[Westerhout, 1966]
Westerhout with the 300 foot, 1966 (Photo courtesy of NRAO/AUI/NSF)


[Westerhout and Frank Drake]
Westerhout and Frank Drake (Photo courtesy of NRAO/AUI/NSF)


NATIONAL RADIO ASTRONOMY OBSERVATORY ARCHIVES

Papers of Woodruff T. Sullivan III: Tapes Series

Interview with Gart Westerhout
At Max Planck Institute, Bonn, Germany
November 22, 1973
Interview Time: 2 hours, 20 minutes
Transcribed for Sullivan by Bonnie Jacobs

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.

Part 2 | Part 3

Sullivan

Alright, this is talking with Gart Westerhout on 22 November ’73 at Max Planck Institute in Bonn. So how did you get involved in radio astronomy?

Westerhout

In essence by ... you know, when you're a young graduate student you don't really quite know where to go yet. So what I started out doing was working with [Theo] Walraven on amplifiers for photoelectric photometry. I don't quite remember anymore why I sort of expressed an interest in radio or electronics. I fiddled with radio when I was young, and somehow or another that made them assign me to Walraven.

Sullivan

You had studied as an undergraduate in astronomy?

Westerhout

Yes, that's right.

Sullivan

So you're one of the very few early radio astronomers that studied astronomy.

Westerhout

That's right, that's quite correct. [Hugo] Van Woerden is another one.

Sullivan

But he's not quite so early, is he?

Westerhout

Yes, he a year earlier than I. He got his PhD much later but he started in '44. He got out of high school the year before I did.

Sullivan

I see. I didn't realize that.

Westerhout

And there, of course, was a year lost for me during the War. I got out of high school in '44 and of course I lost a full year. Van Woerden got out of high school in '43 and in essence lost two years but did already some astronomy.

Sullivan

I still have to talk to him. That’s why I don’t know exactly when he started. So you worked with Walraven?

Westerhout

Yes. And then, I forget exactly when it was, but that must have been in May of 1950 [Sullivan: July 1950], [John G.] Bolton and [Kevin C.] Westfold were making this trip around the world and they were spending a long time in England and [Jan Hendrik] Oort invited them over to come and give a talk. Apparently they did everything together, they had published this paper shortly before on the distribution of radio emission over the sky, where everything was so beautifully smooth. They had even de-convoluted for the antenna pattern, so-called, which was was 17°. So we really believed that that was the distribution of radio emission at that particular frequency- whatever it was I've even forgotten that.

Sullivan

It was 150 or 200, I think. [Sullivan: 100 MHz, actually]

Westerhout

Something like that, yes. And they came and gave a talk. It was actually rather interesting because there were stages where both of them were standing in front of the blackboard at the same time. I can still see that. Jumping up and down and correcting each other, making remarks here and there. I still remember that colloquium vividly; it was a very interesting one. And I don't quite know how it then came about, but I guess in Oort's inimitable way he simply picked somebody and said, "Would you like to look into this particular problem?" And that's how I started to look into that particular problem. I'm trying to think now whether that was- no, that all went sort of at the same time because I was also looking around that same era at [Walter] Baade's determination of the distance to the galactic center, where he looked at all the RR Lyrae variables. You saw that if you plotted the RR Lyrae variables as function of magnitude, it was a beautiful peak. And making appropriate corrections, you could say something about the mass distribution that governed that spherical distribution of RR Lyrae variables. So all that came in and I don't quite know which came first, the idea of making a model of the mass distribution that fitted the radio data, or the other way around.

Sullivan

But that was influencing anyway?

Westerhout

Those things were all influencing each other.

Sullivan

In the way the final paper came out? What I'm particularly interested in is where did the idea come from to base it on the distribution of stars and the mass distribution of stars? That was the fundamental thing in that paper, was it not?

Westerhout

Yes. That was the fundamental thing in that paper. And that idea came mainly from the fact that when you look- there is a chapter in that paper on the distribution of ionized gas and it was quite clear that the distribution of ionized gas was very much thinner than the observed distribution on the sky. So it couldn't be the ionized gas. Moreover you could show, or we could show, that the intensity from the ionized gas, given certain assumptions and so on, was too low. So although we treated that very carefully, we showed in that paper that it could not be the ionized gas, so what it is you do the next time? You say Ok, the other constituent we know is the stars, if whatever emits that radiation has something to do with stars. And the synchrotron theory was not really known yet. I think that the [Hannes] Alfvén and [N.] Herlofson paper came out in '49 or '50.

Sullivan

April '50.

