Notice: We are in the process of migrating Oral History Interview metadata to this new version of our website.
During this migration, the following fields associated with interviews may be incomplete: Institutions, Additional Persons, and Subjects. Our Browse Subjects feature is also affected by this migration.
Please contact [email protected] with any feedback.
This transcript may not be quoted, reproduced or redistributed in whole or in part by any means except with the written permission of the American Institute of Physics.
This transcript is based on a tape-recorded interview deposited at the Center for History of Physics of the American Institute of Physics. The AIP's interviews have generally been transcribed from tape, edited by the interviewer for clarity, and then further edited by the interviewee. If this interview is important to you, you should consult earlier versions of the transcript or listen to the original tape. For many interviews, the AIP retains substantial files with further information about the interviewee and the interview itself. Please contact us for information about accessing these materials.
Please bear in mind that: 1) This material is a transcript of the spoken word rather than a literary product; 2) An interview must be read with the awareness that different people's memories about an event will often differ, and that memories can change with time for many reasons including subsequent experiences, interactions with others, and one's feelings about an event. Disclaimer: This transcript was scanned from a typescript, introducing occasional spelling errors. The original typescript is available.
In footnotes or endnotes please cite AIP interviews like this:
Interview of Joseph Taylor by Patrick McCray on 2001 October 29, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/34397
For multiple citations, "AIP" is the preferred abbreviation for the location.
In this interview Joseph Taylor discusses topics such as: his family background and childhood; Haverford College; Fay Ajzenberg-Selove; Tom Benham; going on to do a degree in radio astronomy from Harvard University; working in the summer at the Harvard College Observatory on optical astronomy; quasars; pulsars; Leo Goldberg; Donald Menzel and Bill Lilller; Ed Lilley and Alan Maxwell; radio interferometry; lunar occultation; University of Massachusetts; Bill Irvine; Dick Huguenin; National Science Foundation; National Aeronautics and Space Administration (NASA); Dick Manchester; National Radio Astronomy Observatory's telescopes in Green Bank, West Virginia; Russell Alan Hulse.
I received your CV and I know that you were born the same year as my father, in 1941, in Philadelphia. I thought we would just start with some standard questions about your childhood and parents. Could you give me some background on your parents?
My father, Joseph Taylor, was born on the family farm in Cinnaminson Township, New Jersey, in 1914. The farm has been in the Taylor family and before that the Wright family since 1720. A Wright daughter married a Taylor in the late 18th century. My mother was born in 1915 and raised in the Germantown section of West Philadelphia. Her name is Sylvia Evans. They attended, respectively, Haverford College and Bryn Mawr College. They must’ve met there at the time, and were married in 1938.
What did your parents study in college?
Mother studied biology and my father, to be perfectly honest, I don’t remember what he majored in, if I ever knew; probably history, but I’m not certain of that. He became a school teacher. This was just before the war started. He almost certainly would’ve been a conscientious objector, if the issue had arisen; but school teachers were not called to serve during the war. This might have influenced his decision to be a teacher, although I think he had aspirations toward teaching from much earlier in his life. Mother devoted herself to the raising of a family. They were both the oldest of six children and produced six of their own. So I grew up as a member of a large family. Eventually there were eight children because my parents raised two young cousins whose parents were unable to care for them.
You mentioned that your father would’ve almost certainly been a conscientious objector. I’m curious what his background or beliefs were.
Both families, the Taylors and the Evans’s, were Philadelphia Quakers. The family histories go back nearly to the time of William Penn.
Do you have any particular recollections, either from secondary school or high school, when you began to think about science? Was it something that was an interest as a child or did it develop later on in life for you?
I was much attracted by scientific things and gadgetry as a boy. After my first seven years living in the Germantown area of Philadelphia, we moved to the New Jersey side of the Delaware River, back onto the family farm. This was in 1948. Located on a farm some miles from the nearest town, my older brother, Hal, and I did everything together. We did a lot of “experimentation,” with farm and electrical machinery in particular. We became interested in what you could do with the parts of a junked television or radio set, rebuilding them into radio receivers. We got interested in ham radio, became proficient in Morse code, and spent a lot of time doing that. I’m sure these things helped lead to my interest in science.
When you were in high school or perhaps younger, did you have any particular science courses that caught your attention?
I took the standard science and math courses as they came, in the normal school sequence, but mine was not a school with a wide range of options. I did the biology-chemistry-physics sequence. None of these courses was a standout or one that caught my fancy in a particular way. Going off to college, I thought I would be a math major. Of the things I had studied at that time, I had the most fun with math. I suspect that physics would have caught my fancy more at that time if the course had been more up-to-date. It was more like a late-1930s style physics course.
Certainly no quantum! Barely anything beyond ropes, pulleys, and inclined planes!
I’m curious, just to make a connection with something that you did later on, growing up on this farm with your brother Hal and doing ham radio and those types of things. It’s interesting with the later connection to radio astronomy. Were you building your own equipment in that sense and using the ham radio to do recollections?
We were building our own radios, to be sure. We enjoyed it a lot and became adept and well-read in at least the practical aspects of electronics. I hadn’t looked much at the fundamental physics, but I knew much more than how to deal with Ohms Law. I could design vacuum tube circuits. Transistors were just becoming a part of the electronics trade at that time, and I was not as good with them as with vacuum tubes. When you take apart a vacuum-tube television set, you can disassemble and use nearly all the pieces. That isn’t nearly so true with transistorized equipment.
You mentioned when you went off to Haverford for undergraduate that you entertained the thought of being a math major. What attracted you to that?
I knew I was reasonably good at math and got off to a good start that way. However, I soon discovered that I was having more fun in the physics labs than proving theorems in mathematics. I made the change near the end of my second year and decided to major in physics.
Why did you choose Haverford?
It wasn’t a carefully studied decision on my part. As I remember it, we mostly did what our parents and the school guidance counselor told us to do. Anyway, it had been family tradition for some generations that the men who were college bound went to Haverford. This was true of my father and his brother; it was true of my grandfathers on both sides of the family. It was a long-time family tradition. Family members on both sides had been involved with the founding of both Haverford College and Bryn Mawr College, again a reflection of the Philadelphia Quaker background.
Right, I see that later on you were on the board of managers.
Yes, I served on the board of managers at Haverford for about ten years.
Do you recall when you went off to college for undergrad, your parents or you having any particular expectations of what your career might be once you finished school?
No. My parents were not outwardly pushy in such ways. They gave us lots of support but not a great deal of active direction or even behind-the-scenes pushing that I was aware of. My siblings and I had many reasons to consider the teaching profession, because we admired the way my father went about it. After many years of teaching in elementary schools, he became a school principal. Ideas about education were close parts of our everyday lives. Hal and I both developed aspirations to do advanced degrees after Haverford. I must have felt a calling that pulled me toward a research-oriented professional degree. From there to becoming a college professor was a straightforward additional step.
Was Hal older or younger than you?
A year and a half older.
And he went to Haverford as well?
He did. He also majored in physics and went on to do a PhD in physics.
Interesting. Did you two room together in college?
No, but we did many of other things together. We played sports together and so forth.
Before talking more about your undergraduate time, I’m trying to flush out a little bit more of your home environment. It sounds as if your parents took a very active role in your education and were very concerned about it. Were you encouraged to read a lot as a child or were there particular things that you liked to read about?
We spent plenty of time reading for enjoyment and reading things that we needed to understand to pursue our hobby. We liked the classic books and read many of those. We liked participating in and reading about sports.
Did you have a favorite sport?
I played them all: soccer in the fall, basketball in winter, baseball in the spring. Also tennis and golf. Anything with a ball, it seems.
Pretty active. So you did your undergrad from 1959-1963 at Haverford. Were there any undergraduate teachers that you had who made a particularly strong impression on your or what you wanted to do?
