Interview with Wilbur Norman "Chris" Christiansen
Description
Creator
Rights
Type
Interviewer
Interviewee
Location
Original Format of Digital Item
Duration
Interview Date
Interview Topics
Notes
The interview listed below was originally transcribed as part of Sullivan's research for his book, Cosmic Noise: A History of Early Radio Astronomy (Cambridge University Press, 2009). The original transcription was retyped to digitize in 2016, then reviewed, edited/corrected, and posted to the Web in 2016 by Ellen N. Bouton. Places where we are uncertain about what was said are indicated with parentheses and question mark (?).
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.
Series
Unit
Transcription
Originally transcribed by Bonnie Jacobs (1977), retyped to digitize by Candice Waller (2016)
Begin Tape 67A
Sullivan
Now talking with – what is your first name, actually?
Christiansen
It’s Chris Christiansen. But really Wilbur, but I hate that name that I don’t use it.
Sullivan
Ok, talking with Chris Christiansen on 27th August ’76 at Grenoble. The first publication I have for you involved in radio astronomy is ’49, but can you tell me about your background before then?
Christiansen
I think my first publication was actually on deuterium. It started with the determination of the amount of deuterium in common water. This was when I was doing my Master’s degree. And during the course of it, I had discovered that one could actually change the concentration by fractional distillation. This was with a very accurate relative density this system we had. And the result was that this merely became an industrial process when the atomic energy… well, they even, perhaps, before that, they were looking for heavy water and it was seriously considered that an industry would be started in New Zealand using fractional distillation for the preparation of heavy water.
Sullivan
I see.
Christiansen
That was the first one. I’d intended to get a job as an astronomer and I had a job lined up – this was, say, a few years after graduation.
Sullivan
What year are you talking about now?
Christiansen
I graduated in – let’s see, I went to the University in 1931. I did a three-year physics course. In those days it was a three year course of physics, the honors’ course. And then I got my Master’s degree in one year after that and I think that I was the last to do that because they changed the regulations to make that illegal after that.
Sullivan
And which University was this?
Christiansen
That was the University of Melbourne. The head of the department was Professor Laby who was famous for that Kay and Laby physical tables which is still in use. He was a fine old physicist of the old school, one of the Cambridge people. When I left the University, I’d intended, as I said, to get a job at Melbourne Observatory and I had the job lined up and someone tipped me off that they were going to close it down because of the Depression. There was only one job available and that was in a factory in Sydney, a radio factory. Well, my interests in radio was zero at that stage. But as it was the only job, I got a job in the research labs. I was working with some of the people who were actually the pioneers in the ionosphere. There was Green, Builder, and Baker (?) who were all quite well known in the early days of the ionosphere.
Sullivan
Were they doing ionospheric research?
Christiansen
They’d all lost their jobs, too, I think, and got this radio factory. Anyway, it was a good place. At that time, we were – I would say by far the best industrial laboratory in Australia. It was called Amalgamated Wireless Australasia. And since then it's lost its research and development and now it's even lost its manufacturer. I think, in fact, a lot of these industries in Australia are now trading organizations putting together Japanese or Taiwanese. I worked there for a while, a couple of years before the War started and then I, well it gets very complicated – The head of AWA was also the head of some manpower (?) so it was a real (?) on it to run, so we couldn’t do anything, not only during the War, but for a couple years afterwards while the manpower regulators were on. I was put on the long distance communications working particularly on the (?) wireless service (?) there which was the main overseas one. I was working with the American army for quite a bit, too, on establishing new communications in the Pacific. And during that period, I think I became very interested in antennas and I produced quite a few papers which are still referred to fairly extensively. Things like CCR and so on, on antennas, you’ll still find.
Sullivan
I’m not familiar with that.
Christiansen
Committée Council International Radio or something like that. One of the big international bodies. So, even still, some of my designs appear in that.
Sullivan
And when were they published?
Christiansen
They were published actually in a little journal that no one read called the AWA Technical Review. But a lot of that was reprinted in textbooks and things. In fact, it’s one of the few things in that journal that ever did see the light of day. (laughter) This was on multiple rhombic antennas and they were good. They’re still used in quite a few countries and also a few other such devices. So I was very much interested in highly directed antennas.
Sullivan
So, you didn’t work actually in radar, per se, but in communications?
Christiansen
No, it was in communications, and in highly directional antennas for communications.
Sullivan
At what sort of frequencies?
Christiansen
Oh, you know the sort of 6 to 25 MHz.
Sullivan
And in the course of the war-time work, did you become aware of Hey’s discovery?
Christiansen
No, not that. But I had read the original papers, of course, of Jansky. And, I think I read, in fact, I’m sure I read, a paper produced by Grote Reber.
Sullivan
That’s right, 1940 in one of the Proceedings of the IRE.
Christiansen
That’s right. I read that. So I was quite interested in it. And then when the War was over, I tried to escape from AWA and I went to see Joe Pawsey because I was interested in astronomy. And I’d also become, by that time, sort of the expert on antennas for AWA, so I felt I wasn’t learning anything anymore. I was just being consulted all the time, which I found very painful. So I went to Joe Pawsey and he was quite interested in what I’d done while I was in the communications. He offered me a job, but then when the thing came about, I didn’t get the job because, it turned out that AWA still had a war-time agreement with Radiophysics Lab, which was a radar place in those day, in which CSIRO had said they wouldn’t take anyone from AWA that AWA wanted to keep. And they said they wanted to keep me, so I went back very annoyed to the AWA Then a few months later I went again, and, as you see, Pawsey and I discovered that the agreement had now lapsed. So I was given a job there.
Sullivan
What year was this?
Christiansen
When I got to CSIRO and that’s where I did the bulk of my radio astronomy work.
Sullivan
Right, but which year was this?
Christiansen
It must have been 1947.
Sullivan
So there was a two-year period before you were able to get away from AWA?
Christiansen
Yes, that’s right.
Sullivan
Let me also ask, in the communications work during the War, did you ever hear of anyone alluding to background noise as a problem?
Christiansen
No, not a word… rather interesting. Except not as a problem but purely as an interesting fact, of course, from Jansky’s work. This quite intrigued me.
Sullivan
But it was of no practical consequence then?
Christiansen
No, I was actually looking for, wondering whether I could measure it in our own equipment, but none of our antennas were directed to any really hot part of the Galaxy, so I didn’t ever pick up any noise.
Sullivan
Did you make efforts?
Christiansen
Yes, just for fun. Just to see when the thing went through the Galaxy, whether I could see an increase, but I didn’t pick up anything.
Sullivan
I see.
Christiansen
It wasn’t a serious effort, it was just sort of playing around, because, at that time, I was interested in communications.
Sullivan
But what about the communications as vital in terms of measuring solar flares and fade-outs and so forth?
Christiansen
Oh, I was interested in that, yes, especially in fade-outs.
Sullivan
But in retrospect, when you go back and find that amateurs in the late '30s had noticed that the noise level in their sets went up, when associated with fade-outs.
Christiansen
That’s right. Yes, they were right on the ball and they put Appleton onto this so that’s how Appleton got into the scheme from the beginning.
Sullivan
Right. But as far as you know, there were no professionals, so to speak, who made the deduction that actual electromagnetic radiation was coming from the sun.
Christiansen
None that I know of.
Sullivan
Why did you want to became an astronomer after having been working in nuclear physics and so forth?
Christiansen
Well, when I was a child, I had an uncle who lived in the country with whom I was very fond. And he was a complete cripple and had been crippled in childbirth. He left school, I guess, at the age of 14, but he was a very, very learned fellow. And he was a crazy amateur astronomer, so he got me interested in it at a very early age.
Sullivan
So, even though your training wasn’t strictly there, you still wanted to do that.
Christiansen
Yes, that’s right. I’d been interested in astronomy since I was a very small child.
Sullivan
So, coming to CSIRO in 1947, what did you find there?
Christiansen
Well, the first thing I did, I was put in a group with a fellow called Don Yabsley – no, actually with Fred Lehany, who is now Chief of the Division, Chief of the National Measurements Laboratory in Sydney. Have you met him?
Sullivan
No.
Christiansen
It was called the National Standards.
