Andrea Ghez, a professor of physics and astronomy at UCLA, shared the 2020 Nobel Prize in physics for finding a supermassive black hole stuffed with 4 million suns at the center of our galaxy. Among the four female Nobel Laureates in physics to date, Ghez is the only astronomer. Her award is a pinnacle for women in astronomy and astrophysics. Yet women astronomers remain a minority and often encounter a lack of recognition, unwelcoming career paths, and harassment. But today women participate and publish in astronomy and astrophysics at higher rates than in physics overall, producing world-class research.
The first astronomical female was Urania, the Greek muse of astronomy. She was important in mythology as the daughter of Zeus, whose realm was the sky. Besides this divine heritage, Urania came to be portrayed as making measurements on a globe, symbolizing women doing astronomical science. In that ancient era, there was one real astronomical woman: Hypatia (c. 355–415 CE) was a mathematician, astronomer, and philosopher who lived in Alexandria and worked on tables related to Ptolemy’s astronomical treatise Almagest.
Émilie du Châtelet
Centuries passed before other women studying the sky would make their mark. As women become more prominent, we are learning about their past work, including overlooked research. Three particular early astronomical women display diverse scientific contributions, though the paths by which they entered the male world of astronomy are distinct. The eighteenth-century Frenchwoman Émilie du Châtelet and the nineteenth-century Scotswoman Mary Somerville each enhanced existing astrophysical theory, as described in the poet and philosopher Emily Grosholz’s review “Candles in the Dark.” In the era between these two lives, the German-born Englishwoman Caroline Herschel was widely recognized for her telescopic observations of comets and nebulae, as presented in a study by the physicist and historian of science Emily Winterburn.
Du Châtelet was born in 1706 to an aristocratic family. Her father, chief of protocol at Louis XIV’s Versailles, recognized her intelligence and brought tutors and leading scientists who taught her six languages, mathematics, and physics.
This enabled her to contribute to the astrophysics of the time, which asked this important question: what causes planetary motion? Isaac Newton ascribed it to the universal gravitational force presented in his foundational work Principia Mathematica (1687). René Descartes thought instead that particles swirling in the heavens moved the planets and caused the Earth’s gravity. Seeing the superior predictive power of Newton’s approach, du Châtelet, with her lover, the great French writer Voltaire, wrote Institutions de Physique (1740) to present Newton’s theory. Du Châtelet updated it by replacing Newton’s geometric methods with the powerful new tool of calculus. This reworking of Newtonian ideas in French greatly aided their acceptance over Cartesian theory in Europe.
Du Châtelet’s fame faded in time, whereas Mary Somerville was honored in 2017 with her portrait on a Scottish banknote, but her circumstances were far more modest. Born in 1780, this daughter of a British admiral received only limited education, but taught herself mathematics and astronomy and learned French. She found an enthusiastically supportive husband in her second marriage. By 1827, her abilities were well known, and she was asked to write a popular version in English of Pierre-Simon Laplace’s huge compendium, Traité de Mécanique Celeste (1798), which extended the Principia. Somerville’s version, Mechanism of the Heavens (1831), went deeper into gravitational theory and introduced new mathematical methods. Like du Châtelet’s effort, it spread Newton’s ideas. Among other memorable moments in Somerville’s career, she was the first person to be called a “scientist” (in a review of one her books). Before Somerville, researchers were called “men of science.” The reviewer of Somerville’s book coined “scientist” to include her.
Caroline Herschel, born in Germany in 1750, helped her brother William build and operate a telescope in England. When in 1781 he discovered the planet Uranus, King George III gave him a yearly stipend of £200 as the King’s Astronomer. With this, William expanded his efforts: as Caroline wrote:
I found I was to be trained for an assistant Astronomer; and by way of encouragement a Telescope adapted for sweeping… was given to me. I was to sweep for comets…
Comets were of great public interest, and Caroline’s quest made her famous. After finding her first comet in 1786, eminent scientists came to see “Caroline’s comet,” and William was called to Windsor Castle to explain the comet to the royal family.
Caroline’s achievements in cataloging additional comets and many nebulae led to two notable moments for women in science: the King granted her an annual stipend of £50, as William’s assistant, the first professional salary ever paid to a woman in England; and her reports of comet sightings were the first papers by a woman to be read at the Royal Society (though not by her) and published in its Philosophical Transactions (a paper by Mary Somerville was the second appearance by a female author).
These brief histories support Emily Winterburn’s comment that “Eighteenth-century women had to rely on the men in their lives for access to scientific work and education…”, which remained true for much of the nineteenth century. Although each of the three women had her own path into the scientific community, each made her own success.
By the late nineteenth century, rather than depending on the men in their lives, astronomical women were occupying regular, if subsidiary, positions at the Harvard College Observatory in Cambridge, Massachusetts. Starting around 1881, its director Charles Pickering began hiring women, known as the Harvard Computers (in the older sense of a person who does calculations) to analyze the reams of data the observatory collected. Pickering preferred women because they were believed to be more patient than men for this kind of work—and because they accepted lower wages. Even women with college degrees were paid like unskilled workers, at 25 to 50 cents an hour.