Many fond memories! My favorite physics professor was Fay Ajzenberg-Selove, whose autobiography was published a few years ago. In it she gives a very good insight into the life of a woman physicist in a time when there were very few. In fact, I think that’s an AIP book, isn’t it?
It may be.
I believe so, but I could be wrong about that. A second favorite physics professor at Haverford was Tom Benham, who happened to be blind. Tom taught the electronics and electromagnetism courses in a way that most students will never have experienced because most students don’t take courses from blind professors. Tom lectured with occasional sketches on the blackboard (they weren’t very good, but we could make out what he intended). He lectured from Braille notes and gave us difficult problem sets which he graded by having us sit down with him, one-on-one, to our solutions. These were highly effective tutorial sessions, and were workable only because of the small class sizes at Haverford. They were a fine way to teach electromagnetic theory to undergraduate physics students.
That’s really an interesting way to learn. Could you give me some idea of how one of those one-to-one tutorials might work?
Tom taught the first semester of the main electricity and magnetism course by handing out a problem set for the full year, right at the beginning. The problems started with what you could begin to solve from chapter one of Paige and Adams, and they went as far as we would go in the book. Our assignment was to do a reasonable number of problems each week and set up a time each week when you would come in to report on them. It was understood that if you finished some number of problems — and I’ve forgotten what the number was but it was probably in the hundreds — you would get an A, and if you finished some smaller number of problems correctly you would get a lesser grade and so forth. So once a week I would go in to a session with Tom Benham and say, “I’ve done problems one, two, seven, nine, eleven, and seventeen from the section for Chapter 4. Do you want to hear about them?” And he would say, “Yes, tell me about problem seven.” So we’d go through my solution. I would tell how I’d set it up and how I did the integration or whatever was required. The problems were flagged with different numbers of asterisks. The ones with one star were more difficult than the ones without; those with two stars were harder still, and so forth. When you tackled one of the more difficult problems and hadn’t yet gotten all the way to a solution, you were permitted to come in and talk about how far you had gone and ask for some pointers on how to get on with it.
So for the particularly hard ones, if you’d only gotten to a certain point would he sort of help you?
He would often say what you might want to try next.
Tell me about the types of courses you took there as a student, physics-wise. What was being taught?
It was a pretty traditional physics department. The freshman physics course was much the way it is everywhere, even today, with mechanics in the fall semester and electricity and magnetism in the spring. I took that freshman year course, but as a sophomore I was thinking I would probably end up in the math department and did not take a physics course in the fall semester. By the second semester sophomore year I was starting to think of moving back into physics, so I took the second-level mechanics course. By then I had missed the atomic and modern physics course, which normally would’ve been taken in the fall of sophomore year, so I took that in my junior year. I then did an advanced E-and-M course, an undergrad quantum course, and a course in statistical mechanics and thermodynamics. Several others, too, including a course called “Boundary Value Problems in Mathematical Physics.” Lots of good stuff in that course, by another favorite teacher — Louis Green, the only Astronomer at Haverford.
Were there particular topics of study at this time in physics that you tended to gravitate to? Pardon the pun.
I liked them all. The lab courses were great; I enjoyed doing the advanced undergraduate lab, a quick run through some of the great experiments of modern physics. I found it fascinating to measure the velocity of light, to create x-rays, to measure radioactivity, and a few of the other special things we did. I was beginning to get a feel for real research-quality laboratory work as opposed to “tinkering in the lab”, which I was already pretty good at. I continued to develop mathematical skills during these years, but I formed the impression that most of the good math I learned was acquired in physics courses, not math courses. I discovered that the theorem-proving aspects of formal mathematics were not especially to my liking, nor was I very good at them, after all.
You mentioned working in the laboratory and building things. Could you say more about the type of work that you were doing there? Was that something you were particularly drawn to, this tinkering?
By tinkering I meant the building of electronics, mainly in connection with the ham radio hobby. This taught me skills with electronic circuitry that were useful later on in the research laboratory; but it was not the same thing as doing controlled experiments seeking quantitative results. Those were new skills I needed to learn, and I began to do that in these undergraduate labs.
Just to backtrack, something you said made me think of Sputnik. Sputnik happened in 1957, so you would’ve been 16 at the time.
I tuned it in on our ham radio set right away — within days or maybe even hours after it was announced.
What was your attitude and feel about that?
It was a lot of fun! Because of something my dad had been doing in his teaching, we had a tape recorder at home. I tape-recorded the Sputnik signal and took the recording to school and played it. That was great fun.
So the other students could hear it as well.
A lot of different things were happening in the field of physics, applied physics, at the time; the whole space race and all. I’m trying to sort of place your interests in the broader picture of things that were happening.
After his physics degree at Haverford, Hal went on to do a Master’s degree in meteorology at MIT. Partly because of what you were talking about, the space program beginning and interesting experiments and exploration possibilities going on in space, he went on from MIT to the University of Iowa to do a PhD in magneto-spheric physics with James Van Allen. Meanwhile, I was nearing the end of my years at Haverford and realizing that this fun time would end soon, and something needed to happen next. Going on to do a degree in radio astronomy at Harvard was the result of looking for an area of physics in which to do graduate work and trying to combine that with my interest and love of radio science.
Before we talk about Harvard, I’m sort of curious when you were 20 or 21, did you have any thoughts at the time of where your career at that point might go, between research or education, or where you would like to end up?
I wasn’t much given to thinking more than a year or two in advance. I thought about what to do next, meaning immediately next, but did not lay plans for more than several years down the road. I was focused on an advanced degree in some area of physics, probably radio astronomy, but I could not have articulated clearly whether I was picturing myself as a college professor or another sort of researcher. I barely knew what the possibilities were.
Well tell me how you applied to Harvard and why you chose Harvard. What was it about that institution?
I applied to two places for graduate work, Harvard and Cornell. I chose them because in the limited reading that I’d done — this would’ve been in the fall of 1962 — it seemed that the interesting radio astronomy results in the Eastern U.S., where I was focused, were coming from those places. I didn’t know about individuals much beyond having read a few papers. I was vaguely aware of Cornell being connected with the construction of a huge radio telescope in Puerto Rico. For several reasons, probably the strongest one being that a few close friends at Haverford were also heading off to Harvard, I decided that’s where I’d go.
Who were these people?
David Hunt; John Cole; and William Beik, who all entered the history department at Harvard. David, Bill, and I teamed up, the three of us rooming together in our first year in Cambridge.
What was your personal reaction to arriving in Cambridge from Haverford?
Big excitement, being out on my own for once! I arrived first, because I spent the summer at the Harvard College Observatory’s field station in Harvard, Massachusetts, doing optical astronomy. I was awarded a small stipend for this summer course; there was an opportunity to hear some lectures during the daytime and stay up late at night, taking photographs of galaxies.
Was that your first brush with optical astronomy?
Almost. Hal and I had built a telescope or two as kids, and pointed them at the moon and at the neighbors and things like that.
Did you do the mirror polishing and all of that?
Yes, we did.
I’m trying to think of those wonderful books, like Amateur Telescope Making.
I think we got a mirror blank that was almost finished and just did the final polishing.
What were the telescopes like at Harvard College Observatory?
Not very big, but much bigger than anything I’d ever used before. They were also not very modern, but they were of roughly professional quality, so it was a good first exposure to real astronomical instruments.
Had you considered branching off into astronomy before this?