Sullivan
I should try and talk to him as I’m going to Australia.
Christiansen
Yes. He was really one of the early ones. Well, Fred had beaten me from AWA by a year or so – or two years. He got out at the end of the War. So it was Fred, actually, who was about to leave Radiophysics to become Chief of the Division of National Standards that he tipped me off that this job was going. Anyway, I took over from him and with Don Yabsley on just routine measurements of the sun with an old radar antenna. We were doing quite a bit of stuff on bursts and so on, the very early - and then I read a paper of Arthur Covington’s on his eclipse measurement.
Sullivan
Right, in ’47, I think that was, right?
Christiansen
Yes, that’s right. So, I thought to myself there was a partial eclipse coming up in Australia and, I thought to myself, “Well now, we could triangulate it if I could get measurements done at two or three different places simultaneously, we could actually, by triangulation, get the position of these things.” So, I arranged an eclipse expedition in November -
Sullivan
It was November ’48?
Christiansen
Yeah, that’s right, November ’48. And so we did this…several others. In fact, Bernard Mills -
Sullivan
Well, he told me about it a couple of days ago.
Christiansen
Bernard’s first look at radio astronomy, that was. He wasn’t concerned with radio astronomy. So this I show Bernard and I sort of started together at that stage.
Sullivan
Do you remember what results came out of that?
Christiansen
Well, what were the quite important results. We were looking for these regions – well, in those days, it was called the slowly varying component which Arthur Covington had shown there was this component associated with sunspots. So I wanted to get a rough idea of how big they were. And by the triangulation, we not only got them, but we got a size of three minutes of arc. When that was over, I started scratching my head as to how the hell we could build an aerial with a beam width of about three minutes of arc.
Sullivan
Well, before you go onto that. Another conclusion in this paper was apparently an upper limit to the magnetic field of the sun.
Christiansen
That’s right.
Sullivan
Right. I guess this is derived from Martyn’s theory?
Christiansen
Yes, that’s right.
Sullivan
(?)
Christiansen
It was really from a fairly elaborate study of that by Steve Smerd, too, we were using. I think Smerd published a paper on it.
Sullivan
What was the status at that time of the knowledge of what the general magnetic field of the Sun was?
Christiansen
Very little. Some people said it was there, some said there was none.
Sullivan
And when they said it was there, what sort of (?)
Christiansen
Roughly, it was thought to be about four or five (gauss?)
Sullivan
Ok, go one with what you were saying.
Christiansen
So, being interested in antennas, you see, I said, “Well, heavens, there must be some way of building a highly directional antenna,” because there wasn’t any at that stage, not one in the world.
Sullivan
Well, (?)
Christiansen
Not really.
Sullivan
Well, you had the Michelson interferometer that Ryle and Vonberg has used.
Christiansen
That’s right. Oh, yes, and -
Sullivan
And you had the sea-cliff interferometer.
Christiansen
We had the one that was at the same time as that, of course. The cliff-interferometer.
Sullivan
Right.
Christiansen
But that only gave one component sort of at - that was only a - to get a real —
Sullivan
Didn’t give you an image.
Christiansen
It didn’t give you an image of any sort, or even a measurement of size, not really. You’d be lucky if you did. All it gave was upper limits, really.
Sullivan
Yeah. Of course you could vary the spacing.
Christiansen
Yes, but they didn’t.
Sullivan
Yeah, that’s true. But did you work with this sea-cliff interferometer for a while?
Christiansen
No, not at all. I was right out of that. I’d been just working on about an 18 foot antenna.
Sullivan
When is this, that you were beginning to think about what - ?
Christiansen
This must have been after the eclipse, about 1949.
Sullivan
So, how did you come to reason - ?
Christiansen
Well, it was very peculiar, actually. I was reading up about the Lyot interferometer, in which you combined one spacing and then another spacing with twice the length. And then twice the length and then you put that together and you’ve got a thing like that out of it in shape. Instead of getting a thing like – you combined these sine waves so that instead of with one, you would have got something like that. With this combination, you got things like that.
Sullivan
You got responses that were very narrow compared to spacing between them?
Christiansen
Yeah. And I thought to myself, “By God, that’s exactly what I need.” So I thought, “So now what’s the analogue of that,” and I thought it would be a lot of antennas spaced at intervals.
Sullivan
What we’d call a grating array.
Christiansen
Right.
Sullivan
You called it that?
Christiansen
No, I didn’t at the time. That was called that by Laffineur in France when I went to France. At that time, I called it a multiple interferometer.
Sullivan
I see.
Christiansen
And the grating array was a name given to it in France they had a – actually in the, what did they call it – the Musée de la Découverte, they had a model of my Potts Hill antenna and they called it the “Christiansen interferometer” and then in brackets the “grating interferometer.” So, it was the French who really called it grating first.
Sullivan
That’s interesting, as I always thought this was something that was pretty well known in optics and that you just took it over.
Christiansen
No, it had nothing to do with - Well, the optics was just a very indirect one, you see. It was there – it was a multiple reflection effect. Yes, there’s nothing equivalent, really, in optics. There is, a whole lot of flat gratings, a big series of flat holes, multiple slits would be optical, and no one makes those, or didn’t then, anyway.
Sullivan
In any case, that’s not how you came upon it?
Christiansen
No. It came straight from (?) interferometer.
Sullivan
And so what do you do when you have an idea like this?
Christiansen
I talked to Joe Pawsey, and then I thought, “Well, I can make it better than the equivalent optical grating because I can steer it. So I’ll make it of a whole lot of steerable gratings.” I was trying to get it very cheaply because we didn’t have much money to play around with. So, the fact that it was built, was really based on the fact that I said I was going to use open wire transmission lines, sort of thing, instead of coaxial cable which was very expensive then.
Sullivan
I see.
Christiansen
And everyone sneered and said, “You couldn’t possibly do it at 25cm, it’s never been used in radar.” Anyway, it did work, it worked beautifully and it was - So I built this first grating and -
Sullivan
There were no troubles in making the open-wide work?
Christiansen
No. Everything was done very cheaply. We took two standard sheets of aluminum and welded them and spun them into 6ft things and we put the simplest type of control just on posts. We put a polar axis, and as you ran from one end to the other, you just click them so that you’re following the sun; you’re just running continuously from one end to the other. (laughter)
Sullivan
How long did it take to run from one end to the other?
Christiansen
Oh, well, you took it in turns. We’d do half an hour at a stretch each. (laughter)
Sullivan
But how long did it take actually for one set - ?
Christiansen
You could do it – the sun would pass through – They were one degree between the responses, so you had four minutes. It wasn’t so long, it was only about 800 feet long. So you just ran like buggery from one end to the other. (laughter)
Sullivan
Wasn’t quite the four-minute mile, it was the four minute even feed (?)
Christiansen
No, but it was fairly strenuous but it was a nice flat thing. It was on the edge of a – Ah, yes, that was the other thing. I was looking for a nice flat place with roughly east-west and it turned out that we had one that was magnetically east-west along the edge of Sydney’s drinking water along the dam.
Sullivan
That’s the Potts Hill?
Christiansen
Yes. That was working at the Sydney URSI meeting.
Sullivan
The ’52 meeting?
Christiansen
Yes. By ’52, we were producing some quite nice pictures. And it really went down well at the URSI meeting. This was something – the first pictures, one dimensional pictures of the sun. You’d seen radio pictures so it caused an enormous amount of interest. And at that stage, Martyn went to – Because the Japanese were not allowed to come to Australia because after the War, Japan and Australia, even in ’52, it was a pretty sticky sort of situation. You can’t imagine it now, but it was. So the Japanese decided not to come, I think, because of this situation. So Martyn went over there and he told them about my interferometer. So they wrote to me. I can remember. I’ve still got the letter because it was such lovely English. Well, this is a little bit sticky because I… better close this off… (laughter)
Sullivan
This is all in confidence. Anything that I want to quote, I’d certainly ask for your permission.
