November 14, 202420 min readThis Human Computer Created a System for Measuring Vast Distances in Our UniverseVisual artist Anna Von Mertens looks to astronomer Henrietta Swan Leavitt and her vision of the universe for inspiration Lily Whear (composite); MIT Press (image)Attention Is Discovery, visual artist Anna Von Mertenss thoughtful new exploration of astronomer Henrietta Swan Leavitt, describes and illuminates Leavitts decades-long study of stars, including the groundbreaking system she developed for measuring vast distances within our universe simply by looking at photographic plates. Leavitt studied hundreds of thousands of stars captured on the glass plates at the Harvard College Observatory, where she worked as a human computer from the turn of the 20th century until her death in 1921. Von Mertens explores her life, the women she worked alongside and her discoveries, weaving biography, science and visual imagery into a rich tapestry that deepens our understanding of the universe and the power of focused, methodical attention.LISTEN TO THE PODCASTOn supporting science journalismIf you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.TRANSCRIPT:Anna Von Mertens: Hubble's discovery was not possible without Leavitt's work. It is Leavitt's work that began this understanding of our three-dimensional universe.Carol Sutton Lewis: I'm Carol Sutton Lewis, and this is Lost Women of Science Conversations, a series where we talk to writers, poets, and artists who focus on forgotten female scientists.In the late 1800s, the scale of the cosmos was unknowable. But this all started to change at the turn of the 20th century with the meticulous calculations and shrewd observations of astronomer, Henrietta Swan Leavitt. Leavitt, a human computer at the Harvard College Observatory, pouring over glass plate photographs of the sky, discovered a system for measuring vast distances within our universe.She turned what were once unreachable regions of the cosmos into a measurable map of stars, using the power of attention.For Anna Von Mertens, a visual artist based in New Hampshire, the power of attention was nothing new. Anna makes work that investigates science and history, and her use of paper and pencil or thread and cloth requires time, patience and intense focus. And so when she came across Henrietta Leavitt's work, she immediately felt a kinship. After spending many hours in the archives looking at the examples of early astrophotography, which Leavitt used to make her astral discoveries, Anna created graphite drawings of glass plates and hand stitched quilts inspired by Leavitt's legacy.And, going even further, she decided to write a book that merges these visual works with lyrical and detailed essays that delve into Leavitt's science. That book, Attention Is Discovery: The Life and Legacy of Astronomer Henrietta Leavitt, came out in September, and it's the topic of our conversation today.So let's get into it. Hi, Anna. Thanks for coming onto the show.Anna Von Mertens: Hi, Carol. Thank you so much for that lovely introduction.Carol Sutton Lewis: Anna, you're an artist known for your use of various textile processes and quilt making techniques. So, how did you decide to write a book about Henrietta Swan Leavitt?Anna Von Mertens: So as a visual artist, my work often uses observable phenomena, patterns in nature that reveal structural revelations and understandings.And so because of this type of work that I do that is so steeped in history and science, I was invited by Jennifer Roberts to the Harvard Radcliffe Institute, and Jennifer was the Director of Arts at the time there, and she invited me to develop a research-based exhibition.And the various archives and libraries on campus at Harvard University were generously opened up to me to investigate as a possible subject for this exhibition. And we toured exquisite archives. But when I arrived at the Harvard College Observatory, I knew I had found my subject matter.Because there, housed, are over 550,000 glass plate photographs of the night sky. Now this is the oldest and largest archive of those type of photographs in the world. And Harvard, being Harvard, established an observatory in the 19th century in Peru. So that archive covers both the northern and southern hemispheres, and it's the only complete record of the sky.So viewing some of these glass plate photographs, I first heard Henrietta Leavitt's name. I had never heard her name before. And through these objects, these glass plates, I learned of her name and learned of her discovery and struck by its significancestruck by the profundity of her discoveryI knew that I wanted to develop a project around her life and work.Carol Sutton Lewis: And what a project it is. The book is really a wonderful, unusual combination of art and science.It's a very detailed explanation of Henrietta Swan Leavitt's work and the impact it had on science, but it's also a