Westerhout

So when we started that work we certainly didn't know anything about that at all. So Ok, let's look at something that's distributed the same way as the general matter in the Galaxy and see what that gives and adjust it a little bit here and there, and lo and behold it sort of seemed to fit reasonably well. I think the most interesting thing I always find in that paper is the naiveté with which one thought that when you apply a Bracewell-type de-convolution that you then see the true picture.

Sullivan

That you had all the information?

Westerhout

You had all the information and that was the distribution. It wasn't until considerably later- "considerably" means a few years- that we began to realize that, of course, meant absolutely nothing. Side lobes had been removed...

Sullivan

You mean the great smoothness was really leading you astray, and you felt it was actually that way, even with infinite resolution?

Westerhout

Yes.

Sullivan

But this paper, would you not agree, really kept the idea of radio stars alive quite a long while? I mean people had talked about discrete sources as radio stars, but then when you talked about the radio distribution relative to the stellar distribution, then you really began to think of radio stars. Would you say that's fair?

Westerhout

No, I don't think so. Maybe in other people’s minds. But I think neither in Oort's mind nor in my mind did we ever think of discrete objects. Well, maybe we did, yes, because there is an analysis in that paper where you stick in the arbitrary luminosity function and you do all sorts of things that way. Yeah, maybe you're right in that analysis, that one really did think about radio stars. I think we were very careful not to call them stars. We were never thinking of stars.

Sullivan

You never say radio stars.

Westerhout

No, we called- at most we may have talked about objects or emitters or something like that. [Sullivan: "star-like source" in the abstract]

Sullivan

I think that's right.

Westerhout

Radio emitters but we very specifically did not think of stars. That's why I was sort of hesitating there.

Sullivan

So you published this paper in your first couple of years of graduate school then?

Westerhout

Yes, after one year in essence.

Sullivan

That's quite an accomplishment.

Westerhout

And then while I was at it- well, this was, of course, as you may note when you look at the paper, I mean I did the spade-work but Oort did the theory. Oort did a lot of the polishing of the writing and all of that. I mean it was Oort's work and I was the young graduate student assisting in it. But it was a lot of looking up things and finding out everything there was to be found out in the literature up to that time, that's all, including the ideas about the ionized hydrogen, what that would emit. At that same time, [Hendrik C.] van de Hulst wasn't there when we wrote that paper. He was in Harvard that year. The other thing that I suddenly remember, I got when I entered the Observatory as a graduate student, I was stuck in a room together with the Chinese [Sullivan: Indonesian] who had been constructing the 21 cm line receiver.

Sullivan

Mr. Hoo?

Westerhout

Right. Whose building had just been burned down. In other words, I wasn't there [Sullivan: Kootwijk] yet when that building burned down [Sullivan: 3/50]. I didn't participate in that fiasco. But he was sort of sitting there for a while, then he more or less disappeared and as a young graduate student, I never quite knew what happened or what didn't happen.

Sullivan

[Christiaan Alexander "Lex" ] Muller didn't really tell me how that happened, or maybe he didn't know, but what is supposedly how that happened?

Westerhout

It was just an accident. How does anything like that happen? I mean it was a wooden shed in which they were constructing that material, sitting beside the Würzburg.

Sullivan

But there were no people in it at the time?

Westerhout

No! No people at all, that's why it burned down to the ground.

Sullivan

They just came out one morning and found it?

Westerhout

Yes, found it burned down. And it was sort of- you know the area around Kootwijk- if a shed burns there, ok, it burns, that's that. I don't know whether they actually came out one morning and saw it burned down, but it was quite obvious that I don't think it was particularly anybody’s fault. Although I have always had the feeling- people like Oort and van de Hulst would be able to give you more information about that- I always had the feeling that they didn't think much of the efforts of Mr. Hoo.

Sullivan

Well, indeed he wasn't getting very far, apparently. I mean certainly Muller got very fast, very quickly.

Westerhout

Yes, and, of course, Muller just had his Engineer's diploma. They got him as a new fresh guy and he got into it.

Sullivan

So it was while you were working on this paper that the line was discovered [Sullivan: 3/51], I guess?

Westerhout

I think so, yes. It must have been the same time. That was in '51. No, I think the paper was finished at that time or just about to be finished, putting the last touches on it. Because I was still busy working at that time with André Muller, the other Muller, assisting him in observing XE Cygni for his PhD thesis, so spending long nights at the Observatory doing photoelectric photometry. And I continued doing that also after the 21 cm line was discovered. I think the first Kootwijk detection was in May and I went out there almost immediately, a few days later because I was in essence the only student who was involved in radio astronomy at that stage. So I went out there to assist in the observing and then several other students went out. But I only spent a week or two there during that first period... the very first period. Isn't it in this BAN [Bulletin of the Astronomical Institutes of the Netherlands] here that we published that very original line profile- this one, yes. "The first receiver in the summer of 1951." Our switching frequencies were very close together. That’s why you always got that sort of a pattern when you change the frequency.

