[Bracewell touching up signature pier on spectroheliograph dish]
Bracewell touching up signature pier on spectroheliograph dish. (FBOA image)


[Bracewell, 21 November 2004]
Bracewell writing, 21 Nov. 2004. (FBOA image)


[Bracewell, Swarup, and Pawsey, 1958]
Bracewell and Govind Swarup watch Joe Pawsey carve his name on telescope pier, 1958. (NRAO/AUI image)


[Bracewell circa 1955]
Bracewell, circa 1955. (Stanford University image)


NATIONAL RADIO ASTRONOMY OBSERVATORY ARCHIVES

Papers of Woodruff T. Sullivan III: Tapes Series

Interview with Ronald N. Bracewell
At AAAS Meeting, San Francisco CA
8 January 1980
Interview time: 185 minutes
Transcribed by Sierra Smith

Note: The interview listed below was conducted as part of Sullivan's research for his book, Cosmic Noise: A History of Early Radio Astronomy (Cambridge University Press, 2009) and was transcribed for the NRAO Archives by Sierra Smith in 2014. The transcript was reviewed and edited/corrected by Ellen N. Bouton and Kenneth I. Kellermann. Any notes of correction or clarification added in the 2014 reviewing/editing process have been included in brackets; places where we are uncertain about what was said are indicated with parentheses and a question mark, e.g. (?) or (possible text?). Sullivan's notes about each interview are available on Sullivan's interviewee Web page. During processing, full names of institutions and people were added in brackets and if especially long the interview was split into parts reflecting the sides of the original audio cassette tapes. We are grateful for the 2011 Herbert C. Pollock Award from Dudley Observatory which funded digitization of the original cassette tapes, and for support from Associated Universities, Inc., which funded transcription of this interview.

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.

Part 1 | Part 2

Begin tape 132A

Sullivan

Let me just ask you for the record, it would seem to me with your deep understanding of the performance of antennas and the nature of design of antennas and so forth that you might have some interesting things to say about the controversy between the log N-log S counts of Mills versus those of Ryle that went on in the late Ď50s primarily, because I see it as being largely a matter of really understanding the transfer function of the instruments. Maybe you donít agree with that.

Bracewell

Well when you consider that lots of side lobes were just lumped in, Iíd have to agree with that. Then of course some of the very early ones I would see. I lived in the same room with Mills and [Harry C.] Minnett for some time and then with Christiansen. So I would see Mills getting a letter from Ryle or opening up the latest publication and here would be a new log N-log S plot. And Mills could tell the name of each dot and he would look at these dots, which were anonymous, and he knew them as personal friends. And heíd say, "Yes, this is all very well if you try to do cosmology with this. But suppose you take out the Crab Nebula," and he would remove that one. And then remove all the other galactic sources, supernovae and what not, "Look what happens then." So he would redo this thing laboriously and show that that completely altered the result. So for a long time there the situation was polarized on the basis of inadequate presentation of data. Inadequate data I suppose. Then, of course, the question of confusion and the use of surveys that were totally falsified just made it more complex. Itís not a subject I am a great expert on. But I followed it with an amateur interest, but never got my own hands wet with it.

Sullivan

A related question that you may or may not have been involved with was the question of aperture synthesis and its development. Do you see that as being sort of a smooth development really going right back to Pawsey, McCready, and Payne Scott, right up through the One Mile and the Super-synthesis?

Bracewell

No, not at all.

Sullivan

How would you characterize that?

Bracewell

Well I donít think aperture synthesis started off with Pawsey, McCready, and Payne Scott except for the extent that it might have suggested the idea to the Cambridge group because aperture synthesis was practiced in Cambridge. I donít think you could really say that was the way in which the Sydney people thought at all. They didnít really do that.

Sullivan

What was the difference?

Bracewell

Well, see, Ryle made use of small antennas and exchanged hard work. So he would have some research student like Stanier, for instance, slaving day and night, moving antennas during the night and observing during the day until heíd observed the Sun with just a couple of virtually, just dipoles, but with many, many locations. Of course, in the couple of weeks taken to do this the Sun has rotated quite a bit so itís not surprising that you come out with a sort of smeared out Sun and any limb brightening that might be there or any point sources that might get lumped together in the middle. So they missed the limb brightening. But that was the sort of procedure that Ryle preferred to follow, to use minimum equipment and then expend a lot of time and effort. Now the technical resources at that time were generally greater in Sydney. Ryle was starting at a lab where there was no accumulation of equipment whatever. He had moved there from TRE [Note added 2014: Telecommunications Research Establishment, at Malvern] and there was nothing there. Whereas in the Radiophysics Lab there was a major workshop, going teams of drawing offices, machine shop, electronic technicians, a full facility. So they could move on to bigger things. So you see things like Christiansenís original array of 32 dishes, quite an elaborate machine for its time, although reminiscent of a Cambridge tradition very definitely. But on a much larger scale, and followed by a second array, which he built perpendicular to that. And then we have the first Mills Cross, which is a big installation in itself, though we would think of it as small now but thatís only because Mills got them up to a mile long. So aperture synthesis in the notion of doing it square by square on a chess board. Iím thinking now about the paper describing aperture synthesis was not something that was developed in Sydney. The only connection might have been the Fourier transform formula that McCready, Pawsey, and Payne Scott gave out. In fact, Iím sure there was a connection there because that paper was read very carefully in Cambridge. That paper beat the Cambridge group to the identification of the location on the Sun, the diameter on the Sun, and the height. In all those things the Sydney group came in first.