beautiful, artistic interpretation of the glass plates that you saw. And I could go on and on about this book, but we'll come back to it in a bit. Let's talk a little bit about Leavitt herself. She came to work at the Harvard College Observatory in the 1890s.What was known about our universe then?Anna Von Mertens: Right. Leavitt studied these photographs of the night sky, but almost nothing was known about the stars that shone in that night sky. So at the time of Leavitt's research, there was no sense of the chemical composition of the stars, and no way to know how far away these lights were from us. So for example, if a bright light shone in the sky, did that mean that it was intrinsically larger and brighter? Or did that mean simply that it was of equal brightness to a dim star, but simply closer to us? So there was no sense of depth to the stars. There was no sense of structure to this sea of stars that we were swimming in.Carol Sutton Lewis: And tell me a little bit more about the Harvard College Observatory. How did they come to be on the cutting edge of astronomical research? I mean, what were they doing that the others weren't?Anna Von Mertens: So the glass plate photographs that Leavitt studied were a new kind of technology, dry plate photography, and previously its predecessor, wet collodion photography. An astronomer would need to coat a glass surface with an emulsion, expose it to starlight through a telescope's lens, and then develop that photograph all within a span of 15 minutes, but with dry plate photographya much more stable substructurethat enabled exposures that were multiple hours in length.And so with that accumulation of starlight onto the glass surface, these dim stars could be pulled into view over an exposure that might be up to four hours length in time. And so with this new technology, a survey of the stars was possible previously, right?It would be dependent on a single individual's eye looking through a telescope, studying an individual object and finding observations on that individual celestial object. Here the stars could be studied en masse. So, Edward Pickering, who was the director of the Harvard College Observatory at the time of Leavitt's study, he realized that, that no astronomical research could move forward without building an empirical foundation of knowledge that future discoveries could be made from. So he quickly adopted this new technology, dry plate photography.And with those glass plates, a huge inundation of data. It was the first sort of flood of big data into the field of astronomy. So with that influx of data, of course, a workforce was needed to process that data. And Edward Pickering, despite being at Harvard, did not have an enormous budget. There was no funding from the college. He had to simply operate the observatory, based on interest from the observatory's endowment. So he had to be quite frugal in how he proceeded. And he realized that women as a labor force could be hired more cheaply than men, and they could analyze these glass plates, again, sort of organizing the data on them so that they could be more readily available for study. One of the things I love about thinking about Leavitt and sort of this access point to the science is that Pickering opened the door to it. It reminds me of this idea of a Room of One's Own.So here Leavitt and her female colleagues, they had a building of their own. So literally only women during her time worked in the brick building where the glass plate collection was housed. Now, yes, they were cataloging this data, but given access to this data and really given agency within their work from the director, these women not only organized the data, but within that close proximity to the data, went ahead and made the discoveries in their own right.Carol Sutton Lewis: And so Anna, initially, what was Leavitt asked to do? What was her task within the observatory, within this group, this building of women?Anna Von Mertens: So, nothing was known about the stars at this time, and director Edward Pickering wanted to survey the stars, and the most basic element of the star, the information that could be gleaned, was the brightness of that star. So, Leavitt was tasked with trying to assess the magnitude, the brightness of each individual star.And this seemed simple enough. But if you think about what she had to navigate, it is an incredibly nuancing, complex. So the photograph was made by coating a glass plate with a light sensitive emulsion. That plate was placed in the telescope and gathered starlight on its surface.It was then developed and each star would register as a tiny black speck of emulsion. If you think of pepper sort of scattered across the surface of a glass plate that might sort of give a sense of the minute details that she needed to study. So most of the plates she studied were photographic negatives with each star represented as a tiny speck of