observations with the Solar Satellite Project, I didn’t feel myself part of any formal Stellar Atmospheres Group, with Chuck. So, I occasionally touched base with Chuck, and to a lesser extent with Fred Whipple, who as SAO Director formally had hired me, but I thought of myself as pretty much an independent research scientist, like Giovanni Fazio, or other SAO scientists who were quite independently doing their own research. I didn’t feel formally part of any group. Of course some of my work was relevant to the theoretical stellar atmosphere research. For example the infrared eclipse experiment I mentioned earlier had some relevance to the theoretical models of the location of the temperature minimum above the photosphere, and likewise my work with Wolfgang Kalkofen on determining the temperature of the chromospheric layers producing emission in the Lyman Continuum, as we observed in the Harvard solar satellite data, fed directly into Owen’s creation of the “Harvard-Smithsonian Reference Atmosphere”, which stood for many years as the definitive one-dimensional model of the temperature structure of the solar photosphere and low chromosphere.
But then everything changed when Field created the CFA, because you created groups, you created divisions? And you became associate director of one of the divisions?
Yes, as I mentioned earlier, I was appointed as a Professor in the Astronomy Department after Leo left. This happened almost simultaneously with my being becoming an associate director of CFA. When I discussed the associate director position with George Field, I recall he was initially thinking that this division of the new CFA would be the Solar Division, which would essentially carry on the work of the Solar Satellite project. But in discussing this further with George, the idea arose of combining the Chuck Whitney’s Stellar Atmospheres Group along with the Solar Satellite Project in the new division, which would then be called the Solar and Stellar Division. That idea had obvious appeal so that is what was done, and indeed that Division has stood the test of time, with the more recent addition of “Planetary” to its name and scope.
As for my own appointment as Professor in the Astronomy Department, one day in the spring of 1973 Alex Dalgarno, then the Department Chairman, asked me to come to his office and made me the offer of a professorship in the Astronomy Department. In making the offer, Alex made it clear that this offer was totally independent of any other offer that George Field, as the new Director of the combined observatories, might be making to me in the next day or two. I understood that this might have to do with some sort of position within the combined observatory structure, but again, Alex made it clear that that was a totally different issue. So confronted with Alex’s offer of a professorship out of the blue, I gulped and said, “Gee, Alex. That sounds great. I accept.” It was only a few days later that George Field offered to me, quite independently, to be the Associate Director of the proposed Solar Division of the new Center.
Of course I was delighted with the Professorship appointment, which I maintained for many years. As you know, I’ve recently given up that position. And to be honest I never enjoyed formal classroom lecturing all that much; it seemed to take an inordinate time to prepare a first-class lecture. And in fact in the early days, just after I accepted the appointment as Associate Director of the Solar and Stellar Division, I am afraid I threw myself into that role, somewhat at the expense of my lecturing duties. I remember a year or so after taking up the professorship, telling Alex, who was still the department chair I guess, “I seem to be spending an awful lot of time on my Associate Director duties,” and Alex was scandalized. He said something to the effect that, “The duty of a Professor is to profess, and it’s scandalous if the administration of CFA takes you away from your prime obligation as a Professor.” So, he sort of read me the riot act gently.
Did you teach?
Yes, of course. But as I said I considered formal lecturing an obligation that required a great deal of preparation. I guess it’s all a matter of your personal psyche. I was much happier, and I think more successful, in working on research projects with individual students, both undergraduate and graduate, and also with postdocs, and this I have done throughout my career.
Interesting. Now, you got very involved in the ‘70s also in the Interagency Task Force. It ended up with a report in 1974 on the state of solar astronomy. And, it was almost like an intergovernmental thing. It was many different agencies.
I’m sorry I’m a bit hazy on the details here. I think you may be thinking of the Interagency Coordinating Committee on Astronomy, if I have the name correctly. As I recall, this committee was constituted to recommend how to deal with Sacramento Peak Observatory, which at the time was operated and funded entirely by the Air Force. The Air Force felt that Sac Peak was no longer central enough to their mission, and was looking to some other federal agency to take it on. I believe there were representatives from NASA, NSF, the Smithsonian Institution, and perhaps other federal entities. George Field was not very enthusiastic about the idea of taking on Sac Peak, and after some further discussions we agreed that SAO would not offer to step up to the plate. I think the upshot of the committee’s deliberations was to conclude Sac Peak was a very valuable scientific resource and recommend that NSF take on the operation. And, after a further committee study as I recall, this was done, with management by AURA and funding coming by a combination of NSF and Air Force funds.