Sullivan

Yes, Muller showed me an actual strip chart which was about three weeks after the discovery. So then when did you actually get involved in radio astronomy again?

Westerhout

I'm trying to think how that worked because I then...

End of Tape 23A

Sullivan Tape 23B

Westerhout

The van de Hulst, Muller, and Oort paper was in '54. So in between there I spent 8, 9 months in South Africa. But somehow or another I had already gotten enough interest, and, of course, I'd worked closely with Oort on that paper, that I was kept very much informed by Oort in letters and he visited South Africa once and so on. So then I gave lectures and colloquia in several places about structure the 21 cm line and galactic structure in South Africa. In fact I wrote an article in the Monthly Notices of the South African Astronomical Society, a mimeographed pamphlet sort of thing on the spiral structure of the Galaxy as found for the 21 cm. That was in the summer or fall of '52. So by then there was already quite because a bit known, because before this Muller and van de Hulst article [Sullivan: 1954]. They were a few smaller things particularly in the Dutch Academy of Science which already had spiral arms in them.

Sullivan

There was one in Observatory.

Westerhout

And in fact, then on the way back from South Africa I stopped off for a day or two in Cambridge at [Martin] Ryle's place and talked to them. In essence, informed them about everything that was going on. So somehow or another I must have been kept quite well informed by the Leiden group about what was going on, mainly by Oort I would say.

Sullivan

And when you went back you jumped right in?

Westerhout

The guy who did most of the initial observing in Kootwijk was a man named [Walter?] Muller, whose name you might have heard.

Sullivan

No, I haven't.

Westerhout

He did a lot of the initial observing. He was also an undergraduate, I think, at the time. Anyway, he did a tremendous amount of the initial observing. And when I came back from South Africa in the end of November ‘52, all the data, I think, for the initial paper had been taken. And I still remember that at one stage, and that must have been in the Spring of '53, that data had to be reduced properly and all- you may have heard that story already.

Sullivan

I think it's in your paper in the New York [Sullivan: National Academy of Sciences]?

Westerhout

All the graduate students in essence were collected by van de Hulst. I can still see us sitting in the collegezaal or lecture hall, everybody had a stack of chart recorders, they were reduced and more things were done with them. I think that was in the spring of '53.

Sullivan

How many people were doing this?

Westerhout

Oh, I'm sure there were about 6 or 7 of us or so sitting there plus perhaps a few rekanaars, a few calculating people. It was quite a large group and as a result the thing got done in no time at all, like three days or so. That was, in other words, the reduction of the data to such a point that- and then I think van de Hulst took it over again and started working with it from there on. Then however the receiver had been considerably improved and we had already started the observations in Kootwijk for the big survey, which were done in a very systematic fashion. Muller had developed the system to a fine art so that then these profiles came out and in November '53 I came back from South Africa. So that's when I started getting involved in that. I think I more or less did nothing else anymore. One of the first things we did then was this rotation curve business together with [K. K.] Kwee, who was also a graduate student.

Sullivan

What has happened to him?

Westerhout

He's at Leiden.

Sullivan

He’s still at Leiden?

Westerhout

Sure. He's an expert on W Ursa Majoris stars. I mean it was the only thing in radio astronomy he ever did. And I think that also came out of that session in the lecture room where we reduced all that data. He sort of got interested. He was asked if he would take that on and so he took it on, and so he and I went out and observed pieces of profile and he did most of the reduction. And somehow or another we then finally came up with the final paper.

Sullivan

Now what about the actual observing at Kootwijk for the large survey?

Westerhout

Now that's a whole story in itself. That was great fun. I always remember that as something exciting. I don't know why, because it must have been God-awful boring, but I was young enough I guess to always find it exciting because I would spend weeks and weeks there. I was in- there was a hotel right next door, "Hotel Radio Kootwijk" in Kootwijk, and I was in essence just living in that hotel. And when I came in in the middle of the night, I'd go to the refrigerator and get myself some milk and what not. I remember once the hotelier saying, "Now look, don't put milk in our beer glasses, it ruins the beer glasses for good."