emulsion.And so she went about assessing the magnitude of each star by measuring, estimating the sort of diameter of each circle, of each tiny speck. Adding complexity to this task, the photographic medium was nascent and unreliable. And so for example, results would deviate from the center of a glass plate simply to its edges.Also the color of starlight would affect its results on glass. So for example, red stars barely registered with this new medium. And most significantly, Leavitt had to gather information of photographs made by various telescopes, made by different telescopes, made from different exposure times, so comparing a 15-minute exposure taken by one telescope to a three hour exposure taken by another telescope, so she really had to first understand this new translation of starlight onto glass. And then once she had formed that understanding, she could go and further her research.Carol Sutton Lewis: And in the midst of all this meticulous work, what did Leavitt discover? What did she learn about the cosmos?Anna Von Mertens: So in this work of trying to assess their individual brightness and survey the stars, Leavitt noticed that some of these stars changed in their brightness, so called variable stars.So instead of a consistent amount of light, over time that light would shift brighter, and then dimmer, and then brighter again. And at the time Leavitt began this research, only several hundred variable stars were even known. But Leavitt made this a particular avenue of her research, and one of the most inventive techniques of hers that she developed to identify these variable stars, was to take a glass plate negative of a certain patch of sky.And, remember, so each star would register as a black speck of emulsion. And then she would take another photograph of that same patch of sky, but on a different night. And she would translate that negative into a positive. She would then superimpose a positive and negative glass plate of the same patch of sky taken on different nights.And, if it was a traditional star, it would just, right, those specks would fill in the holes on the positive and cancel each other out. But a variable star might announce itself as a tiny white halo of light. And if that indicated that it could be a variable, she would go through time, go through plates and try to track that changing light through time. Now, as I said, only a few hundred variable stars were known at the beginning of Leavitt's research. In her lifetime, Leavitt personally discovered 2,400 variable stars, which is more than half of all known variables at the time. So she was the resident expert in this field of research.Carol Sutton Lewis: That is incredible. So, in your book, you lay out all the many inconsistencies of early astrophotography, the plate defects, the differing exposure times, the blurry edges, emulsions, as you said, with different reaction speeds.She had to take all of those potential inaccuracies into account when she was doing this analysis, which brings me to the title of your book, Attention is Discovery. So why do you think the work of noticing the work of finding patterns was so important to her work? I mean, clearly she could have just been cataloging this, but why do you think that the noticing, helped her make these discoveries?Anna Von Mertens: Well when something is known, when a scientific discovery is announced, it can seem almost self-evident. Like there's such a clarity to its truth, and one can, uh, see and observe that truth. And so it's helpful to sort of go back deeper into Leavitt's methodologies to understand really how there were no guideposts. There were no orientation markers to navigate the sea of data. So within that you have to really have faith in the process of - take an observation, see what you can pull from that, and then repeat that action. And you have to have this, this sort of fluid back and forth where you are open to investigation.You're not closing off certain lines of research, but you have this receptivity to what you are seeing, but then you're allowing that seeing to guide you. And so, Leavitt did exactly that in her groundbreaking discovery is that while she was working, while she was studying variable stars, she decided to turn her attention to the small Magellanic cloud.Now this is a celestial object that we now know as a satellite galaxy separate from our own, but at the time it was just considered a fuzzy patch of sky. And Leavitt, as she turned her attention to the small Magellanic cloud, as she studied variable stars that she found there, she, she made an incredibly important simplifying assumption. She said, I will treat this as an individual celestial object, the small Magellanic cloud, and so therefore any variable stars I find there will be equal distant to us from Earth, right? So, If she finds a bright star there and a dim star, both within the small Magellanic in a cloud, they're