Lost Radio Talks from the Harvard Observatory: Cecilia Payne, Who Discovered the Chemical Fingerprint of the Universe, on the Science of Stars and the Muse of All Great Scientists
“A common chemistry and a common physics run through the universe.”
By Maria Popova
In his stirring poem “The More Loving One,” W.H. Auden asked: “How should we like it were stars to burn / With a passion for us we could not return?” It is a perennial question — how to live with our human fragility of feeling in a dispassionate universe. But our passions, along with everything we feel and everything we are, do belong to the stars, in the most elemental sense. “We’re made of star-stuff. We are a way for the cosmos to know itself,” Carl Sagan proclaimed in his iconic series Cosmos — a scientific statement so poetic and profound that it has enchanted more imaginations and infected more lay people with cosmic curiosity than any other sentiment in the history of science. It is also a statement Sagan could not have made without the foundational work of the English-American astronomer and astrophysicist Cecilia Payne-Gaposchkin (May 10, 1900–December 7, 1979).
In 1925, in her 215-page Harvard doctoral thesis that made her the first person to earn a Ph.D. in astronomy at Radcliffe-Harvard, Payne discovered the chemical composition of stars — the “stuff” the cosmos is made of, which was, much to scientists’ surprise, the selfsame “stuff” of which we too are made. It was a shock and a revelation — a landmark leap in our understanding of the universe and of ourselves.
In early November 1925, the Harvard College Observatory broadcast the first episode of a series of radio talks about astronomy. Every Tuesday and Thursday for the next eleven weeks, Harvard astronomers would take to the airwaves of Boston’s Edison Electric Illuminating Company, WEEI, and deliver short, surprisingly poetic lectures on everything from comets, shooting stars, and eclipses to the evolution of stars and the search for life beyond Earth. Nothing like this had ever been done before — it was the world’s first public broadcast series of popular science and its printed record, published the following year as The Universe of Stars: Radio Talks from the Harvard College Observatory (public library), became the world’s first book of radio transcripts.
In mid-December 1925, having just completed her revolutionary doctoral thesis, the 25-year-old Payne delivered the fourteenth lecture in the series, titled “The Stuff Stars are Made of.”
Five years before the discovery of Pluto and mere months after Edwin Hubble had refuted Harvard College Observatory director Harlow Shapley’s longtime insistence that our home galaxy was the full extent of the cosmos by identifying stars that must belong to another galaxy, Andromeda — a radical revision of previous ideas about the nature and size of the universe — Payne takes her listeners on a journey into our cosmic neighborhood and beyond, into the unfathomed cosmic unknown:
We are going tonight far out beyond the bounds of the solar system, for this talk relates especially to the universe of stars… This solar system of ours is large enough, measured by earthly standards, since the distance across the orbit of Neptune, the farthest known planet, is some six thousand million miles. Even light, which travels at the furious speed of eleven million miles a minute, takes about eight hours to cross that space. But let us go out into the moonless night. Overhead we shall see thousands of twinkling points of light that we call the stars. Although light takes a third of a day to cross the solar system, the light that reaches us from the Milky Way may have been travelling five thousand years.
Echoing pioneering astronomer Maria Mitchell’s lovely incantation — “Mingle the starlight with your lives and you won’t be fretted by trifles,” Mitchell had told her Vassar students, who paved the way for women at the Harvard College Observatory — Payne reflects:
When we direct our thoughts to the stellar universe, the solar system is dwarfed out of recognition. We only notice it because we happen to be living in it. Until we begin to think in terms of the system of stars, we are liable to overrate the size and comprehensiveness of the system of the planets.
Writing in an era when there was only rudimentary awareness of the existence of stellar nuclei and nuclear reactions, she considers the mystery of our ancient nocturnal companions:
When we look at the twinkling light of the stars, we need all our powers of imagination to visualize what they really are. Every one of those points of light is actually a huge mass, often far larger than the Sun. Every one shines because it is hot — so hot that it glows by its own light. And every one of them is pouring out light and heat into space in enormous quantities. Many bright stars pour out hundreds of millions of tons of light every second.