Some sort of astronomy, yes. I was never very serious about optical astronomy, because I was already persuaded that the new radio astronomy field, which had just recently opened, was a fertile and attractive ground. That’s where I was heading. During that summer we also had access to a single radio telescope, a 60-foot antenna outfitted with a very good receiver for the neutral hydrogen line at 21 centimeters. I worked with Sam Goldstein, the local PhD staff member. Quasars had been discovered just a few months before; it was not known for sure whether these objects were galactic or extragalactic. One of the experiments we did over the summer was to look for neutral hydrogen absorption lines in the spectra of quasars. These lines would, if found, show that the quasar was at least more distant than the absorbing gas. By sorting out the radial velocities of the gas clouds and using a model for differential rotation of the galaxy, we were able to show that at least the first two or three quasars were more distant than the most distant spiral arms of our galaxy, and therefore were probably extragalactic objects. That work probably would’ve been publishable, although someone else published it at about the same time, so we never got around to doing that.
When you arrived at Harvard, how were you supported? Did you have a fellowship?
I had a Woodrow Wilson Foundation fellowship starting in the fall. Over that summer I had a small stipend for the summer school course.
Did you work as a research assistant or a teaching assistant?
Later in my Harvard years, but not that first year. The Wilson Foundation fellowship was enough.
So when you arrived at Harvard in 1963, Leo Goldberg would’ve been the department chair, I think.
Leo certainly was before I left, but not at the start. Donald Menzel was Director of the Observatory, and Bill Liller was department chair.
Oh, that’s right; Goldberg was there.
Yes, I think Menzel was the director in 1963.
Okay. Did you have a lot of interaction with either of those?
Very little with either, during my time as a student; but more with Leo near the end. I stayed on at Harvard as a post-doc for a year and a half after finishing, and I certainly had interactions then with Leo. I would have heard lectures from both of them, from time to time, but I didn’t take a course from either one.
A personal interest of mine is Leo Goldberg and his research career, and I was wondering if you have any interest in it.
Leo certainly influenced several of my contemporary students — Ben Zuckerman and Pat Palmer, for example — because at that time that the emission and absorption lines from highly excited hydrogen gas clouds was recognized and widely studied. These were the so-called “recombination lines” in which a free electron attaches itself to a proton, forming a hydrogen atom in a highly excited state, and then cascades downward through lower energy levels…
...combination lines to quantitative detail early on, and that set of observations.
Okay. Who were some of the professors at Harvard that you had a lot of close interactions with?
The radio astronomy faculty was just two, Ed Lilley and Alan Maxwell. In the first year I attended a series of seminars organized by Alan Maxwell, and enjoyed them a lot. Alan lectured occasionally in this series, but mainly he brought in a series of outsiders. Every week or two another radio astronomer from somewhere else would be at Harvard for a week or so, and would give two or three lectures. There would be a social event and lots of “office hour” time when students could drop in and talk with the visitor. It was a great way to provide students with access to the active and productive radio astronomers of the day — leaders who were doing things that would soon show up in Nature or the Astrophysical Journal. It was a great introduction to the people that were setting the agenda in the field during this time. Ed Lilley also gave a series of lectures, a more systematic presentation of the field of radio astronomy. This was a self-contained course, and it was enjoyable as well. Ed was not an extraordinary lecturer, but the course content was well thought out. You asked about the visitors in Alan Maxwell’s seminars. I’ll have to scratch my head to recall very many of them. Cyril Hazard was one; he was working on lunar occultations and sparked my interest enough to get me into the project that developed into my thesis research. John Bolton was another, and Paul Wild — both Australians. Bolton was based at Caltech then. Dick Thompson, who had been Maxwell’s contemporary at Jodrell Bank, would’ve been there. Sandy Weinreb, from MIT, who built the first digital auto-correlator for use in radio astronomical spectroscopy. Derek Tidman, a solar physicist from Maryland. Geoffrey and Margaret Burbidge. That’s a quick rundown of a few of them. There were certainly quite a number more.
While you were a graduate student, what were some of the big topics in radio astronomy that your professors and students were talking about?
This was a time when discrete radio sources were showing up in catalogs in large numbers. The 3C Catalogue came out at about this time. The “2C controversy” (with a lot of spurious sources, as had been shown by the Australians) was about over, and most of the discrepancies had been worked out. Radio source positions were generally not measured accurately enough to provide good chances for optical identification, so one of the outstanding tasks was to measure source positions at the arc-second level, or a few arc seconds at worst, so that one could then go to a sky survey print and try to connect the radio source with something visible. Radio interferometry was starting to be widely used. In the US, Caltech especially was in that game. They could determine source positions to within arc-minutes, but not yet with arc second precision. They were still dealing with instabilities of local oscillator chains and phasing lines, and they hadn’t quite sorted out all those details. So, for a brief time, the technique of lunar occultations was an attractive way to locate some sources with arc-second accuracy. Occultations also provided a means for making crude maps of the sources.
Tell me about the lunar occultation method.
Basically, you point a radio telescope at a small-diameter source at a time just before the moon crosses in front and cuts off the signal. Owing to the wave nature of the signals, the edge of the moon causes a diffraction pattern. Peter Scheuer at Cambridge University had worked out a detailed procedure for removing the effects of diffraction and recovering the one-dimensional brightness distribution of the radio source, in a direction perpendicular to moon’s limb. He showed that the angular resolution was not limited by diffraction, but rather by the signal-to-noise ratio. If you were persistent and observed occultations of the same source a number of times, you’d get a different angle each time. In principle, a number of these one-dimensional maps could be put together to make a two-dimensional map. I worked out some of the details of how to do this in my thesis, and I made some of the first two-dimensional maps using lunar occultation techniques.
Who was your thesis advisor?
Alan Maxwell supervised my thesis, and he was a great advisor. He opened doors, helped me to gain access to observing time on big telescopes, and introduced me to the right people. He then let me my own way. We talked almost every day, but we didn’t directly collaborate very much. At most there may be one or two papers that have both of our names on them.
I noticed your first long paper in 1966 on Lunar Occultations of Five Radio Sources. It says, “Harvard Radio Astronomy Station, Fort Davis, Texas.” Tell me about Fort Davis, Texas.
Alan Maxwell spent part of his time at Harvard but a significant amount in Fort Davis, Texas, where he had built the Harvard Radio Astronomy Station. It was originally built as a solar radio astronomy facility with a 24-foot “dish” antenna that followed the sun every day. There were a number of other antennas, log periodic or Yagi-style arrays that also followed the sun. Together this collection of antennas covered a wide spectrum from some tens of megahertz up to a gigahertz or so. Sweeping radiometers recorded dynamic spectra of the sun, measuring solar flares and their spectral characteristics over more than a decade in frequency. The output medium was photographic film: slowly moving 35-millimeter black-and-white films passed over the focal plane of a specially built camera focused on the face of an oscilloscope, for each one of these swept-frequency radiometers.
So it actually took a picture of the oscilloscope?
Yes, in a moving fashion. Technicians in the laboratory scanned these films, after they’d been developed, of course, and recorded the times and characteristics of solar flares. Somehow Alan raised the money to build a much larger telescope, an 85-foot parabolic reflector. There may have been early plans for it also to do some solar radio astronomy, but the main push was to have a general-purpose telescope at the same site for radio astronomy of other types of objects. Some of my early lunar occultation observations were made with that 85-foot telescope.
So would you go down to Texas and stay there for an extended period of time?
Yes. We would calculate in advance the expected times of occultations of interesting sources. You basically looked at the path of the moon for the next few months and worked out what good 3C sources were in the path. I would make a list of times when observable occultations would occur. Calculations were done for the Fort Davis site, for Green Bank, West Virginia, where the new 140-foot telescope had just been completed, and in a few instances also for the Haystack radio telescope in Massachusetts, another brand new instrument. Most of my observations were made at Fort Davis or the 140-foot telescope.
Was it difficult to get time to do your observing?