Christiansen
Well, actually, the Japanese sent this letter and they were saying this drinking area – I loved that so I kept the letter – which was a mixture of “stinking” and “striking.” Anyway, I sent them all the information and all the figures and diagrams long before I’d published anything. I’ve always been amused that later on, it didn’t take more than a few years, before it became an independent Japanese invention. You might even find that in the literature because it’s been pretty widely pedaled, that one. It always annoyed me a bit because, strangely enough, Bowen, who was the head of our place, when I said I’d had this letter from the Japanese, Bowen said, “You’d better be pretty careful because you haven’t published anything thing and they’ll publish before you do.” And I’m afraid he was slightly right. They had it published first, but of course, it took them a long time to. But they made a scale model at about 10cm of our Potts Hill thing. And Jean Louis Steinberg came over and he’d been playing around with a four element one actually, that he didn’t get any luck with. Just four aerials together.
Sullivan
You say he came over.
Christiansen
He came over to the URSI meeting. And he was so interested that he said, “By God, I’m going to build one of those.” So he went back and they built one at Nançay.
Sullivan
Right.
Christiansen
But it was pretty well to scale, but it was a fixed antenna because their antennas were so small in wavelengths that with them fixed they saw the same thing for quite a long time. Whereas, ours kept on. Well, now that was quite good. And then the next step -
Sullivan
Let me ask you about this step, first. You designed it in order to be able to look at sort of few arc minutes’ structure.
Christiansen
That’s right.
Sullivan
But how did the choice of wavelength come about?
Christiansen
It was pure luck because I had been working at 25cm. This was 25 again, that’s all. Because I’d been working – I knew that at 25cm and 50cm, this slowly varying component was very strong. And 25cm was a nice thing in which I had some equipment and it was really because the equipment was there, I think you could say. It was easy to build; it wasn’t too big. I could have done it at 10, but then you get into rather, what was then rather nasty, electronics stuff which I preferred to work with a field where it was fairly conventional, which was up to 25cm.
Sullivan
Before we go on further, let me also ask about a couple of papers that you published on this slowly varying component. Christiansen and Hindman ’51 in Nature, in which you talk about verifying Van de Hulst’s theory that there should be a variation of the sunspot cycle.
Christiansen
That’s right. That was a sort of by-line. That was just done on the daily observations. We were taking daily observations.
Sullivan
So, you were monitoring them?
Christiansen
We were monitoring all the time, as well as this.
Sullivan
I see. That was with a single - ?
Christiansen
A single dish, yes.
Sullivan
And what size?
Christiansen
About sixteen, I think. It’s a square one. If you come to Australia, you must see if I can get a copy of that because I’ve got one in which we did the first map on the hydrogen line. We used the same aerial and it’s one with all the stars around -
Sullivan
Yes, I’d love to see that.
Christiansen
Actually, it was published by Life.
Sullivan
Oh, ok, I can look it up there.
Christiansen
There was, what was his name, a German photographer, extremely good photographer, and he came to Australia.
Sullivan
So that would be in Life in ’52 probably?
Christiansen
Yes, probably. ‘54 it might have been – ’53, in that region, ’52-‘53. It was whenever that I was doing the work on the hydrogen line.
Sullivan
Was it a whole article on this?
Christiansen
I think he did a whole article, yes, in Australian radio astronomy, that’s right.
Sullivan
Ok, I’ll check that out. What was the result of several years of monitoring, as you say?
Christiansen
Well, the monitoring result – we -
End Tape 67A
Begin Tape 67B
Sullivan
Continuing with Christiansen on 27 August ’76.
Christiansen
We had been monitoring, of course, all the time, the sun, on, I think, 15 and 25cm.
Sullivan
Right, but I said 10 and 3 after ’48?
Christiansen
Yes, that’s right. That was done by Hindman. That’s where Hindman came in. He was on the 10 and 3 and we went through these results and thought we’d found quite an arc change in the base level at the surface stage, that was all. I don’t think it was a thing of any great significance and I don’t know now even whether it was correct.
Sullivan
This was the 30 percent drop, or so, in 1950 that you talked about?
Christiansen
Yes. However, the real things came out of the Potts Hills interferometer. The first one was an estimate of the temperature of these regions, that they were getting around about a million degrees.
Sullivan
So you had that even back in your (?)
Christiansen
Yes, that’s right. But we weren’t so confident about them. But now, we had these things sticking up and we were thoroughly confident. I can’t remember whether this included the north-south – no, I don’t think so. We also saw how long it took for these things to cross the solar disk and from that got an estimate of the height above the photosphere. Also, they saw the polar diagram of them to get a rough idea of what they looked like.
Sullivan
How directional the radiation was?
Christiansen
Yes, that’s right. While that was going on I’d always been at least 50% engineer so I was interested – I felt we’d better get another array going in the north-south. Oh yes, one of things, of course, we found from this immediately was that it looked as though the sun was square (laughter). I mean, instead of this quiet sun looked that (drawing a diagram) square waves, which looked like limb brightening. And I said, “Well, we must have a look in the north-south direction to see what’s happening there, too.” So I built a second one, north-south. And using that too, of course, we got the one-dimensional thing in two directions. And then at that stage, I think, it was the first paper came out on the synthesis technique from Ryle’s group.
Sullivan
(?)
Christiansen
I think it was earlier than that. Wasn’t there an earlier paper than that of -
Sullivan
There was a two dimensional thing that O’Brien did.
Christiansen
Ryle and Vonberg? No, no, it was earlier than that.
Sullivan
No, no that was synthesis.
Christiansen
Oh, no this wasn’t a full one – yes it was. It was on the sun. A solar thing – it was, I think, the earliest of all of them and I think it was before Blythe and long before -
Sullivan
Well, ok, Ryle and Vonberg have a big paper in ’47 in which they discuss their -
Christiansen
It wasn’t that.
Sullivan
Balancing receiver and so forth.
Christiansen
What was the name of this fellow, he’s only appeared once in the literature, never again.
Sullivan
Well, there’s a Stanier who did a -
Christiansen
That’s the one. Ah, no – it wasn’t -
Sullivan
Pat O’Brien.
Christiansen
No, it was before – Stanier, that’s right.
Sullivan
He did a variable spacing thing in one-dimensional.
Christiansen
That’s right.
Sullivan
He didn’t have phase, he had to assume circular symmetry.
Christiansen
That’s right, exactly.
Sullivan
Then O’Brien did the same thing in two dimensions, about ’54 he published.
Christiansen
That’s right, yes. Well, by that time we’d done a rotational synthesis. As soon as we got this one-dimensional one, I remember talking to Jim Roberts in radio physics and I said, “Does this thing work in two dimensions, too?” Oh, I think by that time the first – no, I think by that time with our discussions had gone away a two-dimensional one had been produced - No, it hadn’t. It was assuming circular symmetry. I think the English were assuming circular symmetry.
Sullivan
Right, that’s correct.
Christiansen
And I said to these people, “Do you think that one could do it in two dimensions?” Then someone said, “Well, the English are shifting around aerials to do this – shifting the aerials.”
Sullivan
Right, this was the work of Blythe?
Christiansen
That’s right. At that time, I thought, “I wonder whether you can do it without shifting your aerials around.” And then I thought, “Damn it, the Cambridge boys, of course, can’t steer their aerials, we can steer ours through 12 hours. So we’ll follow the sun with both the north-south and east-west from morning till night and we’ll get our synthesis that way.”
Sullivan
Let the earth do it.
Christiansen
Yes, let the earth do it.
Sullivan
So, you essentially came up with this idea independent of Ryle?
Christiansen
Oh, a long ten years before. Not on aperture synthesis, but on using the sun. Because they had no errors for years.
Sullivan
What do you mean using the earth?
Christiansen
Using the earth’s rotation.
Sullivan
Well, to be fair about this though, Ryle has tracked back in his notebooks in ’54, he talks about the idea of doing a section of the north polar area using the earth’s rotation.
Christiansen
That’s quite possible.
Sullivan
So, I would say that you both came up with it and you used it on the sun and not first before you used it on the -
Christiansen
Yeah, that’s right. Well, I think, probably, we had similar ideas. I don’t think there’s anything very terrific in that. We certainly produced the first map by means of the earth’s rotating synthesis.
Sullivan
You were using it – there’s no doubt about that.
Christiansen
And all these things were not very difficult, of course.
Sullivan
Did that idea come along right with the same time as you were building the second arm of the Cross?