Sullivan

Then what would you say was the concept Ė because once again you cite Stanierís work but Mills also was going out to longer spacings, putting together a visibility functionÖ

Bracewell

Thatís quite right but thatís the great special undertaking to measure the diameter of Cygnus A. That is an example of that sort of aperture synthesis, though only in one dimension. But it had a very specific aim to get to such a spacing that the visibility would be seen to no longer be unity so that you could give a diameter. And as you know he used a radio link to get rid of the cable attenuation problem. Graham Smith just used a longer cable and put up with the attenuation. And [Robert] Hanbury Brown did it with his own inimitable invention. And they all got the diameter at about the same time. That led to nothing in Sydney. They may have been another example later. As a matter of fact I think [Peter] Scheuer spent a year or so in Sydney and did something along those lines. It could be regarded as a continuation. And as a matter of fact there was another example, the Christiansen Cross, elements of that were used as two element interferometers. But thatís a ridiculous way to do aperture synthesis, build the aperture and then select pairs of elements to use. [Richard Q.] Twiss and Little wrote a paper of that kind. [Note added 2014: Twiss, R. Q.; Carter, A. W. L.; Little, A. G. Brightness distribution over some strong radio sources at 1427 Mc/s. Observatory 80, 153, 1960]

Sullivan

Now thatís not what I was going to say. I was going to bring up the Chris CrossÖ

Bracewell

With its outlying antennas, is that what you were goingÖ?

Sullivan

Yes, rightÖ

Bracewell

But theyíre not movable basically.

Sullivan

There not movable but what about the idea of Earth rotation.

Bracewell

Ah, supersynthesis. Now supersynthesis as a word is an invention of Ryle, and for a long time no one could understand what he meant. They thought heíd made some incredible discovery but you couldnít understand his paper very well. Well, in any case, now that we understand the paper, we see that Christiansen invented supersynthesis and had used it some years before. He just didnít have the luck to hit on such a felicitous expression. So I would subscribe to the view that observing with a linear array in different position angles on the Sun as the seasons change, that is as the Sunís declination changes, and as the time of day changes, and combining that with similar observations with a perpendicular array, that is supersynthesis. I prefer to call it Earth rotation synthesis but I think thatís in fact what Chris did.

Sullivan

I donít quite follow you saying that Ryleís paper wasnít understood or his term. Which paper would this be now?

Bracewell

Well I think there was a paper in Nature, which you would be more familiar with than I, in which the word supersynthesis just showed up.

Sullivan

I donít remember where the word first showed up but I think the paper you are talking about is 1960 or something like that. And you are saying there was some confusion over that, what he really meant.

Bracewell

Yeah, I didnít understand it.

Sullivan

Was it because everyone understood that the Earth could change position angles but it must be that he is talking about something different and we donít understand what it is thatís different.

Bracewell

Well, Iíd have to read it again to find out what it was that was confusing, but Iíve got a distinct feeling in my mind that I thought he was saying that because the Earth is rotating, and the antenna in five minutes will be in a different part of a space, that itís as though you had an antenna that occupied all the places that it has moved through in space. And I found that puzzling. Now if I were trying to explain that today I would say, ďHere we have a pair of antennas between which we are measuring the coherence and that vector displacement is changing as the Earth rotates.Ē So I may have misunderstood it, but Iím quite sure at the time from discussions there were others that had difficulty understanding what he was talking about. He obviously understood perfectly well what he was saying. And whether he knew that it was identical to what Christiansen had done and disguised the writing a little bit, thatís a possibility too. Well he was obviously thoroughly familiar with what Christiansen had done, and so I think he must have repackaged the idea with continuity in the Cambridge way of presenting things. So it was the next step beyond aperture synthesis.

Sullivan

OK. Letís shift to some various projects that you were involved in. For instance, apparently you were involved in a proposal while you were at Berkeley for a spectroheliograph at Stanford. Iím not quite sure how that happened.

Bracewell

Well, Iíll tell you what happened. Otto Struve said Berkeley should get into radio astronomy, observational, and that the galaxy was very important. So he took me up to Lick Observatory and found a very steep hillside pointing toward the southern horizon. And inquired whether something could be constructed on this hill, which could look at Ophiuchus, which he liked very much. And I didnít like the slope of the hill, so instead I wrote a two or three page letter in some detail describing how the Mills Cross concept and the discrete array of Christiansen could be combined and that this might be an interesting instrument for various purposes. So Struve took that to the Electrical Engineering Department where they had antenna wizards like [J.R.] Whinnery, for instance, and got a reading on it. And apparently they couldnít find anything wrong with it. It was pretty big by their standards. Well, of course Sam Silver was there too. They thought in terms of antennas of up to about 6 feet in diameter in ones. And here Iím talking about 32, every single one of which is bigger than that. So that sounded to them more like Livermore Labs. So it was given to [Edward] Teller. I got to know Teller a little bit. He came and saw me when he found out I was there. He wanted to find out everything I knew fast. That took him about half an hour. But whenever he saw me again, he would pump me very hard and drain my brain. But this proposal was sent to Teller and he gave it to one of the important engineers whose name escapes me for the moment, who ultimately wrote a report on it with a cost estimate. And Iíve got that somewhere. And he said that everything I was proposing was mechanically quite feasible and it would cost about $5,000. Well he didnít cost everything. I think the $5,000 listed covered the cost of 32 dishes. So the Electrical Engineering Department, that would represent Sam Silver, decided that theyíd make me a job offer. Meanwhile I went and spoke to Tuve and somehow mentioned that Teller had seen this. And he said, "Donít touch it. The money is stained with blood." That impressed me immensely. I had no idea what that meant. I knew nothing about the atom bomb at that time. But I was very impressed. I recoiled. But as a matter of fact I then went and spent six weeks at Stanford where I already knew some of the people. I gave them a course of lectures during the summer of í55. And they decided theyíd make me a job offer. They must have liked these lectures. And being a private university they were able to move much faster than Berkeley, which is a great administrative giant. And the people at Berkeley never materialized with an offer. As soon as they heard that they had competition, they felt this was more than they could overcome. I think I had some other job floating around too. Yes, as a matter of fact, [Donald] Menzel had a job offer too, now that I come to think of it, at Harvard. But Stanford moved much faster and in those days, it was easy to get on the faculty. These days you have to be a genius. But I got in before the barriers were lowered. They just led you up to the chairman of the department and he looked at you and if you didnít have two heads you were in.