Yes and no. Usually there was a significant lead time involved, at least several months, but occultations are predictable events. We had to plan carefully, but observing time was usually made available. At the telescope and occultation observation was a high-pressure time, because you only get one chance. If something didn’t work, you were out of luck on that occasion. You might have another chance a month or two later, but you might not.
Would you prepare the proposal yourself or would it be something your advisor would prepare that you would collect the data for?
I prepared the proposals. They were not lengthy; something like one- or two- page letters to the Observatory director. You outlined what you wanted to do, why it was scientifically important, and sent it to the director… and time would usually be scheduled.
I think historians have some idea of what using a big optical telescope is like from this period in time, but I don’t think there’s a whole lot of discussion or information on what actually being a radio astronomer was like in the 1960s. Could you say something about what a typical night would be like?
Or day, yes, okay. Thank you.
These radio telescopes were brand new, so they were equipped with technology not yet available at many optical observatories. We used to joke about the “20-year time constant of optical astronomers,” folks who hadn’t yet introduced digital equipment into their observatories. Or maybe a 50-year time constant, when we weren’t feeling very generous. As an example, digital readouts of the telescope’s pointing were becoming common in radio control rooms. However, computers were not yet embedded as part of most telescope control systems. These systems were partly analog and partly digital: analog servomechanisms but digital readouts, and in some cases analog machinery to convert from polar coordinates to azimuth and elevation. The 85-foot Fort Davis telescope and the 140-foot Green Bank Telescope were built with polar mounts because of the perceived difficulty of doing coordinate conversions in digital computers — or because of suspicions held by many engineers and astronomers about the reliability of digital computers. The 140-foot telescope was much more difficult to design and build because astronomers insisted on a polar mount. It was the last large telescope ever built that way. Since then, all big dishes have been built with azimuth/elevation mounts
I wasn’t aware that it had a polar mount. So it really followed the tradition, then, of sort of the optical telescopes in that sense.
Indeed, only one motor was required to track any astronomical position. Anyway, to get back to our observing mode… The coordinates of the source I wanted to observe would be written down on a piece of paper and handed to the telescope operator, who would dial them into digital thumb-wheel switches. The tracking system would then attempt to track that position… I was observing at relatively low radio frequencies, wavelengths from twenty centimeters to a meter or so. Therefore, the telescope beam widths were relatively large. The minimum would’ve been half a degree or so, so tracking accuracy was never a serious issue; the tracking was essentially perfect. I usually had a computer printout in front of me with the expected position of the moon as a function of time, and we’d watch the effect of the moon coming into the beam, typically producing some change in signal level as it did so, because its temperature would be different from that of the cold sky behind it. We always had a moving paper strip-chart recorder on the detected output of the radiometer, just to keep an eye on what was going on. Sometimes this was the only recording mechanism; at other times we also had a means for recording the data in digital form. Some of my occultations were analyzed from the analog strip chart records, digitizing them with a ruler or by counting squares on the graph paper. Others were reduced from digitized data as it was recorded on magnetic or paper tape.
This is a picture from one of your observations. This is a strip chart recording?
Yes, that’s a strip chart recording. The slope here is the moon drifting out of the telescope beam, or perhaps temperature variations in the receiver causing some instability. That slope would be removed during the processing. The abrupt increase to a higher signal level near the middle of the chart is where the radio source reappeared from behind the moon. There is probably a small amount of diffraction there, although it’s hard to be sure because in this case the signal-to-noise ratio was not very high.
So at this point the source is behind the moon and then it reappears here?
Exactly. There’s another region over here where there is some structure and perhaps even another re-appearance. This may be a double source with a bridge of emission between the two components. I’ve forgotten whether we restored that one eventually into a picture that shows additional components — I’d have to reread my notes or my thesis to be sure.
So this would be an example, then, of something that would then be converted into a digital form?
Would you do that conversion yourself or would that be something —
No, I did it myself.
Okay, how did that go?
It takes a few hours to do it carefully. You draw some lines on a piece of paper, make columns, and start writing down numbers as you proceed along the chart. You then go through it a second time and make sure that the numbers agree, and you check any discrepancies. You had to be careful to note the accurate time marks on the chart, and to take into account the speed of the chart paper.
You mentioned at the beginning, when you were describing what an observing run would be like, the 20- to 50-year time lag between radio astronomers and optical astronomers. Why do you think that lag existed at that time?
That was silly talk from brash young scientists having fun with their new equipment, and disparaging their colleagues still doing things the old way. It was true that not many optical telescopes had computers or digital readouts associated with them. Radio telescopes were all new, since the field was new; they tended to use new technologies that hadn’t yet found their way into the optical observatories. One more point is probably relevant — Since radio telescopes are fundamentally electronic to begin with, the detected signal comes out in electronic form. Electronic analog-to-digital conversion was well understood and was used early-on in radio astronomy. Optical astronomy is not so inherently electronic. Photography was still the main recording technique at the time. Digitizing the results was not a straightforward thing to do, or even an obviously desirable thing to do. That was another reason for digital methods coming later to optical astronomy.
Do you recall there being any concern in the radio astronomy community about the complete reliance on electronics and using relatively new technologies to collect data?
No. I think we were enthusiastic about going in that direction. We thought it was the right way to go and that these modern techniques would in time be adopted in other areas as well. I do remember the concerns expressed by some about using digital computers to actually point the telescope. That was certainly the reason the 140-foot was built as a polar-mount. That sort of worry was already diminishing, I think, and if the 140-foot design had been frozen five years later, it would not have been an issue. Computers were developing very rapidly at the time.
Do you recall there being anybody who was particularly instrumental in taking some of the techniques of radio astronomy and helping transfer them to the optical community? People who would serve as conduits for that?
In those days most individual researchers identified themselves with a wavelength region and pretty much stayed there. Today, someone studies a class of objects and collects radio data or optical data or x-ray or gamma ray data, whatever is important to solve the problems. That sort of person can very easily take the techniques from one wavelength or energy range into another and help to cross-pollinate with the people working on instrumentation in those areas. This wasn’t happening so much in the 1960s, and that is one of the reasons it took longer for good ideas to spread to other subfields.
I just have one last question about the practice of radio astronomy. I understand that some optical astronomers were hesitant to have other people collect their data for them. You mentioned in your case that you would give the coordinates to the telescope operator and he would point and do those. Was there ever any concern in the radio astronomy community of having people collect your data and then give it to you in a certain form?
I’m not aware of any big differences between optical and radio people in that respect. It is true that skilled optical observers like to take their own photographs, to do their own tracking. Those were good mechanisms for quality control of the data they were trying to acquire. Radio astronomers were also careful about things that mattered. Giving the coordinates to a telescope operator was a perfectly sensible thing to do: let him take care of it, if telescope pointing is not a critical issue — as it wasn’t in these observations. Other experimental tasks such as adjustment of the radiometer, being sure that levels are set correctly just before the expected time of occultation… these were not things I would have assigned to someone else. I wanted to be sure that if someone made a mistake, I made it myself.
More back to your experiences as a graduate student, were you building any of the equipment that was being used at this time?
Yes, some. I built some low-noise preamplifiers for the Fort Davis Telescope, for example. If I wanted to use a frequency that wasn’t already available or to have a better noise figure than presently available, I would build something. But I wasn’t in the shop every day, and I wasn’t building things that had long development times. Alan Maxwell started giving me the task of dealing with vendors and ordering equipment. When we decided to provide an analog-to-digital conversion system with a magnetic tape-recording facility, so that the strip charts would not have to be digitized by hand, I was given the job of procuring whatever was necessary.
Were there companies that existed that would provide the specific tools that you needed, or was it a matter of getting something general and then adapting?
There were some such companies, largely sprung up around the space program as it was then developing. So yes, there were some small companies that would make things to order, to your specifications.