For that Meneer Zwaak or one of these people- I think it was Meneer Zwaak- had calculated these extensive tables, which must still be around somewhere in Leiden, for each - let me think how did it go- There were tables in the galactic plane for a start of azimuth and elevation- not for each day- as a function of sidereal time, of course. But all the scans in the central regions of the Galaxy were made as constant declination scans. And I think that was done because our initial set of tables contained only values for the galactic plane. And, of course, for constant declination scans you simply move the time. You add 5 minutes to the time and...

Sullivan

You move along the plane.

Westerhout

You move along the plane. Well, I have to think of it. They were constant declination scans so we didn't move at all. That's right, it was only later that we got sophisticated. Right, we had azimuth and elevation tables for the galactic plane only, so we would set at the azimuth and elevation for that particular longitude 10 minutes beforehand and then just let the plane drift through during that time. So we did not have to follow a point in the sky.

Sullivan

So you were integrating only with the natural drift rate, I mean they were drift scans really? You weren't following the source at all? Well, this is probably described in the procedure.

Westerhout

I’m trying to think, suddenly, I’m trying to think what the integration time, what the integration time was...

Sullivan

Ok, so in fact you did follow a point for 3 hours.

Westerhout

Yes, we did follow a point for 3 hours, but then we could use the same tables by just moving the time forward by 5 minutes for the next point on that constant declination circle. That's how it was. But then in the outer parts, after we'd done that first thing, of course, more had been calculated and we gained more experience, and we decided to do it at neat intervals of 2.5° in galactic latitude and galactic longitude. And therefore we had a set of tables for each point as a function of time. And what you did-that Würzburg had a motor to drive it in azimuth... In fact it had two motors. It had a motor to drive it in elevation also. But they were fast motors. And then there was a little crank sticking out of the wall for fine adjustments and there was a little crank sticking out of the floor, and the one at the floor was here [Sullivan: demonstrating] the one at the wall was here [Sullivan: demonstrating] and you looked outside and there was an indicator on the big circle and you looked through the floor, there was a hole, and there was an indicator on the azimuth then you stood there and you usually had to crank three or four times here, and three or four times there- We did that every 2.5 minutes. So certainly you were busy all the time. Then every now and again you'd write the frequency by one of those spikes that appeared every 10 kHz as the one-channel receiver slowly but surely swept through the line.

Sullivan

How accurate was its pointing actually? Just roughly. The beam was 1°or something?

Westerhout

No, the beam was 2.5°, so every 2.5 minutes it was better than a 10th of a beam width. I mean there was no doubt about it. I'm trying to think whether I calibrated - I think I did - on point sources. I made a number of calibrations of the positional accuracy of the telescope. Yes, I certainly did that because I also have a paper somewhere of an initial survey with that same telescope of the continuum radiation at 21 cm. Yes, that's right, I made a continuum survey with that.

Sullivan

Is this in the BAN?

Westerhout

Yes, it's also in BAN, There's an article in '56 in the BAN called "Search for Polarization of the Crab Nebula and Cas A at 22 cm Wavelength." In fact, I found the polarization Of the Crab Nebula, but didn't believe it so I said, it is certainly less than 1.5% Well, it was 1.2% or so. I mean, it was clearly there at the right position angle but it was...

Sullivan

But you didn't believe it.

Westerhout

If I had sat there for another two days I would have had it. Alas, that's one of those things, you know.

Sullivan

Is this in the paper, what you just told me?

Westerhout

No- well, what I just told you is in the paper. The result was negative.

Sullivan

I know but from the paper can you see...

Westerhout

Yes, from the paper you can see that I had it. Where the heck is that article on the distribution of radiation along the galactic plane?

Sullivan

Continuum?

Westerhout

Continuum - that material was used by Schmidt at the time to reduce his data for the central parts of the galactic plane. We then split the data up in two the parts, Maarten Schmidt's the central part and mine the other part. In any case, I think all that was to figure out who actually did the pointing calibration. But I'm sure I did the pointing calibration because there is a '56 paper on the galactic center and a '56 paper on the polarization and a '54 paper where it was Kwee, Muller, and Westerhout. So I must have done all the pointing calibration.

Sullivan

Who else was observing out there, students like you, for this survey?

Westerhout

I don't really know.

Sullivan

You did the bulk of it?

Westerhout

No. Because it took more than a year to collect all that data. So I certainly didn't do the bulk of it. I think there were a whole lot of students going out regularly.

Sullivan

Rotating?

Westerhout

Yes, it was usually two weeks at a time.

Sullivan

Well, what about the reduction of this data after it had all been gathered tediously over a year?

Westerhout

It was more gathered tediously over two years, sort of.

Sullivan

Did the reduction proceed in the same sort of "line everyone up in the room"?

