Interview with Russell M. Sloanaker

Sullivan: 00:05

This is the interview of Russell Sloanaker at NRL on 9th April 1973. So you came to the Radio Astronomy Branch in 1949 -

Sloanaker: 00:16

Yeah. And by that time, was that [inaudible]. And wasn’t called the Radio Astronomy Branch, at that time.  It was called the Radio -- I think it was called the [inaudible] Radio Frequency Section or something like that. Some people though were already doing radio astronomy. Dr. Hagen was the Branch Head, and Haddock was there and Mayer

Sloanaker: 00:51

was here and had been for several years before that, I don’t know how many years before that. And I think just a year or two before I came they had started to do some radio astronomy. [inaudible] was interested in doing radio astronomy. And at the time I came at around 1949, he was going to Georgetown, at night school, to get his Bachelors degree. And they were studying the sun. They had a couple of six-foot dishes up on the roof [of Building 1?]. And the 50-foot dish hadn’t come [inaudible]. Oh, I don't know, about half a dozen - it was a very big branch in those days. About a half a dozen people or so, Haddock, Mayer, [inaudible], [inaudible] was there, had been here just about a year before I came, and a couple of other people. We were using some of those six-foot dishes and measuring the Sun and the Moon at 10 centimeters and 3 centimeters wavelength. And not too long after I came, within the first year, it was already planned before I got here. There was in a total eclipse of the Sun in Alaska in which my [inaudible] so they [inaudible] the dish to Attu in 1950. And I was working at the time with Connie Mayer. And it was completely rained out and so we didn't get any good data there, but it was a chance to measure the brightness distribution of the Sun at 3 centimeters and 10 centimeters. It was a giant [inaudible]. Reber was working at the Bureau of Standards.

Sullivan: 02:41

Was he?

Sloanaker: 02:42

And I can't remember the person's name, but somebody with him, went with us. We all went by plane. And they set up their antenna nearby, it was about, I'm not certain, but it was about [50?] centimeters or something like that, six foot or something.  And they took some data because rain didn’t hurt them. Well you probably don’t want this much detail, but my memory’s not too good.

Sullivan: 03:06

Well, let me just ask, were you the only people operating at such high frequencies at this time?

Sloanaker: 03:14

Boy, I don't think-- or I think there were other people probably measuring the sun at fairly high frequencies [inaudible]. But in about 1953, at the time I came, the 50-foot dish was already in the planning stages. And as the 50-dish got into operation early in 1954, and I think as of that time nobody had measured discrete sources other than the Sun [inaudible], so the [inaudible] 21 centimeters. And when the 50-foot dish was then in operation well, Haddock was a section head at that time and when the branch-- just like mail is divided into sections. And Haddock was one of the section heads. McClain was in the branch all this time, too, but he was still working on applied research, not radio astronomy. Although, he got into radio astronomy about 1954, I think. But Mayer was in Haddock's section. I was in Haddock's section. McClain, some other people.

Sloanaker: 04:35

Then, when the 50-foot dish first got into operation sometime in early 1954, it had been planned. But Hagen and McClain, who were working on a 21-centimeter receiver, were going to be the first ones to use it. But they had some trouble with the receiver. It wasn't built yet. In the meantime, Haddock's branch, mostly Mayer-- Mayer was the main electronics engineer who had experience at that time. We had a 10-centimeter receiver ready to go when the 50-foot dish was finally ready. So we got to use it first. Well, Haddock and Mayer and I were the first ones to use it, at 10-centimeters. And we were lucky and then, [we were real fortunate?]. We discovered quite a few discreet sources right off the bat. Hagen and McClain? had their receiver ready in about a week afterwards and they sort of kicked us out and they went in for a few weeks.

Sullivan: 05:47

I see.

Sloanaker: 05:48

But I think the measurements that we made at 10 centimeters in 1954 were the first measurements of discreet sources. [inaudible] at wavelengths shorter than 21 centimeters. We measured--

Sullivan: 06:00

Which sources were these?

Sloanaker: 06:00

Well, we measured a total of 22 sources. Some of them extragalactic, Cygnus, Centaurus, and some galactic sources. These had all been seen at [crosstalk].

Sullivan: 06:13

Did you finish your paper just based on that first week?

Sloanaker: 06:16

Yeah, we finished the paper based on the first week.

Sullivan: 06:18

In Nature, I guess, or something like that?