Sullivan

Well, Iíll discount that statement. But how did this report get to be under Stanfordís auspices? You were doing it all at Berkeley.

Bracewell

Well, you see. At Stanford, [Oswald G.] Mike Villard was the instrumental figure here. He said, "Why donít you write a proposal for the Air Force, and weíll see how they like it?" Well, as I have told you, I was very young and naÔve. And if someone told me to do something, generally speaking, I did it. So I wrote a proposal and itís a very good proposal. I believe itís the first description of what is now known as the Chris Cross. I donít believe there is any earlier description than that. I wrote this proposal and I sent a copy to Pawsey at the same time. Well it was looked at favorably by the Air Force and it asked for $80,000, which they said, "Fine, you can have it." So when that money became available, I returned to California from Sydney.

Sullivan

So you went back for a period of a year or so?

Bracewell

Well it would be more like three months, at the end of í55. And during those three months something favorable happened in Washington or Boston, somewhere. So I came back and within a few more months cash actually materialized and I started work.

Sullivan

Which is í57 now?

Bracewell

It was December í55 that I started back in Stanford. And by mid í56 I must have had my cash. But I only had myself, no technicians, no drafting, no machine shop, no nothing.

Sullivan

So we come now to the building of the cross at Stanford, which is then í56 through, what year was it finally finished?

Bracewell

Well if I could tell you the date of the first Sun map that would fix everything. I believe we have Sun maps in 1960. Iím just picturing in my mind a contour map and I think it says May 1960.

Sullivan

Now this once again seems to be a wholly new venture for you. You had not been in charge of building a large instrument before.

Bracewell

Well, right, correct. I really felt cut adrift when I left Radiophysics because I was accustomed to working with the machine shop, a drawing office, and technicians. I knew how to interact with that sort of person. And if I wanted to know something I knew who to go and see down the hall because Radiophysics was a big place with experts on almost everything that I needed to know about. So I felt very much cut adrift and somewhat on my own. I was with other radio scientists but no one in the microwave field. Anything from about 5 Hz up to about 20 MHz, they knew everything. But I was way out on a limb technically. The only people who knew about microwaves at Stanford were the linear accelerator people, who by some miracle were on the exact same wavelength as I was. In fact, the reason I wound up on 9 cm was that the linear accelerator was at 9 cm and there was the possibility that if I needed a T-junction or something like that of going and scrounging it.

Sullivan

But what was the attraction of this for you?

Bracewell

Well, it didnít seem any risk. I went on two years leave. The people in Sydney didnít particularly want to see me take off. And I had found the people at Stanford congenial. I liked the look of the main quadrangle, which was like the quadrangle in Sydney, sandstone arcades. And there were lots of eucalyptus trees and the Pacific Ocean wasnít very far away. The only thing I didnít realize was that the water is so cold you canít swim in it. But there were lots of non-negative aspects. And the year I spent in California had revealed to me that it has a pleasant climate. So there didnít seem to be any risk entailed. If anything fell through, I could call it quits and there would be no problem. But at the end of two years I had made so much progress and things were really moving along. And I was beginning to feel the personal advantages of being in control of your own destiny. Working for a government lab, you are a cog in a wheel. And when I go back to Radiophyisics labs these days and meet my contemporaries, I see that I might have developed the way they have developed. They are great experts but generally fairly narrow now and extremely obedient. I see now where I got my obedience because I grew up in a slightly military atmosphere in that lab. There was a definite hierarchy. As soon as I came to be a professor I was astounded to find there was no one to tell me what to do. As a matter of fact, at Berkeley when I had to give grades to my students, I went to Struve after Iíd figured out all the numerical grades and said, "What letter grades do I give?" And he said, "Thatís your responsibility." And I said, "Well, I understand that, but how many As should one give and how many Bs? What is the custom around here?" And he said, "We leave that entirely to you Mr. Bracewell." Well, I just staggered out and took a guess. Iíve always wondered how people decide grades. [Laughter]

Sullivan

So can you tell me what you considered to be the unique aspects of that cross?

Bracewell

At Stanford?

Sullivan

Yes.

Bracewell

Well, Iím not quite sure that there is anything unique about it.

Sullivan

Thatís a fair answer. It certainly was much larger than anything of its kind, had more sensitivity. Is that not true?

Bracewell

Well, we have to compare it to the Cross that Christiansen built at the same time. Now he built a 64 element cross at 21 cm. I have a 32 element cross at 9 cm.

Sullivan

Whatís the size of the dish in each case?

