NATIONAL RADIO ASTRONOMY OBSERVATORY ARCHIVES

Papers of Woodruff T. Sullivan III: Tapes Series

Interview with Sebastian Von Hoerner
At NRAO, Green Bank, West Virginia
February 23, 1977
Interview Time: 18 minutes
Transcribed by Sierra Smith

Note: The interview listed below was either transcribed as part of Sullivan's research for his book, Cosmic Noise: A History or 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.

Sullivan

Ok, this is taking to Sebastian von Hoerner in his office at Green Bank in West Virginia on 23 February 1977. Well, could you please tell me a little bit about your educational background and when you first became involved in radio astronomy and heard about radio astronomy?

Von Hoerner

What I originally studied was theoretical physics.

Sullivan

Where at this?

Von Hoerner

This was in [University of] Göttingen after the war and then I got interested in hydrodynamics and finally made my thesis with [C. F.] von Weizsäcker and we applied hydrodynamical concepts, like turbulence and later on shockwaves, to astrophysical problems and this is the way I came to astrophysics.

Sullivan

I see. What kind of problems did you use?

Von Hoerner

Well, in general, the behavior of gas in the Milky Way, let’s say, or in some stars, clouds, and what kind of turbulent motion you have and could we apply our laws of turbulence, like [?] spectrum to the motions we see and, in addition, what do we do if it gets compressible because all our laws of turbulence are confined to the incompressible case.

Sullivan

I see. Did you go to any of these conferences, like there was one in Cambridge?

Von Hoerner

Not recently. Yes, in Cambridge I was.

Sullivan

’53 was it?

Von Hoerner

Yes, yes. That was my first conference.

Sullivan

There were some radio astronomers there. Do you remember that at all? Did it strike you in any sense about what was happening?

Von Hoerner

Somehow at this time radio astronomy hadn’t appeared on my horizon.

Sullivan

So when did you finally obtain your PhD?

Von Hoerner

’51 or ’52.

Sullivan

And you stayed on in Göttingen?

Von Hoerner

Yes and I stayed with von Weizsäcker and we worked on astrophysical problems, mostly in connection with hydrodynamics. And later on I got very interested in other things like dynamics of groups of stars, star clusters, so I busy on the n-body problem and actually I was the first to just integrate the n-body problem on the computer starting with a random configuration.

Sullivan

Which computer was this?

Von Hoerner

This was a very slow computer and in order to work it work, I could only use weekends when nobody else wanted it and I had to make my own program completely automatic so that when the next user came on Monday morning, he just pushed a certain button and all the present state was punched on tape and so I could enter that and continue next weekend, and so that took many weekends.

Sullivan

Right. But when was this about?

Von Hoerner

This was around ’60.

Sullivan

And what kind of computer was this?

Von Hoerner

This was finally Heidelberg’s. This was after I moved from Göttingen to Heidelberg. I was at the Astronomische Institut in Heidelberg, and we had a Siemens, I’ve forgotten the number, and you would now consider it impossibly slow.

Sullivan

But that’s not really relevant. Was it one of the best at that time available in Germany?

Von Hoerner

Yes and actually I have been in the computer business from the very start on in Max Planck Institute in Göttingen where I grew up, so to say. We developed and built the first electronic computer on the continent. At this time, America had some and England had one but, on the continent, we developed the first.

Sullivan

And what was the name of that computer?

Von Hoerner

G1, Göttingen 1 and it was not built for computing with it; it was built for learning how to build computers, and when it was finished we found out, gee we can use it. It made five operations per second and it had a memory of 26 words.

Sullivan

That’s five times faster than a human.

Von Hoerner

And finally we found all kinds of tricks and we solved even partial differential equations with it. After that [???]. It was very exciting.

Sullivan

What is the title of the Max Planck Institute at Göttingen?

Von Hoerner

The overall institute was for physics, theoretical physics, and Heisenberg was the director and it had a department for astrophysics and there was [Ludwig Franz Benedict] Biermann and von Weizsäcker and I was in Weizsäcker’s group and he is a very fascinating man. Actually, he is the reason I came to astrophysics. I wanted to be his student no matter which field.

Sullivan

I see. What was it about the man that fascinated you?

Von Hoerner

Tremendous, broad background. For example, he had studied physics but he got offered a chair for philosophy, which in Germany is next to impossible to get a chair offered for something you hadn’t studied, and also a very remarkable person, personal stuff. So I was very glad I was his first student and [???].

Sullivan

So when was it that you first began to be cognizant of radio astronomy?