Sloanaker: 06:20

Yes, it was in Nature, a letter that we [added?]. And we also detected four or five H II regions, Orion, M17. I think that was the first detection of discreet H II regions. Although people had prior to that, a couple of years before that, there had been articles where-- well, I think [inaudible] was an author of one of them and I'm not sure. Some other people. Three or four articles, where in attempting to describe the--

Sullivan: 07:08

The [inaudible] background?

Sloanaker: 07:09

The [inaudible] background of our galaxy as being made up of a large number of discreet sources. People had [computed?] a lot of the background to discreet H II regions, especially on the galactic plane. I mean, near the galactic center. But people had tried to measure some of the nearby discreet [inaudible]. But where they had a bright band along the galactic plane where they're going to describe this H II region.

Sullivan: 07:43

Yeah, there were a lot of different theories as to wherever that came from. That was one of them, yeah.

Sloanaker: 07:47

So when we went in the antenna, that was one of the first things we looked for, were H II regions in, some of the nearby ones, Orion -.

Sullivan: 07:56

Did it seem to you that their signals were strong enough, that this other theory was

Sullivan: 08:01

Likely to hold on to.

Sloanaker: 08:02

Yeah. That's right. They did great with the numbers but [inaudible]. I mean, we've got brightness temperatures pretty clearly. I can't remember but I think [inaudible] got brightness temperatures of 100 degrees, something like that. [Seemed to fit in with] the other [inaudible]. And then, as I said, within a week or two Hagen and McClain had their receiver ready, 21 centimeter, and they measured all the same sources, plus a lot more. [inaudible] had a plan [inaudible] H II regions..

Sullivan: 08:49

What was the Navy sponsoring this for do you think at the time?

Sloanaker: 08:53

Well, at that time-- I can't remember the details to well but they were definitely in favor of basic research for basic research's sake. I mean, we'll be out there but you couldn't tell where it would lead and it might bear essential benefits for humanity. I remember right about then, the Director of the Laboratory at one of the [inaudible] made a speech [inaudible] basic research [inaudible].

Sullivan: 09:29

Yeah. This was when ONR I guess was really developing--

Sloanaker: 09:32

Right. Right.

Sullivan: 09:36

How did it change?

Sloanaker: 09:38

Yeah. I guess that. Yeah.

Sullivan: 09:43

So what happens next after that? Then you must have done some more work over '55.

Sloanaker: 09:48

Right. Well, after that, there were several more solar eclipses [inaudible].

Sullivan: 09:56

Yeah. Connie [Mayer] told me--

Sloanaker: 09:56

- solar work. [inaudible] on the Sun. So he was constantly--

Sullivan: 10:06

He probably went on all of those I think, or did he?

Sloanaker: 10:09

Well, no, he didn't go on all of them. I think he went on two of them. I was lucky. I went on all of them.

Sullivan: 10:15

Could you tell me about the ones you went on that Connie didn’t, because I've talked to Connie--

Sloanaker: 10:18

Well, the one I went to that he didn't go was the one [inaudible]. This was 1954. [inaudible] Khartoum, Sudan. Haddock went on that and I went. Cornell was going to go and I wasn’t. Last minute. And I wasn’t. It wasn't planned that I would go, I wanted to go. But at the last minute, Cornell's wife got sick and he couldn't go. I [inaudible].

Sullivan: 10:47

So what happened there?

Sloanaker: 10:49

We got very good data. Very good data. It was a beautiful, clear day. It was out in the desert [inaudible]. We were there a couple months. It was clear so it was beautiful [inaudible] very good data [inaudible] a beautiful view of it [inaudible] and the only one I've seen-- although I went on three expeditions, the other two [inaudible].

Sullivan: 11:23

You didn't go down to [inaudible] a few years ago?

Sloanaker: 11:25

No. No.

Sullivan: 11:27

I did. Yeah. That was fantastic.

Sloanaker: 11:30

It's really [inaudible].

Sullivan: 11:31

What was the scientific value of these eclipses? What were they finding out?

Sloanaker: 11:37

Well, of course, the purpose was to find the brightness distribution across the sun and-- I think, in the short term, the next eclipse was in Africa couple years later. We had, in Khartoum, we had 10 centimeter radiometer, a 3 centimeter radiometer and an 8 millimeter radiometer. A man named Gibson was working on--

Sullivan: 12:07

I don't know him but I've heard of him.