Christiansen
Yeah, that’s right. Well, it was very funny. Now, this is a strange one and this is one, too, that I don’t like to say it because it’s not against anyone, but it’s just for the history of it. And it shouldn’t be published ever. But Bernard Mills came along one morning, he looked at our two errors, and he said, “Why don’t you combine those two damn things at right angles?” And I said, “Well, if I knew how to multiply the bloody things together, I could, but I don’t.” And the next day, Bernard came in and he said, “I do know how to multiply those things together because Ryle’s done it.” So, hence, the Mills Cross came out exactly that. But you don’t ever mention that one.
Sullivan
Surely.
Christiansen
You can save these things, all these things for people talking to each other.
Sullivan
But now, you’re going back to ’52 or ’53, weren’t you, in the story you’re telling now?
Christiansen
That’s right. And that was about the time, you see, so that’s why I said we would do it this way by using the earth’s rotation. Well, this had impressed me, so that what I’m really getting at, is that if you like to look at it, in radio physics at that time people were talking to each other all the time. We used to have these sort of, what Americans call “bull sessions,” and thinking of every conceivable sort of aerial and we just about invented every sort it’s possible to invent. It was really good stuff.
Sullivan
This was throughout the ‘50s?
Christiansen
Yes, the early 50s. Particularly the early 50s.
Sullivan
That’s an interesting point you bring up, because I get the impression just from what I’ve been able to uncover, that there were several rather independent groups in radio physics, yours and Bolton’s and Mills'.
Christiansen
That’s quite true. At that stage, Bernard was just coming into radio astronomy at that time. He’d been working on linear accelerators.
Sullivan
For instance, Mills told me that there was very little contact between him and Bolton’s group.
Christiansen
They were rather at loggerheads, I must admit. I was in between. I got along quite well with both of them. In fact, despite that, despite the fact that they were independent groups, we did have these sessions.
Sullivan
Were these regularly held things?
Christiansen
Every couple of months, I suppose. And a really good one would last all day. Joe Pawsey was one to stimulate that. He was a marvelous chap.
Sullivan
I just made a note to ask about that. Can you tell me about him?
Christiansen
Joe was a fellow with an enormous interest in science. Just a real fanatic, really, in science. He had enormous enthusiasm and he infected everyone with his enthusiasm. He didn’t do any work himself – in fact, about the only paper he ever got his name on, I think, while I was there, apart from the review papers, was one that I put him on, one that we did, because I said to him, “Bugger, Joe, you did half the work in this place and you never publish anything.”
Sullivan
That was Christiansen, Mathewson, and Pawsey in Nature?
Christiansen
That’s right, and old Joe was quite thrilled to have his name - he was the absolute keystone of the whole thing, but he didn’t publish anything.
Sullivan
That’s right.
Christiansen
He just went from group to group stimulating them, giving them ideas, criticizing them, and stuff. Which was a great shame because he loved playing around, but he just didn’t have the time. And he was a great fiddler. This eclipse expedition that I described, he turned up and I was working inside, I had the receiver – I’d just got it going. And Joe took to me in a big way, because I’d heard someone saying, “Ah, Christiansen’s lucky – his gear never works except when it’s needed.” And Joe said, “I like lucky people.” (laughter) I think you could say he’s a very simple soul, he used to sometimes he was quite innocent, too. But he’d floor a speaker (?) turning up a great piece of astrophysics. And Joe would get up at the end and say quite innocently, and it was innocent, “I can’t reconcile this with Ohm’s Law.” (laughter) It would absolutely torpedo - (laughter) He was absolutely first class.
Sullivan
And a fairly – not at all – mean, very modest.
Christiansen
Very, very modest, extremely modest.
Sullivan
Not caring for a great amount of personal gain.
Christiansen
I’ve got a lovely story of Joe when he was staying with us when I was working in Holland in 1960. This wasn’t long before Joe died. Joe and his wife were staying with us in the Sterrewacht in Leiden. Joe was talking about Jan Oort and he said, “You know, Jan (we were staying in really a part of Oort’s house) could never have done his work without Mika (?), because Mika has just done everything. She’s protected him, she does this, that, and the other.”
Sullivan
That’s Jan Oort’s wife?
Christiansen
Yes. And he said, “Whereas you and I, Chris, just have to get along as best we can.” And our two wives were there, you know. (laughter) Quite innocently – he wouldn’t think for the moment that there was anything offensive in such a statement. (laughter)
Sullivan
It seems, from what you were saying, that his style really did set the tone for -
Christiansen
It set the tone completely. I don’t think the place would have been anything without Joe Pawsey.
Sullivan
And was he also vital in terms of securing necessary support?
Christiansen
Well, that was a peculiar one. He was a very, very unworldly fellow and he was working with Bowen, who was actually the Chief of the Division, that’s Eddie Bowen. Bowen was the man who got the money, he was the sort of tough business man. Joe was the rather academic scientist. And it was an excellent combination. And, I think, that was really the combination that was good. I doubt if Joe would have gotten much support on his own. I think it was Bowen fighting for the money.
Sullivan
Yes, like you say, you need both.
Christiansen
Yes.
Sullivan
When you got the two-dimensional sun with the earth’s rotation synthesis, what did you find out?
Christiansen
We did that only for the quiet sun. That had to be done – getting the lower limits. There’s a whole lot of records and I superimposed them and took the lower envelope.
Sullivan
Right.
Christiansen
In fact, my son, who is a lecturer at Sussex, told me the other day that he saw something called a “Christiansen Plot.” And I said, “What in the hell is a Christiansen Plot?” He didn’t know but he wondered whether it was that type of ‘plotting’ -
Sullivan
Maybe you had a lower envelope -
Christiansen
(laughter) He was most amused to see that.
Sullivan
I’ve never heard that term.
Christiansen
No, he struck it just the other day. Oh well, that’s quite irrelevant. But that was an essential part of this work, of course, taking the lower envelope to get the quiet sun.
Sullivan
Are you saying that you didn’t have to worry about that before you went two-dimensional?
Christiansen
Well, I’d done that in one dimension and now I’ve done it north-south and east-west. But, I wanted to get the real shape of the sun so I combined all these low things for the different angles, lower envelopes.
Sullivan
I see.
Christiansen
So it wasn’t a sort of one-day job, it was a many months’ job.
Sullivan
And did you realize before you made the antenna that this was going to be a problem?
Christiansen
No, that was one of the problems. I wanted to get the quiet sun – that was one of the problems.
Sullivan
This is your ’53 Nature article, “Christiansen Diagram” it’s called?
Christiansen
(laughter) “Plot” sounds worse. Sounds like a Gunpowder Plot or something. This is different in each scanning direction. And then putting those together and combining them in two dimensions, you see. I got this at different angles. Particularly when I did the main stuff was really at quiet sun period this became almost like that and then you could get the change during the one day even.
Sullivan
In the quiet part of the solar cycles?
Christiansen
Yes.
Sullivan
Let me ask about Warburton.
Christiansen
Joe was a very active fellow who was working with me and he didn’t work with me for very long, but he got out into – he’s now running some meteorological unit in the United States. He’s got right out of radio astronomy.
Sullivan
But he must have worked with you for several years?
Christiansen
Yes, he did.
Sullivan
And what was the (?)
Christiansen
No, he came as a young graduate.
Sullivan
In what field?
Christiansen
Physics, I think, yes, it was physics. I graduated in physics, too.
Sullivan
So was it basically your ideas and it was a joint - ?
Christiansen
Yes, it was really because Joe, at that stage, hadn’t - But he was very helpful on the other hand on this two-dimensional synthesis, the earth rotational one. Because I was away for some of that time and he did a lot of that synthesis. And it was all done by hand, something that would take us now…this was before electronic computers. We had tables of sines and we just – cosines – and we just moved them along. I’ve still got the old pieces of paper. I think they were called something-or-other strips.
Sullivan
(?) Beaver Strips, I’ve been told about them by the Cambridge group.
Christiansen
Yes, that’s right. (laughter)
Sullivan
They used those also. I have here, also, the Australian Journal of Physics article in ’53 in which you describe the aerial and then at the one-dimensional observations. Let’s just take a glance through here and see whether I had any points.