traveling an equal amount of distance to each other to us, and therefore, equally dimmed by that distance. So that means she knows that relationship within the cloud is true. That bright star is truly brighter than the dim star next to it and so, as it translated onto glass, she would know that that relationship held true there. That meant she could turn to her glass plates and study variable stars in the small Magellanic cloud and see what she noticed. As she started to track these stars in their brightening and dimming cycles, she noticed that the brighter stars seemed to take longer to complete their pulsation period, as it traveled through that curve of dim to light and back to dim again.And it took her several years to follow up on this line of thinking and confirm that, indeed, it was true that the brighter the star, the longer it took to pulse. And Leavitt in 1912 published a paper that graphed this relationship and the smoothness of the logarithmic curve of that graph was so smooth and so pronounced that it was, indeed, a direct relationship.And in, in fact, it was law. It's now known as the Leavitt Law, the period-luminosity relation, that establishes that the brighter a variable star is, the longer it takes to pulse. And astronomers immediately recognized the significance of this finding. So astronomers could simply observe a variable star pulsing, and based on that observation, determine how bright it should be.And if it was not as bright as it should be, they could calculate the amount of distance causing that light to dim.Carol Sutton Lewis: So, Anna, for those of us listening who are, like me, not quite as well versed in the field of astronomy, in just a sentence or two, can you please summarize for us why Leavitt's Law changed our understanding of the cosmos?Anna Von Mertens: Sure. Leavitt provided an astronomical tool that allowed. astronomers to simply observe the pulsation period of a variable star. And from that, determine how far away it is from us. And so this gift of being able to see something quite clearly, just the changing fluctuation of a star, and being able to calculate astronomical distance, opened up an entire new field of research.Carol Sutton Lewis: More after the break.Carol Sutton Lewis: So Henrietta Swan Leavitt, after all of this painstaking detailed work, determined a system to help us measure the distances to pulsating stars, also known as Cepheid variable stars. How is this groundbreaking discovery then used?Anna Von Mertens: So once this tool was established that astronomers could simply observe the changing brightness of a Cepheid variable star and based on those observations calculate its distance to us. This was most significantly put to use with Edwin Hubble was studying spiral nebulae. And perhaps the most famous astronomical glass plate photograph in the history of astronomy is a plate taken in 1923, where Hubble photographed the Andromeda Nebula, as it was called at the time, and he noticed three new lights. And he identified those as Nova, new star.But the next night he went back and noticed that one of those Nova, one of those new stars, it changed in brightness. And he realized, aha, that is a Cepheid variable star. That's one of Leavitt's Cepheid variables. And so he crossed out N, Nova for new star, and wrote V A R exclamation point.And I like to point out that exclamation points don't show up in scientific data very often, but there was good reason for it. Is that Hubble knew just based on that one single star, he could observe its changing brightness over time. And once he established its pulsation period, he could calculate its distance to us.And so with one single star, he could show that Andromeda was so far away from us, it had to be outside the scope of the Milky Way galaxy, and was a galaxy in its own right. And now, think about that. Think that with one Cepheid variable, he could make this determination. Now, if we go back to the fact that Leavitt discovered 2,400 variable stars in her lifetime, and then within that discovery made this important singular discovery that Cepheid variable star, the brighter it is, the longer it takes to pulse. Hubble's discovery was not possible without Leavitt's work. It is Leavitt's work that began this understanding of our three-dimensional universe.Carol Sutton Lewis: So you've just brought up the 2,400 variable stars that through incredibly meticulous, detailed work Leavitt discovered during her lifetime. And so this brings me back to the attention to detail theme that runs through her work and through your own artistic practice. And I want to turn to your art for a moment.You have a series called the Artifact Series, which was inspired by Leavitt's work. Can you tell me about that, how you put it together?Anna Von Mertens: I wanted to practice, as it were, the way that Leavitt studied these glass plates. So I turned and, looking at these glass