Sloanaker: 12:09

Well, he [inaudible] to work with the 8 millimeter radiometer. The trouble with eclipse measurements like that-- we had large [beams?], six-foot beams [inaudible]. And the trouble with the thing is that you can have-- the eclipse curve is why the [flux?]-- the received signal variance would-- as the Moon covers the Sun it's pretty insensitive to the brightness distribution it turns out. And so to reconstruct the brightness distribution from the eclipse curve in the first place, it becomes-- it's a very sensitive thing working backward, and you have to make a lot of assumptions. You have to assume, say circular symmetry, and then you can represent the Sun by a lot of concentric rings. And then as the Sun gradually gets covered up by the Moon, you can calculate the brightness of these rings one by one. And the brightness of successive rings hinges on the brightness that you’ve already determined for the outer rings. Do you know what I mean? In other words, say as the Moon first cuts across-- say you divide the Sun into an arbitrary number of rings. The Moon’s eclipsed a little bit of the outermost ring, and you can then form an assumption of circular symmetry. And this ring has a constant temperature, correct? You can calculate the brightness [by adding up the rings?]. And when the Moon has bitten into the Sun a little further, you get the brightness of the outermost ring. You can then calculate the brightness of the next ring, and so forth. But as you go in, the brightness gets--

Sullivan: 14:12

More and more shaky, yeah.

Sloanaker: 14:13

It's getting shaky because it depends on the outermost ring always. So I don't think it's the best way to study the brightness distribution across the Sun. An interferometer would be much better. And like I said, a lot of assumptions. But anyway, based on circular symmetry, we did get brightness distributions which then we published. Which agreed pretty well on the average with what people have found since with the brightness--

Sullivan: 14:44

Shadow and brightening and the--

Sloanaker: 14:45

Shadow and brightening and so forth. And we went into great detail in the announcement. And also, there were always sunspots on the Sun. And so you'd see those obscure and we'd have to subtract this from the data before we tried to analyze the underlying brightness distribution.

Sullivan: 15:01

Where was this work mostly published?

Sloanaker: 15:04

Oh, I can't really remember exactly. I thought I had copies, but [inaudible].

Sullivan: 15:16

Well, another question is, was there successfully more information being obtained from the various eclipses, or was it just a habit to--

Sloanaker: 15:26

Well, the first one was the one that-- that 1950 one. And it was completely washed out by the [inaudible]. The one in Africa was successful. We got pretty good data. And then there was one more, one in Sweden, I guess in 19-- I'm not sure when that one was. 1955 or something.

Sullivan: 15:51

So there were three altogether?

Sloanaker: 15:53

Three altogether. The one in Africa was successful and the one in Sweden was successful. But the one in Sweden didn't really add an awful lot to what we found out in the one in Africa. [inaudible] because I had the receiver [inaudible]. Well, after that--

Sullivan: 16:15

Did you work anymore in the 50-foot?

Sloanaker: 16:17

Oh, yeah. Well, I’m trying remember-- around 1955 or thereabouts, I guess. Haddock left, went to the University of Michigan. And Mayer became the Section Head. And there were quite a few people in the branch by this time, but by that time, the branch was doing nothing but radio astronomy. [inaudible] was here and--

Sullivan: 16:52

[Barrett?] came out, shortly after--

Sloanaker: 16:54

[inaudible] quite a few people. But anyway, Mayer took Haddock’s job about 1955 as one of the section heads. And I was still in the section and Mayer became my supervisor and [McClain?] was in a section and quite a few other people and so on, and yeah, we used the 50-foot dish quite a bit. We measured Venus with the 3 centimeter and that was supposed to [inaudible] 1956. Now, [inaudible].

Sullivan: 17:40

Is that one where you got the brightness [temperature of?] 600 degrees?

Sloanaker: 17:43

Right.

Sullivan: 17:44

Which was a complete shock--

Sloanaker: 17:46

Right. It was completely unexpected. And, well then, we devoted about a year to measuring Venus [inaudible], nothing difficult. And we weren't in the books for an entire year. I mean, the other people in the branch [inaudible] used it from time to time, we [inaudible]. But we worked almost exclusively Venus for about a year. And another thing we did, we measured Mars. That was the first detection of Mars, I guess. [inaudible] its radius, brightness aperture [inaudible].