Westerhout

No, the reduction was done in essence by myself and Maarten Schmidt with the help of several computing aides, both the old and experienced guys, as well as some young girls that we had, we would tease to tears every now and again. I remember one of them once threw an ashtray at our heads, one of these big, fat, glass ashtrays, which burst in a thousand pieces against the wall and then she ran screaming out of the room. I mean, heck, there were all these young graduate students teasing this poor girl who was sitting there measuring things with a ruler the whole bloody freaking day. That was a pretty horrendous job. What it amounted to was reading off the data from the chart record and tabulating them and fitting a baseline and subtracting it. Well, the whole procedure is given in that paper of course. Then Mr. Zwaak made all the second differences. I still remember that. At one stage I was always trying to get people interested in what they were doing, so I'd given Mr. Zwaak all sorts of- he was close to retirement, almost 64 or 65 and he'd been at the Observatory since the age of 12. So I was giving him nice graphs to make and I'd explain to him exactly what it was. Then at one stage I went to him with this enormous job for 600 profiles, each consisting of 150 points or so to make second differences. And I didn't quite know how to give that to him, but he had to do it. We had decided he was the man who could do that. And after a day he came back and he says, "Meneer Westerhout, I like that job. All those graphs, I really like this job." Oh boy, was I happy. He was really happy there. And he was one of the really good old fashioned people you know, he would make his little - when the numbers became too large and he couldn't do it by heart anymore, do you think he’d use Observatory paper? No, he used pieces of brown wrapping paper to make his calculations on, thousands of little pieces of brown wrapping paper spread around his desk every evening, which he brought from home.

Sullivan

Who was directing all of this? Was it really Oort that was coordinating all of the work that's in that BAN in '57?

Westerhout

No, that's what I was doing with the help of van de Hulst. Oort was relatively little involved other than in the scientific discussion of the matter. No, these were basically, you could say, two pieces of thesis research. One by Schmidt and one by myself. Even though neither of us bothered to make it into a thesis.

Sullivan

It could well have been.

Westerhout

Yes. But I was at that stage, of course, interested in the new telescope that was beginning to come up, the Dwingeloo telescope. And Schmidt got more and more interested in modeling of the Galaxy.

Sullivan

That was his thesis, the mass model?

Westerhout

Yes.

Sullivan

And yours, the continuum survey?

Westerhout

Right. Which is sort of paper number 12 or 13 on the list.

Sullivan

Before we get off to Dwingeloo stuff, is there anything more about this? You haven't really talked about the scientific interpretation of that. Was that sort of straightforward? I mean, it was the same sort of principles as were used in the '54 paper, it's just more data and more complete.

Westerhout

It was very much more complete and in particular, of course, there was a lot of discussion on the accuracy of the data and the very complete way in which we tried to remove the smoothing due to cloud velocities and so on, in defense of that, a big story about accuracies.

Sullivan

I've forgotten now, this sort of thing wasn't going into the '54 paper? Is that correct?

Westerhout

Yes, this didn't go into the '54 paper at all. The '54 paper only has a relatively short section on the reduction.

Sullivan

Well, maybe the way I should ask you is, other than the completeness which enabled you to get an obviously more complete picture, were there fundamentally different things in this paper from the '54 paper?

Westerhout

Yes. Fundamentally different things in that there was very much more detail available. And therefore this paper here, particularly in the conclusions in our interpretation and discussion, there are descriptions of each of the spiral arms, there's a discussion about random motions which, everybody overlooks. The first discussion about random motions, namely the fact that you see, when you look at the galactic anti-center, you see that there are features of 20 or 30 km per second, and I figured out supposing that there would be that same feature at longitude 150° or 140°, how much wrong would we place the spiral arm? And it came out to 2 Kiloparsecs, and I mentioned it here. And it was only very much later that people started coming up with that idea again, that those positions of those spiral arms weren't accurate at all, even though it said so right in the initial paper. And I think the reason is, of course, because it was too long a paper for people in general to read and absorb, like all Dutch papers.

Sullivan

Do you think that was a tactical mistake, perhaps?

Westerhout

Maybe it was. A lot of things there that sort of faded into the background because of such an enormous amount of work. Another basic new thing was, of course, the z distribution.

Sullivan

That's right.

Westerhout

The first paper was only along the galactic plane- we determined the z distribution, we determined the position of the galactic plane. Or rather I did all that. Schmidt used the data in trying to get near and far points in the inner parts separated, but I collected the whole lot together. I missed the fact that in the Southern Hemishpere, I mean I mentioned very precisely that in the Northern Hemisphere quite clearly the plane curves up tremendously, in fact, there's a picture in there which shows it. But I missed the fact that in the Southern Hemisphere it actually turns down. As a result, it's [Frank J.] Kerr and [Bernard F.] Burke in the same year.