Von Hoerner

Well, this came much later. I was in Heidelberg, and I think it was the end of ’59 or the beginning of ’60 that I got a letter from Otto Struve, who then was director in Green Bank and he invited me to come for one year as visitor and I thought, gee, this must be a mistake. And I wrote a letter back to him that I was very honored and pleased by his offer but I should honestly tell him that I never had the slightest touch with radio astronomy. I just barely know it exists and he wrote back he’s well aware of this and he still invites me and I could do whatever I like. My second letter was, "Well sir, I have warned you but now I accept." And so I came as a visitor and I really got fascinated by the field of radio astronomy and by the people I met here and by the whole spirit of the place.

Sullivan

What do you think was Struve’s motivation. To have a theorist on staff?

Von Hoerner

Yes and just to get more people with broad backgrounds, I think.

Sullivan

Rather than electronic engineers or people that knew radio receivers?

Von Hoerner

Yes, yes. He just wanted to have a broad variety of people.

Sullivan

And so, you came here in 1960?

Von Hoerner

I came in 1960 and just with my wife and we left the children at various places in Germany and stayed here for a year and I got completely fascinated by all I learned here.

Sullivan

Now tell me about who was here and [people and ?].

Von Hoerner

Well, I like Struve very much and I got very fascinated and (was?) good friends with Frank Drake and this was just the time of Project Ozma and now that was a really great thing. Actually, I had thought about life in space long before that, but I wasn’t aware that this was something to take serious scientifically.

Sullivan

That it was feasible to actually...

Von Hoerner

Yes, that you really could so something. See, that was a great time.

Sullivan

Did you participate in Project Ozma at all?

Von Hoerner

No, just over coffee breaks. Had lots of them. Actually coffee breaks are very important thing here at Green Bank and from the beginning on [???]. We had lots of discussion and sometimes we claim all the important things were discussed over coffee breaks and the rest of the time we work out the details.

Sullivan

Well, I’ve always been impressed by the cafeteria which has paper and pencil at every table just ready to go.

Von Hoerner

Well, the first years we used the place mats and napkins.

Sullivan

Do you know who came up with that idea originally? I’d be interested.

Von Hoerner

No, no. That was long ago.

Sullivan

Now Struve was only here for a year or two years after you...?

Von Hoerner

Yes, it might be two years and he was a modest man and a very good scientist but the trouble was he was just too old to build up something completely new and out of his field. If it had been an optical observatory it would have been ok. Or if the place had been built up already and you could take over that would have been ok. But it was just too much and so he also felt frustrated and didn’t feel that he had enough strength and insight to really do the job as good as he wanted. So he felt frustrated and also his health was very bad [???].

Sullivan

Yeah. Sure, sure. Why was it at least to your knowledge that the directors picked a prominent optical astronomer, that AUI [Associated University, Inc.] picked an optical astronomer?

Von Hoerner

You know, this I cannot tell. I can only guess and I think the idea was that it should be someone with a lot of experience which means older. At this time, there was no older radio astronomer around. Struve just was well known and had a very broad background and was very open minded ([???]

Sullivan

Well, [in particular, Ozma apparently was all [???]]

Von Hoerner

And he was [???]. Only the problem with the 140 foot was overwhelming and other things.

Sullivan

What other people fascinated you and what other conditions here fascinated you here at that time?

Von Hoerner

Well, there was [David S.] Heeschen and Roger Lynds, and I think [T.] Kochu Menon was also here but I have a very bad memory, infuriating. What fascinated me was- so this is the total of it, not so much the details but the spirit of the place. It was something, at this time coming from Germany which was just tremendously different.

Sullivan

Can you describe how?

Von Hoerner

Things in Germany were much more formal and stiffer at this time, old fashioned and traditional. Here all of a sudden everything was possible and the contact between people was much closer.

Sullivan

On the staff, you mean?

Von Hoerner

Yes, on the staff and also to director and to the students on the other side. It was much more personal and free and frank and lots of cooperation, not so much competition. Nobody gave a damn for [???]. They were all just interested in what we were doing.

Sullivan

Now, you say that all things were possible but still there was only a single 85 foot dish here?

Von Hoerner

Yes, but I mean if someone came up with an idea for a new telescope it was consider possible. Why not? It’s only a few millions, well sure.

Sullivan

Ok. So I guess that’s the way the 300 foot got built, would you say?

Von Hoerner

Yes, yes.

Sullivan

Were you involved at all in thinking about the design of the 300 foot?

Von Hoerner

No, not at this time. I started to think about telescope designs very early, even in this first year as a visitor. The way it went was I got very interested in cosmology and by studying it for awhile, I had the feeling that we don’t need any more new theories. We have already much too many, and we cannot make a decision between any two of them. What we was need was more of a baseline. When I looked into that, I found out we needed large telescopes and at this time, I tried to design a telescope, [one purpose?] telescope for cosmology purposes. But later on this was given up. It turned out it was too expensive for a single purpose telescope.