Sullivan: 18:22

The 50 foot was the biggest microwave dish in the world, wasn't it?

Sloanaker: 18:27

Right, it was. [inaudible]. And we measured Jupiter, at 3 centimeters-- all this was at 3 centimeters. And I guess that was the first detection of Jupiter but this [inaudible] with the optical [inaudible] classically determined temperature of the outer layers. We didn't get non-thermal radiation. 3 centimeters [inaudible]--

Sullivan: 18:56

I guess you were sort of hoping that you might--

Sloanaker: 19:00

Well, yeah. Venus was the first one. It was unusual but then Mars and Jupiter were not.

Sullivan: 19:06

Especially with Jupiter, you knew there was low-frequency activity.

Sloanaker: 19:09

Right. But I think we captured something like a 145 [inaudible] with Jupiter which could have [paired well?] with the thermal radiation from the [outermost layers?] [inaudible]. Mayer had always been interested in polarization. Back in the very early days before I came to the Branch, he was trying to measure polarization of the Sun. 10 centimeters, it was. [inaudible] And so he had always been sort of pushing to measure polarization. But he was the leader of the—[McCall?] and I worked well and attempted to measure polarization of discrete sources. I think that was the first and sometime around 1956, we did measure the polarization of Cygnus at 3 centimeters. Centaurus, I think that was the first measurement of polarization on galactic and extragalactic sources other than the Sun. And like I said [crosstalk]--

Sullivan: 20:23

At any frequency?

Sloanaker: 20:25

[inaudible]. And I think Mayer should get complete credit for that because he was always, had that in the back of his mind, that he wanted to measure polarization. [inaudible].

Sullivan: 20:37

What about the Crab?

Sloanaker: 20:39

Oh, and then the Crab Nebula, too, Taurus, Centaurus, and Cygnus were the first ones we measured [inaudible] polarization. That was about 1956. Well, then in 1958, [Townes?] brought the first maser here. 3 centimeters. For this [first maser, really outstanding?] All right, I guess I better not tell you about that [inaudible] Cornell probably already has.

Sullivan: 21:13

Yeah.

Sloanaker: 21:14

I [inaudible]--

Sullivan: 21:15

Right, yes. Yeah, he has told me about that.

Sloanaker: 21:17

And at that time, the 84 foot dish was [inaudible] some time around the spring of 1958, just about the time Townes arrived with his 3 centimeter maser, the 84 foot dish was ready for operation. and I thought the 10 centimeter receiver [would be tested on the?] 84 foot [inaudible] and in addition to what I'm-- what I worked with that for quite a few months. The 84 foot antenna, 10 centimeter receiver. And Mayer and the other people here were trying to come up with more. And in testing the dish, one of the things McClain was trying to find out how [inaudible] anymore. So we measured the positions of the last 10 centimeter sources [pretty accurately?], went in about a minute of arc pretty [inaudible] massive. And I also measured Jupiter with 10 centimeters, and that was the first indication of the-- not the sporadic non-thermal radiation, but the static decameter non-[inaudible] Jupiter's spectrum. Very shortly after that, within a few months [inaudible] Green Bank was my Jupiter [inaudible] we measured 10 centimeters about 600 degrees.

Sullivan: 23:02

And what was the idea of the 84-foot? It was twice the collecting area of the 50-foot.

Sloanaker: 23:07

Right.

Sullivan: 23:09

But it was not good to better than 10 centimeters.

Sloanaker: 23:10

No, even with 10 centimeters, it wasn't [inaudible] like 20--

Sullivan: 23:16

Well, was it mainly just to get away from Washington with the other [inaudible] that, or?

Sloanaker: 23:19

Well, that was-- McClain is the one [pushing this?] and I think it was determined that he was pushing the section to acquiring such a dish, he was mainly interested in 21 centimeter work and [inaudible]--

Sullivan: 23:39

Hydrogen line?

Sloanaker: 23:40

Well, although the way it turned out, not much hydrogen line work was done there--

Sullivan: 23:47

Right.

Sloanaker: 23:48

So that goes up to about 1958. Well, in the meantime, [inaudible], people like [inaudible] and McClain were doing quite a bit of 21 centimeter research. I wasn't involved in it. This was my [inaudible]. Seemingly important [inaudible]--

Sullivan: 24:27

But what did you work on after the first testing out of the 84-foot?