Bracewell

My dishes are 10 feet. Of course, they are solid aluminum. His dishes are bigger, perhaps 18 feet, Iím not sure, and theyíre mesh dishes made in the bent tube and mesh arrangement. That cross is operated by pulling a cable that runs the whole length in a very ingenious way. And mine is operated by rotating drive shafts, which came in during the Industrial Revolution, you know. And all I can say in their favor is that they operated every day for eleven years and never had to be attended to, even if not oiled. They worked very well. So mechanically that turned out to be quite good. And Christiansenís transmission lines are essentially open wire lines in a kind of guide that surrounds them. And my transmission line is waveguide throughout. Now I did get away with half as many antennas as his. I built the same beam width and he was quite conservative by a factor of 2. He put in 32 extra antennas that were not actually needed. That makes his repeats of the Sun twice as far apart as mine. But my Sun doesnít repeat until the first one is completed. So I think I might have had a slightly superior confidence when I came to design that. I had been thinking about these things very carefully and I didnít want to build more than I needed. In particular, I had thought up the T by that time, and I realized that I didnít need to build all the cross. I could build three quarters of it and it would still work.

Sullivan

This wasnít appreciated until you saw to this?

Bracewell

Well, Christiansen said in a letter to [Charles] Seeger that I invented the T. Well, if he says that, it means he didnít, doesnít it? I was impressed by that letter because Charles showed it to me, and Iíve got a copy of it. It was getting pretty apparent at that time that you didnít need them. However, although I knew that, holes were being dug to pour concrete and I had to make a decision in a hurry, so I went the conservative way there. And it turned out later on that Swarup did the sensitivity analysis for the T and showed quite clearly that it is much more critical an adjustment. The cross is rather basically a good idea and the T is rather sensitive.

Sullivan

Errors balance out.

Bracewell

Right, well you donít have the centroid offset. Thatís what works in your favor. But as to unique things, the one thing we did that I believe was important and got into the whole mainstream of radio astronomy large antennas was the method of calibrating that array. You see, with a three minute of arc beam, thatís about 1/1000th of a radian, if you are trying to hold phases to, letís say, 1/10th of that, you working at 1 in 10,000. Now thatís the precision of geodetic survey. Geodetic survey, which is the best we do on the ground, works to 1 part in 104. So just to set those antennas out required some rather careful survey, which is why Chris and I are both expert surveyors now. We know a little bit about surveying. But after you have done the best you can like that, you still have to tweak that thing into the last millimeter. In our case, to the last millimeter in something 100 meters long. Thatís 100,000 millimeters and we are working to the millimeter everywhere. Thatís kind of a bit hairy. So what I invented was a method of making a twinkling reflection at each feed horn. And I got a fluorescent tube about 4 inches long, just a fluorescent tube you could buy in the shop and mounted it across the mouth of the horn, where just being made of glass, it had no effect whatsoever on the incoming radio waves. But if you turned on the discharge, the electrons there would constitute a conducting path for microwaves. Therefore a signal sent from the center of the cross out through the branching waveguide structure, up to that horn would be reflected and would come back with a modulation, which enabled you to discriminate from all the other much larger standing reflections due to mismatching. And you would know which horn it was coming back to because you would turn on the modulation at that horn. Furthermore you could measure the amplitude at which it came back. So the very first thing we found was that one of our feed horns had a piece of unwanted brass strip in it about three feet long and an inch wide, that had not been removed during fabrication. So we got that out.

Sullivan

So this is the first time a signal had been distributed more or less as a calibration in an array?

Bracewell

Yeah. Christiansen attacked that in another fashion and there is more than one way of doing it. But that way of doing it centrally, starting from indoors and getting your reading indoors, just pressing a button to determine which antenna you are going to look at, was quite a step forward. The other thing that was of a pioneering nature about that antenna is the fact that it was the first radio telescope to produce its output in publishable form. We just tore the stuff off and sent it in for publication, month after month for eleven years all told.

Sullivan

To the solarÖ

Bracewell

Well it went to various placesÖ

Sullivan

What was it called?

Bracewell

Mostly we worked through Boulder under their assorted initials which have changed several times and it came out in their monthly bulletins. The very first time we got that going, computers didnít really exist, but we had a Flexowriter, which could be operated by punch tape. And Flexowriter was controlled by the antenna so that it moved, carried, shifted, and the carriage return operated and came to the next line. And everything was correctly spaced despite of the fact that typewriters have ten characters to the inch this way and 6 lines to the inch the other way. In spite of all that we managed to produce something that could beÖ

Sullivan

I remember it was arrays of digit on a circle. Wasnít that the way it was given?

Bracewell

Yes. And, over the course of time, we improved that as things came along. After a while we abolished their analog computer, which computed hour angle and computed them and made punched cards and then used a deck of punch cards to control the thing. And then more recently it was elaborated even more. The whole eleven years of that was duly published, which is more than can be said for any other radio telescope.

Sullivan

Thatís true in many cases.

Bracewell

And the whole of the eleven years is available in uniform format throughout, in machine readable form on tape or cards. I canít tell you the number to write for to get it in Boulder.

Sullivan

Was the purpose of the instrument from the beginning primarily as a monitoring instrument, to do a couple of experiments with it, but mainly to serve as a monitoring instrument.

Bracewell

Well, I hoped that it would do a variety of things. And we did publish a range of things. For instance, we discovered the central component of Centaurus was double.

