Interview with Dr. Theodosios Chatzistergos

Winner of the Alexander Chizhevsky Medal

by Tinatin Baratashvili and Enno Mueller

[editing: Iulia Chifu]

[editing: Iulia Chifu]

Since its establishment in 2013, the Alexander Chizhevsky Medal has recognized and inspired early-career scientists whose innovative research has made a notable impact in the fields of space weather and space climate. Named after the renowned biophysicist Alexander Chizhevsky, a pioneer in heliobiology and aero-ionization, the medal celebrates those who have demonstrated remarkable achievements within eight years of their PhD, promoting advances in understanding solar and space influences on Earth. This year, Dr. Theodosios Chatzistergos from the Max Planck Institute for Solar System Research has joined the ranks of these distinguished medalists. Dr Chatzistergos’ expertise in solar physics, honed through an impressive international academic journey, has led to transformative insights into historical solar activity. By developing a novel method to cross-calibrate sunspot records, he has refined our understanding of solar activity over the past three centuries, and through detailed analysis of Ca II K observations, he has reconstructed critical facular data—key to addressing uncertainties in irradiance trends and improving long-term models of solar magnetic variability. His work not only offers a window into the Sun’s past but also provides invaluable data for understanding its influence on Earth’s climate. In our interview, Dr. Chatzistergos delves into his motivations, challenges, and future aspirations, shedding light on the persistence and methodological rigour that has characterized his groundbreaking research.

T&E: What initially sparked your interest in space weather and space climate research and how did your career path lead to this field?
Theo: I don’t think I have a good answer.
I took a rather unconventional path. Starting as an undergraduate, I initially explored the atmospheric physics of other planetary bodies, specifically focusing on Titan. After obtaining my master’s in astrophysics, I looked for a PhD. I found Max Planck Institute for Solar System Research (MPS) with the group of Sami Solanki and Natalie Krivova, which were proposing some projects related to solar activity, and that seemed very interesting to me. One very intriguing idea was trying to delve into the history of the Sun, and in particular of its radiative output. Starting with the spacecraft era, we can say we have continuous and direct measurements, but such measurements are impossible from the ground. However, before the satellite era, we had ground-based observations of different layers of the solar atmosphere, which luckily provided direct information on all the phenomena that drive the variations in the Sun’s radiative output. But for most of the data the information you want is somehow hidden and to extract it one needs to do a lot of extra work. This whole work seemed to me very challenging and intriguing.
As an undergraduate, some of the lab courses I followed showed us such historical data stored on photographic glass plates, and I found it impressive how people took those images of the Sun from the late 1800s. One of these data’s main drawbacks was that, as the recorded information was analogue, it was very complicated to derive consistent measurement values from them. Nowadays, with the data available in digital form and our better understanding of solar physics, we have a chance to extract meaningful information from those old recordings, which I find rather extraordinary.

T&E: It’s very interesting! I find you still kind of switched even if within astrophysics. You started from physics and changed from the atmosphere of planets to the solar atmosphere. Do you think that switch was very difficult, or very different, or you think that was not a big step?
Theo: Technically, there was another deviation in my path. I also worked on orbital dynamics in between. But, to answer your question, I don’t find it was difficult. I think I learned different skills from all the places I have been and all the subjects I have been studying, and that was very useful for me. In general, every time you need to start with a new subject, you need to get acquainted with the topic, with the past research. So, I don’t think that it’s different than when I get now a new project. But I am happy I changed, and I am happy with my research.

T&E: I asked specifically for young scientists to read.
Theo: I want to add very quickly. When you switch from one place/subject to the other, you interact with people from different fields. This is good for you because it trains you how to communicate with different characters and personalities; you are not all the time with the same supervisor, for instance. Also, different fields might have different tools, or different ways of doing certain things, and that’s also something that might be very beneficial for you.

T&E: Was the field you did most of your recent studies established in MPS or it was something rather new?
Theo: In MPS there was already an established group studying irradiance variations. By starting my PhD, I joined their group.
The group was using various approaches for irradiance reconstruction, and my role was essentially to help expand this aspect of their work.
Now, there are also students and interns working on this, though they come and go. I’ve always found the historical data particularly fascinating which we have emphasized more now, though it wasn’t a very active area initially.
The analysis of the historical data was initiated more than a decade ago, and now with new ways and methods, we have significantly expanded the analysis.

T&E: Together with you?
Theo: Yes. It certainly became a very big international collaboration, so, it includes a lot of people from many places.

T&E: What would you consider as the main challenge or setback throughout your research, how did you overcome them, and what did you learn from them?
Theo: What I found interesting, I can say in retrospect, was the challenge of the project itself. When I learned about the project, which sounded super exciting, I was very excited to do that. Once I started, having read in more detail what I had to do and received the data, I started feeling it was impossible to fulfil the task in the given time frame. Mostly because things assumed to have been done or corrections that have been supposedly applied, didn’t work. We realized the existence of a lot of issues with the data and the ways that they were typically handled. We had to deal with something new and identify different ways to solve the problems. This was a bit of a challenge, and it keeps being a challenge in the sense that there are still issues appearing that keep us active.