Sloanaker: 24:32

Well, after that, well, we continued to make, we made a lot of polarization, actually. By we, I mean Mayer, [McClain?], myself, and other people at 10 centimeters, using the 84 foot antenna. And then some time around 1961, I guess. Another of [inaudible] graduate student came with a 10 centimeter maser. William Rose or [inaudible]--

Sullivan: 25:11

I don't know him, I know his name.

Sloanaker: 25:13

That was used for the 84 foot antenna. [inaudible] and I worked with Rose and so we measured quite a few of the extragalactic sources. Attempted to measure the [inaudible] and did it. At 10 centimeters. And made measurements of Saturn. And that would've detected polarization of Saturn, very strong polarization. The other people have since attempted to make it and did not find it. See, one of the problems with the 84 foot antenna at 10 centimeters is that it has a very large instrumental polarization. I can't remember exactly, but it was something like 12% or 15% of normal polarization. Which was as big as [the effect you were?] trying to measure.

Sullivan: 26:09

Yeah.

Sloanaker: 26:11

Well another instrumental polarization threshold [inaudible] Saturn at 10 centimeters [inaudible] the wave, with the high [inaudible] so [inaudible] but we got polarization measurements for quite a few extragalactic sources. But an awful lot of [inaudible] at 10 centimeters [inaudible] that was still [inaudible]-- and that made [inaudible]-- Then after that, I got involved with McClain, and Rose and Bologna in making polarization measurements at 21 centimeters and 25 centimeters at Green Bank with the 300 foot dish. We spent a couple of years making polarization. Several hundred sources.

Sullivan: 27:04

That was the one with [inaudible] wasn't it?

Sloanaker: 27:05

Yep. It was 300 foot dish, most of them were in 1963. We measured the polarization of about 98 extragalactic sources. And then in 1964, we measured more. 60 or 70. In 1965, we measured all the sources again at 25 centimeters. And--

Sullivan: 27:34

The first time was at 21 centimeters?

Sloanaker: 27:36

Right. Near 21, not exactly 100--

Sullivan: 27:39

21 and 25, you get the rotation?

Sloanaker: 27:41

Right, to try to get the rotation.  In conjunction with other people’s measurements. People count  [inaudible] from Australia, we're also making a lot of point sources at different wavelengths. And from the early, the first measurements were about 90 sources. We had what appeared to be a very strong galactic depolarization effect. Sources, it was [inaudible]. Sources at low galactic latitudes, we can't confirm our measurements as extragalactic sources. Completely. We only looked at sources that had been identified by other people, either extragalactic or optically. On the average, there appeared to be a fairly strong depolarization effect in our galaxy. That's the [inaudible] several sigma above basically what was predicted from the [inaudible] effect. I guess. And sources at lower galactic latitudes, at latitudes fairly close to our galactic center, a least not in the center, seemed to be [inaudible] two or more, 21 centimeters.

Sullivan: 29:03

Relative to highlighted two?

Sloanaker: 29:04

Relative to highlighted sources. But it was a statistical thing. Well, other people tried to measure the same thing. The people at Caltech, Radhakrishnan, [inaudible], some others, found the same stuff we did. But over period of years, people agreed with what we-- we continually stuck to the depolarization. Over a period of several years, though, the thing fluctuated back-and-forth, other observers in some cases agreed with us, in some cases didn't see the effect. The last paper that was written on it was written by, these are all people [inaudible] large samples of sources. Large samples of sources. Finally, just a few years ago we sent our last measurements. Gardner and Whiteoak measured something like on the order of 400 sources at about three wave lengths. And they did not. Although there's still [sort of?] a statistical effect in this general direction, they don't think it's significant.

Sullivan: 30:17

Well, what's happening do you think?

Sloanaker: 30:18

Well, I don't know what, maybe our effect isn't real. Maybe it is just a physical fluke. But we found that if you included any center sources, you don’t see the effect. Only if you stay away from the galactic [inaudible] center at low [latitudes] do you see the effect. I mean, since we're near, you might expect it since we're near the edge of the galaxy. If you look straight out away from the center, you're not looking through much gas even at low latitudes.

Sullivan: 30:49

I see.

Sloanaker: 30:50

At least you might expect the effect to be less there. Looking within about 60 degrees, the [inaudible] center, we didn't see any effect either. But if we confine our observations to more than 60 degrees from the galactic center, we tend to see a fairly strong effect. In this final paper on about 385 sources or something, Gardner makes no distinction between center and [out of center?] and rules out our effect. I still think [inaudible], if you don't include [inaudible] center sources and those very large number [inaudible] center sources in his paper.

