My parents brought me up to have unlimited ambition, and to keep asking questions. Thankfully, in the late 20th Century, these traits alone were enough to propel me towards a career as an astrophysicist.


I was lucky enough to attend an all-girls high school and our A-Level physics and maths classes were small, but without stigma. When I went to university to study physics in 2006, I was one of a few women, but the numbers were significant enough that I didn’t feel too uncomfortable. It was only when I started my PhD that I accepted sexism was something that affected me.

My experience still marks significant progress since the early and mid-20th Century experience of women in science, though. Cecilia Payne-Gaposchkin walked into her lecture halls to whistles and the stamping of the men’s feet in the early 1920s, and Northern Ireland-born astronomer Dame Jocelyn Bell Burnell suffered the same humiliation in the 1960s. How slow we are to change.

© Smithsonian Institution from United States / No restrictions
Cecilia Payne-Gaposchkin © Smithsonian Institution from United States / No restrictions

Payne-Gaposchkin (1900 – 1979) endured this indignity because she had an unparalleled need to understand and to discover something new. I will refrain from diving into detail into what is a fascinating and eccentric life (my favourite quirk is that her daughter describes her as an “inventive knitter”). Instead, I will concentrate on how that life continues to inspire astronomers through the ages.

There are a lot of references to Payne-Gaposchkin in popular science astronomy books now. A good portion of the books sitting on my shelf mention her scientific contribution… almost always alongside the fact she was given less than what was due in terms of credit.

In one book, Out of the Shadows: Contributions of Twentieth-Century Women to Physics, there is a contribution about her from none other than Vera Rubin, another pioneer, this time in the field of dark matter. While mentioning the context of Payne-Gaposchkin’s discoveries, Rubin focuses mostly on the science. And quite right, for her work shifted the ground beneath our feet.

Payne-Gaposchkin changed our perception of stars from merely hot planets, to vast bodies made of only the simplest of elements: hydrogen.

In the early 1920s, Indian astrophysicist M N Saha had deduced that the absorption lines in the spectra of stars were related to the presence of certain atoms, but also the degree of ionisation of those atoms. The Sun, like all stars, emits a broad spectrum of light, a continuum like a rainbow.

If a certain element, let’s say iron, is present in the solar atmosphere, then the photons at certain wavelengths will be missing from the continuum. We observe a dark line called an absorption line. Iron naturally has 26 electrons and so will produce absorption lines at the energies that the atom favours absorption of photons.

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What Saha realised is that atoms that had been ionised (stripped of some or all of their electrons) produced distinct absorption lines, almost like a barcode.

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This made life much more complicated for those who aimed to deduce the chemical content of the stars. Each atom didn’t just produce one barcode. They produced multiple variations depending on how many electrons they harboured.

Payne-Gaposchkin applied this ionisation theory to the spectrum of the Sun, as the subject of her PhD thesis at Harvard University. After months – “almost a year as I remember it, of utter bewilderment” – she painstakingly identified each line, by comparing to the barcode that could be produced in the lab. By doing so, she inferred the temperature and chemical content of the stars rather more precisely than had been done before. Her results suggested that hydrogen was the most prevalent element in a star by a long way, and that the heavier elements such as iron, while present, were a mere garnish.

The idea that the Sun was predominately made of hydrogen was revolutionary. Until 1925, astronomers took the presence of heavier elements in the Sun as evidence that the Sun was similar in constitution to the Earth. We could find the same elements in our backyard and, if heated enough, they postulated that the Earth would just naturally become a star. It’s easy to smirk at these views now, but I’m sure we hold scientific beliefs now that will be thrown out by the end of this century, so don’t get too smug.

At the time, Payne-Gaposchkin’s thesis was not taken well, and Princeton astrophysicist Henry Russell stated plainly that he did not believe it. It is thought that his reaction led Payne-Gaposchkin to add a sentence to her thesis stating that the abundances derived for hydrogen were “almost certainly not real”, perhaps due a mistake in the application of theory to experiment.

Well, we know now there was no such mistake and actually it was only a few years later that Russell himself wrote a paper setting out the same conclusions. Payne-Gaposchkin’s reaction is lost to us now, but one can only imagine the vindication she must have felt. If only she could have been rewarded then and there.

Instead, Payne-Gaposchkin faced a long struggle to gain any recognition at all. She taught several astronomy courses, but her contribution went unlisted in the course catalogues, and they paid her as a technical assistant. The president of Harvard, Abbott Lawrence Lowell, stated that: “Miss Payne should never have a position in the University while he was alive.” Indeed, she was only awarded full professorship over a quarter of a century later.

The composition of the stars concerns me now still, back in the 21st Century, almost one hundred years on. Payne-Gaposchkin’s work led to people reconsidering how the stars formed, and what older generations of stars might look like in terms of their spectra. It was eventually deduced that older stars had fewer heavy elements in, and that after the Big Bang there were so few heavy elements that the very first stars would have been made only of hydrogen, and a little helium. No heavy elements at all, no garnish whatsoever.

It is these first stars that I pursue in my career. The first stars were massive, about a hundred times the mass of our Sun, and they lived incredibly short lifetimes of only 100 million years or so. A different star altogether from our Sun. We know very little about this Era of the First Stars. But, we are up to the challenge of finding out.

It is a missing billion years from the timeline of our Universe and I am driven by the need to have our understanding completed or, even more excitingly, changed completely. Payne-Gaposchkin’s discovery is one of the foundation bricks to my research. It is vital and so ingrained in our understanding of the stars that it seems nonsensical that we ever thought anything else.

In the women’s astronomical community, Cecilia Payne-Gaposchkin is a household name. Payne-Gaposchkin tore down the obstacles presented to her and threw them aside so that the next generation of women could follow.

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Women in astronomy still face obstacles to true equity with their male counterparts, and I think that she inspires so many women because she reminds us we too can lay waste to the obstacles presented to us. And there are still obstacles, more subtle as they may be. Before the #MeToo movement there was #astrosh (sexual harassment in astronomy), a Twitter hashtag replete with stories of life-altering cases of discrimination and misconduct.

Payne-Gaposchkin’s pioneering effort as a woman astronomer is important to me because I have faced my own battles in academia, experiencing discrimination because of my gender on multiple occasions. It would do her a great disservice to remember her only for that, though, and it is Payne-Gaposchkin’s science that inspires me the most. In her words: “It has been a case of survival, not of the fittest, but of the most doggedly persistent.”

And so we persist, however slow the change.

At the turn of the 21st Century, officials hung a new portrait on the walls of Harvard University. The likeness of Cecilia Payne-Gaposchkin looks out of a window streaming with sunlight, one hand on an open book, the other arm behind her back in a relaxed position.

Payne-Gaposchkin was not one for subtlety when it came to her discontent and I think she would enjoy the victory of her portrait finally gracing the walls, and only feet away from Lowell, the Harvard President who tried (and failed) to block her ascent to become one of the truly great astronomers of the 20th Century.

First Light: Switching on Stars at the Dawn of Time by Emma Chapman is out now (£16.99, Bloomsbury Sigma).
Cover of First Light by Emma Chapman

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