T&E: The candidate for the Alexander Chizhevsky medal must have taken unsteady ways, potentially at risk, to reach an achievement. Theo, did you seek out something less established in this field, where you had to demonstrate initiative?
Theo: The historical data have been there for quite some time, and I was not the first one to try to use them, so it is not something new or a new initiative. So far, there were quite discrepant results between different groups, and even within the same group. In that sense, it was a project that needed a good strategy and thinking and had a very high risk that you would not obtain meaningful results. We are glad that, in the end, we managed to obtain good results, but the work continues. I would say, in that sense [of the medal description], there was the risk of not getting something meaningful, something new out of these old data.

T&E: Usually, when you’re doing your PhD, you need results, right? You need certain applications. It is a certain routine you need to follow, but then, if you follow something unexplored, then the risk is high. But then, if it’s successful, like in your case, you get amazing results. So, what do you think was the main factor that nudged you to continue?
Theo: I don’t want to say naivety. I’m not sure, I remember feeling incredibly grateful at the time just to have the opportunity to pursue a PhD in a topic that fascinated me, so I was determined not to let it go just because of the first complications.

T&E: Did you feel this kind of pressure described by Tinatin that you have to publish, and did you have doubts about not obtaining results in the PhD time frame?
Theo: It was maybe a point when I realized that the original three-year timeline had completely gone off track. It was a strange feeling, but we decided to just keep pushing forward. We had some projects in parallel. This means, in terms of PhD even if that one did not work which would still be a very bad thing, there were other parallel projects I could have still been doing for the PhD.

T&E: From an interdisciplinary perspective, do you see your research valuable and do you hope that other fields or related topics might benefit from your research?
Theo: In general, yes. There are different applications for what we do besides the obvious related to solar magnetism. The way the magnetic field was watched a hundred years ago has implications for the reconstruction of solar radiance which influences the research performed in space climate which has connections with other effects on the system of the earth. For instance, our data are included in the solar forcing datasets of CMIP7 to be used in the next run of Earth’s climate simulations for the next IPCC report. For space weather, there are some small implications too. In some of the historical data one can find drawings of the sunspots, and some are very detailed drawings, like for instance the one from February 1872, when a very strong event (flare/CME) occurred. So, we have very good information about the sunspot group that led to that CME. The same is true for the Carrington event and a few others. This is one case where historical data are valuable for space weather and not just space climate. But who knows, maybe there will be more information which we can extract later from the drawings.

T&E: What insights can we gain from the information we gather on the solar magnetic field, and how might it aid us in understanding space weather and space climate? On a more local level, in the research you’re involved in or observing, what are areas where you see potential for improvement, or factors that might be slowing down the growth and advancement of the community or a specific research niche?
Theo: I cannot really answer for space weather because that mostly relates to prediction of flares and CMEs. I’m not really in a place to speak on this part.
I think there are a lot of aspects we lack as observational research, like how we see the poles, how do we see the Sun out of the ecliptic plane or from different vantage points, but I know that these are in some way kind of tackled and there are plans in the future to keep doing that.
What I want to emphasize though is that a potentially significant amount of data is being lost which would be of utmost importance to preserve. Ground-based solar observing programs oftentimes get discontinued, or at some point upgrade their systems to make use of CCD cameras, or even because observatories sometimes repurpose themselves, such as switching from solar to night-time observations, which all lead to the historical solar data being easily overlooked. Photographic plates containing valuable information may simply be left in storage or discarded, as people no longer recognize their importance, or those who do might be retired. Preserving this data has become increasingly challenging, yet maintaining these archives is critical. Another point is that it is very important for the ground-based programs to continue being active. That is because such data are essential for linking historical data with current space-based observations. Without this continuity, we risk losing the ability to accurately connect past insights with our modern understanding.
I am not sure that is what you asked.

T&E: I think this is exactly what we asked. Thank you very much. Very good answer. One more question. You are awarded for being a very young, early career scientist. You have achieved a lot in the years after your PhD. Is there a specific piece of advice you would like to give young scientists or students interested in pursuing a career in space weather or space climate?

Theo: Yes. I’m not entirely sure what to say. I like to see the whole process as kind of, like small puzzles every time, so it’s not that it’s a very difficult puzzle and I drop it, it’s more like a new challenge. I advise to take every step at the time, try to find with patience each piece of the puzzle until you obtain the final picture; don’t rush and don’t get the hardest puzzle to solve. Also, I think everyone is different and everyone needs to find their path and what it suits to their personality.

T&E: Thank you very much for the time and the answers.