Interview with George A. Seielstad
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The interview listed below was either transcribed as part of Sullivan's research for his book, Cosmic Noise: A History of Early Radio Astronomy (Cambridge University Press, 2009) or was transcribed in the NRAO Archives by Sierra Smith in 2012-2013. The transcription may have been read and edited for clarity by Sullivan, and may have also been read and edited by the interviewee. Any notes added in the reading/editing process by Sullivan, the interviewee, or others who read the transcript have been included in brackets. If the interview was transcribed for Sullivan, the original typescript of the interview is available in the NRAO Archives. Sullivan's notes about each interview are available on the individual interviewee's 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 a 2012 grant from American Institute of Physics, Center for the History of Physics, which funded the work of posting these interviews to the Web.
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.
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Sullivan
Ok. This is talking with George Seielstad at Green Bank on 22 May 1985. George, would you tell me where you went as an undergraduate, what you studied, and then how it was you came to Caltech, and how you came in contact with radio astronomy first?
Seielstad
I was an undergraduate at Dartmouth College, majored in physics. I went to grad school at Caltech. I got my degree from Dartmouth in 1959 and went as a physics graduate student to Caltech. I chose Caltech partly because of the excellence of its astronomy, but when I went there I had no idea that they did radio astronomy. As a matter of fact, I didn’t know what radio astronomy was.
Sullivan
You had not been a radio ham or anything like that?
Seielstad
No, I didn’t have that kind of background either. The graduate program at Caltech had a lot of coursework for about two years but in that time you were supposed to find someone to work with on a thesis and in early in 1960, I had a chance to go to the Owens Valley. Well, it was very funny. A chemistry professor on leave from Dartmouth was spending a year at Caltech. He had heard about the radio observatory, wanted to drive up and see it, wanted to know if I wanted to go, and I did with another chemist and John Bolton was there. We stayed overnight. He put us to work in his characteristic style. I mean, he welcomed us, took care of us, showed us everything, let us stay all night, and then said, "You know now you should do something for us," and we dug holes for planting trees and the guy was amazing. Anyway, Bolton, as far as an individual having an influence, it was John Bolton. He was really dynamic but heart of that program. He lifted it off the ground alone, I think, and deserves a big place in the history of radio astronomy. He was really a dynamo and I was very attracted to his group and talked to him- could I get into it, and they were dying to get people in. He took everybody he could get his hands on and I consider I arrived at the perfect time at the perfect place because the field was still so young and so many things were about it happen at Caltech. And it was little bit, like Frank explained yesterday, you made a discovery. I mean you know, you did something with a telescope, it was a discovery because so little was known.
Sullivan
That was Frank Drake referring to the early days of Green Bank.
Seielstad
That’s right, yeah.
Sullivan
Now, why do you say it was the perfect time? What was actually at Owens Valley? What was happening at that time?
Seielstad
Well, this was early 1960. They finished one of their 90 foot dishes at the end of 1959 and the second one at the end of 1960, or early in 1960, so I was there just as the interferometer was getting started. Frank talked yesterday about an 85 foot dish here. Well, at least there had been some research in that. Interferometry wasn’t a new technique but it was newer than say having a single 85 foot dish. There was a lot of work to do, and there it was and they needed manpower to get involved.
Sullivan
So you started working up there as a research assistantship or something like that?
Seielstad
Yes. I got into the Bolton group, the radio astronomy group. I spent the summer there. But I still had a lot of class work, but during every break and vacation, you would go up to the Owens Valley. And while you were in Pasadena, John would ask you to make power supplies or, you know, in some way you were still involved in what was going on and still helping him a lot. And the group was John Bolton and Gordon Stanley mostly handling the electronics and then Jim Roberts came occasionally. Rad [Venkataraman Radhakrishnan] came later. There were really very few people involved and the few who were there sort of worked around the clock to make things go.
Sullivan
And then three or four students besides yourself?
Seielstad
And then he picked up students. Ken Kellermann and well, the initial grad student in radio astronomy at Caltech was Dan Harris. Following him, Dick Reed, Bob Wilson, and Al Moffet all came in the year before me. And then my year was Barry Clark, Ken Kellermann, and Fritz Bartlett who ended up in computer programming and high energy physics and then we were followed by others, Glenn [Berg/Berge?] and Ed Fomalont.
Sullivan
So it sounds like you just learned radio astronomy by doing it there?
Seielstad
Yes.
Sullivan
There were no formal courses?
Seielstad
No, but they did then have a course, a one semester course, and Martin Schmidt taught it. But Martin, although we think of him as an optical astronomer, had done 21 cm work at Leiden and he tried to keep in touch. So there was a course. But see the nice thing was in those days if you entered radio astronomy then someone would say, "Why don’t you read the literature?" You could read it all. You could read every radio astronomy paper. You only had to go back- well, if you went back to [Karl] Jansky, ok 18 years but then it was a handful of papers.
