skip to main content
Home  /  Interviews  /  Judith Cohen

Judith Cohen

Judith Cohen

Kate Van Nuys Page Professor of Astronomy, Emeritus

By David Zierler, Director of the Caltech Heritage Project

December 17, 2021

DAVID ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It is Friday, December 17th, 2021. I am so happy to be here with Professor Judith G. Cohen. Judy, it's great to be with you. Thank you so much for joining me.

JUDITH COHEN: Oh, it's a pleasure, for me, too! [laughs]

ZIERLER: [laughs] To start, would you tell me your title and institutional affiliation?

COHEN: I am the Kate Van Nuys Page Professor of Astronomy, Emeritus.

ZIERLER: Can you tell me about being named Kate Van Nuys Page Professor?

COHEN: Well, I thought it took them a bit too long to do that, but they did finally do it! [laughs]

ZIERLER: Who is or was Page and what might be the connection to your work?

COHEN: I don't really know who Page was because when I asked, they said that the person was deceased.

ZIERLER: How do you understand the honorific of having a named professorship at Caltech?

COHEN: I understand it as a symbol of achievement and of doing something important.

ZIERLER: When did you go emeritus? What year was that?

COHEN: I'm 75 right now. I think it was about five years ago.

ZIERLER: What were the circumstances of going emeritus, for you?

COHEN: What changed? You didn't have to teach anymore. That was the major issue. I didn't feel that I should teach anymore. The field was basically running so fast that I was running behind, it kind of seemed. I thought it was better not to teach, especially not people who had already committed to astronomy.

ZIERLER: Without having the burdens of teaching and committee work and things like that, were there areas of the science and research that you were looking forward to becoming more deeply involved in?

COHEN: I had this big project running with some people from Carnegie, and I was hoping that we could devote our attention to that. They're my age, my two collaborators at Carnegie. It was moving along pretty well. I had a postdoc working on it. But then I got sick, and things fell apart again.

ZIERLER: Just as a snapshot in time, what are you working on currently?

COHEN: What I'm working on currently is trying to finish this big project that I started about five years ago. We made a lot of progress, and then I got sick and my postdoc took off for—she's at Vanderbilt now. My colleagues at Santa Barbara are good people, but they're not as aggressively ambitious. It did not bother them that this thing was dragging on more than I think it should have, and it bothered me, because I wanted it done. The net result was that they didn't do a damn thing over the past year and a half at all, and I want this thing finished. That's my goal.

ZIERLER: What is the project?

COHEN: It's a project involving the outer halo of the Milky Way, as defined by the RR Lyrae. The advantage of RR Lyrae stars, which has been known for years and years, is that it's a variable star, and if you know the period of the star, then you know the luminosity. If you know the luminosity, you can find the distance. And distances are hard to get. Our goal was to make a sort of map of the outer halo using the resources of both Keck and their big telescope in Chile, Las Campanas telescope. We thought we could make a nice map of the outer halo using these stars as tracers and learn something interesting. That was what we were trying to do.

ZIERLER: Do you see this project as a capstone of your career, a culmination? Or is it just the thing that you happen to be working on at this stage in your career?

COHEN: I've worked on a lot of different things, so I see it more as this is what I'm working on now. I don't like spending probably about 100 nights of telescope time on big telescopes and then leaving all these loose ends. It's not good. Now, one of the collaborators, of my two Carnegie collaborators, his wife—they're both Canadian, and his wife lives in Vancouver, and he was spending a lot of time here, and then he'd go to Vancouver for a while. But during the past two years, flying between California and Vancouver was impossible, so this whole pandemic has messed this up, too. It wasn't just an issue that we couldn't do it. It was that he couldn't fly to the United States.

ZIERLER: Even more recently, what are some of the big takeaways for you from the Astro2020 decadal report, both in terms of what it means for astronomy and what it means specifically for Caltech?

COHEN: I must say that I was somewhat surprised that there was so much space and effort and clear strong feelings about the issue of women in astronomy. That is the first decadal report that I've ever seen that addresses that issue head-on and really hard. I've never seen anything until that came out that was that strong and public.

ZIERLER: Strong in a good way, you mean?

COHEN: In a good way, except I think they almost went too far. You don't want to feel like you're compelling people to respect you. You hope people will respect you for what you do; that was almost compelling. That's the way I looked at it. But since it's a problem that has never been discussed in such a high-level forum before, and there were a lot of strong women on the committee, I guess that's how it came out.

ZIERLER: What did the report say? What were the takeaways in terms of the issue of women in astronomy? What are some of the solutions that the report suggested?

COHEN: Oh, I can't tell you that, but there's a lot of issues that are tied to this. There's the issue of children, and the support of the children. Caltech now is great. They have that nursery thing over there near the parking lot. I know a lot of the women use it, but you wouldn't want to hear the shit that I heard [laughs] 30 years ago! That was really poor! [laughs] Now, and I can't tell you exactly who's pushing harder, but it's clear that the president is concerned about this issue. It's clear that the shit that I went through, they don't have at all. [laughs]

ZIERLER: What about on the observation side? What are some of the takeaways on where astronomy might be headed as a result of the decadal's recommendations?

COHEN: I thought the decadal recommendations were quite—first of all, they were the recommendations on the large telescopes, which was no great surprise, but making that real hopefully it will become easier, now that they played such a prominent role, in particular in the parts of the report that people from the Senate and such might read. The fact that that was very strong and that apparently they have strong support from the people in Congress and in the Senate that they've spoken to, I think that's very interesting.

ZIERLER: Do you think that the TMT is more likely to get built as a result of the decadal?

COHEN: I don't know about the TMT. But the TMT has been such a mess for such a while, and it has spent so much money getting no place. That's not fair; they've done a lot of design. But they haven't built anything. And they haven't solved the problems with the Hawaiians, and those are big problems. I'll tell you a little story. A long, long time ago, probably at least 30 years ago, my husband and I were sitting on a beach, not on the big island but one of the other islands. My husband is not white. He's not Black but he's not white. And if you think about it, that's the description of the Hawaiians, right? Anyway, we're sitting there, and this Hawaiian guy comes up and he starts talking to my husband in Hawaiian! [laughs] That got straightened out, and then he started talking in English. He sat down and we spent an hour talking to each other. He was just livid about what was going on, on Mauna Kea, and in particular on the TMT and on all these issues. It was clear that he felt that they had been totally bypassed in the decision-making processes, and that the decision-making was not reflective of the will of the Hawaiian people. This was many years ago. That's a really tough problem, because I would go up to the summit—now, you never go to the summit, but in the early days, you had to go to the summit, because there was no high-speed links and this, that, and the other thing. I spent a lot of time on the summit.

ZIERLER: The summit of Mauna Kea, you mean?

COHEN: Yeah. They have a dormitory-like thing at about the mid-level, where people sleep, because it's too hard to sleep on the summit, and so the dormitory is not on the summit. They have a kitchen and a cook and the whole shebang. If you walked around and looked at the people, on the summit there were very few Hawaiians. They were all cooks in the mid-level facility, and the cleaners, and the this and the that. It was pathetic! I understand the issue, in that the schools in Hawaii are quite poor and can't really educate people in the way they've been doing so that they can get a job at Keck or any of the other observatories. These are really long-standing issues that have been, to some extent at least, neglected by the owners at, Caltech, UC, wherever. It's only when they started trying to get permission to build again that all of this surfaced, but it has been there for a long time.

ZIERLER: To what extent is TMT essentially paying for the sins, as it were, of previous generations in astronomy, with Keck and other projects?

COHEN: I think that's exactly what's going on. I think the TMT now is trying really hard to demonstrate that they can be a good partner for the Hawaiians. They have been helping pay for the big luau events and this and that. The director of the TMT is now living in Hawaii. He has moved to Hawaii, I don't know, maybe six months ago, and he's going to stay there for a year or two. He said he wants to understand the Hawaiian point of view and see how one can make progress.

ZIERLER: Are you optimistic? Do you think consent can be achieved, whatever that might look like?

COHEN: I don't know enough about the distribution. I suspect that, as everyone says, there's a set of hard-core dissent, which is actually quite small, and then there's a lot of people in the middle, and then there's a small number of people in favor. I don't know how they're going to deal with this.

ZIERLER: What might you say about the fact that the decadal is agnostic about Hawaii or the Canary Islands as a site for the TMT?

COHEN: I think they have to be, because it might well come down to having to go to the Canary Islands, even though most of us think, evaluating all the evidence, that Hawaii is a better site.

ZIERLER: Observationally, you mean?

COHEN: Observationally, yeah.

ZIERLER: I wonder if you can explain in some technical detail why Hawaii is better than the Canary Islands.