When you look at the night sky, you are looking at an almost inconceivably great quantity of matter; and therefore when I talk about the stuff the stars are made of I am telling you what we know of the Chemistry of the Universe.
Payne examines the essence of the question itself: When we ask what things are “made of” in the world around us, we answer by pointing to their material — clay and rocks and water and wood — and then further analyze each material into different kinds of atoms. But because it is impossible to physically fetch atoms directly from a star the way one might fetch a fistful of clay from the ground, scientists can only analyze another aspect of the stellar “stuff”: light. Three centuries after Newton first used the word spectrum — Latin for “appearance” — to describe the beautiful band of rainbow produced when sunlight disperses onto a glass prism, giving rise to the science of spectrography, Payne explains the study of stellar light:
[Stars] are all pouring out light into space and we can catch that light as it strikes the Earth, and analyze it. In a fundamental sense, that light was once as much a part of the stars as clay is a part of the Earth. Light is a form of energy, and it is the energy of a star that makes it shine, and keeps it going, and enables it to survive. A star literally lives on its light.
Analyzing that light makes it possible to discern what stars are made of, because matter in the gaseous state emanates light of specific wavelengths, with each atom occupying a different set of wavelengths and thus appearing at a different spot along the color spectrum when its light passes through a prism. This method, Payne notes, revealed that stars are made of the selfsame elements found all around us, even though conditions on those stars are dramatically different from those on Earth, with temperatures reaching tens of thousands of degrees centigrade. After a necessary detour to physics, explaining how the structure of the atom factors into this commonality of matter, Payne concludes with the kernel of the poetic and profound sentiment Sagan would popularize more than half a century later:
In the spectrum of the Sun, we can pick out all the two thousand colors that are given out by an atom of iron; they are exactly the same as the colors that would be given out by a piece of iron, heated in the electric arc in the laboratory. A common chemistry and a common physics run through the universe.
The story that I have told you is one that has wide implications. Not only does it confirm us in our belief that a common physics and chemistry underlie the universe, but it suggests a basis for the study of the fundamental problem of the stability of matter. [This] implies that all stars have the same composition… that the relative amount of the different elements are in some way fixed, and have some fundamental significance in the universe.
This was a revolutionary idea that would lead to entirely new theories about the evolution of the universe. Payne herself would devote the remainder of her life to illuminating these mysteries, becoming the first woman to chair a Harvard department. But such honors meant little to her — she stood with Maria Mitchell, who famously asserted that honors “are small things in the light of stars.” Six decades after her doctoral thesis, Payne ended her autobiography with a short poem of her own, celebrating the scientific muse that governed her trailblazing career — a beautiful articulation of the universal motive force that impels all great scientists to do what they do.
At the third annual Universe in Verse, astrophysicist Natalie Batalha — project scientist on NASA’s Kepler mission, responsible for discovering more than 4,000 exoplanets: whole new worlds unimaginable in Payne’s time, when the very notion of another galaxy was a shock — returned to read Payne’s poem, with a lovely prefatory mediation reaching across space and time to connect Payne to Sagan to her own work and the largest questions human beings bring to and ask of the universe:
by Cecilia Payne
O Universe, O Lover,
I gave myself to thee
Not for gold
Not for glory
But for love.
Our children are immortal,
I am the Mother.
The offspring of our love
Will bear the image of a humble mother
And also a proud imperious Father.
I saw him in a stream of glowing stars;
Long, long I lay in his terrible embrace.
Their sons go striding round the firmament;
My children gambol at their heels.
Couple with Cecilia Payne’s advice to the young, then revisit other highlights from The Universe in Verse: Regina Spektor reading “Theories of Everything” by the Canadian astronomer, poet, and tragic genius Rebecca Elson, astrophysicist Janna Levin reading Adrienne Rich’s tribute to the world’s first professional female astronomer, Amanda Palmer reading Neil Gaiman’s tribute to Rachel Carson, poet Marie Howe reading her homage to Stephen Hawking, U.S. Poet Laureate Tracy K. Smith reading her ode to the Hubble Space Telescope, and Rosanne Cash reading Adrienne Rich’s tribute to Marie Curie.
Published May 8, 2019