Sullivan

Thatís with Little in í61, the AAS abstract here? [Little, A.G.; Bracewell, R.N. The Central Component of Centaurus A. AJ 66, 290, 1961]

Bracewell

Now there was a suspicion that it was double as a result of work that Little had done before he came to spend a year with us. But we looked at five or six of the brightest sources and found out a little something about all of them. But the instrument did not have the sensitivity to go into a second order of investigation. For instance, with a 3 minute beam you can map Cassiopeia but there are not very many elements. And after youíve mapped Cassiopeia and Taurus, there are no other sources accessible to the instrument. Thereís just not enough collecting area. We also added outrigger antennas and got down to 50 seconds of arc, which for a time, I think, probably held the record for resolution of any radio telescope. I know that there is no radio telescope even to this day that can make Sun maps of the kind that we made. There is no 100 meter, 10 cm dish that can make some maps on a day to day basis. Of course at Bonn they can make an occasional Sun map which is comparable.

Sullivan

There is nothing that is devoted to it in any sense. Let me got back to 1958 at the Paris Symposium. Of course you edited the proceedings of that meeting. It seems to me that was a rather interesting and perhaps critical meeting in the history of radio astronomy. What thoughts do you have on that?

Bracewell

Yes. Well it was a great meeting and it was probably the last meeting at which all the radio astronomers could talk to one another and cross the boundaries from topic to topic. Since then, of course, there have been many radio astronomy sessions with radio astronomers presence but with a tendency to emphasize instrumental aspects. The Paris Symposium was definitely of the scientific kind. No undue emphasis on instruments. It was truly scientific.

Sullivan

Do you have any particular memories of sessions or papers there?

Bracewell

Well I do remember that it was agreed that all the discussion would be published. And consequently some careful organizing was required. And as the person entrusted with editing the thing, I saw that I had better be the person that got the discussion. My experience with organizing the URSI assembly in Sydney stood me in good stead here. So I had people posted at the four corners of the room with slips of paper. Something youíve seenÖ

Sullivan

Thatís probably the first time that was done. Itís almost alwaysÖ

Bracewell

Well, I couldnít claim to have invented it. Itís often done now because it works. And I appointed a whole group of people right there at the meeting. I had found out how to appoint people. You just go up to them and you say, ďBetween 2pm and 5pm, you will be in charge of collecting the pieces of paper that will be handed to you by four people who will appear mysteriously in the room.Ē I would make the four appear, you see. I would say to them, ďAll youíve got to do is stand in the corner.Ē But I told this one other guy, ďYouíve got to collect all those pieces of paper. And furthermore, youíve got to spend the rest of that night chasing down the guys who didnít give their pieces of paper in. And I donít want to see you until youíve got every paper from that session. And then I want the lot on the last day. And there will be no opportunity to add or subtract.Ē And if you appoint enough people Ė of course, if the fellow says, ĎI wonít do it,Ē you get someone else. Itís really very simple. They always say theyíll do it. Some are better than others.

Sullivan

Were there recordings also?

Bracewell

No. I have all those slips of paper, the manuscript writing of the people, many of whom are no longer with us. [Note added 2014: The discussion slips are now with the Bracewell papers in the NRAO Archives.] So if you find an interesting quote in the book and you would like to have the piece of paper and frame itÖ

Sullivan

I might just take you up on that. Do you remember if there was much editing for whatever reason?

Bracewell

The editing was incredible.

Sullivan

No, I mean of these remarks.

Bracewell

Well, in a few cases I think I might have recirculated that discussion because it clashes.

Sullivan

It didnít make sense orÖ

Bracewell

Well, people stand up and say something, then they hear what the other man says and then they write down what they would have said. And consequently when you get these two pieces of paper they just donít make sense. But my feeling was that we didnít need a verbal record of exactly what was said. The purpose of the discussion, of course, was to illuminate what was said. So if people wanted to change it we just updated it as much as possible.

Sullivan

Another interesting paper of yours Iíd like to ask you about is the one in 1960 in Nature on extraterrestrial communication [Note added 2014: Bracewell, R.N. Communications from superior galactic communities. Nature, 186, 670, 1960], which I think may be number two after Morrison and Cocconi. [Note added 2014: Cocconi, Giuseppe; Morrison, Philip. Searching for Interstellar Communications. Nature 184, 844, 1959] Itís certainly amongst the first few. Were you basically inspired by Morrison and Cocconi to do this?

Bracewell

Yes.

Sullivan

Or had you been thinking about these issues beforehand?

Bracewell

I donít recall that. All I recall is that I read their paper and began talking to people about these fascinating thoughts. And I thought that was a pretty good paper. I found out a few things. I discovered that there is a relationship between how far away the nearest community is and how long theyíre likely to survive. And that idea has been so difficult to grasp that people reading the paper generally havenít noticed that. Everybody who read it notices that there is a reference to Van der Pol and long delay echoes. But the discovery that distance to the nearest advance community is connected to the average longevity is a very striking result. And it slowly filtered into the literature, which is now quite extensive. But it was there all the time.

Sullivan

Did you feel any social pressure that maybe you really shouldnít publish this sort of thing? You know that this was going out on a real limb.

Bracewell

People, strange to say have asked me that from time to time. No, I didnít.

Sullivan

It seemed to you like a perfectly acceptable topic for Nature?

Bracewell

Yes, but some people reading it obviously thought they wouldnít have published it. There are a number of people who conveyed that impression to me. No, it seemed to me that it was a perfectly bone fide topic. But no, I must tell you that I had had some previous contact with this because I was in Berkeley with Su Shu Huang in 1954 and this is six years later. Now, Su Shu had written papers on the habitable zone so I already knew this was a reputable subject. And Struve was there, and he had been very interested, and later encouraged Frank Drake in what he was doing with Project Ozma. And I went to Green Bank when Struve was Director there, probably in 1960, and gave a talk on my Nature paper. And I know Frank Drake and [Sebastian] Von Hoerner were there, and I donít know who else. So I guess that this didnít come out of a clear blue sky but clearly the Cocconi-Morrison paper stimulated my paper.