COHEN: It's slightly higher, and I think the weather pattern over Hawaii is very predictable because it's all that ocean. The Canary Islands are islands, but they're pretty close to the mainland. Also you can get dust from the Sahara, what they call Sahara dust, that just blows in across the—I don't remember the name of the waterway between the mainland and the Canary Islands. You can actually get what they call Sahara dust. [laughs] I think Hawaii is a better site. It's higher, and it's more built-up in the sense that we already have a lot invested there that can be used. But if we can't, so be it.

I have friends on the committee that are going to have to do this and deal with this, and if you want to talk to people who are in the know and actively involved, then you've got to go up to the level of Ed Stone and company, and not me. We know generally what's going on, but not totally. I don't think it's hopeless. I think it just requires a sustained effort and an agreement about what to do. That N percent of the workforce is going to be Hawaiian. A couple years ago, we started a program where high school students from the big island would go to UC and other places for the summer, and try to get them interested in science, and get them to a point where they could go to graduate school in the U.S. if they wanted. Not many wanted, but they're in general not prepared. The schools are terrible!

ZIERLER: Based on how the decadal report uses its wording, do you see TMT and GMT more as partners, or more as competitors?

COHEN: Well, we should hope that we're partners in some sense, but undoubtedly, there will be a little fraying of that. I have worked with people from Carnegie for many years, and I have no problem with that, but the GMT is a much bigger collaboration than my dealing with my friends at Carnegie. I don't know how it's going to work out. It's a touchy issue because there's a lot of pride and history in there.

ZIERLER: Because the Europeans are already so far along in their large telescope program, which is essentially going to be a neighbor of the GMT in Chile, if GMT is viable, how important is it for the astronomy community not to just have two ELTs next to each other in the southern hemisphere and possibly no ELT in the northern hemisphere? How important is it to avoid that situation?

COHEN: You don't want to have no ELT in the north. That would be very bad, because after all, the north is much better, you might say. There's some good astronomers in Chile at the University of—it's not Santiago; it's a different place. There are some good people, but not very many. Many of them come up to California, getting in the swing of things. But I really can't see the point of having the successor to our current big telescope being right next to the ELT. That's not very productive. That will breed competition.

ZIERLER: If the TMT does not go through, what does that mean for Caltech and its long history of leadership in ground-based astronomy?

COHEN: It's going to be hard. There are certain things that we do very well, and we have some really great people in certain areas. But you're not going to attract that quality of people unless they can be on the front line. I think that will be a larger—could be significant.

ZIERLER: For your own research, to move away from the politics and the budget and all of that, if the TMT is built, what will that mean in terms of some of the biggest questions in the fields of research that are most important to you?

COHEN: If the TMT is built, then we can nail down the whole local universe in a way which we just simply couldn't do before. But of course saying that the TMT is built is not quite enough. You have to have the funds that the decadal survey points to as supporting astronomy from the Congress, to maintain an active staff and maintain the astronomy departments at, at least, the best universities. Otherwise, what's the point of having a TMT? In the past, I don't think that the Congress was quite so enthusiastic, maybe because the financial situation was much worse ten years ago, at the level of the government. But it seems like now, from what I keep hearing and what was written in the decadal survey, they are interested, and they are viewing it maybe not so much as a competition with the Europeans but certainly as an important thing. And maybe also a competition with the Europeans.

ZIERLER: I'd like to ask you some questions about terminology. Let's start at perhaps the most basic level. Are you an astronomer? Is that the best identifier for you?

COHEN: Yeah, I think it's fine.

ZIERLER: From there, what role does theory play in your work?

COHEN: In my work, over the last ten years or so, it doesn't play a very big role, but that's because I'm an antique. [laughs] There's a lot of computer modeling, but that's not theory; that's computer modeling. Theory, we have I would say three or four people that are theoreticians at Caltech, and none of them have been to a telescope for significant amounts of time. Theory is great, it's really important, but that's not a place where we excel. We do have some good people, but—

ZIERLER: As a self-identified antique, I wonder if you can bring a little historical perspective to the way these terms are used currently and how they've been used over the course of your career. There's astronomy, there's cosmology, and there's astrophysics. Where's the overlap, where's the distinction?

COHEN: Astronomy, at least in the way I use it, there's something called observational astronomy, which involves getting data from the telescope, turning it into something that is measurable and can be modeled, and if you can produce numerical quantitative results from the model, that's even better. Then there's a whole bunch of people who are pure modelers, in some sense, and who may collaborate with people who observe but really have never done it. On our faculty, for example, there's Sterl Phinney, who's absolutely brilliant beyond belief, but I don't think he has ever been to a telescope. [laughs] But his knowledge of physics and astronomy and how to put the pieces together is fabulous. I don't know if you know all these people, but Phil Hopkins is in the same class, although I think Sterl is more brilliant. I don't think Phil has ever been to the telescope, but he sort of does something between modeling and theory. Sterl is much more pure in his theoretical work. To have a good department, you have to have all of these things, because if you discover something interesting and you tell them about it, they'll walk off and work in a parallel direction and produce some great insights [laughs] hopefully. So you need both of these. They don't necessarily have to be in the same physical location, but they have to be friends.

ZIERLER: Is the unique or even idiosyncratic way that Caltech organizes itself at the divisional and not the departmental level, is being in the Division of Physics, Mathematics, and Astronomy, being in PMA, is that useful for you, the way that Caltech organizes itself?

COHEN: Yeah, I think it's useful. For example, I never would have understood very clearly the beautiful work that came out from Kip Thorne and company, except that because we're close and we talk to each other and we can go to their colloquia and they come to ours if they're interested, you can gain insight into something that is not up your alley, you might say. You actually learn something interesting in the juncture.

ZIERLER: More specifically from observational astronomy, there's lots of different kinds of telescopes. What kinds of telescopes have been most important in your career?

COHEN: Big optical telescopes. I was one of the people who helped build Keck. I worked on Keck, for a long time. That was very bloody. It was not so bad for the first few years, but then you know what happens. You always overrun on some project like that, and the leaders in Caltech at that time were screaming that they couldn't go back to these people and try to get more money and we had to economize. We were under tremendous financial pressure at the end of the Keck project. It was a horrible situation. It was so bad [laughs]. I inherited, from Bev Oke who retired because he had heart problems, the leadership of the group that was building one of the three first-light instruments. We were so short of money that at the end, we couldn't even buy computers. I'm not talking about big ones; I'm talking about this kind of computer. Well, that didn't exist, but something similar to that.

At the time, we were installing this big thing that we had built, and we had to go up to the summit with a fairly large truck that I had rented at the airport there. I rented this truck. It was about maybe $75 or $100 a day. We got up there and we unloaded the truck and we were going to be there for five or six days putting everything together. We were so damn short of money, and they had refused to pay—well, I'll tell you what they refused to pay in a minute—that I decided I would drive the truck back to the airport to avoid paying the five days of fee for the truck, and then I would try to hitchhike back. Now, people don't hitchhike much anymore. It's quite rare to see anyone hitchhiking. Anyway, I thought I would try it. Otherwise, if I couldn't get out hitchhiking, I would rent a car and drive back. I managed to get up there, hitchhiking, no problems at all. I figured, "Come on, it's an island. They're nice people. What can happen?"

Anyway, here's an example of how tight—Bev Oke, who was the PI and who had to retire due to heart problems, and I, we were doing the testing, and so there was a lot of data floating around. At that point in time, all of this huge storage capacity just didn't exist. A big computer had maybe 512. Remember that? I wanted to buy a computer for me, and Bev said he wanted a computer. I said, "Yeah, yeah." I call up the guy from Santa Cruz who was in charge of investigating money matters. I had to call him up for two $500 toys. And this thing cost $100 million or whatever the hell? He told me, "No, you can only have one." That was crazy! That was the level of pressure that everyone was under, trying to finish Keck, and then Keck opens, to some extent. We're starting the commissioning. There's actually some light going through and everything. They started to ask people what they wanted to do on their first Keck night, what their first project was. I said something like, "I want to take some images of galaxies, and see what you can find." Deep images of galaxy clusters. One of my colleagues got really angry and said, "That's my project." Then all hell broke loose! [laughs] Everybody knew that the first images, if it worked, were going to be really interesting. And they shoved us aside. They really tried to shove us aside, after spending five years working in the lab and leading this team and running myself ragged. Bev got a heart attack. I was younger; I didn't get that, thank god. [laughs] But he had to retire. That was horrible. It was because there was no slack anyplace. It was private money, and when you spent all the private money, what do you do?

ZIERLER: You can't ask for more.