Christiansen
Oh, yes we did some polarization work, too.
Sullivan
And how did you measure polarization?
Christiansen
Well, this way here. We just put (?) circularly polarized in opposite directions (?) this arrangement we had of connecting the aerials.
Sullivan
Oh yes, shown in Figure 4. And there’s your open line.
Christiansen
Yes.
Sullivan
Was this method of distribution, was that something unique also?
Christiansen
Yes, I think the whole thing was quite – nothing of that sort had ever been done before, I guess.
Sullivan
Ok, here I’ve got a question. In paper II, you talk about Stanier’s work.
Christiansen
Yes.
Sullivan
Stanier found no sign of the (?) 60cm (?) “The results obtained, however, must be treated with some reserve since the relative phases of the Fourier were not determined and it was necessary, therefore, to assume that the one-dimensional brightness distribution was symmetrical.”
Christiansen
That’s right.
Sullivan
“The published experimental curves show the presence of localized bright areas.” I’m wondering what you’re referring to there because all that I’ve ever found from Stanier is a short thing in Nature.
Christiansen
Yes. What did I mean by that - ?
Sullivan
Maybe his thesis? Did you have a copy of that?
Christiansen
I must have something which showed lumps on one side or another. Something I must have gotten hold of, but I don’t know what. I can’t understand it. It’s too long ago. As a matter of fact, I got Martin Ryle to change one of the papers. I’d been at Cambridge at this time, and I said to him (?) quite a bit a lot of rot this not measuring phases you know, you draw conclusions from it. (?)
Sullivan
I see, you got him to change (?)
Christiansen
Yes.
Christiansen
You see, we were the only ones really, who could, in effect, measure phases. At Cambridge, at that time, they couldn’t do it. And whereas by making it a log system we could fix our phases and we knew exactly where we were. So that’s really what the difference was.
Sullivan
Now on the two-dimensional synthesis you apparently found a different amount limb brightening at the equator than at the pole.
Christiansen
That’s right, yes. Have you got that paper?
Sullivan
I don’t have that one, no. That was ’55 Australian Journal of Physics.
Christiansen
That was one of the most important ones.
Sullivan
Why?
Christiansen
Well, that was the one really in which they got this earth-rotational synthesis put down. And it was also very important as the quiet sun as this had been suspected that there might be – should be limb brightening. But it hadn’t been suspected that it would only be a purely equatorial effect. There was something quite clear about the poles. This was quite a new sort of thing.
Sullivan
So you would vote if you had to say which one of the papers was more important, you’d vote for this one rather than the first one describing the one-dimensional grating array?
Christiansen
Yes. And there was a fourth one, too, I think that was quite important. A series of four of them. Those first two, I think, were just relatively unimportant compared to the next two, three and four.
Sullivan
But, of course, the first one brings forth the whole concept.
Christiansen
Yes, that’s right. Well, all right, one, three and four were the important ones, I think. Two is not very important.
Sullivan
Ok. Let’s see if there is anything else on the solar work before we got back to the hydrogen line business. Now what did you make of this business of different amount of limb brightening?
Christiansen
Well, no one could make much about it because it was a matter of really throw it back on the optical boys to find out whether there was any difference between the corona and the poles in the equator. And it was years later… well, there were two more solar papers that came out. One of them was a combined one with lots of astronomers. I don’t know whether you’ve got that?
Sullivan
Yes, I have that. Christiansen, et al., with about 10 people.
Christiansen
Yes, that’s right.
Sullivan
In Annales d’Astrophysique?
Christiansen
That’s right. The other thing was the one that I did with Mathewson at, I think, Paris -
Sullivan
The Paris Symposium?
Christiansen
That’s right. And that really summed the whole results up, I think. The fact that we had now got a model roughly of what they were, that these, in fact, these black regions were simply regions of enhanced density in the corona.
Sullivan
I have here 20,000 to 100,000 km in heights.
Christiansen
Yes.
Sullivan
And that you said they were similar in size and shape to the underlying plage in the magnetic field region.
Christiansen
That’s right. Well now, fundamentally, I think, that still stands, more or less. So that was the sort of conclusion to all this work.
Sullivan
But how did this come about? It seems, to me, if you’re going to be studying the slowly varying components, it’s a matter of monitoring. So you were monitoring daily, then, with the Cross?
Christiansen
Yes, we were monitoring daily. Yes, every day we took a picture and we watched these things travel across the sun. And we saw what happened to them and what happened when they came back again for a second rotation and all the rest. What their lifetime was, and what this velocity was and roughly what their height was. We got all of that.
Sullivan
What about this international paper published in 1960?
Christiansen
This was just an effort to get all the equipment, both optical and radio that we had at our disposal together and see what came out of it.
Sullivan
And did anything?
Christiansen
Yes, I think it gave a fairly good model of what the -
Sullivan
I must admit; I haven’t look at that paper.
Christiansen
Its nothing really staggering, but it more or less set the - After that people felt a bit easier that they knew what really was going on, what was the sort of general structure.
Sullivan
This also brings up the question of the general relationship between optical and radio solar astronomy. When you first began - ?
Christiansen
Well, I had no relation with any of them really. Except in Australia with, who was it —
Sullivan
With Harley(?)
Christiansen
No, it wasn’t with Harley. It was the chap who became the first —
Sullivan
Allen, Clabon Allen
Christiansen
Yes, “Cla” Allen. Now he was very interested in our work and for a while he was doing a bit of radio astronomy himself.
Sullivan
At Mount Stromlo? I’d like to talk to him.
Christiansen
Yes. He’s a good chap. Well, Cla Allen was the one very much interested in our work.
Sullivan
But he was primarily an optical astronomer?
Christiansen
Oh, completely.
Sullivan
Do you have any idea why it was that he, a rarity in those days, saw there would be some worthwhile - ?
Christiansen
Well, he was very interested in solar astronomy. Stromlo at that stage was a solar observatory.
Sullivan
I see.
Christiansen
And Woolley was out to wreck it as a solar observatory. He said he’d have that name off that thing very quickly, which he did. So that that’s why Allen left and took the Chair in London. Woolley definitely was determined to close that thing down as a solar observatory.
Sullivan
But as you went to meetings and so forth in the early 50s, did you feel yourself as an astronomer or more as a radio engineer?
Christiansen
No, we called ourselves radio astronomers and we felt as though that’s what we were, and we weren’t optical astronomers or engineers. We were really a closed group.
Sullivan
But did you make efforts at meetings to talk with the optical solar astronomers?
Christiansen
Ah yes, but we found we didn’t talk the same language – we didn’t in those days.
Sullivan
But even though you were giving them what we would now say was vital information on the chromosphere, they weren’t particularly interested?
Christiansen
The only ones I knew who were really interested was a Swiss fellow, Waldmeier. He was very interested. And who else -
Sullivan
Unsöld had some interest.
Christiansen
Yes, he had. Yes, I visited him once and he was quite interested. But Waldmeier was very interested and always getting out results.
Sullivan
Do you know if he’s still alive, by the way?
Christiansen
I don’t – I haven’t seen him. He usually comes to these. And the other one, of course, was Newkirk. He was one of the younger generation. But he was very interested in the radio work. Gordon Newkirk.
Sullivan
And where was he at?
Christiansen
At Boulder, I think, the High Altitude Labs. So we knew him and we were very friendly with him. Of course Paul Wild’s work in the sun was going on at the same time as this, but it was a complete split between the quiet sun slowly varying component group which was mine and the other, Paul’s which was these bursts.
Sullivan
I see. Did it just sort of happen accidentally?
Christiansen
No, it just happened that he started off to do this work with McCready on building this equipment for the spectrograph. He was working at a different frequency and in a different place.
Sullivan
Ok, that pretty well covers the observations you made in Australia. But there’s several other things that I wanted to talk to you about.
Christiansen
By the way, during that process I spent a year at the Institut d’Astrophysique in France. And I did one -
Sullivan
Which year was that?
Christiansen
That was ’54. And I helped Laffineur, I think got a joint paper there.
Sullivan
That’s right. About this Swedish - ?
Christiansen
That’s right. But I did the French end. They went off to Sweden and I did the one at Meudon, part of the observations at Meudon.
Sullivan
It was partially there?