Sullivan

The data was available?

Westerhout

Not really, but there must have been ... I mean when you look at it, you see it going up here and you see it going down here. So one could have...

Sullivan

You could have speculated?

Westerhout

Speculated, yes. But it was in that same year Kerr and to Burke to whom the discovery of that effect is attributed, even though it's quite clearly there and described in the paper.

Sullivan

What about the reality of all these spiral features? Did you believe in them too much then, I mean looking back on it now? Or did you really have the right idea that - or not the right idea, but a more modern idea that this needs to be taken not too seriously?

Westerhout

Well, since I knew how they were arrived at, I was fairly convinced that the contour map, this one here

Sullivan

The colored one.

Westerhout

The colored one was pretty good. In other words that, given the mass model of the Galaxy and so on, you knew that the mass model wasn't quite correct because at that time already Schmidt was busy on his PhD thesis, so we knew that the tail of the mass model, particularly for the outer parts, could flip up and down somewhat, which would move things in and out.

Sullivan

By changing the rotation curve?

Westerhout

Changing the rotation curve. I think I have a remark somewhere that such things as these splits in the spiral arm might not be actual splits but might be simply due to random motions. So I certainly was aware already at that stage that it was certainly not necessarily on small scale a true representation of the distribution of neutral hydrogen. On a large scale there was, of course, no doubt about it- when things connect there beautifully. And then, of course, this so-called artist's impression was quite a major effort. I think we spent a month on that, just day and night trying to figure out which is the best representation of that, looking at all... This contour map here is a projection on the galactic plane - no, sorry, it's the maximum densities in the z direction. Well, of course, you would have a spiral arm going up here and another one going sort of underneath it and it's only the underneath one which has more intensity that would be shown on here. And realizing that there was much more in all these charts which represent the real data than there was in this map, I decided to make that one up.

Sullivan

We're talking about plate A and B in the '57 group of papers.

Westerhout

So that really tried to represent everything there was in these bifurcations and so on, you still see in more modern things just as much as you saw in those old data.

Sullivan

So in other words you don't think you over-interpreted the distribution of the hydrogen, looking back on it now?

Westerhout

No: There was no over-interpreting in the sense that I simply represented what I had observed.

Sullivan

Do you think it may have been taken that way by other people? In believing every little feature too much? I mean, this is a very striking map- it’s even in color - so people might take that too much at face value at what you would really see if you were outside the Galaxy.

Westerhout

Yes. People were taking that far too much at face value, and in particular they did not read the paper that went with the picture, which made comments about random peculiar motions of clouds or cloud complexes which could change positions of things rather drastically. And, of course, objects like this here, these beautiful smooth spiral arms that you see, I'm thinking of the Sagittarius arm and the Norma-Scutum arm, sort of in the range of 4, 5, and 6 kiloparsecs. I know exactly how we got those features. We had some gas left over and we decided to distribute it evenly along the circle where it was probably located. And it said so in the Schmidt paper. People then right or wrong don’t realize that anymore. That's why later on, and even now, you see no detailed maps of the central part of the Galaxy. People have never redone the Schmidt work and the same work that Kerr did on the other side simply because it's too damn hard and we'll have to do a lot more modeling before we're able to do it. That's why you see that the Sagittarius arm on all these maps always has a dotted thing and another dotted thing for the Norma-Scutum arm. While in the outside people draw all these little lines and small connections because there it is much more unambiguous. It's quite clear that there are two major features going around here, but you can't say at all where to place it.

Sullivan

Ok, then this was published in '57.

Westerhout

Let me say one more thing about Kootwijk before we step off Kootwijk. You may have that piece of information already, but Muller told me once, and I certainly believe him, that he blames a good deal of the success of his receiver on the fact that he was working right in the middle of the Dutch transmitting station. And as a result he had to shield every single part of his receiver so unbelievably well that all the problems that people got later, who built 21-cm line receivers and got birdies and all sorts of things, all sorts of interactions and all these problems, Muller never had, from the beginning he never had them, because every piece of equipment had to be completely encapsulated or you would get something. And he was sitting right in the middle of a transmitting station. Funny that...

Sullivan

Yeah, he mentioned that to me.

Westerhout

He has mentioned that to you, Ok. I remember one man, one instance where one of the engineers said, "Now I’ll show you something neat." At that stage the Dutch still had their long wave transmitting broadcast at 1800 meters or something like that. There was this enormous antenna mast, with great big guywires and enormous numbers of insulators on it, and this was sort of a wet day, so he said, "Now come along to the bottom of one of the guy wires," and with a great big screwdriver in his hands and he held it by the guy wires and there came a huge big spark jumping over, and the spark was modulated, so in the crackling you heard the music of radio Hilversum. And it was in that environment that we were observing all that stuff. Unbelievable!