COHEN: Well, we couldn't ask for more, and they decided not to ask for more, for whatever reasons. Probably the reason was you're supposed to be able to estimate things appropriately. Anyway, building Keck was a very interesting experience, but it was hell.

ZIERLER: Some terminology questions of increasing specificity—let's start first with near-field cosmology. What does that mean, near-field cosmology?

COHEN: In my book, near-field cosmology means that you can actually see the objects that you're interested in, and maybe you can get spectra, and you can actually look at them, and they're not so far away that they have to be five million supernovae to see what's going on. That's near-field cosmology.

ZIERLER: How near? What's the dividing line? How near is near-field?

COHEN: I don't know, maybe a couple hundred mega parsecs, something like that?

ZIERLER: What would be the antonym? Far-field cosmology?

COHEN: Well, far-field, we don't really use that.

ZIERLER: Where are we looking for near-field cosmology? Is it the Milky Way?

COHEN: No, no. Near-field cosmology is sort of beyond Andromeda but not too far beyond Andromeda. The trouble with that version of near-field cosmology is that there's only two big galaxies, the Milky Way and Andromeda, and then you have to go out a fair distance to get to the next really bright ones.

ZIERLER: What telescopes would you need to go beyond Andromeda?

COHEN: It depends on what you want to know. If all you care about is how bright the galaxy is, you can go pretty far out, but if you want to see the spectra and individual lines and stuff like that, you can't go too much past Andromeda, even with Keck.

ZIERLER: Next, the chemical evolution of galaxies—what does that mean, how galaxies evolve chemically?

COHEN: What that means is that you imagine that a galaxy collapses from a bunch of gas, and the bunch of gas has the composition of the universe outside galaxies. As it collapses, you start producing elements beyond hydrogen and helium, and you want to measure those. Hydrogen and helium is nice, but it's not very informative. [laughs] It's also hard to observe helium. There's not a lot of lines. Very hard to observe helium, at least within the optical range. Astronomy has broadened out a lot since I started. There's tremendous gains in the infrared, tremendous gains beyond the normal infrared. The only part that's left unexplored I think is the ultraviolet, and sometime in the next N years, somebody will put a big space telescope up to test UV sensitivity. Maybe.

ZIERLER: What has been preventing us from understanding the UV?

COHEN: Because it is absorbed in the Earth's atmosphere, so you have to get above the atmosphere to see anything, whereas optical astronomy goes right through. Infrared astronomy goes right through until certain wavelengths and then it gets bad. So it's the window that we can see from the ground easily. Because you're not going to—kudos to JWST, but putting something much bigger than that in space is hard, and it costs a lot of money.

ZIERLER: Next up are galactic globular clusters. What are they?

COHEN: Galactic means that they're found in our galaxy. They're found in all galaxies as far as we know, but the ones that are nearby and bright are the ones you can study the easiest. Globular clusters are basically self-gravitating aggregations of stars that move around each other, and that belong to a single entity, you might say. They're individual clumps of stars bound to the central galaxy. That's interesting because you know where they are, and you can compare cluster A to cluster B to cluster C in a specific galaxy and then go look at another galaxy and see if you get the same trends, and you should. Probably, you do, actually.

ZIERLER: How has our understanding of galactic globular clusters changed during your career?

COHEN: It has gotten much more detailed. [laughs] Basically you couldn't do any of that stuff until Keck. That was part of the fighting around who would get what pieces of the sky to look at. But with that large a telescope you can study globular clusters out to fairly large distances around many galaxies in the local group. It can do anything you might want to do, to first order. After that, it gets harder.

ZIERLER: What about supernovae? What has been some of your work on supernovae?

COHEN: I don't think I've ever worked on supernovae. I've taken some spectra for people if I'm on the telescope. Now, we have formal mechanisms for handling situations like supernovae where you don't know when, nor where, but it does happen. And when it does happen, how do you arrange to be able to interrupt someone, because that's what you're going to have to do. The night is going to belong to somebody, and you're going to have to convince them that getting a spectra on the supernova is important enough that they stop doing what they're doing and look at your supernova. That kind of policy has took a long time to work out, but now it works pretty well. There's paybacks, and there's ways around it, and stuff, but of course the more you subdivide the time, the harder it is to make a scheme like that work.

ZIERLER: How does extrapolation work in your research? In other words, taking data from things that you can work with pretty easily, and extrapolating that to understand bigger questions about how the universe works?

COHEN: I would say that I sort of have kept pretty close to home. I've never gone much beyond Andromeda. That's not true, but most of my work, I really haven't gone much beyond Andromeda. I've done some things right when Keck came up, which were clearly some of the great treasures was the ability to jump beyond Andromeda. But in my personal work, as collaborative work with lots of other people, I haven't gone much beyond Andromeda.

ZIERLER: For you, in terms of the observation, is it all about stars? Are you interested in exoplanets, comets, meteors, things like that?

COHEN: I'm interested, but I'm a spectator. I think the exoplanet game is extremely interesting. I'm not quite sure who's pushing whom, but the technology for accomplishing it has become much better over the past five years than in the past. I think that's a reflection of the much better infrared detectors, the much better control of pointing, all this stuff about active optics. It's a very tough technical field, but it's fabulously interesting.

ZIERLER: What are the big questions that have always been with you in your research? What are the things that you always come back to, that you've asked, about galaxies, about the universe, about stars?

COHEN: I've done a lot of work on globular clusters, and that was because with Keck, you could pick them apart and get good info on the individual stars in some of them, and eventually, at least if you stayed within the galaxy. If you wanted to do globular clusters in Andromeda, you could get an integrated light for the cluster but not individual stars. I worked a lot on the chemistry of all of this, but that was leaning on other people for guidance and help.

ZIERLER: In your education, how important was a chemistry background, or did you get all of that in astronomy and physics courses?

COHEN: I didn't have a chemistry background. I had a little bit, but very minimal when I got into this. But it was an area where, at least when I first came to Caltech, nobody else was working on it. Jesse Greenstein, who was the founder of astronomy at Caltech, he was immensely interested in that. He was retiring and old and all that, and there was a hole, and I jumped into the hole. Of course, with Keck, the whole field opened up, but I was working for 20 or 30 years before Keck became real. No, more than that, actually. I was sort of Jesse's heir, his scientific heir.

ZIERLER: To switch gears entirely, let's go back to hallowed ground. Let's go to Brooklyn!

COHEN: [laughs]

ZIERLER: We'll start with your parents. Tell me about them.

COHEN: My father was an accountant. He had his own private practice. We lived in Brooklyn, New York, and he had a number of big companies that for some reason or other needed his services. All I can tell you is he was an accountant. We were not poor, but we were not rich. My mother was a nurse. She worked as a nurse during World War II in Panama, and then I guess after that, my parents got married, after the war. I have three sisters, so it was a family of four girls, and so she didn't work for a long time, and then she started working part time. Towards the end of her working days, she was basically teaching nursing at Brooklyn College.

ZIERLER: How many generations back does your family go in New York?

COHEN: One more than my parents. My grandparents were born in Russia and Poland.

ZIERLER: They came here before World War II?

COHEN: Yeah, but not by much.

ZIERLER: What neighborhood did you grow up in?

COHEN: Flatbush.


COHEN: Brooklyn. East 19th Street.

ZIERLER: Was your family Jewishly connected at all? Did you go to synagogue, have High Holidays?

COHEN: My family was Conservative. They were more secular Jews. I went to the Workmen's Circle. Do you know what that is, the Workmen's Circle?


COHEN: The Workmen's Circle was basically sort of like a union for Jews. But it was directed religiously rather than—it also had things to do with employment and stuff like that. It doesn't exist anymore, but at that time, it was a pretty powerful organization. They had a system of Jewish schools. These were not Hebrew schools; these were Jewish schools, throughout New York City and in other places, I guess. I went to their public school, which was after the regular standard public school, and then I went to the high school. They only had one high school; it was in Manhattan. On Sundays, I would take the subway to Manhattan to go to that school. So I had a fairly—they weren't religious. They were sort of old union hands.

ZIERLER: What was the education, in addition to your regular academic public school education?

COHEN: I didn't learn much Hebrew, but I learned a lot of Yiddish. We had plays and shows and reading Isaac Bashevis Singer and all that stuff. All the teachers at that time were concentration camp survivors. I don't know why I kept going, because all of my sisters, we all went to the primary part of the Workmen's Circle school system, which as I said was after regular school. It was not on top of it; it didn't cover that. But I was the only one who went to the high school. I enjoyed it. I enjoyed reading the stories.

ZIERLER: Were you always interested in science?

COHEN: Sort of, yeah.