Sullivan

What was this telescope going to do?

Von Hoerner

It was a reflecting cross. It’s like a big cross antenna but reflecting from both arms into open mirrors into one focus so it would be [?] instrument with a very high resolution, but with a limited steerability.

Sullivan

This would have been, what data were you interested in getting?

Von Hoerner

Well this was [???] and more resolution.

Sullivan

So it appears then that you had hope that log N- log S would be critical?

Von Hoerner

Yes, at this time, we had a lot more hope than we have now about...?

Sullivan

But you would be a good person to ask since you came...?

Von Hoerner

But higher resolution for example, this was also badly needed and would have been one was of getting...

Sullivan

What sort of frequency were you thinking?

Von Hoerner

I don’t know.

Sullivan

Low or high end roughly?

Von Hoerner

Well, let’s say 20 cm. Down to 10 or 5 cm it was accurate. Yeah, down to 5 cm.

Sullivan

So you greatly helped the confusion problems which hurts low frequency surveys?

Von Hoerner

Yes.

Sullivan

But you would be a good person to ask being somewhat unbiased at that stage if you can remember how you were thinking. Here you had the 2C and 3C surveys and you had Mills’ survey and of course the battles going on, how did you view these?

Von Hoerner

Yes, at this time they didn’t agree at all. And I studied this for awhile and I actually came up with a solution that they both had underestimated the confusion limit and had badly underestimated it so they were both confused and because of that didn’t agree and had lots of wrong sources.

Sullivan

Yeah, that was basically right.

Von Hoerner

Yeah.

Sullivan

Mills perhaps not quite as much as Cambridge. Now, did you ever publish?

Von Hoerner

Yes, I published a paper about the confusion limit and this has been used later on widely.

Sullivan

Where was that?

Von Hoerner

[???]

Sullivan

Ok. And so you didn’t lose faith in radio astronomy because of this discrepancy?

Von Hoerner

No, on contrary, lots of things to be done.

Sullivan

Right but I think some theorists perhaps did or at least, optical astronomers. They looked at it and said, you know good lord get your house in order and then we’ll listen to you or something.

Von Hoerner

Well, yes and that is a good statement and we tried to get our house in order.

Sullivan

Do you remember this attitude at all in talking with other cosmologists?

Von Hoerner

Oh yes, yes, sure.

Sullivan

Can you name any names?

Von Hoerner

[?].

Sullivan

Ok. So how did you get into antenna design [???] [talking over each other] cosmological?

Von Hoerner

Yes, first I was here only for one year and then we went back to Heidelberg and because of our children we had this feeling- I mean, I was offered to stay here but we had the feeling that we had to go back. And then later on came the big meeting in Berkeley and I saw all these colleagues again.

Sullivan

That’s the ’61 IAU [International Astronomical Union meeting]?

Von Hoerner

Yes and I found all my love for Green Bank came back and it didn’t need much talking to talk me into coming back, and we found that we just could make it. My wife stayed with one of our two children a little longer for the oldest to finish high school and I came here with the second boy and a year later my wife came with the rest of the family, and so we somehow managed. It was difficult with schools, but we somehow managed and the children haven’t been hurt by it, not at all.

Sullivan

And you’ve been here ever since.

Von Hoerner

Yeah.

Sullivan

So why was it that you got more and more into antenna design even though it wasn’t really cosmology? Your training had not been in structural engineering and so forth.

Von Hoerner

No, but I have changed my field of activities several times in my life, many times, and that was just one of these things where all of a sudden a new field which I hadn’t thought of before, I had never touched, got so fascinating that I forgot about everything else. So the last 10 years, I have devoted most of my time to [?].

Sullivan

What was it that fascinated you about this?

Von Hoerner

Well, I think I got this idea fairly early that there are natural limits in telescope design- well, let’s say, I discussed it with engineers. What defines the accuracy of the telescopes between the shortest wavelengths and what defines the cost, the price of a telescope. And I was completely dissatisfied with their answers, and I had the feeling that nobody had studied these things from scratch, from basic physical things on. And so very early I developed what I called natural limits of telescopes regarding the accuracy which means that for a given size you cannot make it more accurate than a certain accuracy given by that size, no matter what you spend, but up to that limit the cost shouldn’t depend much on the accuracy. So building a sloppy telescope is not much cheaper than building the best for that size. So that was the first and when I developed these natural limits, the most important one was what I called the gravitational limit, that gravitational deformations really define the precision of a telescope. So the next question was what can you do about it. And then I found that it is not the deformations but the deviations from a parabola which [???] and that the receiver automatically makes, so to say, the best fit or finds the best fitting parabola...

Modified on Wednesday, 30-Jan-2013 09:50:01 EST by Ellen Bouton, Archivist (Questions or feedback)