Sullivan

No, he did mention that. He didn't mention though, you said that other people did have a lot of trouble with birdies and so forth in the early days.

Westerhout

Oh, yes.

Sullivan

Now that I didn't realize.

Westerhout

[Harold "Doc" Irving] Ewen later then built a receiver for [Bart] Bok at Harvard and always had trouble with that. Always things here and there and everywhere. Anybody who built receivers in those early days had problems with signals leaking through for spectral line receivers. After all, this was the first spectral line receiver. If you have a birdie in a continuum receiver all right, it doesn't matter, your total noise goes up a little bit. In those early days there were lots of problems of that kind with the spectral line receiver.

Sullivan

So, about this time the Dwingeloo dish came into operation. I guess it was actually in '56, wasn't it?

Westerhout

Yes.

Sullivan

When it was commissioned?

Westerhout

That's right.

Sullivan

And did you immediately begin to work with that?

Westerhout

Have you interviewed [Ben G.] Hooghoudt?

Sullivan

No, I haven't.

Westerhout

Because he was, of course, completely in charge of that.

Sullivan

Of the building of it?

Westerhout

Of the building of that.

Sullivan

I'm afraid I won't get to him, at least this time I won't.

Westerhout

Because he'll certainly have a tremendous amount to say about all the various problems. I wasn't really much involved in the design of that thing at all. For one thing I had my hands full with this thing, of course. It wasn't until we actually started getting receivers ready for it that I started getting involved. And the first time we got involved was the two occultations of the Crab Nebula in November of '55, where Seeger at that stage had developed a very good 400 MHz receiver. It was more or less the first time- and I do not recall who thought of the idea that the Crab Nebula was going to be occulted by the Moon- I have a strong feeling that it originated in Leiden, but I can hardly believe that because I can't imagine who would have originated that. It must have been one of the clever chaps in Cambridge. In any case, that opportunity was grabbed. The telescope for the first occultation, was the beginning of November- this is the Dwingeloo telescope now- this was November '55 - could not move yet in elevation. It could already move with the fast motor in azimuth, but not yet in elevation. It was sitting vertically. For some reason or another it was not - no, the manufacturer must have done that for us, put it in a vertical position. The took occultation took place just after the Crab Nebula rose or just before it set, either one or the other, so it was relatively close to the horizon. So the manufacturer set the telescope for us with a big metal boom that stuck out from the edge of the telescope and thereby tightened it at an elevation of 7°. That's where the telescope set.

Sullivan

At your request?

Westerhout

At our request.

Sullivan

Where the occultation was going to be?

Westerhout

That's right. And the occultation however, of course, took an hour. So how do you follow? Well, we followed by moving the focus, the big pole on which the antenna was mounted, up and down. All that I calibrated beforehand and I was entirely responsible for that. In other words, I had to calibrate the telescope in azimuth and I had to calibrate the telescope in elevation. The elevation one was rather remarkable. One of the inventions that I had that also made me famous in the early days of Green Bank, namely the top guide wire was the one with which you could lower the boom on which the feed was hanging sitting at the end. So we used that lowering mechanism so that simply, if you can think of the dish here Sullivan: drawing at blackboard] and here's the apex of the dish, there's a box here, this wire came down here and then somehow or another there was a crank here. So I attached to that wire, a thin little wire that went down here, over a little pulley there because it was in the way somehow or another and down there again, and on here had a little pointer and I had a long ruler here, and that was the elevation scale which then had to be calibrated. Similarly in azimuth, we looked over various drawings and we found that there was one axle, one little axle coming up out of the azimuth shaft, which actually went around as the telescope went around.

We were not allowed to disturb the manufacturer. So we settled on that axle and we said, "Now, how are we going to read off that axle?" So I went to Ruinen, the nearest town, and bought an alarm clock. We dug into the alarm clock and attached it with tape and baling wire onto that axle and somehow or another attached the things that set the hands to that axle. So when the telescope rotated, the alarm clock hands go around ticking off the hours and the minutes. And I calibrated that in degrees of azimuth. That was an unbelievable system. So during that first occultation there was- after having done all that and made all those calibrations for which I think we only had two days because we worked on and off again, because we were disturbing these guys- we were actually able to point at the Crab Nebula and follow the Crab Nebula during the entire occultation. One guy standing upstairs with a table in his hand, which I had also calculated, and one guy downstairs with a table in his hand, cranking in azimuth and cranking in elevation. The second occultation...