ZIERLER: You can't really see too many stars from Brooklyn, though, growing up.

COHEN: No, but we—this is a really crazy story—there was a group that met in Manhattan called the Junior Astronomy Club. Joel Levine, who is a bigwig in AAS, was affiliated with that. I would go to the meetings occasionally. The meetings were in Manhattan, but once in a while they would have an observing trip. People would bring their telescopes, and we would go to Woodlawn Cemetery, because that was the nearest place that was dark. [laughs] That was all we could do from New York!

ZIERLER: What high school did you go to during the day?

COHEN: Midwood.

ZIERLER: Was it a strong program? Did you get a solid education there, would you say?

COHEN: Oh yeah, I had a very good education there. I was the valedictorian of a class of probably 500 people or something. It was a big school.

ZIERLER: When you were thinking about college, what options were available to you, both in terms of being a New Yorker and as a woman?

COHEN: As a woman, I had never encountered any kind of discrimination until that point. I encountered it later, but not then. I had to get a scholarship. My parents had four kids, and they certainly couldn't afford an elite school if they had to pay, but I got a National Merit Scholarship, I think it was, that paid my full tuition. Or between that and Radcliffe support—I'm not really sure—it was made feasible that I could go to Radcliffe.

ZIERLER: How did you understand Radcliffe relative to Harvard?

COHEN: At that point in time, the classes were all together. If it had been 20 years earlier, then what Radcliffe was was the place where the Harvard professors would go in the afternoon and give their class again for the women. But that was over by then. Not by law, but it was over, and the classes at Harvard were open to women who were students at Radcliffe. I got a diploma that was signed by the president of each of them.

ZIERLER: Even though the diploma says Radcliffe, it was a Harvard education?

COHEN: I think the diplomas are actually signed by both, the president of each. In any case, yes, effectively it was a Harvard education on a different social basis.

ZIERLER: Had you traveled widely? Had you ever left New York before going to college?

COHEN: I had never been east of Long Island, west of Buffalo, north of Buffalo, and south of New Jersey. [laughs]

ZIERLER: What were your impressions when you first arrived in Cambridge? Did it feel like an elite place, a very different kind of place than you were used to?

COHEN: Yeah, it was pretty hoity-toity. [laughs]

ZIERLER: [laughs] What was your major? What did you want to study when you first arrived?

COHEN: My first year, I was poking around, but I went over to the Math Department. Well, I didn't even bother to go, because unfortunately, the first math class I took was extremely devoted to formulae and it was too abstract. It was like abstract mathematics without anything underneath it. It turned me off math. Then I went over to biology, but I didn't like that. That was the end of biology. Then I went to the Smithsonian Astrophysical Observatory. Do you know about that?


COHEN: I went over there, and I met this young guy, Steve Strom, who you may or may not have heard of.

ZIERLER: Sure, sure.

COHEN: He had just joined the faculty or something, he and his wife Karen, and he said, "Oh, come work with me. We'll have fun." That's how it happened.

ZIERLER: Do you remember what he was working on?

COHEN: It was the early beginning of abundances. Ah! I remember what he was working on. He was making the first model atmospheres of stars on a computer. That's what he was doing.

ZIERLER: Being at the Observatory, how did that influence what your major was, as an undergraduate?

COHEN: Well, I was an astronomy major, as far as I remember. I was taking classes. I wasn't doing a lot of research. It was just part-time, so it didn't matter.

ZIERLER: What about physics? How much physics did you have as an undergraduate?

COHEN: I had a fair amount.

ZIERLER: Who were some of the professors that were mentors to you, or who you got close with?

COHEN: I would say the one I was closest to was Steve Strom, who was not on the faculty, I don't believe. He had a research title rather than a faculty title. I met Cecilia Payne-Gaposchkin but she was too old, at that time. It was like meeting your hero. I was not particularly adhering to any specific person.

ZIERLER: As a woman at Harvard and Radcliffe in Astronomy, were you sort of exotic? Were there other women around?

COHEN: In astronomy, there weren't very many women, but it was not a very big department, either, so that didn't bother me. I never felt anything too disastrous in terms of women at Harvard. I did have lots of issues later, but at that time—for example, when I applied to graduate school, I applied to Princeton. I got a letter back saying, "We do not accept women in the Department of Astronomy at Princeton." [laughs]

ZIERLER: You didn't know that; otherwise you probably wouldn't have bothered applying? Or you wanted just to—?

COHEN: No, I didn't know that. Didn't cross my mind. I was having such a good time with Steve, it didn't occur to me. [laughs] I was a junior or something, and we wrote two papers! [laughs] That was great.

ZIERLER: What did you do during the summers? Did you go back home? Did you stay on campus? Did you have fellowships?

COHEN: I went home most of the time.

ZIERLER: On the social side, was it interesting to you to be at Cambridge during all of the protest movements?

COHEN: I wasn't paying much attention to the protest movements. Let's put it this way; I never had a date until maybe my second year at Harvard, so I was trying to get some social experience. I met one or two guys that were interesting, but it didn't work out. Then I met another guy that I liked but my parents were horrified because he wasn't Jewish. But we decided to get married. He had applied to Caltech. He was in astronomy, and he had applied to Caltech, and he got in. The next year, I applied, and said that I was going to marry X, and here I am, and I got in. Then the guy came back from California—and my parents had already spoken to his parents and all this other crap, and they had a wedding and invitations had been sent, and the guy comes and he says, "I'm not going to marry you. I've met somebody else." That was pretty poor. [laughs] So I show up at Caltech, and I was going to work for Jesse Greenstein for the summer, because our interests overlapped. Jesse said, "Oh, you should go to Europe. You'll recover from all this stuff." [laughs] I said, "Jesse, I can't afford to go to Europe!" [laughs]

ZIERLER: How far ahead was Caltech from Princeton in terms of admitting women graduate students?

COHEN: Not much. They had at that time two or three in Astronomy.

ZIERLER: Who were still there? You interacted with them?

COHEN: Yeah. One of them was Vicky—what's her last name? Vicky from Australia, and she was married to one of the other graduate students. Then there was Virginia Trimble, who was a graduate student there, and that's probably it. But that was more than [laughs] most places, I think!

ZIERLER: It was the Astronomy Department that you came to?

COHEN: Yeah, I came to the Astronomy Department.

ZIERLER: What did you think of Pasadena when you arrived?

COHEN: I had never lived anyplace except for Harvard and New York. That was a pretty big change.

ZIERLER: Do you have a clear memory of when you first met Jesse?

COHEN: Yeah. I remember him telling me to go to Europe for the summer. [laughs] He didn't mean it as a joke. He meant it! Jesse was very kind to me. I had dinner at his house maybe two or three times. That's a big deal for someone in my position.

ZIERLER: What were some of the exciting things happening in Astronomy at Caltech at that point?

COHEN: I don't know. I honestly can't remember.

ZIERLER: What was the process of defining a research agenda, getting a graduate advisor?

COHEN: Jesse was my advisor. No, that's not true. Guido Münch was actually my advisor, technically. I'm sure you've heard about Guido! It was hard to tell how much of it was bluster, if you know what I mean, but he was a real smoothie! [laughs] I just shined on that stuff. I figured, "I'm here. They're giving me an education." [laughs] But I had a tough time, because I was just so lonely. The men that I had affairs with—there were several of them—they weren't at all sincere. They weren't looking for a partner. They were looking to have fun. And I was looking for a partner. That's the way it went.

ZIERLER: What was Guido's research? What was he doing at that point?

COHEN: He was working on Fabry-Perot, mostly at Mount Wilson. That was part of my thesis, was a lot of work at Mount Wilson, with this Fabry-Perot interferometer.

ZIERLER: Tell me about working at Mount Wilson. What was it like?

COHEN: It was crazy! [laughs] They were very hierarchical, very formal, in their equivalent of the Monastery. When you went to dinner, the head of the table was the 100-inch observer, and the next person down the line was the—basically, that guy always sat at the head of the table. It was crazy. I couldn't stay in the Monastery. They had built a little cabin for somebody who wanted to bring their family up or something, somebody from the staff. I had to stay in that cabin, which was quite a distance from the dining area. When I first went to the Monastery on Mount Palomar, I had to sleep in an attic. [laughs]

ZIERLER: As a single woman, this is what you had to do?

COHEN: As a woman, period. Yeah. It was pretty crazy. Then they progressed, and they had—that Monastery had two bedrooms sharing a bathroom in the middle. They finally got the bright idea that they would just not assign someone to the other bathroom, and they'd give me like a two-bedroom suite, and everybody was happy. It was nuts! [laughs]

ZIERLER: What was the process for putting your thesis research together?