plates, tried to apply my own attention to them. And one particular plate caught my interest because at the edges of the plate, there was this very pronounced warping.So as the starlight traveled through the telescope's lens, it warped at the edges of the plate. Now, this was a phenomenon that Leavitt knew well, and she needed to navigate as she tried to pull set data from these surfaces. But I was quite enamored of these artifacts, of the way that the starlight was warped, because it almost seemed to sort of attach wings to these stars, as if they were sort of moths and dragonflies and birds almost taking flight.And the specificity of those objects caught my attention, and reminded me of how Leavitt built her discovery, that she needed to build it star by star by star. And so I decided to appreciate that specificity by magnifying sections of the plate and drawing these particular artifacts across the surface.And what I was surprised is how easily my attention was held by their, their elegance, their transparencies, their depth, their peculiarities. And It reminded me how Leavitt, just how evidently committed and engaged Leavitt was in her own work. And so I've mentioned that part of what drew me to Leavitt's story is that she had this profound discovery that launched modern cosmology, but because she herself did not live to see the impact of that discovery, I wanted to know, well, was she satisfied in her own work?And reading her scientific papers, reading her letters, and looking at these glass plates myself, I could see how transfixed and engaged and delighted she was by this dedicated work.Carol Sutton Lewis: Anna, your enthusiasm and admiration for Leavitt's work is wonderfully clear. But you just mentioned that Leavitt didn't live long enough to see the impact of her work. So, can you tell me about the end of her career? What happened after her groundbreaking discovery?Anna Von Mertens: So, Leavitt spent her life studying variable stars on these glass plates at Harvard and announced her discovery to the world, Leavitt's Law, and astronomers sort of immediately understood its significance and sort of discovery tumbled forth from there. But, Leavitt sadly died in 1921, and, if you think about that famous glass plate photograph that, Hubble took, it was in 1923. So only two years after Leavitt died, Hubble found a Cepheid variable in the Andromeda galaxy and proved it was, indeed, a galaxy. And from there, right, that, that Hubble's work continued, that each time Hubble identified a Cepheid variable star in a spiral nebula, he could calculate the amount of distance to it and prove that. How far away it was and culminating at the end of the 1920s with his 1929 paper showing that not only were there galaxies all around us, but he proved in the redshift of their light, that the farther a galaxy was away from us, the faster it was receding. So, our universe was expanding.So you think within just a decade, there is this profound shift in our awareness of going from, right? In the night sky, unsure of any sense of depth to them to understanding the shape and scope of our Milky Way and galaxies outside our own. So, I wanted to celebrate this woman, who truly founded modern cosmology, but then also celebrate the life that she lived within it.Carol Sutton Lewis: Earlier, you mentioned that Leavitt was one of the many women working at Harvard, and they had their own building to do this work. And yet, even though they had jobs in the field, astronomical work was still very much divided by gender. Women could only catalog and analyze the data while the men collected it. Can you talk a little bit more about the impact that women generally had on astronomy at this time?Anna Von Mertens: You're right in that uh, women were not allowed to make the photographs or observe at night through the eye of the telescope. They worked by day analyzing the glass plates. What's interesting there is there was sort of a hierarchy given thinking that observations directly made through the telescope was where the science was. The science was actually on, on the plates. That is where the data was and that's where the discoveries were latent. And so the women Leavitt and her colleagues, now known as the Harvard Computers, were given access, this first access point to the data. And yes, it was, there was only one job description for the women at the time, they were called computers and there was only one pay rate and no sort of chance of ascending up a ladder on a career, but given access to this world, it is evident how committed and dedicated Leavitt and her colleagues were to this work, and you know, Leavitt spent her entire adult life there working at the Harvard College Observatory until her death.But alongside her were women who you know, I have a list of of certainly, Annie Jim Cannon is well known as her work focused on the studying of stellar spectra, but she worked