So you began to wrap up your thesis work around 1968. You’d published some papers by then. Do you have any particular recollections of finishing your thesis or what that process is like?
I should say just a word or two about those papers. I published the results of the occultation observations made during my graduate years. Some of those papers were coauthored with either Marvin DeJong or Sebastian von Hoerner, both at Green Bank. I’ve forgotten whether Sebastian asked to be an author on one or more of these papers, or not. He acted in some ways as a secondary thesis advisor. I was often at Green Bank for several weeks at a time, making several occultation observations, and von Hoerner was the person I would go to for advice. He had done some occultation observations and was familiar with the restoring procedure proposed by Peter Scheuer. He had produced some Fortran code that he shared with me, which I then adapted for the purposes I needed. It was a very good early collaboration for me.
Was he on your dissertation committee?
No, but he could easily have been. The normal process at Harvard was to have a four-person thesis committee, three of whom would normally be from the observatory staff and one from outside. In my case the outsider was Bernie Burke, from down the road at MIT.
Did you have many interactions with him, then?
No, although I was very much aware of Bernie. He was always fun to be around. For example, during Alan Maxwell’s sequence of radio astronomy seminars, the MIT folks would often attend. There would be a dinner or lunch or something and Bernie was always there and usually the life of the party. The students were well aware when he was around.
Who else besides Bernie Burke was on your committee?
Gosh, that’s a good question. I’m not sure I can remember. Alan Maxwell would certainly have been one of them. There must’ve been two others but I —
They must not have given you two —
I would guess Chuck Whitney, probably, and maybe David Layzer. I remember Ed Lilley was not, though I don’t remember why; he probably wasn’t around on the day of my defense. By tradition there’s always an outsider’s question that has nothing to do with the thesis. That seems to be the tradition almost everywhere. Bernie was the one that asked it, and it turned out to be a softball question. It was something to do with converting flux densities to brightness temperatures.
As you were finishing up, there was sort of a question in a variety of ways throughout, but at this point did you have any sense of what direction you wanted your career to go?
By this time I knew that the occultation method — even though I’d had a lot of fun with it — had limited usefulness because radio interferometers were quickly overtaking what you could do with occultations. Interferometers were less constrained by any peculiarities of the motions of the moon; with occultations you were limited to what happened to lie in the moon’s path. It was clear that mapmaking and precise position measurements of extragalactic radio sources would soon be taken over by interferometers and the aperture synthesis instruments being developed at Cambridge, England.
Pulsars were discovered while you were a graduate student.
I turned in my thesis in January 1968 and pulsars were announced to the world in February. At that time I had agreed to stay on at Harvard as a postdoctoral fellow, and I was looking for something new to work on. When the paper came out, Dennis Downs, a contemporary student in Alan Maxwell’s group, told me I’d better go check out the latest issue of Nature. I found the announcement of a “new pulsating radio source,” as they called it. I remember reading the article carefully, making notes as I went...
Richard Huguenin was running a low-frequency solar radio astronomy effort, funded by NASA. The project’s funding was in some jeopardy, and he was looking for other good science to do with the infrastructure he had in place. When I suggested that we mount an effort to observe the new pulsing radio source he was quick to agree. We quickly put together a proposal to use the 300-foot telescope at Green Bank — the biggest instrument we could get our hands on. We sent it off, asking for some director’s discretionary time that might be scheduled more quickly than the usual three to six months for refereeing and proposal evaluation. My recollection is that we were in Green Bank and observing the first known pulsar within about six weeks of publication of the Nature article. Probably it was sometime in late March.
So this would’ve been March 1968?
March 1968, right. The Nature article mentioned that three other pulsating objects had been found, but coordinates were not disclosed. There was some criticism of the Cambridge group for being too secretive about all of this. Anyway, that’s what we had to deal with. We guessed that by the time we arrived in Green Bank in March or April, we might already know the coordinates of the other sources, but in fact we didn’t. So our first observation was of just one source. By our second observation, sometime in mid-April, we knew the coordinates of the other sources and observed those as well. We were also starting to think about how to conduct a survey of our own, looking for additional pulsating objects. It was pretty clear there must be more, so we were planning how to do a full-scale, Northern sky survey with the 300-foot telescope.
Before we talk more about pulsars, I’d like to talk about how you made the transition from Harvard to the University of Massachusetts. How did you learn of the position? What brought you to Massachusetts?
The University of Massachusetts at Amherst was trying to build up a substantial astrophysics effort in its combined department of physics and astronomy. Bill Irvine had gone there to lead this effort. He’d come from the Harvard College Observatory, so he contacted people at Harvard that might be interested in a position at Amherst. Partly because of the funding difficulty that I mentioned, Dick Huguenin was interested. Bill recruited him, and I think Dick and his group moved to Amherst in the summer of 1968. Thus, during our early collaborations Dick, two engineers and a technician were at UMass, and I was still at Harvard. We did a lot of driving back and forth on the Massachusetts turnpike when building the receivers that we took down to Green Bank. Within a few months it was pretty clear that I should join them in Amherst. I made the move in the fall of 1969, rejoining the group that had worked well together.
But you were already involved.
I was already involved, right. In those early observations of pulsars we had a mixture of UMass and Harvard people, including some Harvard students.
Were the projects fairly big in terms of teams? You mentioned your group of engineers.
This was a sizable group. It would’ve been difficult to assemble it from scratch so quickly, in response to the announcement of the discovery of pulsars; but this group was already available and looking for new things to do. It was fairly easy to transform it into what we needed. The originally planned solar observations were at frequencies close to what we needed for observing pulsars, so the radiometers and antennas could be easily adapted. We had access to good skills in both antenna design and receiver design.
Was there something unique about the antenna design or the receiver design that needed to be taken into account?
For the 300-foot telescope observations we needed a feed that would move along a track in hour angle. The 300-foot was a transit instrument and, until that time, had never had any tracking capability. You could do strip scans of the sky but could not track a particular source. We wanted to do both. The strip scans would be good enough for surveying the sky, but following a known pulsar for more than a minute or so required a feed that could track in hour angle. One of our first efforts was to design a “traveling feed” for the 300-foot telescope. It was built and installed permanently on the telescope for everyone to use.
I’m trying to imagine something. So you have this large dish, and if you don’t have this traveling feed, the sky is passing overhead and this is recording whatever is going, so the traveling feed then actually allows you some variability, then?
The traveling feed allowed us to move up to about five beam widths off axis on either side, so you get a total of ten beam widths of tracking time.
How was equipment like this designed and built? How would the process work?
Often there were sketches made by Dick Huguenin or me, then discussions with one of the three engineers. Al Rodman was the antenna man, George Orsten and Antal Hartai were the electronics guys. Antal worked mostly in the RF regime, George in the digital or data handling area. We had a range of skills, and it was a happy and collaborative effort. We all pitched in and worked together. We all signed the published papers describing the instruments and the science, at least in the early years.
One of the things that astronomers seem to talk a lot about lately is the role of people who design instruments and assign them credit for doing this. How did that work at this time, around 1970, when you were building and designing equipment for radio telescopes? Was it considered as an equal contribution to design the equipment and help build it versus using it?
How did that break down?
We knew that instrument design was essential to our success, so the engineers as well as the scientists were authors on many of the papers. There were also some papers on instrumentation alone, which the engineers would publish themselves. Scientific papers describing first observations with new instruments included everybody as coauthor. I don’t recall that we ever spent much time discussing these things; it just seemed like the right way to do it.
With this fairly large group that you and Richard Huguenin had assembled to do the initial work on pulsars, was that unusual at the time to have a group of that many people?
Yes, it was somewhat unusual. We were fortunate to have the technical abilities and the manpower to develop what was needed to use the 300-foot in a tracking mode, and to make polarization measurements. None of this had been possible before. We built our own feeds with full polarization capabilities, and we built the multi-channel radiometers that were necessary to record the polarization data. Some of the earliest polarization observations of pulsars, particularly of individual pulses, were done with this equipment.