COHEN: What do you mean?

ZIERLER: What did you want to work on? What was your thesis?

COHEN: Oh! My thesis was on—I don't remember anymore! I remember basically talking to Jesse a lot—oh, now I remember more. My formal advisor was Guido, and I used his instrument, which was a Fabry-Perot, to do some measurements which today we could probably do in 20 minutes, but then took a long time. [laughs] Guido was really crazy.

ZIERLER: What were some of the big questions at that point? How did you define your thesis topic based on those bigger questions?

COHEN: I defined my thesis topic by trying to do something interesting with this new instrument that Guido had built. That's how I defined it.

ZIERLER: What was innovative about this instrument? What could it do that wasn't possible before?

COHEN: It was the multiplexing of the instrument, that you could get measurements of the spectrum, different chunks of the spectrum, simultaneously, that you couldn't do any other way at that time.

ZIERLER: Which allows you to do what, to conclude what?

COHEN: That allows you to measure abundances and lines in a finite length of time. If you have to measure one by one, and then adjust A, B, C, D, E, and move the grading and do this and that, it takes forever. This was a pretty revolutionary instrument that he had built, and I was his graduate student, so I got to do this. It was fun.

ZIERLER: What were your conclusions?

COHEN: What were my conclusions? It was a thesis on stellar abundances. That's all I remember. I can't remember the most interesting conclusions, actually. It was so long ago. [laughs]

ZIERLER: Do you remember who was on your committee?

COHEN: Yeah, I remember it was Guido, and Jesse, and two other people that I don't remember. I remember they asked me a bunch of questions with one or two tricks in them that I managed to make it through. I wasn't sure, but I did it. [laughs]

ZIERLER: Do you remember any of those questions?

COHEN: No. I might remember them tonight, and if I do, I'll tell you.

ZIERLER: After you defended, what opportunities were available to you? What did you want to do next?

COHEN: What I wanted to do next was I wanted to live in Berkeley. [laughs] This was the middle of the 1960s, 1970s. I had a cousin that lived in Berkeley, and I had been visiting Berkeley occasionally.

ZIERLER: It was a lot more exciting than Pasadena?

COHEN: A lot more fun than being in Pasadena. I wanted to be in Berkeley. There's a thing called the Miller Institute in Berkeley, and I managed to get a Miller Fellowship, so I went to Berkeley for three years. I had a blast. It was a really exciting time for Berkeley.

ZIERLER: Are all Miller Fellows in the Astronomy program?

COHEN: No, no, it's a wide range of areas of study, but I managed to get one. That's all I can say. Even before I moved to Berkeley [laughs], I was very upset with Vietnam and all that kind of stuff, but I started going to meetings and marches. When I would go to Berkeley, I would be a political person, which you couldn't be in Pasadena. [laughs] I did some really crazy things in those days. I thought to myself, "I should save the money, and driving to Berkeley is a waste. For one person it's a little crazy. I'm going to try to hitchhike to Berkeley." I said to myself, "Okay, if I can get a ride in an hour, and it points me in the right direction, I'm going to do it." And I did it. I hitchhiked to Berkeley. [laughs]

ZIERLER: Safely.

COHEN: Safely! In those days, it was okay. Now, forget it! But yeah, I had no problems at all. I got there, and there was some big peace march going on, and so I joined that, and I ran into my aunt and uncle! [laughs] They were heavy into that. My parents were never into that thing, but they were. I had a great time in Berkeley. I did a lot of work, but I also had wonderful trips all over, hiking trips in the Sierras, and it was wonderful.

ZIERLER: Did you work mostly solo, or were you in a group at Berkeley?

COHEN: No, I was solo. I was in the Astronomy Department, but I wasn't collaborating with anybody.

ZIERLER: What was the work? What were you researching in those years?

COHEN: What was I doing in those years? God! I was doing stellar abundances, I think.

ZIERLER: As a continuation from your PhD?

COHEN: Yeah, that's what I was doing.

ZIERLER: What were some of the questions in stellar abundances?

COHEN: How much you could reproduce all this with the miserable knowledge that existed in those days of atomic spectra and structure and line lists and stuff like that. That's what I did.

ZIERLER: How long did you stay at Berkeley for?

COHEN: Three years. Then I got a job at a place called the Kitt Peak National Observatory in Tucson, and I went there.

ZIERLER: As an assistant professor?

COHEN: No, no. Well, they had the equivalent of different titles, more or less. I went in at sort of the middle bottom range, I guess you could say. I had a lot of trouble the first year or two, because I had started traveling to Chile. Tololo was opening up at that time, so I had started traveling to Chile. I basically had a lot of trouble with men. I don't know what it was, but all these years, I was looking for a man [laughs]. I wanted some company! I met this Chilean guy and we hit it off. We got married. He had to get a visa, and it was all very complicated, and it was a big mess, and it was an even worse mess because he had to get a divorce, and there was no divorce in Chile. It was a huge mess! He didn't speak hardly any English at that time, so I had to straighten all that out. That was a complicated mess.

So my first year or so at Kitt Peak, I was not as productive as I should have been or might have been or whatever. They told me they were going to not renew my contract. I said, "Okay." I started taking classes at the University of Arizona to become a civil engineer. Meanwhile, we finally fix him up so he was legal [laughs] and also we finally got enough money—obviously he didn't have any money, but when we moved to Tucson, I didn't have much money either. He wasn't white; he was brown. I had to buy a house before he came, so I thought it was going to be better for us if we lived in a not pure-lily-white neighborhood, so I bought a house in a not so—what people in Tucson would say was a Black neighborhood. It was cheap. We could afford it. It wasn't a big house, but it was okay. And we were robbed about 15 times. The police came several times, and the last time they came, they said, "Look lady, they don't want you here. This is not going to stop, and you have to move." This is the police in Tucson! So we moved. I told the man who I had selling the house, the realtor, I said, "I want you to sell this to a Black person. I don't want you to sell it to a white person." I don't know if he did or not. And we bought a house in a much nicer neighborhood.

Anyway, getting my husband settled and all of these problems fixed took a lot of energy, and that energy had to come someplace, and it came out of Kitt Peak. So my first year at Kitt Peak was I would say not the greatest, and the second not the greatest. Then, everything was fixed up. They had already told me they were going to kick me out by then, and I started writing all these papers and doing all this stuff, and they said, "Well, Judy, you can have another year." [laughs] After that, they said, "Oh, you can have another year." [laughs]

ZIERLER: And you stayed with the bachelor's program at University of Arizona?

COHEN: Yeah. I was going to become a civil engineer because I figured I could live anyplace. Yeah, I stayed with it to finish, because I was almost there. Meanwhile, my husband, he never had a great job, but he was a very talented man, so he got jobs here and there. I was writing all these papers and we were all very happy, and then I got a phone call from Peter Goldreich, who said, "Why don't you apply for a job at Caltech?" I said, "Okay." I applied, and I came for a visit, and they offered me a job. They said, "What do you want?" And I was such a fucking idiot! I was so overwhelmed by this thing which was so unimaginable to me given all the shit I had been through [laughs] that I didn't ask for anything! Which was totally stupid! I could have asked them for $100,000 startup or this or that or whatever; I didn't ask for anything! That was really stupid.

ZIERLER: What was it that garnered Peter's attention? What were you doing that made him reach out to you?

COHEN: I had written a whole series—Steve Strom wrote the first abundance analysis program for individual elements. I had basically taken that program which he wrote, and I may have fixed it up here and there, but basically, he wrote it, and I used it to analyze a huge number of stars—not huge, but a large number—and to discuss chemical [analyses] that kind of stuff. That was really frontline work at the time. Today, it's common. Then, that's what I was doing.

I made a lot mistakes. And because my parents of course didn't approve of the marriage, I just wouldn't listen to any of their advice [laughs] which was not smart either! [laughs] They accepted him, but they never went beyond acceptance, you might say. But he was a brilliant man. He had very little formal education, and he was the top fix-it at Tololo. Extremely handy. When the Keck project started, I had a book of sketches that we were looking at, and I took it home, and he looked at it, and then he asked if he could keep it for a while. A month later, he made a model of Keck out of wood, and I put it on my desk. Ed Stone walked by and saw the model and he said, "Where did you get that?" [laughs] I said, "My husband made it for me." He said, "I'll buy it!" [laughs] I said, "Well, he can make you another one." So he sold that one to Ed, and then he made me another one. [laughs]

ZIERLER: Did you come to Caltech with tenure?