Sullivan: 31:30

Well, what was it like using the 300 foot in those early days?

Sloanaker: 31:34

Oh, it was nice to use even in 1963. I mean, it was all--

Sullivan: 31:46

But your data was in strip chart form?

Sloanaker: 31:49

Well, yeah, that's right. In 1963, we took the data on punch paper tape, but we had never taken any digital data before. William Rose and Bologna and McClain and myself, none of us had ever taken any digital data before. And we used there-- yeah, we took the data, but that time, 1963, they did have digital recorders, paper tape recorders, at the 300 foot plus strip chart recorders. And so we took all our data using paper tape recorders and strip recorders. But we had never taken any digital data, never written any computer programs or anything. And we hadn't prepared for it. And so when we got back about a day before we started to, at that time, they didn't [inaudible] us required to be with [inaudible]. And so we took the data on punch paper tape, but we weren't in a position to check it or anything. And when we were all finished and finally tried to start reducing the punch paper tape data, because I had to learn something about running the programs and so forth. They didn't have any programs written at time, for us. It turned out that there was something wrong with the punch, and so the punch paper tape data was not good. So we ended up reading all the strip charts.

Sullivan: 33:22

I see. Just like the old days, huh?

Sloanaker: 33:24

But later when we went back the next year though, by that time they had magnetic tape recorder, and by that time also we had learned something about programming with the Branch got one of those IBM 1620 computers, and we had learned the right FORTRAN program for it, so forth. So our later data we took on magnetic tape, and we did reduce it from the magnetic tape.

Sullivan: 33:47

How would data be pulled at on the 84 foot and 50 foot [crosstalk]?

Sloanaker: 33:50

All [digital recorders?]. And now at one time, they did, somebody pulled up a punch paper tape digital recording machine. [inaudible] get [inaudible] and attempted to get digitalized, but never had much success. It was a man name Charles [Baddon?] that worked here for a few year. And he tried to get things [inaudible], but he didn't have too much success. It wasn't his fault, but this thing was very unreliable and we didn't have a computer. There were some there in the laboratory, but there wasn't any in the Branch. He worked on them, but never got anywhere with them.

Sullivan: 34:44

I know this question just popped in my mind is that the pointing on the 50 foot telescope for the steering was an old gun mount. Was it? But what set of guns was it then? Do you know?

Sloanaker: 34:56

Twin 5 inch gun mounts. It has twin something. It used to. I don't know if they’re still there or not. Twin 5 inch guns that worked simultaneously. And so that meant two 5 inch guns simultaneously. That's right, the pointing was the [inaudible] was [inaudible] at 3 centimeters, the thing was 9 inch [inaudible] 3 centimeters. The pointing was not that good.

Sullivan: 35:18

Was this the famous alt-az converter thing, was that regulated of the 50 foot from the beginning, or?

Sloanaker: 35:24

No. That's something I forgot to mention [inaudible]. When we first started, that wasn't working yet, and so you couldn't track the source. We had to take all of our data in the form of drifters.

Sullivan: 35:35

I see.

Sloanaker: 35:36

Using the, you know there are hand dail controls outside? So we had to go out and set the hand dails in altitude and azimuth. In other words, we had calculate what the altitude and azimuth of the source was at a given time.

Sullivan: 35:54

That’s the same sort of thing that the gunner set his [crosstalk]?

Sloanaker: 35:57

It's the same altimuth-azimuth dials gunners used. You could read them very accurately. And [inaudible] altitude and azimuth and then wait for the source. Well, all our first measurements were made that way.

Sullivan: 36:09

You can go up and reset it and source come through again?

Sloanaker: 36:12

Right. And to simply things, though, we mostly made measurements right at transit.

Sullivan: 36:19

You just moved it up and down?

Sloanaker: 36:20

So we just moved it up and down. So we'd wait for the next day to get a slightly different information just to simplify the calculation.

Sullivan: 36:28

So you [when you took?] the converter thing along then you were using it mainly as a transit instrument.

Sloanaker: 36:33

That's right, mainly as transit. We could've [inaudible] but it's just too difficult. See, we didn't have computers. In fact, we didn't even have electric desk calculators, they were old [crosstalk]. They were they were electrically operated, but--

Sullivan: 36:48

Mechanical.