Christiansen
Partially, yes. Such a terrible – I can remember very well because it was a receiver with such a terrible temperature coefficient that I had a piece of string on the door and it was an old (?) thing and I kept it to within half a degree. I had a thermometer hanging onto the receiver and I kept it to within half a degree by, as the temperature went down slightly, I’d close the door, and then open the door, because there were big temperature changes during an eclipse. (laughter)
Sullivan
Normally you wouldn’t have to worry about it (?) a bit more temperature stable. What was the purpose of spending a year in France?
Christiansen
Well, I’d never been away from Australia and I just wanted to go away. France appealed to me. I’ve always done that, whenever I’ve gone away on sabbatical, I’ve always gone to a place where they didn’t speak English. I had a year in France and I spent about 2-1/2 years in Holland and had a year in China.
Sullivan
Let me ask about your impression of what was going on in the French group in ’54?
Christiansen
Well, Laffineur was working completely on his own. And the other group was Denisse and Steinberg.
Sullivan
I’ve talked with them about how they saw it. I’m interested in your outside opinion.
Christiansen
Well they were really the better group. They were the up-and-coming group, no doubt about it.
Sullivan
As opposed to Laffineur, you mean?
Christiansen
Yes. Laffineur was a first-class engineer but somehow or another he didn’t get on with the others. Being on his own, it was, well, he didn’t get off the ground.
Sullivan
It’s my (?) opinion that French radio astronomy which was purely solar until the 1960s, never really quite made it.
Christiansen
Not compared with some of the other countries, that’s right. So you compare it with the English and the United States and Australia – they were always behind. I don’t know why because their people were very brilliant people.
Sullivan
Maybe they never had tremendous funding.
Christiansen
Partly that, I think. I don’t really know. And Denisse was a very bright fellow.
Sullivan
Yeah, oh yeah. Ok, that was one visit, but to keep things chronological, let’s go back to the hydrogen line first. How did you get involved with that?
Christiansen
Joe Pawsey had a letter, I think, from Purcell. And he said they’d discovered this and, of course, ‘ol Joe went rushing around madly in the department - And he also said we might like to have a go at - So Hindman and I started off independently with our equipment to do it and then we decided to pool it because we were both having trouble – but complementary troubles.
Sullivan
Can you say what they were?
Christiansen
He had this front-end work and I had the back-end (laughter) – something like that. So we said, “Well, we might as well pool it because it would work that way.” So we put it together and, God, it was the most terrible piece of equipment I’ve ever seen in all my life. We did the frequency switching by – we had on the floor an old war-time radar oscillator and we just periodically switched(?). And it was a monster. I can remember working day and night on that. The first time I saw the line, I’d given it up. I thought the gear would never work. And then I went to sleep and came back and there was a beautiful curve sitting up on the chart… After that, we kept going and -
Sullivan
How long did it take you to (?) put the (?) together?
Christiansen
It took us about a month to get the thing working. Because, actually, Ewen came out to the URSI meeting. No, it couldn’t have been the URSI meeting -
Sullivan
Well, the URSI meeting was the summer of ’52.
Christiansen
Yes. And when was the hydrogen line?
Sullivan
The hydrogen line was June or July ’51.
Christiansen
That’s right. Well, it was then. Ewen came out. He said he had to come to see how these God-damned Australians did, in three weeks, what took people 18 months to do. (laughter) And when he saw the gear, he just about passed out. Junk lying all over the room and on the floor. Anyway, we did something that hadn’t been done before, you see. Jan Oort at this stage…Ewen had provided – had really found the thing with a fixed horn sticking out the window. The people at Leiden had done something, but they had done it on two positions – or something like that.
Sullivan
That’s right.
Christiansen
So, we decided we’d do the whole sky that we could see. And I sent our first map to Jan Oort and he was very pleased with this – I’ve got his letter. And he took it all around the world with him at that stage. But we got two, a couple of things that looked like spiral arms so that we said this is the first evidence – we thought we had the first evidence – radio evidence that we were looking in the spiral galaxies. And I remember making – I think it must have been that same URSI meeting – Morgan.
Sullivan
(?)
Christiansen
It couldn’t have been URSI. I met him somehow or other. And he was, of course, very interested because he was doing the optical stuff, too.
Sullivan
It’s rather interesting that optical came up in the same time as the hydrogen line.
Christiansen
That’s right, exactly.
Sullivan
Now wasn’t the entire survey done with the same bit of equipment?
Christiansen
Yes. It was a miracle we ever got anything out of that junk. It was really incredibly awful stuff.
Sullivan
Why were there two efforts originally? It would seem to make sense to pool you from the beginning.
Christiansen
It was, as you say, rather independent groups. Two lots went flying into the back room to try and build some equipment to look for it. And Joe rather encouraged it, I think, because he liked to have two lots of people in case one lot succeeded and one didn’t. He wanted two strings for his bow, I think. But then we had enough sense to – when it came to the point to -
Sullivan
Hindman was in which group then?
Christiansen
He was working with a group of Piddington.
Sullivan
Another group.
Christiansen
Piddington and Minnett, yes. They were sticking to the centimeter wavelength stuff.
Sullivan
(?)
Christiansen
All sorts, yes.
Sullivan
I haven’t talked to either of them, but I plan to. Now about this HI survey, it strikes me as interesting that your approach was different. Well, you actually haven’t said that… was different from both Harvard and Leiden in that you presented a contour map of brightness temperature.
Christiansen
Yes, just peak brightness.
Sullivan
Right. And sort of analogous to how one would do continuum radiation.
Christiansen
That’s right.
Sullivan
And you talked about what could make the variation in the brightness. You said, “Well, according to this abstract I have here – that it could be due to differing line widths,” you really had the same amount of hydrogen (?) spread out or it could be due to different intensity of the hydrogen.
Christiansen
That’s right, different sort of temperatures and things, thickness probably optical.
Sullivan
Perhaps associated with continuum radiation. I think the idea may have been, well, if it’s hotter in the continuum… in the hydrogen or something like this.
Christiansen
Yes, it could have been, I can’t remember. We were just flapping around in the dark. (laughter)
Sullivan
You undoubtedly were not aware of (?)
Christiansen
No, I’d just come in out of the dark, really, and looked at it. But it was a useful map because for many, many years, radio astronomers used that map to find where the hydrogen was.
Sullivan
For the southern sky?
Christiansen
Yes, that’s right. Even some of the northern ones because Weaver told me they used it for years.
Sullivan
I see. Now how long did it take to make this whole survey?
Christiansen
We got the thing going about 2 months after we started, and I guess it took us about 4 or 5 months. We were just about dead at the end of it, I remember that. We had no sleep for months.
Sullivan
And the idea of the spiral structure, did that come from (?) Morgan and (?)
Christiansen
No, we didn’t know anything about that.
Sullivan
So how did that come about?
Christiansen
Well, it just looked like it. Two things like that looked like a spiral structure. You see, we got on our map two continuous -
Sullivan
Two things at different places on the sky?
Christiansen
Yeah, two long arcs around the earth. We found two long arcs.
Sullivan
I see what you’re saying. But how did you come up with – in the abstract it says you had distances of one and four Kpc from the sun. How did you deduce those?
Christiansen
Just from their frequency, from the rotation.
Sullivan
(?)
Christiansen
We knew as much as that, yes. We knew about rotation and Oort’s - Yes, I’m sorry. We knew the elements. I’m sorry, I shouldn’t have implied that we didn’t know what rotation was. We did know that.
Sullivan
Yeah. Well, of course, Oort had talked a little bit about that in the Nature article. Well, that finishes the formal papers. But now, I’d also like to ask you about the years you spent in Holland, in particular, the early years at the Benelux Cross.
Christiansen
Yes, by the way, there’s this cross grating, too. You haven’t got onto that.
Sullivan
Well, my bibliography, I thought, was complete through ’60. When would this be?
Christiansen
Oh, perhaps we didn’t publish the main paper… Oh, yes we must have. We published quite a bit on IEE, Institute of Electrical Engineers. You’ll find a big article on the Cross grating interferometer.
Sullivan
Right, but I think that was ’63 or ’64, that special issue.