Right. But, there was a big issue in the termination of the OSO series, as I understand it. I’ve interviewed Ball people and various other people. The only person that I never was able to meet, unfortunately, was John Lindsay, of course. But, OSO was a great continuing program and the way the Ball Brothers people say it was a shift in contractors. Ball didn’t get the contract for the later OSOs. But, you were one of the principal investigators, instrument scientists, for one of these OSO programs that didn’t fly, so to speak. Does that ring a bell? This was before this task force, I thought.
Well, my recollection of this time is pretty fuzzy, I’m afraid. But as I recall, around 1972 the Solar Satellite Project did indeed develop a proposal for a more advanced spectrometer to be flown on OSO-J. This would have had much higher spatial and spectral resolution than the OSO-6 spectrometer, so that one could even measure velocity fields in various EUV coronal lines. I think Leo Goldberg was PI. I was not a lead player, although I was doubtless involved in some capacity on the investigation team. I think the instrument was tentatively selected for flight on OSO-J. But then something happened which led to Ball Brothers losing the contract for the OSO-J mission, and OSO-J never flew. And in fact that was the end of the OSO satellite series, even though additional missions had been on the drawing board. I’m afraid I’m not up to speed on the details. But this setback, I think, was not a major problem at Harvard, because at the time we were ramping up for the ATM mission on Skylab, which became all-consuming, leading up to the launch of the mission in mid-1973 and a very intensive 9 months of observing activities centered at the Johnson Spaceflight Center, including not only observations with the Harvard instrument alone but also coordinated observations with the other instruments on ATM. Then, after Skylab we proposed for the Solar Maximum Mission, with Ed Reeves as the PI. This proposal was successful, but unfortunately the project ran into fatal problems.
Oh, what happened?
Well, the project was finally cancelled. We had major overruns. The instrument was quite complicated, recall involving a new micro-channel plate detector under development by Gethyn Timothy with the help of Ball Brothers; in addition I think there were new spectrometer optics, so there was a fair amount of new development required. We planned to build this in-house. Subcontracting to Ball Brothers would have been a possibility, but we thought we could do it in house, since we had a great deal of technical expertise in our engineering staff which we had assembled for Skylab. But in the end it was NASA’s judgment that the technical problems could not be resolved while still meeting the cost and schedule requirements, and they cancelled the experiment. Those were not happy days. Eventually the Solar Max mission flew without the Harvard experiment aboard.
What kind of deliberations went on in terms of how to either fix the problem through program management or move in a different direction?
Well, there were many discussions between the solar satellite project members, and Ball Brothers, and the program overseers at NASA, trying to see if we could de-scope to keep within time and budget and retain the key science. I recall there was ongoing consideration of turning over the entire job to Ball Brothers, but upon reflection we still thought we could do it, so we elected to keep the main portion of the development in house. But NASA did its own technical review and decided to pull the plug.
Looking at your vitae you stuck pretty much with the sun through certainly this whole time. But, I’m wondering if you started getting more and more interested in the sun as a star. Because, I see a series of articles by you; Solar Phenomenon, Stellar Applications, and things like that. How was this growth of awareness of the use of the sun as a star developed? Did it develop here or how would you characterize it? How did you become aware of the need to go beyond the sun or use the sun as a basis for studying stars?
Well, it’s a pretty obvious extrapolation, of course, and so it’s not surprising that I moved in that direction. A lot of people did that and I was one of them. I think the most significant thing that pushed me in that direction arose from a scientific meeting at Santa Fe that I attended, around 1980 I suppose, which was also attended by solar researchers from Sac Peak and Kitt Peak and from the High Altitude Observatory and a few other places in the southwest. One person who attended was Art Vaughan from the Mt. Wilson Observatory, whom I had met years earlier while at Caltech. Art and I talked in great detail about Olin Wilson’s observations of the analog of solar activity cycles in other stars. Wilson had started a long-term program of roughly every month monitoring the emission of the H and K lines of ionized calcium in other stars, which everyone knew were strong in the solar chromosphere above magnetic active regions. And that program was showing that other sun-like stars had cycles of chromospheric activity, with characteristic timescales of order a decade, reminiscent of the solar 11-year activity cycle. Furthermore, when he looked at the H and K data on a nightly data, it was clear that the H and K emission varied on shorter time scales, due to the rotation of the stars, which caused the emission to increase when a stellar magnetic active region rotated on to the stellar hemisphere facing the earth. So this was a way to measure stellar rotation periods. And another scientist from the High Altitude Observatory, Andy Skumanich, was writing interesting papers about how the strength of stellar activity as shown by H and K lines seems to track the rotation rate of stars — the faster the rotation, the greater the activity. I found this all very exciting. And, so I had lunch with Art Vaughan at the Santa Fe meeting, and we discussed how important it was that Art was continuing Olin Wilson’s stellar activity cycle stuff since Wilson was now retired. I thought this was a very promising idea, so when I came home I began working to help make that happen.