Sullivan

A month or two later?

Westerhout

No, it was one month later- 28 days later, in fact. The elevation fast motors worked and we decided not to lower the boom anymore, but actually use the elevation thing. Moreover, it was at a different altitude. However, we still needed a calibration. This time we needed the calibration of the elevation angle. So somehow, on some member, I made markers to calibrate the elevation angle, and we fed up from directly out of the box in which the elevation motors were located a little cable out with a pushbutton and there was a lot of training involved in that because you could give it only tiny little bursts- and another 20 second later- oomph- another little burst of power to make it jump up in little pieces. That was the second occultation. So that was approximately half a year before the telescope was officially finished.

Sullivan

That was [Charles L.] Seeger and you and...

Westerhout

That was Seeger and myself.

Sullivan

That's all?

Westerhout

Yes.

Sullivan

And what were the results?

Westerhout

The results were two beautiful occultation curves of the Crab Nebula indicating that the center of the Crab Nebula - because the Moon of course, on those two occultations went through at different angles, so we could really get almost a two-dimensional picture- indicating that the radio center of the Crab coincided to within a small fraction of a minute of arc with the what was then assumed to be central double star, one of which we now know is the pulsar. And [Gijsbert] van Herk measured to unbelievable accuracy the position of the central double star, which had never been done before. In or so other words he took a Mount Palomar plate or so to the plate measuring machine and measured and applied all the corrections, attached it to the fundamental catalogues that were then in existence. So the position of that double star in that particular paper is in essence the standard position of the center of the Crab Nebula. I don't think anybody has done it with that sort of accuracy anymore.

Sullivan

And that's published in BAN?

Westerhout

That was a BAN article, right.

Sullivan

That's very interesting. I haven't heard about that.

Westerhout

That was published in '56. We published that pretty soon afterwards because we were all very excited, of course, about the whole thing. And that was absolutely unbelievable that that came off.

Sullivan

That it all worked.

Westerhout

Yes. Both occultations.

Sullivan

So then the dish came into proper use in '57 or...

Westerhout

In '56. In May of '56 or so, the Queen [Juliana] had to dedicate it.

Sullivan

Oh, she came out?

Westerhout

Yes. Oh, you haven't heard that story?

Sullivan

I knew about her coming to Westerbork, but I didn't know she had gone to Dwingeloo.

Westerhout

Oh, yes, she officially dedicated the telescope and it was all beautifully rigged. And the last few weeks we lived there day and night, Hooghoudt and I mainly again. At that stage I got involved because there was a lot of astronomy to be done. The automatic pilot, which I presume is still there, probably still sitting there, in Dwingeloo. Have you ever seen that thing?

Sullivan

Not knowing that I have, anyway.

Westerhout

I mean it's the big gray thing that's sitting in a box on the floor in the observing cabin, which looks a little bit like a telescope with two axes.

Sullivan

I don't remember but it was four years ago that I was there. I haven’t been there since I’ve been in Holland, I mean in the telescope itself. I’ve been in the lab.

Westerhout

No, I'm sure it's still sitting there. That was a masterly invention of Hooghoudt's, I think- Hooghoudt together with Rademaker. It was an analogue computer converting right ascension and declination into azimuth and elevation simply mounted, in essence, like a little telescope. Just two sets of...

Sullivan

There was a similar thing on the NRL [Naval Research Laboratory] 50 foot.

Westerhout

Right, except that one was unbelievably sloppy. The internal accuracy of the pilot you will find in my thesis paper. I calibrated that whole thing, first internally and then its connection with the telescope.

Sullivan

But anyway, back to the Queen.

Westerhout

That’s right. I’m trying to- Muller at that stage had moved to Dwingeloo and installed his receiver in there. And the day came nearer and nearer and we couldn't point that telescope and there were all sorts of things wrong.

Sullivan

But why did it still matter for the Queen? She wouldn't know.

Westerhout

Well, you know, the thing had to work. Somehow or another, the thing had to work. In fact, the first line profile was obtained the day before the official dedication-showing that the receiver worked which was rather important.

Sullivan

It was a line receiver, the first one that was on there, besides from your occultation?

Westerhout

Yes, that occultation thing was at 400 MHz.

Sullivan

Yes.

Westerhout

Then the line receiver went on. We had a recorder outside with a table, a recorder on it and a great big gold-looking...

Part 2 | Part 3

Modified on Tuesday, 17-Jun-2014 07:45:53 EDT by Ellen Bouton, Archivist (Questions or feedback)