Sullivan

Just a couple more questions here. You took a tour of the Soviet Union in í61, I believe,or just before then. You reported on it in Sky and Telescope. [Note added 2014: Swenson, G.W., Jr.; Bracewell, R.N. Some Russian radio telescopes. Sky & Tel. 22, 77, 1961] What was your impression of radio astronomy in the Soviet Union at that time?

Bracewell

Well, we visited the enormous structure that [Viktor] Vitkevich had going at the time, which was never completed, huge towers and a great cylinder which could be tilted. A great idea. Why it slowed down and never produced, Iím just not up to date on. But the Vitkevich unfortunately died and he wasnít regarded as very important by the other Russian radio astronomers. So perhaps he ran into some funding problem. We also saw the great 20 or 25 meter millimeter wave dish at Serpukhov, very interesting mechanical thing. It looked something like the interior of a submarine. It was obviously built by naval engineers. Iím not sure Iím right about that. It was technically very interesting. And George Swenson, of course, was mechanically inclinedÖ

Sullivan

He was with you on this trip?

Bracewell

The two of us went together. He thought of it as a matter of fact. And we spoke to the engineer, whose name escapes me for the moment, which it shouldnít, and he spoke German and Russian. And I could read German, but if they spoke it at me fast, it wasnít too good. And I certainly didnít know the German words for gear teeth, things like that. As a matter of fact, I think I do know that but I think I know what a (Verzahnungen?) is. But in any case, there were lots of technical words, mechanical terms I certainly wouldnít know the German for. So we had very interesting exercise in communication. And when they tell you in the university that there are three modes of communication: writing, speaking, and drawing, we donít pay much attention to drawing. But, by golly, when the other two close down, drawing is most helpful. So we had lots of good discussions, found out a lot of things. Then we went and saw the fantastic installation at Leningrad and Pulkovo with all the multiple plane mirrors, which we thought was crazy. And when they built an even bigger one, RATAN, more recently, I thought that was even crazier. So I was very impressed by the magnitude of the mechanically undertakings. But on the whole, we thought the Russian were stronger on giant mechanical things than they were at the underlying science. On the other hand we went and visited [Josef S.] Shklovskii and [Vitaly L.] Ginzburg and these people were right at the heart of the theoretical side. But they were quite disconnected from these other people who obviously had large sums of money. I never really understood the funding situation there.

Sullivan

I would agree with you. What do you think it is that the Russian donít come out with any useful data from their instruments?

Bracewell

I think that they have several places running in parallel. Itís a much bigger country than Australia, which can only afford to do one thing. And if astronomy isnít competing very well with botany, well theyíll cut astronomy. But in the Soviet Union they can have many projects going in one and the same field, and clearly all these places somewhat independent, some of them totally independent. They fed back to the government through channels had no relationships at all. And theyíd managed in different locations for various reasons to start a whole lot of project and they were very diverse in their quality. Some were just not really very inspired but theyíd managed to, locally at least, get the financial support. Others were very good, just all over the shop as you might expect.

End of Tape 132A

Begin Tape 132B

Sullivan

So you were saying that the situation that you saw in the Soviet Union in 1961 is not unlike what was in the U.S. 10 or 15 years ago?

Bracewell

Yes, we had dozens and dozens of radio astronomy projects, all supported in diverse ways and of varying merit.

Sullivan

It just wasnít efficient use of funds.

Bracewell

I wouldnít like to argue about the efficiency or not because if you have a program that doesnít seem to be as good as what is going on at the University of Michigan, is that inefficient? Youíve got no way of saying whatís happening in Florida and how that will feed into other values in the country. There is no one wise enough to say.

Sullivan

No but, of course, you canít do everything. You have to make decisions.

Bracewell

Well, it depends on who makes the decision. You see, if the local chamber of commerce will fund a radio astronomy venture in Florida, that sort decision doesnít arise.

Sullivan

But that wasnít really the case in the U.S. 10 or 15 years ago. It was ONR [Office of Naval Research] and NSF [National Science Foundation] pretty much.

Bracewell

And about six others at least.

Sullivan

Oh really?

Bracewell

Well letís start naming them: the Carnegie Foundation, the Ford Foundation gave out lots of money including giving money to AustraliaÖ

Sullivan

Well I know that but did they actually fund anyone in the U.S.?

Bracewell

I suppose so. I wouldnít care to say. There is the Army Signal Corps.

Sullivan

Who did they fund?

Bracewell

Well Iím just talking about 10 or 15 years ago.

Sullivan

Yeah but who did they fund?

Bracewell

Well, they got the first Moon echoes.

Sullivan

Thatís í46 now. They didnít stay in the game.

Bracewell

Yes they did. You could still apply to the Signal Corps for cash for all sorts of assorted things. Iím sure youíll find there are some radio astronomers getting money from there. There was, of course, the Air Force Office of Scientific Research. But there were also the Air Force Cambridge Research Labs [AFCRL]. Now you could also get money from Sacramento Peak, which got its money from AFCRL but nevertheless it was a quite different procedure. Now if I had to scratch my headÖ and there was the Research Corporation. I got money from them myself. So did Reber.

Sullivan

Reber still does.

Bracewell

Now we are up to at least six or seven and Iím sure there were 12 or 15 if you went and counted them.

Sullivan

In 1962 was published your review article on radio astronomy techniques in the Handbuch. [Bracewell, R.N. Radio astronomy techniques. Handbuch der Physik 54, 42, 1962.]