I think it was the same year that you started at Massachusetts that the first optical observation of a pulsar was made by Disney and two other scientists.
Did you have any particular interest or reaction to that?
We were excited about it, but we didn’t try to duplicate or improve upon those first observations. We were observing the crab pulsar at radio frequencies, but were diverted our efforts into the optical regime.
So what were your duties like at Massachusetts when you first started there?
I was a beginning assistant professor and doing the kinds of jobs such people do. At UMass we had a modest-sized astronomy group — six or seven of us in the combined physics/astronomy department. We started a graduate program at about this time, and were beginning to admit some Masters and PhD students. We were not attracting the very top students, but we still got some good people. The department offered a good range of undergraduate and graduate courses — enough for an effective major in astronomy (or in physics with a heavy concentration in astronomy), as well as a sound graduate program. But the department’s largest teaching efforts, by far, were the introductory astronomy courses for non-science majors. As at many other universities and colleges with a science requirement, many students chose to take astronomy because they figure it’ll be easier than physics or chemistry and perhaps even more fun. They can fool around with watching the sky at night, and get credit for it. Astronomy is just interesting to many people. I taught that course many times, and many different flavors of the course. We had a one-semester version that satisfied some requirements and a two-semester course that also satisfied a lab requirement. Most of us taught one or more of those lecture courses, or a discussion section of one of them, fairly frequently. Our teaching loads were normally one course each semester. It was understood that at the same time you would also be seeking sponsored research support from federal or other agencies.
Was there a lot of pressure on young faculty to bring in research credits?
Yes, there was. It was clear that promotion and tenure depended on establishing a track record in that area. I think it was somewhat easier for those of us working in group situations. I wrote parts of the proposals for research grants supporting the radio astronomy effort, but I did not have to go it alone. It was easier to be a significant player in a group than to strike out on one’s own, trying to establish a reputation for funded research. I think this remains true today. It’s not easy for a new person to break in with an office at the National Science Foundation, no matter how smart and how accomplished he or she may be. For a beginner, it’s hard to break the ice and make the federal agencies aware of what’s going on.
Was the NSF the major funding agency for this type of work?
Yes. We had some limited NASA funding early on, because of the solar work, but that was mostly disappearing. We were funded primarily by NSF and by a couple of key grants from less traditional sources: one from the Research Corporation, one from the Cottrell Foundation. A major contribution of Bill Irvine was the creation of what became known as the Five College Astronomy Department — a collaboration of the University of Massachusetts, Amherst College, Smith College, Mount Holyoke College, and Hampshire College. This consortium provided a mechanism for the small astronomy faculties at the smaller colleges — one or at most two astronomers at each place — to enjoy interactions with a larger group of colleagues. Together with the six or eight of us who were by then at UMass, we made a fairly sizable astronomy department. The distances between institutions are small enough that we could get together once a week for lunch. People who would otherwise have been relatively isolated now had colleagues, and we organized course offerings so that students at one college could cross-register for a course at another campus.. The college administrators were enthusiastic about it, and this helped our funding as well. For example, one grant that paid for a computer needed for one of our projects came directly from startup funds at Hampshire College. That sort of thing helped us a lot.
When was that consortium finally established and formally enacted?
The first piece was already in place when I arrived in 1969. There were some adjustments later.
Okay, and then it just continued to evolve, then, throughout the 1970s?
In terms of the specialties that were encouraged at UMass, what were these? Was there any particular departmental emphasis?
The radio astronomy group was the biggest single effort in terms of manpower and funding, and it attracted the most students. There was a small but significant theory effort. Ted Harrison, Tom Arny and David Van Blerkom all worked in theory, as did Bill Irvine to some extent. Bill Dent headed a second, smaller, radio astronomy effort, making long-term synoptic observations of the flux density variations of quasars.
So as you’re starting out as a young tenure track assistant professor, were there particular people who had a strong influence on your career at this point?
We were a happy, free-wheeling, and collaborative sort of department. I don’t recall ever feeling under the gun there, or being especially treated as a “junior member” of the group. We were together frequently. I went to Ted Harrison often for advice, but mostly scientific advice rather than personal or career-oriented kinds of advice. Ted was a man whose opinions you wanted to listen to, if astrophysics was involved. Dick Huguenin and I worked very effectively together in the years we were both interested in pulsars. When he began to have aspirations for building a millimeter wavelength observatory, we divided things up so that I directed the pulsar group and he worked on the new telescope he wanted to build.
Okay. People might be interested in the future in the fact that the department that you were in at this point was both the physics and astronomy department. What types of interaction were you seeing between astronomers and physicists; or was there no real divide?
A subgroup of us knew we were the astronomers and were there to teach the astronomy courses, but we operated as a single department. I thought it was the right model, but since I left they’ve broken apart. There is now a separate department of astronomy at UMass. More commonly, these days, the divisions between astronomy and physics have become smaller rather than greater. Many colleges and universities now have combined departments of physics and astronomy. In any case, astronomy students are always urged, at both Undergraduate and Graduate levels, to take all the basic physics courses. I am sure this is the right way to do it.
I think your first paper on pulsars was published in 1970. I printed out this one page, “Properties of Pulsars” from 1971, and just scanning the list of publications, I noticed...
Well, there would’ve been a number of papers in 1968-1969 as well on pulsars.
Your first paper was not in 1970?
No, okay. One of the names that popped up a lot was a person by the last name of Manchester; I’m assuming it’s a man.
Yes, Dick Manchester.
I can’t recall how many papers the two of you published, but it was 30 over 30 years.
Many. I wouldn’t be surprised. And a book.
Right. How did that come about?
Dick and I are contemporaries. He came from New Zealand and did his PhD at the University Of Newcastle, New South Wales, at about the same time I was finishing mine. His degree was in geophysics. He then went off to do a post-doctoral fellowship at the Parkes, Australia, radio telescope, with the goal of learning radio astronomy from John Bolton. That would have been in early 1968, and pulsars had just been discovered. Dick got involved with observing the first pulsar at about the same time I did. I first became aware of his work when the group in Australia observed a “glitch” in the period of the Vela pulsar. That was late 1968, or perhaps early 1969. They observed a sudden discontinuity — a small but easily measurable change in the pulsation period — which gave some hints about the structure of the neutron star. I probably had some communication with Dick about that paper, at the time. Not long afterward he came to the U.S. to continue post-doctoral work at the National Radio Astronomy Observatory in Charlottesville, Virginia. He and I started to collaborate with observations at Green Bank, probably in 1970.
Was there something special about the relationship that the two of you had that just-
We became good friends very quickly; we always enjoyed working together. We developed some of the early tools for doing high-precision pulsar timing (or what seemed like high precision, at the time). I did a lot more work, later; in developing that precision to much higher levels after binary and millisecond pulsars were discovered. In the early 1970s, Dick and I worked together on observations of individual pulses, the rapid variations of intensity and polarization from one pulse to the next. We wrote a series of papers, the two of us and Dick Huguenin, outlining those characteristics. These were published in 1973 or 1974.
I just have the front page of one paper called “The Properties of Pulsars.”
Yes, okay. That was an early beginning. We developed those ideas further over the next several years.
I’m curious as to how this research field developed. This particular paper. I printed it out fairly randomly. I think it was one of the first ones that had both you and Manchester on it. But the idea that a lot of the work at this time was perhaps to classify these before going on to explain it.