Sullivan
And so, in fact, was that the typical thing that you did?
Seielstad
Yeah, you would sit down and think well, I’m going to learn something about radio astronomy and you’d start reading the papers and you know, after a few weeks, you’d realize there were no others to read.
Sullivan
So, what about the other optical astronomers? You mentioned Martin Schmidt. Do you feel that they had an influence on what was going on from your point of view as a graduate student?
Seielstad
No.
Sullivan
It was really just Bolton and [Gordon J.] Stanley [???]?
Seielstad
No. I think it was a really strange story. I think the radio astronomy group at Caltech started because, I think, the vision of the Office of Naval Research which felt we wanted to get some radio astronomy going in the U.S. and Lee DuBridge, who was president of Caltech, and Bob Bacher was the chairman of that Division of Physics, Mathematics, and Astronomy, and they wanted to start radio astronomy. The radio astronomy group, it was my impression, was treated by the optical astronomy establishment as sort of second class citizens. None of those people had faculty appointments and, in fact, it was probably late in the 1960s before they appointed a radio astronomer to the tenure stream faculty and that was Al Moffet. The rest of the people were research fellows or senior research fellows and I think there was always a feeling in the optical astronomy group that radio astronomy was like ham radio or something.
Sullivan
Well, they were willing to say it had exciting results apparently but that the people didn’t have the right pedigree?
Seielstad
Well, I think that’s funny. Yeah, they certainly didn’t have the right pedigree. I don’t even think- well, Bolton may have had a Ph.D., I’m not sure about that, he may not have. And they were a different- they were not as gentlemanly as the old line optical astronomer with Palomar Observatory. Now John mingled well with people; John Bolton did and I think commanded a lot of respect but it was rather a separate enterprise. The optical identification work was mainly Tom [Thomas A.] Matthews and Allan Sandage, I guess, and maybe some others. Tom Matthews got more involved with the optical astronomers than anybody but that was kind of an individual basis.
Sullivan
There was just one graduate student who sort of had a link?
Seielstad
He was a research fellow at that time. Tom had his Ph.D. from Harvard and he got into the optical identification business and then he’d feed positions to the optical astronomers and they’d do identifications, but I wasn’t- no, I think it was a bit unfortunate.
Sullivan
Well, this is interesting because one person you haven’t mention is Jessie Greenstein who I always think as being another key person besides DuBridge and Bacher and then, of course, [Walter] Baade and [Rudolph] Minkowski made important contributions in the ‘50s.
Seielstad
Yeah, yeah, that’s true. Now that connection between Bolton and Baade and Minkowski had been- well, I think John wrote them a letter from the southern hemisphere asking about various radio sources way back before he came at Caltech. And John may have moved with those people but see not only were there no real tenured positions in radio astronomy but Caltech had put a lot of private money into Palomar [Observatory] and into the astronomy operation in general but it was a long time, it was into the ’70s probably or ‘80s maybe before a sort of equivalent amount of private resources were put into the radio observatory. It was a long time.
Sullivan
Before that...
Seielstad
You got your own money. You know, you got a grant or something and did research with it and that difference persisted for a very long time at Caltech.
Sullivan
That’s very interesting. Well, let’s switch to the science that you were doing there. What was seen to be the important problem to do with this interferometer or setup problems?
Seielstad
Of course, the main things were position measurements fast, and that got them into the optical identification business. Then the Moffet and Maltby research. John’s idea of the interferometer was- I don’t know if he was thinking mapping but he was certainly, the structure of radio sources, angular sizes.
Sullivan
The visibility curve?
Seielstad
Visibility curves and that kind of analysis so that was regarded as big. When Rad came, he was very interested in polarization. At that time, it was still- no, I guess we thought synchrotron radiation was the mechanism but polarization still hadn’t been discovered, and it was quickly. But Rad had clever ideas about how to use an interferometer, cross dipoles, and the coherence between them to measure polarization. And he, Dave [David] Morris, and I spent a lot of time developing that technique and then measuring the polarization of sources.
Sullivan
This was extragalactic radio sources primarily?
Seielstad
Nearly all extragalactic, although we had the Crab Nebula in there. And then we tried to go- well, we did two things. We measured the polarization at several frequencies and got into the rotation measure business and the galactic magnetic field. And we also then tried mapping with, how did we call it, well, we called it interference polarimetry but then we also tried mapping the polarization distributions across some sources.
Sullivan
Across the source?
Seielstad
Yeah.
Sullivan
How the vector changed.
Seielstad
That’s right.
Sullivan
And that was basically your thesis which came out in ’63?
Seielstad
That’s right. I got my Ph.D. from Caltech in physics actually in 1963.