Christiansen
Was it? No, this was the Institution of Electrical Engineers, not the American one.
Sullivan
The British one?
Christiansen
Yes. I’m sure it must have been by then because – well, the thing is, we did start using this in ’54 and I’m quite sure we must have written it up before ’60.
Sullivan
Oh yes!
Christiansen
I’m sorry, we started using it – the first maps were ’57.
Sullivan
Yeah. There’s lots of papers on write-ups of – you had one in the special issue of the Proceedings of the IRE in ’58 on radio astronomy and you had one in the IRE Australia in ’59.
Christiansen
Ah yes.
Sullivan
I haven’t mentioned those explicitly because we’ve been talking about -
Christiansen
Well this is a different bit of equipment, you see.
Sullivan
Well, maybe I’m not sure what we’re referring to. Can you be more explicit?
Christiansen
This is going to Fleurs when we get to there – ’56-’57. I decided to build another antenna, but a Cross one this time. You see, Potts Hill we had this two little, a north-south and an east-west interferometer. OK? Eight six-foot diameter dishes. Then I thought, “We should be producing daily maps of the sun, two-dimensional maps of the sun.”
Sullivan
OK, I didn’t realize that there were two.
Christiansen
Oh, yes. This was quite a different instrument.
Sullivan
OK, tell me about this then.
Christiansen
I had got one two-dimensional thing from the – using the earth’s rotational synthesis but that’s quite unsuited to daily maps of the sun. For one thing, the, you can’t do a – the sun rotates during the say so that the sun is not a good thing for doing earth rotational synthesis. And I looked around and I thought, “Now, the best thing is to combine the grating with the Cross.” In fact, as I said to Mills once it went the other way, really. That the Cross came out of the grating rather than vice versa, you see. So I built a Cross out at Fleurs, and it was bigger – the elements were much bigger.
Sullivan
Single dishes still?
Christiansen
Single dishes. But they were 20 feet in diameter and it was longer. Then combined that with the – or steered one. So you had two sets of grating. And then you used this as a Cross so each of those became a point, and steered one of them by putting in quite an elaborate array.
Sullivan
Ok, this is all coming back to me now. That’s very different. With the Potts Hill thing, all you were doing was two separate one-dimensional scans.
Christiansen
That’s right, exactly. And you didn’t steer anything, you didn’t do anything. So this was a steering one and now this one produced the first daily map of the sun. We produced our first in ’57 and it’s still doing it.
Sullivan
This same array is still operating?
Christiansen
Yes, but we’re using it for different things now.
Sullivan
Is this the same array that’s being used for 21-cm continuum on galaxies and so forth?
Christiansen
It’s really part of it, it forms part of this new system. You see, we’re using the same array for different purposes.
Sullivan
I see, and this was also the basis of the Cross that Bracewell built?
Christiansen
That’s right. And he got his going a few years later. Well, of course, Ron Bracewell was with us in Sydney.
Sullivan
But not in your group specifically?
Christiansen
Well, no, he worked in the same room. Ron and Mills and I shared the same room so we were very close together. Ron built one at 10cm and we built one at 21cm.
Sullivan
And you also had – well, it was his idea that the different longitude would also give you -
Christiansen
Well, he wanted to – he was really wondering what to do when he went to Stanford and he was… We were only at the stage of – we’d been talking about this, you see, at the place with Ron and so on, and he’d been entering in the discussions. So that when he decided to go and we decided roughly at the same time to build one – build this in Sydney, but with Joe Pawsey’s permission, but Ron left and decided to build one there. So it all came out of the same group. Don Mathewson who wrote the papers.
Sullivan
That ends this portion of the interview with Chris Christiansen on 27th August 1976, more to come later, and that’s the end of this side of the tape also.
(interruption)
End Tape 67B
Begin Tape 68B
Sullivan
Continuing with W Christiansen on 28 August 1976.
Christiansen
Perhaps I should have mentioned some of the people that were working with me on that solar work in the early days. There was Govind Swarup, he started his work in radio astronomy (garbled) (?) been up in Alaska. And Rod Davies also.
Sullivan
I see; I’ll be talking to him next week.
Christiansen
I just thought I’d mention those three things.
Sullivan
Now, we’ve talked about your visit to France for a year. Where else did you spend more than a month or so outside of Australia?
Christiansen
I spent about three months with Ron Bracewell at Stanford. I can’t remember when that was. It must have been at the time of the Boulder meeting of URSI. Was there an URSI meeting in Boulder? The only occasions I’ve been in the United States was one of the Boulder meetings of URSI, I think it must have been ’57, yes that would be it. Then I went over there for the 1960 IAU.
Sullivan
Was his Cross under construction?
Christiansen
Yes, it was being made at that stage. That was the reason for the visit. To see if I could help with that.
Sullivan
This ’61 IAU meeting at Berkley, do you have any recollections from that, the radio astronomy sessions that might be of interest?
Christiansen
No, the only thing is I can remember we said something about our ideas for the Benelux Cross, I think that’s the only thing I can remember. Now, you wanted to talk about the Dutch thing.
Sullivan
How was it that you got involved in that?
Christiansen
Well, first of all, Oort had been trying to get some people with some experience to go over to Holland for this idea of the Benelux Cross (interruption) He asked me whether I’d go over there for a couple of years or 18 months. And I’d arranged to do this and at that time the thing blew up in the CSIRO and Mills and I left. And I got the job at the University of Sydney. One of the conditions I made on taking this job at Sydney was that I could fulfill my obligations to Oort and go to Holland.
Sullivan
When was this now?
Christiansen
This would be in 1960. In 1960, I took the job at the University and immediately went away for 18 months in Holland.
Sullivan
Right. And without getting into nitty gritty, can you just explicitly say who disagreed with who and then what happened?
Christiansen
You mean in the University? Well, it was fundamentally a dispute between two groups - there was the Pawsey, Mills, Christiansen and, I guess, Paul Wild group. We were the sort of ones who like innovations. And then there were the one who were developing into astronomers rather than innovators, John Bolton, for example, who had left. I think he had gone to work as an astronomer at that time in California. But he was a bit of support for Bowen who was very anxious to have the biggest aspidistra dish in the world. That is the new Parkes telescope. And there was a real conflict developed which ended up in our leaving. There was quite a lot of amusing things. I remember I gave the – I called this new thing ‘the last of the Wind Jammers’ (laughter) Actually that term is now quite well-known throughout the world. It’s been applied to the Bonn one.
Sullivan
So it wasn’t the last of the Windjammers.
Christiansen
No.
Sullivan
So, what did you do in Holland?
Christiansen
We had a specification as to what Oort wanted. It was for 400MHz device with one minute of arc resolution at 400MHz.
Sullivan
Set by Oort himself for astrophysical (?)
Christiansen
Yes, so I was put in charge of this group which didn’t exist at that time and I had to sort of build it up. I submitted two designs with quite an elaborate report. There was a fellow over there already, a young fellow Högbom, who was, at that time had no reputation at all in Holland. And my first job was to make sure they changed their mind about him because I could see he was jolly good. And he was looked on as being quite a useless young man, which was absolutely unfair because he’s quite brilliant. So anyway, we worked together. I produced two – in fact, I’d done the designs almost before I arrived there on the boat going to Holland. Two types of Cross – one was a thing with novel feature of a sort of semi-something in between a “T” and a Cross, in which sections were taken out of one side of a “T” antenna and put in the other. And this was a – I always like this. No one had ever built one, but it’s a jolly good idea.
Sullivan
And what is the advantage of it?
Christiansen
The advantage of it is that you can have separated elements so that they don’t look into each other.
Sullivan
Oh, you mean shadowing?
Christiansen
Yes. It overcomes the shadowing completely because alternate section you just transfer to the other side. A jolly good device. It’s never been used, as I say, which is a pity. Then the second one I made was a whole lot of parabolas in the form of a Cross with a very elaborate one to give us a single response. And Högbom helped me with that second one. And we submitted one and in the meanwhile Oort decided he ought to go to a higher frequency. Then the whole thing blew up with the Belgian’s, they withdrew. So the Dutch then … By this time, I was only going over every year roughly for a couple of months just to help with advice on the thing. And we finally persuaded Lex Muller to take over the work. He’d been opposing this project from the beginning.