COHEN: That was my other big mistake. I made a lot of mistakes. I didn't. I was a fool! I didn't ask for anything. I was so honored. Somebody who had been thrown out of Kitt Peak, almost, I just felt so—I did a lot of stupid things in my career, and I often wish that there were some people who took more interest in me and said, "Look, this is how you play the game." I didn't know how to play the game, and that's the result of it. I didn't get tenure until I had been at Caltech for three or four years. I spent a lot of time on instrumentation, and some people didn't value that as much as others. But that's how I got into the Keck game. I had spent a lot of time on that kind of stuff.

ZIERLER: How different did your experience feel coming back to Caltech as faculty, not as a graduate student?

COHEN: There was still tremendous problems, on the women's side. At that time, there were five women on the faculty, maybe? I in my usual crazy fashion, I started a deal where we would all have lunch together once a month. I actually persuaded the faculty office to pay for the lunches. They agreed. [laughs] For several years, we had lunch, and we worked our way up from four or five to maybe 20 after which the lunches stopped. The first five of us would meet, talk for a while, once in a while, when there were only five. One of them kept saying that she thought we were being underpaid compared to the men. I said, "Let's have a study. Let's ask Caltech to do a study. Let's ask for a raise!" We did that, collectively, and it was very hard. They said, "It's very hard to do a study, because Caltech doesn't have fixed salary ranges." And because there were so few people. But they did agree to do the study, and they agreed that Anneila Sargent would be our representative, because she was more acceptable to them, I would say. Anyway, they did this study and they agreed that we had been significantly underpaid.

ZIERLER: Who was on the committee? Was this the provost?

COHEN: Yeah, it was the provost, the provost and Anneila, basically. They agreed, and they raised all of us to exactly the same amount, which happened to be—I think it was $220,000 a year, and I was getting like 150 or so before then. I mean, they were guilty as hell. They had already been sued once by this woman—she was in English—Jenijoy La Belle. There was a woman before Jenijoy who had sued Caltech also, I think, but it had been thrown out. So we felt like we were pushing the envelope, sometimes.

ZIERLER: Were they starting to talk about Keck by the time you joined Caltech?

COHEN: No, no. That was in the future.

ZIERLER: When did that start? What were the earliest planning discussions for Keck?

COHEN: It took 20 years to build, and it was finished in about 2010 or so. I would say that things didn't start for at least ten to 15 years after I arrived.

ZIERLER: What were you working on? What was your research by the time you joined the faculty at Caltech?

COHEN: Once Keck became more real, I spent most of my time on instrumentation. Bev Oke—heard of him?


COHEN: Bev was on the faculty. He was the main instrument builder for the 200—he built many of the instruments of the 200-inch. He worked with Jim Gunn a lot. He and I started working on Keck instruments together. Then unfortunately he had had heart problems and had to retire, and I was left holding the bag. That's the way it was. But I guess that discussions for Keck, the early discussions, started maybe five or six or seven years after I arrived. There was no discussion—that's not true actually, because there were discussions at that time, so I take that back. The reason I know is because there were simultaneous—it was like everybody was trying to figure out how to do this. There was a guy whose name escapes me at the moment who was on the faculty of the University of Arizona, who was trying to spin mirrors, spin cast mirrors. Then I remember going to meetings in Berkeley. Jerry Nelson was a good friend of mine. I had known him for years. I think there were discussions at the time that I arrived, between UC and Caltech, but there was no agreement yet. It took at least a year after I arrived before there was a formal commitment to work together, and then another year maybe to get the money all arranged.

ZIERLER: In terms of your observation work, was it all based in Chile?

COHEN: A lot of it was, but not all of it, mostly because Chile was relatively unexplored. They had had those small telescopes for a while, but they were getting up to an 80-inch or whatever it was that they finally ended up with. It wasn't so small a telescope. It was okay. And the southern sky was—there's a University of Chile Department of Astronomy and there's a Concepción Department of Astronomy, but they were hopeless, so it was open season.

ZIERLER: What was some of the work you were doing on modeling stellar systems?

COHEN: I was interested in globular clusters and how much of a diversity there was in the range of metallicity within a given globular, and then as you looked over the whole galaxy, what the range was. The whole of our galaxy. Then towards the end we started playing with M31 but didn't get real far.

ZIERLER: When did infrared photometry really get started?

COHEN: Gerry Neugebauer started all that. He started it at JPL, actually, and did some work at Mount Wilson. That was just getting going when I came back. Just getting going. Then Tom Soifer was involved, and he was sort of Gerry's right-hand man. Then after Gerry became too ill, he took over.

ZIERLER: How was this relevant for your research?

COHEN: The infrared was a new thing at that time, and so you could get a lot of good stuff. But it wasn't tremendously important in what I was doing. It was fun to watch other people, but I wasn't involved in that much.

ZIERLER: Tell me about the project to design and build the low-resolution imaging spectrograph.

COHEN: That was Caltech's big instrument for Keck. We had a good engineering team. Bev had built it up over the years, and how he paid for it, I don't know, but he did, so we had a good engineering team. But it was a big project, and I think neither of us were really prepared for the complexities that you get into with such a big project. As I said before, towards the end, the financial pressure was terrible. Since this was the first-light instrument, or a very important component—it wasn't actually the first one on. The first ones on were some infrared instruments that could take a picture to convince Mr. Keck that it was working. Then they took it off and brought it [to him]. But the first real instrument on there, I'm not sure if it was ours or Gerry's. Those were interesting days. I remember Bev was very upset because his doctor wouldn't let him go to the summit because he had heart problems. He would go out to Hawaii, but he would be in what today is the observing room. You've probably seen it. Have you seen it? Well, it had none of that stuff there. He got so frustrated, because we'd be running around madly on the summit trying to make things work and he couldn't follow what was going on. It was terrible. Then eventually it got so bad that his doctor told him he had to retire.

ZIERLER: Was building the spectrograph your entrée to the larger project of making Keck a reality, or had you already been involved in that?

COHEN: What do you mean by making Keck a reality?

ZIERLER: Building it. Just getting it done.

COHEN: I guess I was always interested in getting it done. I don't know. I took some engineering courses here and there, and I felt that I could do it. What can I say?

ZIERLER: Did you ever have any interactions with Mr. Keck?

COHEN: I was presented to him. I doubt if he ever remembers meeting me, but I have been presented to him. I would say that I really haven't had any interactions with him. I was too junior.

ZIERLER: At what point, given the difficulties, did you realize that the project was viable, that Keck would be built?

COHEN: We all understood that we had to build it because the man had given the money, and that Caltech would scrounge the rest however the hell they could, but that unless it got totally out of hand, they were going to do it. That was the attitude.

ZIERLER: How did you get involved leading the Caltech Faint Galaxy Redshift Survey?

COHEN: That was my prize for all the shit work that I did to try to make the thing real! [laughs] I was friends with Roger Blandford, and he had this brilliant student, David Hogg, who is now at NYU. While I personally didn't have much training in that kind of thing, it was interesting to be involved. I can remember X, and I'll be kind and not say who X was, at a faculty discussion, and he said, "That's my field! I want that!" Bev or somebody else—I can't remember if it was Bev or Gerry or whom—beat him up privately and said, "Judy gets what she wants because she has put all her time into this, and you haven't." That part was nice. I liked that. [laughs]

ZIERLER: How was this a game-changer for astronomy, just in terms of what could be observed now?

COHEN: Between Keck and before?

ZIERLER: With the Redshift Survey.

COHEN: We could now do, for a large number of relatively nearby galaxies, what people could do before for the Milky Way. It was fabulous. In the past, we had real numbers for one galaxy. Everything else was very flaky. Suddenly, you have real numbers for let's say 20, 30. It's a big difference.

ZIERLER: What are you learning when you have access to understanding all of these different galaxies?

COHEN: How they evolve. Their stellar population varies from galaxy to galaxy and how they evolve. Astronomy is kind of a funny thing, because it's all hypothetical. Proving something is kind of hard, sometimes.

ZIERLER: What is gravitational settling?

COHEN: Take a bunch of pills and you take a bottle of water, and you put the pills in the water, and they sink to the bottom. Gravitational settling. [laughs]

ZIERLER: How does that apply in astronomy?

COHEN: For example, the stellar atmosphere is like the water, and if you have features in it, they're going to sink, and you can pick out the features. Astronomy is all very wishy-washy, because you can't touch anything, so it's all these indirect observations and trying to get a bigger data set, but not by looking at what's near X and Y but by finding more objects you can reach.

ZIERLER: In the 1990s, when LIGO was getting started, were you following that?

COHEN: Oh yeah, that was great! [laughs] That was really amazing.

ZIERLER: You realized how exciting it would be, right from the beginning?