Bracewell

That was my best selling reprint. I blackmailed those chaps, they were three years late printing that. They got my article in on the deadline and then they waited for another several years until the other articles came in. So I blackmailed them, and the result was that I got 500 free reprints. Itís a thick reprint. Itís a book.

Sullivan

Do you still have it?

Bracewell

Do I still have any?

Sullivan

Yes.

Bracewell

I may have one.

Sullivan

Iíd love to have one if you have a spare.

Bracewell

Each year from Manchester, I would get applications, individual hand-written letters from about 15 research students who wanted one. And Iíve sent them everywhere.

Sullivan

But I wanted to ask you, it brings up the question of techniques in radio astronomy and so forth. And another theme I would like to look into in my overall study is the relationship between the technology and the science. How do you see that relationship? Do you think that it is sort of a willy nilly thing, whatever could be done did get doneÖ

Bracewell

No, Iíve got quite a systematic view on that, which is shared by lots of people. For instance, there was a committee which Jesse Greenstein chaired that brought out a report on astronomy. And in that, it points out that there are two ways of going about astronomical research.

Sullivan

This is the 1970 committee?

Bracewell

That sounds about right. Iím just thinking of the National Academy of Sciencesí Newsletter. No, Iím thinking about their buff colored 4 or 6 page newsletter that comes out every now and again. And I remember it had an excerpt from the Greenstein Report reproducing this material. Iím now going to have to paraphrase for you. There are two things you can do: One is to sit down and theorize about what might be there and then design observations, a crucial experiment perhaps, to decide if this is the case or not. The other thing you can do is look at what phase space has been explored by instruments, what bandwidths, what frequency coverage, what wavelength, whatever. And then imagine an instrument which would explore things which would not have been observed by existing instruments. Now you build that instrument, and in the expectation that you will discover something. There are two different modes of going about it. Now there are people who do not know about the other mode. And you discover the existence of these people in reviews of your proposals that you get back from NSF, where someone will say, ďThis man hasnít said what heís going to discover.Ē So you realized that there are people who are unaware of and certainly donít subscribe to this other way of doing it. Now the Greenstein Report says that 90% of all discoveries in astronomy have been made by building a new instrument regardless or in the absence of an idea of what you will discover. Now that is astounding news to a lot of people. I believe it because Iíve seen all through my life both in ionospheric and in radio astronomy and some other things Iíve had experience with, thatís been inevitably the case. You push the instrument beyond what you had before, and nature will provide you with occupancy of that new space you are observing. If you expand your instrument to observe polarization, you will discover polarization. It will be a discovery because it was not measureable when the instrument that did not have polarization.

Sullivan

So you have a philosophy that nature will take up all these degrees of freedom that are possible in essence?

Bracewell

Iím persuaded to that by experience. Iíve applied this once or twice. When the 3k radiation was discovered it was reported as isotropic. Well, of course it was 3 Ī 1 degrees. I said to myself, either this is going to be a new branch of science or not. If it proves to be perfectly isotropic then there is only one number to measure. When thatís been measured, and of course, as a function of frequency, that will be the end. If it is to be a new branch of science then there will be structure to be observed on the sky. So I began to imagine what the structure might be. I thought you might see a lacy network. You might see cracks between the parts of the universe as it broke up, or you might find three great lumps.

No one would ever do the theory of a universe that broke up into three lumps. They will do the theory of an isotropic universe, or they will do the theory of a universe with homogenous turbulence, thatís to say with an infinite number of things. Something thatís Gaussian, that sounds like a good theory. Or they might do something with a dipole or a quadrupole moment. But if the universe broke up into something like a pyramid with four points, no one would ever do the theory of that. That is the sort of thing one discovers. And if you were to look at the sky and find there were three great big lumps there with cracks running between them, everyone would say, "Great." Then theyíd do the correct theory.

Sullivan

And say, "We should have known it all along."

Bracewell

Alright. So I said, "Letís have a go at this." So we did two things. I had one 60 foot dish and I thought of a very ingenious instrument that could be put at the focus, and look for variation from three degrees. So we did that. Ned Conklin had just joined me as a young student and he did the observations. And he hated to do it because for the first few weeks he couldnít see anything. And I kept telling him, "Ned, this has got too much thermal instability here." So weíd bring all the equipment inside and we turned lamps on at hourly intervals during the night. Weíd turn the lamp on for an hour and then turn it off. Then weíd look at the record to see if this modulation got through. So gradually this instrument became more and more stable. But still we didnít see anything. It was a null experiment. Well some of the best experiments are null experiments. The outcome of that was that we were able to show that 3 millidegrees, 3 milliKelvins, Iíd never heard of a milliKelvins, 3 milliKelvins was the biggest that the departure could be from isotropy in the strip of sky that we observed. For some years nobody could beat that. And it hasnít been beaten by much now. But itís been quite impressive how much it fit into cosmology. All sorts of people use it. The next thing we did was to say, "Well, that was too bad. We didnít find all these cracks and things. That was too bad. But letís have a look for the absolute velocity of the Earth through the cosmic sea of photons." And we were the first to find what is now known as the great cosine in the sky with an amplitude of about 3 milliK, about the same as before, about 1 part in 1,000.

Sullivan

About 300 kilometers a second.

Bracewell

About.

Sullivan

With what kind of reliability?