I think it’s rather like botany or zoology must have been a century or so ago. You don’t have many clues as to how nature is really working, but you have a lot of phenomenology that can be observed, so you start to classify things. You sort them out into categories. It’s like what happened early on with stellar spectra, before anybody understood that it was really a temperature sequence. You have A stars and O stars and other classes of stars classified according to their most prominent spectral characteristics. Eventually, after sorting them into categories, you begin to see just what properties give them the characteristics you’re observing. That’s what we were aiming at. In that paper, “Properties of Pulsars,” we were starting to sort pulsars out into ones that had simple pulse shapes, a single peak. We called them type S, for simple. We had complex pulse shapes, type C, with more than one peak; typically two, but occasionally more. And there was a third category called type D, with sub-pulses that drifted across the pulse from the trailing edge to the leading edge. These things were readily observable, but we had no clue as to what they meant. The phenomenology was presumably telling us something about electro-dynamical processes taking place in the pulsars’ emission regions, perhaps above the magnetic polar caps of the spinning neutron stars, but details of that physics were not understood. In many ways they are still not understood today.
Were there alternate classification schemes that people were proposing for these?
I don’t recall any that were fundamentally different, but yes, the scheme has evolved a bit over time. Also, frankly, it never bore much fruit, so gradually it became disused. Clearly there are different categories of the shapes of the pulses, but it does not appear that they’re telling us something fundamentally illuminating about the emission mechanism.
Okay, so at some point people realize that the classification didn’t have a strong correlation to anything physical about it?
Yes. The bulk of observational effort was redirected into areas where the returns promised to be larger. To me, study of the pulsar emission mechanism began to look rather like studying the weather or some other complicated phenomenon, sunspots let’s say, where there’s lots of observational detail but no theoretical framework within which it can be interpreted.
At this time, say early 1 970s, were there conflicting ideas or research schools when it came to what pulsars were and what their nature was?
Very early on, before a case was persuasively made that these must be spinning neutron stars, yes — there were other models around. White dwarfs were thought capable of pulsating radially at about the right rate, and that idea was entertained for a while. But convergence onto neutron stars as the correct answer came within about a year. By late 1968, Tommy Gold had predicted that the crab pulsar, then just discovered, should be slowing down, and sure enough it was. The crab and the Vela pulsars were found to be embedded in supernova remnants, so pulsars obviously had something to do with exploded stars. We had good reason to think that neutron stars could be created in supernova explosions. These things gave us good reason to believe that pulsars are neutron stars. Beyond that, many details remained unsettled and were very much under discussion. For example, even if a pulsar is a rotating neutron star that’s strongly magnetized, is the emission region located in the first few tens of kilometers above the polar cap? Or is it happening out near the so-called velocity-of-light cylinder, where anything co-rotating with the magnetic field would approach the speed of light? There was very active discussion of that question for a number of years. In the end, the light cylinder models pretty much faded away, largely because of some qualitative successes of the polar cap model. It seemed to need fewer ad-hoc assumptions. Even though it became the favored model, it was in no sense a complete theoretical framework. We still don’t understand many details of the emission mechanism.
Was there one central research problem where people studying pulsars were pretty much in agreement and were pointed to this and say, “That’s what we need to find out. That’s the most important thing to understand.”
Well, I think many people would’ve agreed that the emission problem was not going to have an easy solution.
. . . It was clear that the solution to that problem was not going to be easy and might not be achievable with the sort of accuracy you might hope to achieve. After all, we really didn’t have much data available. Most pulsars were observable over only one to two decades of radio frequency. Optical observations were not generally available; x-rays and other wavelengths also. In a few special cases pulsars were detectable in other energy ranges, but they didn’t seem to settle the questions either. The problem began to be looked upon as one which would be nice to solve but might well not be solvable with present-day techniques.
Before talking about the work in 1973 and 1974 with Russell Hulse, I just have sort of a general question. I think this would be something that people in the future will be interested in. Why pulsars? What about this particular topic drew you in?
The original attraction for me was how different pulsars were from any other astronomical radio source — or, for that matter, any astronomical objects that we knew of. Pulsars are not constant and stable like nearly everything else in the sky, at least over human lifetimes. Pulsar signals have rapid variations — millisecond and microsecond variations, even. The study of pulsars was a made-to-order problem for the rapidly developing capability of making high-speed observations with digital techniques. These new techniques were easily adapted to making observations of pulsars. The super-dense neutron star material provided a hope that we could study what amounted to nuclear matter in bulk rather than in atomic sizes. In some ways, a neutron star is like a single atomic nucleus with an atomic mass number of 10^57, or something like that. Pulsars seemed to offer a fascinating opportunity for studying nuclear matter and gravitational forces at extraordinary densities, conditions impossible to replicate in the laboratory.
Did you ever consider studying another phenomenon or leaving the field of pulsar studies?
Yes, several times, but it was always “maybe a few years from now.” Probably the first time was in 1973 or 1974. I was thinking we might finish the “pulse characteristics” project and then maybe I should think about doing something else. I had similar feelings once or twice in the 1980s or 1990s, but nearly every time I’ve thought that way seriously something would come along to reignite my interest. The discovery of the binary pulsar in 1974 was certainly one such case and the discovery of the first millisecond-level pulsar in 1982 was another? Both provided fascinating reasons for remaining very involved for another decade or more.
Prior to those events, if you were to have shifted your focus to something else, what would that have been?
I never got to the point of deciding that. It probably would’ve been something else in radio astronomy, but it could have been something quite different. I could imagine going off to do something in x-ray astronomy, for instance. There were lots of opportunities then for proposals to NASA for interesting work in other wavelength regions. I never got far enough to have a particular project in mind.
In just looking at your CV, one of the things that you listed from 1972 to 1976 is a consultant in mathematics and neural surgery at Massachusetts General Hospital. What is that?
That was an interesting project that came up over a cocktail-hour conversation with a friend named Dan Pollen. He was then at the Harvard Medical School and is now at the UMass Medical School, in Worcester. Dan was conducting research on the visual system — the visual processing of information by animals and even humans. His experimental technique was to insert microelectrodes into the brains of anesthetized cats, and then, with the cat’s eye focused on a screen, flashing various light patterns on the screen and recording the neural responses. When discussing some of their experiments, it seemed plausible to me that the brain of the cat was processing information in rather the same way that I had done with my lunar occultation observations. This was little more than a suggestion, a conjecture — but we wrote one or two papers about it. The authors would’ve been Pollen and Taylor, and maybe one or two other collaborators for the laboratory experimental parts. We were suggesting that the cat’s brain was doing something closely akin to spatial Fourier analysis of the data, to sort out the various patterns that it can recognize.
What eventually happened with that project?
Others pushed it somewhat farther; I think it’s still clear that the brain does something not so very different from Fourier analysis, but it’s certainly not doing a directly analogous “calculation.” We now know more about the way inter-neuron connections are made in the brain, and it’s not anything like what is done to calculate a Fourier transform.
That’s a very interesting connection between pulsar research and initial processing.
The same kinds of mathematics arise, of course, in many different areas. We can often carry over a useful technique from one field to another.
In 1974 you have a paper with Russell Hulse called, “A High-Sensitivity Pulsar Survey.” Why undertake a high-sensitivity pulsar survey?