The Harvard Computers analyzed photographic images of stars and their spectra, to find the brightness of stars and the wavelengths of their emitted light. This painstaking labor yielded new science. One result, developed by the Computer Henrietta Leavitt in 1912, altered our view of the universe. She studied Cepheid variable stars (named for the constellation Cepheus), whose brightness fluctuates, with a period of days to months, and found that longer periods correlate with higher brightness. But the brightness of a star as seen from Earth depends on its distance as well as the power it radiates, its intrinsic brightness. Using a group of Cepheids all at the same distance, Leavitt calculated the exact mathematical relationship between period and intrinsic brightness. An observer could use the period of a Cepheid to find its intrinsic brightness, then compare that to the brightness seen on Earth to obtain the distance to the star.
This was a unique tool to measure vast cosmic distances. In 1923, the astronomer Edwin Hubble found Cepheids in a dim patch of light then called the Andromeda spiral nebula. He used them to calculate its distance as 900,000 light years, which put it far outside our own Milky Way galaxy. Hubble had found the Andromeda galaxy, the first of many billions of separate galaxies in the universe and a stunning discovery at the time. At least one contemporary astronomer thought that Leavitt’s research deserved a Nobel Prize, but she received little credit.
Leavitt and others, hired as assistants, could indeed do significant astronomy, but worked on assigned projects. They were not independent researchers who could pursue their own ideas, nor were their accomplishments always recognized. To reach a higher professional level, women had to earn PhDs. This was not easy, even into the twentieth century, but Cecilia Payne-Gaposchkin (née Payne) did it
Born in England in 1900, she had always wanted to do research. A scholarship to Cambridge University allowed her to study science but only in a non-degree program, and her physics professor, Ernest Rutherford, regularly humiliated her as the only woman in his class. On the other hand, the noted astronomer Arthur Eddington inspired her to choose astronomy. But the UK lacked graduate opportunities for women, and she left for a graduate program at the Harvard Observatory under its new director, Harlow Shapley. In 1925, with her thesis entitled “Stellar Atmospheres,” she became the first person to earn a PhD in astronomy from Radcliffe College of Harvard University.
Her thesis answered an old question: what are stars made of? Payne-Gaposchkin carefully analyzed stellar spectra measured at the Harvard Observatory, whose patterns of wavelengths are fingerprints of the elements in the star. Her conclusion: stars are made mostly of hydrogen, with some helium. This was completely contrary to the then prevalent view that the Earth and the stars have the same composition. Pressure was put on Payne-Gaposchkin to insert the caveat that her results for hydrogen and helium were “almost certainly not real.” But four years later, independent research by others validated her findings. It is now taken for granted that hydrogen is the most prevalent element in the universe and that hydrogen undergoing nuclear fusion powers stars. In 1962, an extensive review of twentieth-century astronomy called Payne-Gaposchkin’s research “undoubtedly the most brilliant PhD thesis ever written in astronomy.”
One lesson from all of these women’s stories is the need for access to high-level education, by which women can attain the necessary professional status for research. Only since the mid-twentieth century has science education become more open to women. The current and preceding generation of women in astronomy have doctorates from first-rate institutions, and with these credentials, have been highly successful.
One area of success is the study of planets outside our solar system, called exoplanets, which began in 1992 with the first observation of a planet orbiting another star. Today, around 4,576 exoplanets have been found, and researchers are examining them to find planets that support life—or that might even resemble Earth. With the potential to answer the question “are we alone?,” exoplanet research is a vibrant area. Sara Seager, an astronomer and planetary scientist at MIT, has been a leader in seeking new exoplanets and in analyzing their atmospheres for signs that life—or its precursors—are present. She has received a MacArthur Fellowship (also known as a Genius Grant) and numerous other awards, and is featured in the documentary The Hunt for Planet B (2021).
A second area of interest in astronomy, astrophysics, and cosmology is the study of black holes, regions of spacetime where gravity is so intense that nothing, including light, can escape. Einstein’s general relativity predicts the possibility of such regions, and indirect evidence suggests that they actually exist at the center of galaxies, including our own.
Andrea Ghez, who wanted to be an astronaut as a child, found a way to test the possibility of a black hole in the Milky Way when she became an astronomer, using huge telescopes to obtain high resolution images of distant cosmic objects. Since the 1990s, she has tracked the paths of stars that orbit the center of our galaxy 26,000 light years away. When she analyzed the orbits (using the same Newtonian mechanics championed by her forerunners Émilie du Châtelet and Mary Somerville), she found that the stars are held in their paths by a central mass equal to about 4 million of our own suns, contained in a comparatively small volume. This clear evidence of a supermassive black hole within our own galaxy won Ghez a Nobel Prize.
These examples demonstrate the important astronomical contributions women make if they have appropriate opportunities. In a society devoted to equity, it should be a given that these opportunities be the same as those for men. Long ago, Émilie du Châtelet expressed this more pungently, with her customary brilliance. “If I were king,” she wrote, “I would redress an abuse which cuts back, as it were, one half of human kind. I would have women participate in all human rights, especially those of the mind.”