Bracewell

Well we donít know what the plus or minus would be on that. Itís probably 20% or so, you see. But we do know now because itís been confirmed. Now the history of that is kind of interesting. That was done about 1968, I suppose, more than ten years ago. And the outcome was that we measured the velocity component parallel to the Earthís equator. We did not measure the component parallel to the Earthís axis because we used the rotation of the Earth to do it. Now the instrument was very clever. It consists of a pair of electromagnetic horns inclined about 45 degrees to the vertical, comparing whatís happening in the east with whatís happening in the west. And at intervals of a few minutes we interchanged the two horns. Now the horns are made as identical as possible. The T junction between them is made absolutely symmetrical and tested and reversed and all sorts of things done to it. And then on top of that weíd just rotate the whole set up. Well that proved to be a very clever thing to do and revealed this sinusoid. It also revealed a bump where the Galaxy went overhead. And so for that reason, but really more for another reason, I wasnít sure that this result was right. The other reason is, suppose there is a gradient of temperature in the atmosphere, suppose when you look towards the east itís hotter than when you look towards the west, which it might well be. We were on top of a mountain at 14,000 feet but nevertheless there is a sea in one direction and the continent in the other direction. Now supposed there is 3 millidegrees resulting from that. Oh, boy, you see. Youíd have to repeat this on the other coast. So we didnít advertise that much. That was duly published in Nature [Conklin, E.K. Nature 222, 971, 1969] and Ned Conklin reported on it at an IAU Symposium in Stockholm and that was duly written up and of course thatís available in his thesis. But we did not go around shrieking that weíd discovered the absolute velocity of the Earth. However, about seven or eight years later, with vastly improved instrumentation, Berkeley using U2s and Princeton using balloons repeated this. And in right ascension and in velocity they bracket us. Our result agreed better with Princeton than Berkeley agreed with Princeton. And we agreed better with Berkeley than Princeton agreed with Berkeley. Neither of those chaps, theyíre about two standard deviations apart, and we agreed within one standard deviation with both of them. So Iím convinced now that that was the first detection and a reasonably accurate measurement of the absolute velocity of the Earth. Whether itís with respect to what, I donít know but there it is.

Sullivan

But you bring this up as an example of just do it, and see whatís out thereÖ

Bracewell

Absolutely right, thereís something there.

Sullivan

One final thing is Iíd like to hear your version briefly of the famous polarization of Centaurus A on the 210 foot story.

Bracewell

Well we had been observingÖ

Sullivan

Who is we now?

Bracewell

Now who would we be? There is a paper of which the authors are Cudaback, Little, and Bracewell. [Little, A.G.; Cudaback, D.D.; Bracewell, R.N. Structure of the Central Component of Centaurus A. Proc. Natl. Acad. Sci. 52, 690, 1964] Thatís David Cudaback, now at Berkeley. [Alec] Little you know. We wrote a paper based on observation with the east-west arm of the solar cross at Stanford. And we measured the separation of the components of Centaurus A at 5 minutes of arc. That would be a precision measurement, about 5.0. It was a precise value. And we also knew that those two components were of different widths, a couple of minutes of arc in one case and one minute of arc and I forget the decimals, in the other case, but distinctly different and of distinctly different central intensities, not so very different in flux density. So it was very hard information. We knew which one was which. Now I had that information with me when I went to Parkes, and the resolving power of the Parkes dish with the receiver which was then available at 10 cm was about 5 minutes of arc. The beam width Ė youíd have to check this Ė was about 5 minutes.

Sullivan

No, thatíd right.

Bracewell

So at first sight it doesnít sound as though you can do this. Youíve got two things 5 minutes apart. But, we also knew from looking at the picture of Centaurus A that these components were not likely to be on an east-west line but were going to be either up and down on this diagonal or on the other diagonal. We didnít know which but from the symmetry of the gadget you could see it would surely be one or the other. So I knew that was going to be some diagonal thing here. Trouble with the way the dish was set up, if you did ordinary TV type scans they were not compatible. You do one scan and the next scan had a zero error that was not right. So as soon as I found that I said, "What weíll do is this. We will do an unusual thing. Weíll scan diagonally. Weíll get both drive motors going together and we will scan up the diagonals, so we will go through one source and then through the other on the same scan, so we wonít have this loss of time while all this happened you see." Now the facility for rotating the horn had just been installed. And as you will of heard, I was the first person to make good use of that ability which that instrument had. However I was a bone fide guest observer and the facility was there; so naturally I wanted to turn this knob. So I took laborious scans on three nights doing this work entirely on my own. All this observation was done with only myself and the man who drove the telescope. They wouldnít let you touch it there. And Tom Cousins, who was down in the next floor, controlling the receiver which was still a bit sensitive. He had built it but he made sure the gain stayed constant, watching a monitoring meter and so on. So I scanned up this thing and did these diagonal scans. And because of hysteresis in the drive, I had to scan horizontally, turn on the north-south drive. It would go up this way. Turn the north-south drive off and go that way. Then back up. And then determined what the hysteresis would do, I did staggered diagonal scans like that. They were a very unusual thing, never been done since. But it was just what was needed to go through these two components in quick succession and see what was happening to the polarization. So immediately Iíve got 15% polarization. Now that was staggering because for years Iíd been watching what Connie Mayer did measuring 1% polarization in this, and the half polarization in that. And polarization had become a very tedious thing which one didnít want to launch into lightly. And all of a sudden we discover that if youíve got the resolving power, youíve got the polarization. It revolutionized polarization. So thatís the story of what happened.

Sullivan

Anything else you feel should be covered up through í62 orÖ

Bracewell

Thatís the whole story of my life.

Sullivan

The whole story. Thank you very much.

End of Interview

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Modified on Wednesday, 17-Dec-2014 08:40:19 EST by Ellen Bouton, Archivist (Questions or feedback)