That project was started in late 1972. There were only a few dozen pulsars known at that time, maybe 50. It seemed to me that the Arecibo Telescope, with its large collecting area and sensitivity, should be capable of detecting at least a comparable number of new ones. If we could double the number of known pulsars and find ones substantially farther away from the sun, I thought we could better establish the statistics of how they are distributed throughout the galactic system, whether they were concentrated in spiral arms or not, and how much they are concentrated toward the galactic plane — in short, how they fit into the whole scheme of stellar evolution in throughout our galaxy. This was a time when reasonably priced minicomputers were becoming available and being added to many physics labs. I was fascinated by their capabilities and decided that a very attractive project would directly interface a minicomputer to a radio astronomy receiver and use it at Arecibo for a large-scale pulsar survey. I talked to Russ Hulse, then a beginning graduate student in physics at UMass, suggesting that he consider doing a thesis in astrophysics. That’s not what he was planning at the time, but I had a feeling this project might be attractive to him. It was, and we agreed to tackle the project together. My first task was to try to talk the NSF out of $25,000 or $30,000 to buy the computer. Fortunately, my proposal arrived late in their fiscal year. A small amount of un-allocated money was sitting around and they decided, “What the heck? We might as well let them try it.” This was the first grant I had requested on my own, and it was enough to buy us the computer. The receiver was already being built for the radio telescope we had constructed in the Massachusetts woods, for observing pulsars. We could borrow one of those receivers for a while, taking it to Arecibo. We could test everything on the Massachusetts telescope before moving the computer and receiver to Puerto Rico, so we could make sure not to waste any time on the big telescope. There was just enough grant money to send Hulse off to the computer company in Florida, to learn how to program our machine in machine language. Compilers for Fortran or other high-level languages were not available for machines as “bare” as ours was to be. So, our plans started coming together. I had the basic algorithms for a pulsar search already developed, from our work at Green Bank. I had sketched out some fairly substantial enhancements, and they were ready to go, as well. Once Russ had learned the programming fundamentals of the arcane assembly language for the Mod comp computer, he got busy and translated a version of that pulsar search code to run on the new machine.
What kind of computer was it?
Modular Computer Systems, or “Mod comp”. It was a great machine. Roughly the same vintage as the much more famous Digital Equipment Corporation, PDP-l 1. In some ways they were similar machines, but we thought the Mod comp II had a much richer instruction set. It could do a Fourier transform considerably faster than the first PDP-l1.
How big was it?
About the size of a refrigerator, and about as heavy.
What was required to interface the computer with the radio dish and all of that?
Our receiver provided 32 spectral channels, so it put out a constant stream of 32 voltages — each the detected signal power in a quarter- megahertz pass-band. Thirty-two times one-quarter is eight megahertz, and that bandwidth fit nicely into the pass-band of the Arecibo linefeed at 430 megahertz. So we would have an eight-megahertz pass-band centered at about 430, with 32 streams of voltages coming out continuously. We needed a multiplexer to allow an analog-to-digital converter to sample each of those 32 voltages at a regular rate, something like 200 times a second. The Mod comp was ordered with a 32-channel multiplexer and A-to-D converter. Other than that, the computer had a teletype for keyboard input and printer output, and a magnetic tape drive, and that was about it; no disk drives, and no operating system. It had a total of 16K (16,000) words of memory, 16 bit words. We wrote software by keying assembly language statements onto punched cards. This information was processed by a cross-assembler that ran on a mainframe at the university computer center. The output was written in binary form onto magnetic tape, which was then bootable on the Mod comp.
I see. Before talking a bit more about the computer, how did you and Russ Hulse just first meet?
I don’t remember our first meeting, but I think I must have been grading the qualifying exams when Russ was taking them. It was clear he was an excellent student, and I found out more about that fairly quickly. He was planning a thesis, probably in atomic physics. He had wide-ranging interests in physics and may not have made up his mind, when he arrived as a beginning graduate student, what his field would be. He also had had an interest and background in ham radio, but to my knowledge he was not especially thinking of radio astronomy at that time. But that may have been one of the reasons why the pulsar project was a little bit more attractive than it could’ve been otherwise. He was easy to persuade that the Arecibo pulsar search was a good thesis project, because pulsars were a hot topic then. It looked as though this was a field ripe for additional surprises and interesting discoveries. I think it was easy for Russ to imagine getting himself involved with it. We got along well from the start. We were not so far apart in age, and we enjoyed talking about how we might better optimize the computer program, and other ways to do what we wanted in a more efficient way.
So when he’s in Florida he’s learning how to do the punch card, the machine language aspects of it, and the brain it’s fed into?
Okay, and then the computer is crated up and shipped down to Puerto Rico?
Yes. We built it into a plywood crate, and the whole thing weighed 700 pounds. We air-freighted it down to Puerto Rico, with our fingers crossed. We were worried, and didn’t want to do that again! We bought an insurance policy on it before it left.
Who would insure such a thing?
I’ve forgotten, but they did.
That’s interesting. So did he fly down with it, or he went down and was waiting to receive it?
We both went down with it, the first time. We arrived first, and when it a truck drove up and our crate was unloaded, we realized that we hadn’t really asked anybody in the electronics division where we should put it — or whether we could put it anywhere! Buildings at Arecibo are not very big, and there is always a space issue. The Head of the electronics division, an engineer named Miguel Feyjo, a very scary guy. The technicians lived in fear of Miguel’s wrath. When he saw two young astronomers pulling in a huge crate of electronics, he wondered who we were and what we were doing there in his lab. But we got along well in the end, and Miguel found a place for us. I remember our first few attempts at getting underway. An early problem was a familiar one: most radio astronomy equipment picks up some vestiges of the 60-cycle power line frequency. We were looking for pulsars that might have some variations at a frequency not very different from 60 hertz, so we knew we would have to deal with this problem at some level. We soon discovered was that in Puerto Rico, the power line frequency might be 60 hertz, but it might be a bit more, or a bit less; it wandered around, not very stable. Our initial mechanism for eliminating that interference relied on stability, so we quickly had to design a new system for getting rid of the 60-cycle power line interference. There were a few other details that we wanted to change. It was hard to change the program once we were in Arecibo because the complicated process of writing the software on another machine and moving it over to the Mod comp was hard to replicate in the field. But we could make small changes in the program in other ways, and we did that. The search software was split into three phases. The first phase operated in real time, during the observations. The receiver output was sampled, digitized coarsely, and written on a magnetic tape. The tapes would eventually be played back into the computer for detailed analysis, looking for evidence of pulsar signals. But our computer did not have enough memory to allow the necessary transposition of time and frequency dimensions. So phase two used the Arecibo Observatory’s central computer, a Control Data Corporation 3300. This computer would do the large transpose and then write all the same data onto another tape in the new order. The second tape was played into the Mod comp, which carried out phase three of the analysis. In principle we could have done the full analysis on the CDC 3300, but it was the only observatory computer. Fair is fair; of course we could use the central computer some of the time, but we couldn’t use it 24 hours a day. The Mod comp was our own machine and we could do what we wanted with it. We arranged things so that our observation time was concentrated in the hours of the day when the galactic plane, the Milky Way, was overhead. This amounted to three or four hours of observing time each day, which left the remaining 20 or 21 hours each day to be used for the analysis. We kept that Mod comp busy 24 hours a day, either observing or analyzing the data from the previous day.
Why time the observations so the galactic plane was overhead?
We expected that pulsars, like most other stars, would most likely be concentrated in the disk of the Milky Way.
Was getting time to do the observations difficult?
Happily it was not. Arecibo was just going into a major upgrading phase. The mesh surface of the antenna was being replaced with more precise panels that would permit use at much higher frequencies. We were still using a fairly low frequency and had modest pointing requirements, so we could observe during the upgrading and use plenty of observing time.
How long did it take to get all of the equipment up and running and connected?
We were operational after the first tests; within a couple of weeks. We made a few trial observations of known pulsars, established that it was working, and started making scans looking for unknown pulsars not long afterwards. Our assigned time was spread over a number of months, and we both traveled back and forth to Puerto Rico a few times. Eventually Russ rented an apartment in Arecibo and stayed there for the best part of a year, accepting observing time whenever it was available.
Okay, so you would go there and make the observations for a couple hours a day.
Russ spent nearly all his time at the observatory, either taking the data or analyzing it. I think I’m going to have to call it quits at this point, but that’s a good start.