Sloanaker: 36:48

--[crosstalk] mechanical desk calculator. And so it was quite a job calculating altitude and azimuth except at transit. So we [inaudible] with transit

Sullivan: 37:00

Even for the Sun and Moon? Or were they studied at all with the 50 foot?

Sloanaker: 37:04

Oh, well a little bit, but not much. The 6 foot dishes they used for the Sun and Moon they were all [inaudible]. That's right, all our first, it was about a year, I guess, before the axis inverter was operating. And I think when we used the altitude-azimuth controls, hand operated controls out on the roof,

Sloanaker: 37:38

the dish pointed pretty accurately. After the axis inverter got into operation, the pointing was a big limitation of using the 50 foot dish [inaudible] with a nine-minute reading. When you had it, we still-- you could track a source, but not very well. I mean, you'd have to constantly catch up.

Sullivan: 38:05

It was wobbling what, something like -

Sloanaker: 38:08

Not one, a few arc minutes at least. So you'd have to constantly watch whether the output would match.

Sloanaker: 38:14

Yep. Strip chart recorder right in front of us. You'd have to constantly adjust on the [declination?] to keep the thing picked up.

Sullivan: 38:22

Right. So you just saw the tendency fall down and you bring it back on?

Sloanaker: 38:25

Right. So we [took?] almost all of that in the form of drifts, all our measurements of Venus and Mars and Jupiter at 3 centimeters were in the form of drift. What we would do would take a series of drift curves then change the declination by one minute of arc. And so, well, that happened mostly when we carry this [inaudible]. But here's the way we made all our Venus measurements. So this is a plot of [inaudible] on declination, we’d have a series of drift curves spaced one minute apart in declination. We’d start well below the peak declination, get drift curves, and then some of that [inaudible moved up. And then some [inaudible] and go, "Good drift curve, [inaudible]" And then we’d start over again, and would read the intensities of each of these drift curves and make a plot like this and pick out where we thought the peak declination was. And it would not necessarily fall on any particular drift. So in the hope in quite a few hours of observations we’d have a lot of these measurements from the [inaudible] smooth curve where you’ve got the peak [inaudible].

Sullivan: 39:45

[inaudible] really tell there in the pointing in declination.

Sloanaker: 39:48

Right. And then would correct them across the strip curve to that smooth curve by the amount they differ from it to try to get the peak [intensity?]. And so it was a real laborious thing. But then it gets--

Sullivan: 40:06

Yeah, I didn't realize it was-- but it was all drift curves.

Sloanaker: 40:09

You had to take about at least five or six drift curves for every peak drifter. You just could not reliably set the thing to peak definition. And even after you had done this all day for Venus, you couldn't come back the next day and take peak drift curve. You still had to go through the same thing every day. So you had to take about six drifters for each peak curve.

Sullivan: 40:32

It wasn't even repeatable.

Sloanaker: 40:33

It wasn't repeatable. But it meant we're fairly [inaudible]  on a short time basis. But you couldn't make maps this way at the point.

Sullivan: 40:41

But not day-to-day.

Sloanaker: 40:42

Not day to day. Have to do it again each day. So that's one reason it took us so long to make the Venus map.

Sullivan: 40:51

That was a nice thing about the 84 foot also.

Sloanaker: 40:53

Right. Pointing was so much better. That's right. The 50 foot dish, the [inaudible] even though [the offset?] is something like 56% or 55% for [inaudible].

Sullivan: 41:04

Yeah, with really good preference.

Sloanaker: 41:06

Yeah. And very low incremental.

Sullivan: 41:12

Let's see. So we got the 300 foot polarization project that takes us up to what year?

Sloanaker: 41:17

Oh, that's up to '55.

Sloanaker: 41:20

And we worked on the data for a couple of years, up to about 1960 to have an idea.

Sullivan: 41:28

Okay. That's about where I'm cutting off my history because things just get too big past the mid-sixties.

Sloanaker: 41:35

All right, that's compiled very good.

Sullivan: 41:39

All right, thank you very much. Do you have any other things that I've skipped over or things that you should be included?

Sloanaker: 41:47

You must have not. [inaudible] just about all of these things.

Sullivan: 41:54

Yeah. Well, it is not exactly, but, okay, thank you.

Sloanaker: 41:56

Well.