COHEN: It's a whole new world. You've got the optical. You've got the infrared. It's very hard to do much in the UV because of the Earth's atmosphere absorbing everything. Then you have all this high-energy stuff, and you have LIGO. It was a new world.

ZIERLER: Tell me about the 0Z project, the high redshift universe work.

COHEN: Well, that was the clear thing to do, because with the Palomar telescope, you could just about do what we were trying to do for one galaxy, and suddenly you go to Keck, and you can do it for 25 or 30 or 40. This was a tremendous jump forward of a known problem where you knew exactly what you wanted to know, and what you might expect to see, but you just couldn't do it. The jump between Palomar and Keck was a very big jump. It's not the mirror size; it's the mirror size squared or cubed. It's a big factor, makes a big difference.

ZIERLER: Did Keck essentially replace Chile for you in terms of where you would go?

COHEN: Not all the time, because first of all, my husband and I always liked to go down to Chile to visit [laughs] his family, and I like Chile. It's a beautiful country, and there's a lot of really interesting things there. It's on the coast. So I didn't mind going to Chile. In fact, one time they had this program to go for three months or something. I think we were down there for three months. They gave us one of the houses to stay there for three months. Also, the southern hemisphere has more points of great interest than does the northern hemisphere, many areas. So yeah, I liked going to Chile.

ZIERLER: To return to globular clusters, what's the difference when we talk about the inner halo and the outer halo of globular clusters?

COHEN: Are you talking about the clusters or about the parent galaxy?

ZIERLER: The clusters.

COHEN: Well, I've not heard the term used that way. The inner halo in the vocabulary that I've heard is for the galaxy, and the outer halo is for further out in the galaxy, and it applies to clusters as units, and not within each globular cluster there's inner and outer. I think you're a little confused there.

ZIERLER: When did you first start to think about exoplanets not in a theoretical sense but you could actually see them?

COHEN: I would say that I thought there was promise there, but when Dimitri Mawet joined the faculty, when he came to give a talk so we could decide to appoint him to the faculty, he blew me away. That man is brilliant. He's working in a field which is very competitive, but the combination of brilliance and knowing what to do and having Keck has pushed him to the absolute forefront of this very compelling field. You should talk to him, if you haven't.

ZIERLER: Absolutely. Now it would seem again, just purely theoretical, shouldn't it not be surprising at all that there are exoplanets? If our Sun is a regular star, shouldn't there be planets all over the universe, because we know there are stars all over the universe?

COHEN: Yes, yes, but it's always nice to see them! [laughs] To be able to detect them in one way or another. It's not like the Christians are lined up against the wall saying, "Hail all Earth" or whatever, but certainly there was some element of that.

ZIERLER: Is the excitement about exoplanets mostly about the possibility of discovering other life forms, or is there something more intrinsic about exoplanets that's of interest?

COHEN: Oh, I think excitement of possible life forms is fascinating. I think most people believe that's just fabulous.

ZIERLER: What was the telescope or what was the first project that confirmed the existence of exoplanets?

COHEN: I don't know if it was Dimitri or somebody else. It may have been some other Europeans. The big European telescope was more set up for that than we were, at that time. Of course now Dimitri has fixed 50 million things, and it's much better, but at that time, the instrumentation was not very good.

ZIERLER: As the field was developing, exoplanet research in the early years, what were your contributions in terms of looking for stars that might be host to exoplanets?

COHEN: You don't need my help to do that. Their initial efforts were so difficult that they would just take the brightest thing around and not even try to do—maybe they'd try the first brightest three things, but that would be it. It's a hard slog. That was a brilliant appointment. We got lucky.

ZIERLER: Did you take on graduate students right away at Caltech?

COHEN: I have had very few graduate students. I don't know if that's because I'm a woman, or because I'm working in a field which is not as sexy as exoplanets or something like that. But I've had very few graduate students.

ZIERLER: What about in terms of women coming to Caltech as graduate students? Have there not been that many? Has that been part of the problem also?

COHEN: Surely that has been part of the problem. It has gotten better with time but not—it's too late for me.

ZIERLER: Besides time, did you ever get out in front of those issues about calls to diversify the program, bring in more women and minorities?

COHEN: I know a lot about the efforts that they were making at that time. You can always say do more, but they did try a lot. For example, at one point, every professor that went on travel, they would ask you to go and visit prospective women students in their homes and talk to their parents. I did that a couple times. I would go visit people who were at—the Punahou School, I think it's called—Hawaii has terrible schools, but there are one or two good ones. I would be directed to stop off at the home of a woman student who was at that school and try to persuade them to apply to Caltech. They have tried very hard. I'm sure they could try harder, but I don't blame them for the women situation. It's a disgrace of our time, but not particular to Caltech.

ZIERLER: What about among undergraduates? Have you seen more women undergraduates coming into Astronomy over the years?

COHEN: I think there are more. I had a brilliant SURF student. My last SURF student was absolutely brilliant, and she's now applying for grad school. My letters of reference say basically, "She's the best there is, take her." I'm sure this woman is going to be a huge success. I really don't see much discrimination of that kind anymore. It was bad before, but I think it's okay now, or close to okay. I think the real problems start when you start talking about having children and stuff like that. It was horrible before, and now it's—medium? [laughs] But if you look at the younger faculty—I'm too old for this, but the younger women faculty do have families, and they have managed—not all of them, but many of them have managed to have children and have them be decent human beings and all that. But in my generation, it was harder.

ZIERLER: More recently, tell me about the work from the Pan-STARRS survey which looked at dark matter distribution in the Milky Way.

COHEN: I am not overly familiar with that survey, so I'll keep my mouth shut, but the Pan-STARRS survey—let's retreat a little bit. The Pan-STARRS survey was the first really good, accurate photometry over the whole sky, uniform, and producing a database. Just the fact that it had this big database and you could look up position A and position B, what was there, that was a really big thing in that time. Big Data was tiny then. Today, of course Big Data is enormous. But that was an immense success. It was the first all-sky—not all sky, but all—I guess it was all southern sky. It was the first all-sky survey like that, that had a format that you could use! It wasn't just some pile of papers; it was something you could really use. That was the great thing about Pan-STARRS.

ZIERLER: Tell me about being elected to the National Academy in 2017. What was that like?

COHEN: I didn't know I was going to be elected! I didn't know anything about it until it was over. [laughs] Caltech handles those things sort of in that way. Right now, I spent a large chunk of my time this spring writing two things. One was a biography of Jerry Nelson, who was the father of Keck, and who died several years ago. I was asked to write a memorial for him for the National Academy, which I did. Took a long time, but it was good. Then I called up Fiona [Harrison] and I said, "I want to nominate X." You'll probably guess who X is later, but I'm not going to tell you. I'll tell you if you're right or wrong, but I'm not going to tell you the name. "I want to nominate X for the Shaw Prize," which is basically one below the Nobel. She said, "Okay." I asked her last year, and she said, "I can only nominate one person, and somebody has beat you to it." It wasn't an astronomer. Whoever it was, A, it wasn't an astronomer, and B, they didn't win the prize, because nobody knows nothing about it. But I'm trying to get that Prize for someone, and I've spent a fair amount of time this year writing a beautiful encomium. Hopefully, this will work. Won't know for another few months, but that would be great. That's the kind of thing I do now.

ZIERLER: A question about committee work. Given that you were on the steering committee for Keck for so long, what has been useful with regard to your committee work for TMT, knowing all that you do about Keck?

COHEN: Knowing all that I know about Keck, I think the TMT project is ridiculous at this point in time, that the way it's being run is ridiculous, that they're spending a fortune and not getting any place, and that they should shut down until they can straighten out the site situation. But it's not just that. It's that astronomy has become so big now that the way we ran Keck won't work. It's too big for that. The TMT is such a huge project that it's got to be highly bureaucratic, lots of committees and all this kind of stuff. With Keck, we could avoid it, to a big major extent. This is just insane.

ZIERLER: How much of that is about the fact that Keck was a private benefactor, whereas TMT is multiple countries and the NSF?

COHEN: That's a big effect. For Keck, there was a budget laid down from ground zero, and we tried to adhere to it as best possible. Maybe we missed by 5% or 10%, but we didn't miss by a huge factor. The end was horrible because we did miss by 5% or 10%, maybe more. But if you miss by 5% or 10% for the TMT, that's a shitload of money. The engineering is so much more complicated, so you have these platoons of people, who have no experience with big telescopes who are on these committees and don't understand how it has to run. I think that the TMT project is never going to get done, personally.

ZIERLER: What do you think the implications are for the master lease in Hawaii?