I tried to get some support for that project through SAO, as a matter of fact. I remember going down and talking to David Challinor about getting some funds directly from SI, and I believe I got a little support from NSF. Also Sallie Baliunas at SAO had already become very involved with the Mt Wilson program, and in fact she played a pivotal role in the program and its continuation for many years. She deserves enormous credit for the continuation and success of this program. Also, I became interested in some work by Peter Gilman, at the High Altitude Observatory, about the predicted relation between stellar dynamo activity and the Rossby number, which is the ratio of the stellar rotation period to the convective overturn time within stellar convection zones. The H and K line data from Mt. Wilson gave information the stellar rotation periods, and the spectral type of the star gave information about the convection turnover time, using Peter’s calculations. This all came together in a paper which Art, Sallie, Lee Hartman, Doug Duncan, and I wrote in I wrote in 1984; this laid out an empirical relation between stellar spectral type and rotation rate on the one hand, and on the other magnetic activity as shown by H and K line emission.
That’s the Rotation, Convection, and Magnetic Activity in Lower Main Sequence Stars? APJ 1984, 279.
Yes. And it turns out, I suppose because this paper gave a simple empirical recipe to describe how the rotation and activity are connected for stars of different spectral type, it became a useful tool for all sorts of stellar investigations, including for example the X-ray emission from stellar coronae. The relation we came up with is purely empirical, but it seemed to hold up pretty well, and it is pretty widely used even to this day more than twenty years later.
What I’m curious about though is that one can see a loose timeline connection that really, if I got it right, after SMM there was no large-scale solar project activity here related to space activity? Am I correct or am I missing that?
Well of course there was another activity that started within the Harvard solar satellite project, and which has come to beautiful fruition with Ultraviolet Coronograph Spectrometer on SOHO. Are you familiar with that?
SOHO, definitely, yes.
I think the germination of that was on an experiment that was flown on during an eclipse in 1970 from Wallops Island by a collaborative effort of the Harvard Solar Satellite project, Imperial College London, Culham Labs, and York University in Canada. A rocket with a far ultraviolet imaging spectrometer was launched into the eclipse path in order to record the flash spectrum of the solar chromosphere and corona. The experiment worked perfectly, and when the films were examined, I think much to everyone’s surprise, there was seen a bright extended emission at the wavelength of the hydrogen Lyman alpha line. I think no one anticipated this; they had expected to see mainly highly-ionized coronal species. But it didn’t take long to realize that what they were seeing was the result of emission from the very strong chromospheric Lyman alpha line, resonantly scattered off of neutral hydrogen in the corona. I guess the reason nobody expected this is that intuitively you would think that in the million-degree corona all of the hydrogen would be ionized. But singly-ionized hydrogen is a bare proton, so it can’t be ionized any more, and so no matter how hot the corona is there will always be some recombination back to neutral hydrogen. Now a key point is that the Lyman alpha emission from the chromosphere is emitted within a wavelength band of only about 1 Angstrom, so if the coronal neutral hydrogen is moving outward with a speed of a few hundred km/s, as it might be if it is carried out by the solar wind, then the wavelength of the Lyman alpha photons from the chromosphere won’t line up with the wavelength of the absorption by the hydrogen in the corona, and to the extent that the wavelengths don’t match up less light will be scattered by the moving hydrogen atoms. So you have a way of measuring the solar wind speed in the corona by this mechanism, which was called Doppler Dimming. Anyway, to make a long story short, it was an obvious idea, since we can’t rely on eclipses to come along very often, to fly a coronagraph that could occult the bright solar surface and allow the measurement of Doppler dimming. And John Kohl, who had been working primarily with Bill Parkinson and others in the shock tube lab at HCO, figured out a way to make an ultraviolet coronagraph that could do the job. This instrument was first developed and tested on some rocket flights, and this then led to the Spartan program, and ultimately to the Ultraviolet Coronagraph Spectrometer, or UVCS, on SOHO — which was launched more than a decade ago and is still going strong.
Oh, I see. So the Spartan was sort of a step to SOHO?
It turned out to be. You really ought to talk to John Kohl about this.
Yes. He signed the paperwork for donating that instrument to us. So, we, NASM, actually have the coronagraph from Spartan on display. Now I much more appreciate its role in development here. And, “you” being Smithsonian stayed in space solar physics?
Yes, SAO certainly has remained a major player in space solar physics. In that regard, I can’t fail to remark about the existence of SAO’s High-energy solar group, which began when Pippo Vaiana came to SAO in 1973 or 1974. This group has been and still is an extremely important player in space solar physics, under the leadership of Leon Golub and others. But I see we’ve completely used up our time.
Okay. Thank you very much. It was really a great session.