Sullivan
In favor of what?
Christiansen
Nothing!
Sullivan
I see.
Christiansen
Lex liked something he could do with his own hand himself and, I thought, didn’t like these big projects. But finally we persuaded Lex to take it over so I more or less withdrew at that stage.
Sullivan
Now when you say you built up a group, who else did you bring?
Christiansen
There was Jean Casse -
Sullivan
Erickson?
Christiansen
Bill Erickson, yes. I arranged from him to follow me when I left after my 18 months, to get Bill in, because I thought he was one of the best of the American radio astronomers at that time. I thought he was just the type. But our efforts, both his and mine, were actually a bit wasted because of the Belgian’s getting out. Well, it was useful work and we built up a good group.
Sullivan
Well, Högbom has told me, though, the final design did not look like yours. It wasn’t really because of the Belgians drawing out because the aperture synthesis was shown to really work and that was more clearly the way to go.
Christiansen
Yes, I think, probably it would have gone but the thing had been held up for so long. The thing then would have been well on its way to completion.
Sullivan
I see.
Christiansen
If it hadn’t been for that and the – I think as Jan says, by that time the real power -
Sullivan
Right, the one mile was in operation.
Christiansen
Yes.
Sullivan
It’s interesting, to me, that Oort did not, at first, want to go to the hydrogen line, 21cm.
Christiansen
Yes, I don’t know why that was. Although there are arguments, of course, for the lower frequency, as Mills used when he built his Cross. You see different things, of course. If you get down to low frequencies. At the moment the low frequency stuff is being neglected to a certain extent.
Sullivan
Yeah. Now, when you went to the University of Sydney, what did you embark upon then?
Christiansen
My first reaction was, I thought my career in radio astronomy was finished. For example, I was going to an engineering department and I’d never done one hour of lectures in engineering in my life.
Sullivan
Well, 30 years of working in it.
Christiansen
(laughter) That’s true. So anyway, for a month or so, I decided I’d do nothing. Then, of course, the old habits got in. I designed something I thought was a damn good thing for a millimeter wavelength telescope with a 100ft diameter telescope, which was a hole in the ground type. It was spherical, but a different type from any of the others inasmuch as it had a secondary mirror which brought the rays to a focus down on the primary mirror. So that it was to have little rats sort of scampering over the surface of this little machines picking up the energy so you’d have quite a number of machines, and so on, picking up simultaneously. And this was put up – I tried to get money from all sorts of people, Ford Foundation and so on. But they all knocked it back. I think a lot of them were sorry they had afterwards because it was a very good conceived design. It cost $200,000. It was to work down to, I think, 2 millimeters. Of course, those millimeter lines hadn’t been discovered. So, I was just doing it on the basis that this part of the spectrum had been completely neglected.
Sullivan
And this was about what year?
Christiansen
This would be 1961-’62. I got the designs out and priced but we didn’t get the money. So I gave it up and at this stage I was tipped off by Paul Wild that Bowen was getting rid of all signs of Mills and Christiansen from the show, that the Fleurs field station was to be bulldozed. So I immediately applied to the CSIRO to give the place to the University. And they did and then I wondered what I’d do with it. While I’d been in Holland, a chap who’d been working with me – Norm Labrum - We got a 60 foot antenna, we’d bought it from America, and I persuaded them to put it at the end of one of our east-west arrays to use as a compound interferometer of the Covington type. Norm Labrum - who was working with him? T. Krishnan, who is in India now. Incidentally, we sent our original Potts Hill aerials to India, I forgot to tell you that. We gave it to Swarup.
Sullivan
That’s right, he’d mentioned that.
Christiansen
Now, so Krishnan and Labrum did some work on the sun with that. Then it went off to Parkes, the 60 foot aerial, and is now used in (?) So I decided to try and get some money to build a really big one with using several of these two arrays. I mean our existing array and a widely spaced array of large elements. And this is what we’ve been doing ever since. And use it as a synthesis instrument.
Sullivan
Right. Once again I guess you were impressed by what the one mile had done.
Christiansen
Yes, exactly. I could see that it was doing very well and I could see also we had advantages inasmuch as our instrument would give the entire picture in one session. You see, you don’t have to vary it, we’ve got all the space available, instead of having to vary the elements. And also it was very cheap, the whole thing. We haven’t yet spent more than half a million dollars on the whole installation. So, its roughly a 20th of the cost of the Westerbork, for example. That’s one of its snags actually because -
End Tape 68B
Begin Tape 69A
Sullivan
This is continuing with Christiansen 28 August 1976.
Christiansen
This is one of the snags – you build a cheap instrument there’s a natural reaction amongst those who built expensive instruments to feel it’s necessary to sweep it under the carpet. You can see the reason for that. And this has happened with Fleurs. It’s only in the last few months that we’ve actually been recognized as a respectable telescope. I think the same thing happened to Ron Bracewell with his very nice instruments in Stanford.
Sullivan
I see. You don’t gain respectability because you haven’t spent enough money.
Christiansen
That’s exactly it, yes.
Sullivan
I think you mentioned to me earlier that the Ford Foundation actually came through with a good bit of the funding?
Christiansen
No, not for this.
Sullivan
I’m getting mixed up with Mills.
Christiansen
That’s right. We got no money. All our monies came from little bits. I even started off with a grant from our local Electrical Power Authority – that’s what got me going. So I got money from something like 20 or 30 different sources. But all of it in recent years has been competitive stuff from the Australian research grants.
Sullivan
Over what period was this instrument built?
Christiansen
It was about 12 years since we started the first vague hits of building.
Sullivan
Sixty-four to the present or so?
Christiansen
Yes. And it’s now, of course, working. But it’s continuing now to be increased in size and that’s going to take another several years to bring it to 8 seconds or arc from the existing 45 result in power.
Sullivan
I’d just like to close and ask you about a rather interesting trip in my view anyway, that you took to mainland China and helped them with some radio astronomy, I believe.
Christiansen
Yes. Well that was quite an interesting one because I went there on my way back from the URSI meeting in Tokyo in ’63. I went to China and I met some Chinese radio astronomers who were - And I suggested – they were thinking of building a grating antenna and they had already built some of the elements. I invited two of them to Sydney and they worked with us in Sydney University for several months. Then when they left they said to me when I had my next sabbatical perhaps I could go to work in China. So in 1966 I went to work with them and we set up quite an elaborate and large grating instrument.
Sullivan
Where is this now?
Christiansen
It’s north of Peking. Unless it’s been destroyed by the quake because it must have been very close to that region. Then last year we had two of the engineers down with us for 6 months and they are at the moment turning it into a synthesis instrument.
Sullivan
I see. Still solar work?
Christiansen
At moment, it’s solar work, but when it has turned into a synthesis instrument, it will be, of course, for general use.
Sullivan
I see, and which institute is this?
Christiansen
This is Peking Observatory which is part of the Academy of Science – the Academia Sinica.
Sullivan
Well, as you look back are there any other general comments that you would like to make about how radio astronomy has developed in your point of view, in particular Australian radio astronomy?
Christiansen
Well, I’ve been a bit disappointment because at the time, Mills and I left CSIRO, at that time – for a long time – we’d had the highest resolving power instruments in the world. For some years. From that time to now, the resolving power, until the Fleurs instrument went in, the resolving power hadn’t increased at all in Australia over ten years, there had not been the slightest. Whereas, in Europe, in the Northern hemisphere it had been just - So Australia is now in poor way, the Southern Hemisphere is in a poor way for high resolution instruments. And I think that the reason that Mills and I left and that Pawsey was about to leave, it had been borne out that we were putting all one’s money into one big basket, into Parkes, was a fundamentally a mistake.
Sullivan
Let me also ask if you have any ideas on why American radio astronomy did not take off right after World War II given that you had a very similar war-time laboratory. Any ideas on that?
Christiansen
I’m darned if I know. That’s always been a great mystery to me. I just couldn’t understand that but then why did the Dutch want about six Australians and Swede and so on to come and build their radio telescope when they had Philips there, the biggest radio organizations in the world. That’s a mysterious one, too. (laughter)
Sullivan
Ok, well, thank you very much.
End Tape 69A