Sullivan
And was this polarimetry was that part of Bolton’s plan also or was that pretty much Rad coming in?
Seielstad
Well, I would probably, Rad’s influence. I mean John had a vision about the interferometer and what he wanted to do but I think the polarization idea probably was Rad’s.
Sullivan
Well, now another question I am interested in is, you have this variable spacing interferometer and can you remind me again, did it start off as just an east-west?
Seielstad
No, from the start there was a T. Well, it was almost more an L than a T. There was a little stub.
Sullivan
And what was the reasoning for making it that way?
Seielstad
Well, I think they wanted 2 dimensional structure and even positions. I guess nobody knew it was aperture synthesis at the time but they had the idea of sampling the UV plane and they did actually. If you look at the Moffet Maltby papers, they started off, I think Al maybe had to write his thesis and he just had the east-west data then or something. But he added north-south things later on and even some hour angle tracks. They measured off at hour angles. I think they had the idea of we’ll get the full two dimensional UV coverage and invert and get 2 dimensional structure and they did a little of that. I know on Centaurus A, Maltby had a- it was fortunate-but they had a long track- not long, sort of an hour and a half either side because the source was at -42° and that was the most you could follow it. But it just happened that the visibility curve had wild ups and downs and they fit a detailed model of Centaurus A to that data. And also in one of Moffet’s papers, Hercules A was picked out with a 2 dimensional structure and he had measured at odd hour angles and with the north-south spacing and east-west and I think they were very much on the track of full aperture synthesis.
Sullivan
Is it correct to say that the reason that it wasn’t quite the same as what Ryle was doing at Cambridge in this same era is that they did it in terms of models of separate visibility cuts and they never did a full Fourier transform? Let’s see, how good was the phase information on all of this?
Seielstad
It was primitive but there was phase data. There was, it was- yeah, no, Al actually had enough phase that you could tell the brighter source was on the east or the west or that kind of thing and, you know, that was to be perfected, but there was phase information. Moffet certainly knew about Fourier transforms and played around with it. But you’re right, the first approach was the models to the visibility curves.
Sullivan
Well, something that hasn’t been explicitly mentioned yet is you’re operating now at very high frequency compared to what Cambridge was using so phases were much more difficult.
Seielstad
Yes, that’s right. They started at 31 cm, 960 MHz and the funny thing is in those days, that was regarded as a high frequency and you hoped your dishes would work at 21 cm because of the hydrogen line and people thought, "Wow, that’s really short wavelengths."
Sullivan
So what was the push for the high frequency? Simply resolution?
Seielstad
Probably that. That was Bolton’s idea too and I don’t how why. I don’t know if he had some strong feeling about sources or just thought this is unexplored and let’s start there. I’m not sure of the answer to that.
Sullivan
Do you think that in hindsight it may have been a hindrance to fully developing aperture synthesis there because the phase thing was so difficult?
Seielstad
No, I don’t think so. No, because I mean look at Moffet’s paper. There was enough phase information there to help with the source structure. I think it would have worked and then, you know, right after Al, [Edward] Fomalont started a similar thing at, I think, 2800 MHz and they were getting phase information and everything. He was more into the... No, I think they could have done the technique then too.
Sullivan
Do you think that the ONR [Office of Naval Research] funding had anything to do with it, that the military would be much more interested in centimeter waves?
Seielstad
No, the ONR deserves a lot of credit. It was not military at all except in the sense, I guess, the big, broad picture, the military thought if we have a lot of very bright people and always continuous, new ideas it will help the security of the country. But they did not direct Caltech in any way about what they were supposed to do. And actually that point should be brought out in history because you wonder if we are doing the right thing now. I can remember, not John Bolton but Gordon Stanley, showing me the proposals, what we would now call a proposal, and basically you wrote a one page letter to [Arnold] Shostak at ONR saying, "Well, we would like to continue our research in radio astronomy." You might say, "We are going to put 21 cm receivers on the interferometer this year and we’re going to do planetary studies and extragalactic and galactic." And the thing was one page. And we’ll need $250,000 or something like that and you’d get it. There weren’t reviews and I mean Shostak either gave it to you or he didn’t give it to you and they didn’t meddle in any way. Their approach was pick bright people and you’d try to size up these people and if those people thought they had a good idea, you’d funded them and they pursued it. It really made something good happen there at Caltech. It worked in many instances. But no, as far the military trying to tell Caltech what they were interested in and what they hoped they’d do, it didn’t happen at all. No connection.
Sullivan
So, in essence you are saying you spent very little time with the bureaucratic aspects of keeping your funding up, reports and proposals and so forth?