COHEN: I don't know. I think that the present administration and the present Keck management fully understand the major problems that the Hawaiians have. Whether they can surmount them or not, I don't know. I don't really know. Because the employment situation in Hawaii is terrible. It's either hospitality or observatories, basically. It's going to be very difficult to change that, because who wants to build any kind of factory in the middle of the Pacific and then you have to ship everything? I don't see their economic—and I think they understand that. Certainly the governor and people at that level understand that statement very clearly. The problem is how to deal with the pride of these people and not antagonize them so much. There's a lot of hurt, pain, in the background.

ZIERLER: Serving as Caltech's member rep to AURA, was that more of a service thing or that was important for your research?

COHEN: No, that was strictly a service thing.

ZIERLER: What did that entail?

COHEN: They had two meetings a year, and they were each two or three days. They were held in a nice hotel up in the front of the mountains in Tucson. AURA is very peculiar, because there's so many members, and every member counts equally, so you can get into these weird situations where people who don't know what the hell's going on are making decisions. That was my problems with AURA. You can't say that to them, of course, because they're responsible to the federal government, and you can't say to a bunch of universities, "Shut up, you don't know what you're talking about." It was kind of interesting. I hope I pushed them around in the right directions.

ZIERLER: What's the status of MAGIQ at Keck, the next-generation guider?

COHEN: Well, how much do you know about recent developments at Keck?

ZIERLER: I've been following.

COHEN: Basically nothing has happened at Keck, substantive, except what Dimitri is doing, over the past few years. It has been partially an issue of money, and partially an issue of nobody is really stepping forward and saying, "I want this, and I'm willing to give up my time to make it happen." People haven't been stepping up. Now, hopefully, that will change. We'll see.

ZIERLER: Some interesting nomenclature. At the Subaru Telescope, the galactic archeology project. What does that mean, galactic archeology?

COHEN: What they mean is that the evolution of the stars as a system, not individual stars—well, they measure individual stars, but they're hoping to measure properties of huge numbers of stars in each individual galaxy. The ticket is Milky Way, the outer part of the Milky Way, M31, and maybe one galaxy further out, but that's it. That's all they can do at the level of detail that they want for galactic archeology. After that, you move over to the galaxy group, where the level of detail is much lower, and therefore you can do it on much fainter and more distant objects. Now, my problem with the Subaru is that the Japanese lack experience, to put it bluntly. Their hierarchical structure makes it hard to criticize things. I'm very worried about that project; let's put it that way. It sounds not so hard, but it's very hard, and the people who are running the show are the Japanese, and the Japanese are not up to it. That's one of the reasons that I got out of it. I may be still involved, but I don't do any work. I listen, I go to the meetings of the steering committee and offer comments, but I am not actively working on that project.

ZIERLER: Do you see any similar issues in dealing with the Japanese for TMT and their very unique approach to TMT issues?

COHEN: It won't be as bad, because the Japanese dominate the PFS project. It's their project. Whereas the TMT, there's a lot of partners in there, and most of them are pretty reasonable.

ZIERLER: To bring our conversation right up to the present, are our computational capacities up to the task of all of the data that's coming in from both space-based and ground-based telescopes?

COHEN: I really don't know. One of the big thrusts over the past two or three years at Keck has been making an archive that's useful. Not that we haven't had an archive; it's that we haven't had one which is easily searchable, and you can find what you want and see what's there in a reasonable length of time without killing yourself. Clearly, this trend, you can go two ways. You can go fainter, and if you try to go fainter, you don't have this problem, because you're spending more time on each object. Or, you can try to do more detailed studies on closer things. Then, you're going to have a problem with too much data. I don't see it yet as too much data, but it could get there. It could get there.

ZIERLER: Are you excited about the James Webb Telescope which hopefully will launch next week?

COHEN: I don't know which way to pray now. [laughs] I really don't know. I hope it works. It will be a tremendous embarrassment for a lot of people if it doesn't! [laughs] And there's so many things that can go wrong. It has been put together and taken apart so many times that you really worry! [laughs] I wouldn't have the stamina for that project. I'd have to be much younger, much more hopeful, maybe.

ZIERLER: If it all goes well, what are you most curious about? What can the Webb Telescope tell us that we don't know yet?

COHEN: I really haven't thought carefully about what to do if I was given the equivalent of a night on Webb, because a lot of my work is fairly high-dispersion.

ZIERLER: What does that mean, high-dispersion?

COHEN: It means that if you look at the focal plane and you divide it up into chunks and look at the wavelength range in each chunk, if it's high-dispersion, there's a lot of detail on a smaller range in wavelength. If you go low-dispersion, you'll get more information but fewer objects, or something like that. Space astronomy in particular, since it's so limited in terms of the size of the telescope—you just can't launch anything much bigger than James Webb—and the cost is so high, you really have to be careful about what science you do. I guess I never got into that game.

ZIERLER: For the last part of our talk, now that we've worked all the way up to the present—we've even peeked into next week—some big retrospective questions for you, thinking about your earliest days at Harvard and your initial interest in astronomy. At the broadest possible level, because of your research, what do we now know about galaxies in the universe that we didn't know before?

COHEN: [laughs] Well, I guess the most interesting thing that has come out of galaxies for the longest time is this whole issue of quote "dark matter" and what that might be. That's a different world, though. I think what we've really been able to do is to show that we can reproduce with our current set of physical parameters and physical understanding practically everything you see in galaxies that you can examine in detail. There hasn't been a shot like here's this guy standing with his hand raising say, "Hey, look at me. I'm different. You can't explain me." I think looking back, everything has sort of fallen into place pretty nicely, and I don't think there have been any great shockers. The whole exoplanet business was just impossible in the past. It was technically impossible. But it wasn't that people didn't believe that there might be other planets; it was impossible. I think a lot of things in astronomy were like that. It was just too hard to do, and now all this stuff isn't too hard to do. I wonder sometimes, if we build a TMT, what we'll learn that will be worth the price. Because it'll be just more microscopy on slightly more distant objects, but what will be the totally new thing that will blow you away? I'm curious.

ZIERLER: It could be technosignatures or biosignatures on an exoplanet.

COHEN: Sure. That would blow us away. But that's something we can foresee. You named it, right? That's it. But I don't see anything else in that kind of category.

ZIERLER: The unknown unknowns.

COHEN: Yeah, yeah. And those are the most interesting ones.

ZIERLER: To flip the question around, not the discovery part but the ongoing puzzles or mysteries, what are some of the things where there really hasn't been that much progress relative to 40, 50 years ago?

COHEN: I think that the technical revolution of the last 40, 50 years has been so great that there aren't many niches like that at all. I can't think of anything unless you start talking about maybe the far UV, where we just can't get it from the ground. But I don't see it.

ZIERLER: Yet with all of these technological advances, we still don't understand how to unify gravity with the other forces. We still don't know what dark energy is. We still don't know what dark matter is. Is that to say that these kinds of breakthroughs will need to happen in the theoretical realm?

COHEN: I wouldn't be surprised if that's where it happens, because I think we're not going to see it in the observational realm. We see too clearly right now.

ZIERLER: Is that to say, then, that with a theoretical breakthrough, our observational capacity, our technological capacity is ready to jump in and demonstrate, test the theory?

COHEN: That's my view, unless this theoretical breakthrough is so far away. We've looked at zillions of galaxies that are close, and more zillions of galaxies that are only slightly more different in great detail, and the laws of physics all seem to work, and everybody is reasonably content that they understand things, more or less. I'm not saying all the details are perfect. But to have a totally new breakthrough, I just don't know. I sometimes wonder about the TMT in that regard, but we'll see.

ZIERLER: In looking at all of these other galaxies, do you come away with more an appreciation that the Milky Way is unique, or not?

COHEN: No, it's not unique at all! [laughs] The question of whether it's unique because it has life is something we can't answer, but in terms of the normal properties you can look at and measure and stuff like that, it's not unique at all.

ZIERLER: And why can't we answer that question about life?

COHEN: Because we do not know what physical scale we should be looking at. If it's a very large physical scale, we may not have it. And if it's too small—we just don't know where to look, basically.

ZIERLER: Last question, to the future. What are you most interested in? For as long as you want to remain active, for as long as you want to follow the field, what are the things that will continue to excite you in the years ahead?

COHEN: I'm real curious to see what JWST is going to do. [laughs] I watch the budgets of those things, especially when I was on the AURA committees, and you wonder at the comparison of the on-the-ground versus satellite game, and how much better it would be if that number were a little different. That's one thing.

ZIERLER: With your appreciation of the vastness of the universe, does that ever lead you into philosophical questions or even spiritual questions, or you keep those worlds separate?

COHEN: No, I keep those worlds separate.

ZIERLER: Judy, I want to thank you so much for doing this. I'm so appreciative.