there for her lifetime. Mabel and Edith Gill were sisters who worked there for decades. Ida Woods, another Harvard computer, worked there for 37 years.So these women were dedicated to the work and around that, an evident warmth developed both for the work and for each other.Carol Sutton Lewis: And it seems that some of the women were given recognition at the time, but why do you think our retelling of history often overlooks the work of these Harvard computers?Anna Von Mertens: that is fascinating component that surfaced in my research for the book, is that I think many of us, assumed that it was the sexism of Leavitt's day that limited her recognition. And looking at that time, the women, the Harvard computers were at the hub, at the very center of international astronomical research. So often in the archive, there's these letters written to the director of the observatory at the time of saying, what are the latest updates? You know, can you tell me more about this finding? Where are we at on this research? So these women and Leavitt in particular with her variable star research, it was well known within the astronomical community, what she was up to and, you know, that their research depended on her work.So what I found it is that actually it is the retelling of history, of that history, that is more problematic. So often the sort of women are sort of dismissed as like, oh yes, it's very tedious meticulous work and it's recognized, but sort of seen as perfunctory, or just sort of, you know, the needed work to get down to the real research. And what I found is that, yes, like all science results need to be repeated. Science has a certain amount of tedium to it, just as Hubble needed to measure circles of emulsion on his glass plates to make his own findings. So the process is the same, but somehow the work of the women is diminished as sort of, being in the background where really they were at the leading edge of research, pushing the field of astronomy forward.Carol Sutton Lewis: That feels like a great place for us to end. But before we do, do you have any final words on how we should all remember Leavitt and this exciting time in astronomical history?Anna Von Mertens: So certainly celebrating her discovery and her legacy is an enormous part of this book of really seeing the science and seeing the impact that her discovery had on all future discoveries. But returning to that sort of elemental unit of measuring a star's brightness and star by star building a finding, that on attention was, was really helpful for me as a reminder that we can apply that skill to whatever endeavor we are undertaking, whether it's an artistic practice or a scientific one. So, the way that I could see Leavitt's engagement with this work, see this dedication, this commitment, even she writes the words pleasure and delight, recognizing how attention builds and provides a richness to the world around us and what is available to see, that that was such a gift, as part of her legacy as well.Carol Sutton Lewis: So beautifully said. Anna, thank you so much for writing this book and for joining us today.Anna Von Mertens: Oh, thank you so much for having me. And yes, thank you for helping tell Leavitt's story.Carol Sutton Lewis: This has been Lost Women of Science. I'm your host, Carol Sutton Lewis. This episode was produced by Sophie McNulty. Our thanks go to Anna Von Mertens for taking the time to talk with us. Hansdale Hsu was our sound engineer, Lexi Atiya was our fact checker, Lizzie Younan composes all of our music, and Lily Whear designed our art.Thanks to Jeff DelViscio at our publishing partner, Scientific American. Thanks also to executive producers Katie Hafner and Amy Scharf, senior managing producer Deborah Unger, and program manager Eowyn Burtner. Lost Women of Science was funded in part by the Alfred P. Sloan Foundation and the Anne Wojcicki Foundation. We're distributed by PRX. Thanks for listening, and do subscribe to Lost Women of Science at lostwomenofscience.org so you'll never miss an episode.HostCarol Sutton LewisProducerSophie McNultyGuestAnna Von MertensAnna is a visual artist and researcher who has exhibited widely, including in Boston, San Francisco, and Oslo. She was the recipient of an Alfred P. Sloan Foundation Public Understanding of Science and Technology book grant to support the publication of Attention Is Discovery. She lives and works in Peterborough, New Hampshire.Further ReadingAttention Is Discovery: The Life and Legacy of Astronomer Henrietta Leavitt. Anna Von Mertens. MIT Press, 2024The Glass Universe: How the Ladies of the Harvard Observatory Took the Measure of the Stars. Dava Sobel. Viking Penguin, 2016The Rise of the Milky Way. Presented by Joo Alves at the Radcliffe Institute for Advanced Study, Harvard University, April 3, 2019Review: How a Group of Women Launched Modern Cosmology, by Lucy Tu, in Scientific American; September 2024