Seielstad
Yeah, that’s right. And there was a quarterly report and again it was a one page letter and that you would just jot down a few things you did and thanks for your support or something like that and send it off. ONR had an office in Pasadena and one Navy officer worked there and he sort of kept track. But no, a minimum, almost zero of fund raising or reporting or, you know, selling your ideas to referees or whatever.
Sullivan
When did that era change?
Seielstad
Began changing, gee, ONR that was a long time. It was into the Vietnam War and the Mansfield Amendment, the military shouldn’t fund universities that ONR funding just sort of dried up and we got, gradually as it was going down, NSF [the National Science Foundation] started picking it up.
Sullivan
In the early ‘70s?
Seielstad
Yeah and it’s interesting but I talked to Kurt Reigel just yesterday about, recalling Frank Drake’s remarks, he said to Struve, "I’d like to try this," and Struve, "Go ahead." You know, no referees, no proposals, no anything and Kurt said, "Yes but astronomers to some extent, users of telescopes brought this on themselves." It’s not quite true the NSF imposed this on everybody. When you reach the stage that there was only so much money and others wanted a part, it began to get into what did you give the money to this guy for. You know, I wanted to do this, my idea is better and then you need to set up some mechanism to start judging and start choosing.
Sullivan
When there were only a couple dozen radio astronomers in the country it was different.
Seielstad
Well, and radio astronomy, remember, it was strange the way it started in this country. It had already started worldwide and in this case maybe even bureaucrats thought, "Why isn’t the U.S. involved in radio astronomy. Let’s see if we can start some centers and we’ll give them the money to do it." So it was the opposite today where you are sort of trying to promote your cause and get money; someone was trying to dump it on you. It was a different scene altogether.
Sullivan
Are there any points about the scientific results we haven’t discussed? I mean, what do you see as the main contribution that came out of that work in polarimetry, I guess, primarily at that time?
Seielstad
Well, the fact that many extragalactic radio sources were linearly polarized even though it was just a few percent did sort of nail sort of the synchrotron theory. Since then everyone believes the primary radiation mechanism is synchrotron radiation. Also it was a nice study of the galactic magnetic field, the Faraday rotation through the galaxy. There was such a nice dependence of rotation measure on galactic coordinates that it was fairly convincing that most of it took place in the galaxy and even though people had talked about polarization of star light and that work had been done in the ‘50s and there was a feeling there was a galactic magnetic field, this helped a lot, I think, to establish the reality and the strength and the direction of the galaxy’s magnetic field. We can’t claim credit for that at Caltech. [Francis F.] Gardner and [John B.] Whiteoak in Australia had the first results and beat us. We were all working at the same time and they got there first but the combination of the southern data and the northern made kind of a nice picture. I think that work was valuable.
Sullivan
Was that part of the original plan in the program or was only developed after it became apparent that there was a lot of polarization that you could measure, and therefore we could do this with it?
Seielstad
I think it developed later. I think we thought let’s see if we can find polarization in any sources and the funny thing was that we all picked, of course, the strongest sources in the sky and that included Cygnus and others and even in retrospect those are very weakly polarized. So we just started with the wrong list and once you went down one order, the next order of magnitude, generally all those sources were polarized and so a little bit of bad luck. People beat their heads against a wall for awhile trying to establish detection of polarization and then it became widespread.
Sullivan
And I’m interested in your assessment of the status of synchrotron radiation. Of course, polarimetry and the Crab had been done at NRL [Naval Research Laboratory] and optically it had been done, M87 optically the jet was known to be polarized but it was still thought that these were just peculiar instances or that might not still be synchrotron?
Seielstad
You couldn’t find it in a lot of sources. I think the prejudice was that it was synchrotron radiation or that was your feeling that it was but then you thought well then these radio sources should show some polarization and they weren’t. I mean it was very hard work to find it at first and then boom, all of a sudden you could find it. And no, [Geoffrey R.] Burbidge had already written his theoretical papers, and [Iosef Samuelovich] Shklovskii, and it was the best idea around but this helped. I mean this added another element of support.
Sullivan
I realize this is before your era but I’d be interested in your comments on why do you think there was this lag in the development of radio astronomy in the U.S. compared to Britain and Australia and France?
Seielstad
That’s a good question, Woody. I’m not sure I know. See, to get it started you brought in foreigners. You know, Caltech brought in Bolton. And NRL started it with sort of a home crew and started before Caltech, I think. But others, even Harvard, every place that got started would go some place in the world and find a radio astronomer, and say we would like to do this too or something.
Sullivan
Or the opposite happened, I mean, Charlie [Charles] Seeger started at Cornell, didn’t get far, and went to Leiden.
Seielstad
Yeah, that’s right. I’m not sure why it was so slow going here, custom or habit or something.
Sullivan
Ok, well thank you very much.
Seielstad
Ok, Woody.
Sullivan
That ends the interview with George Seielstad on 22 May 1985.