Cecilia Payne-Gaposchkin -The astronomer who discovered what stars are made of

In the early 20th century, astronomy was still a discipline built mostly on observation rather than deep physics. The mystery of what stars were made of fascinated scientists, but no one truly knew. Most believed that stars, like the Earth, consisted primarily of heavy elements such as iron and silicon. Into this world of traditional thinking entered a young woman from England named Cecilia Payne.

Cecilia Payne was born in 1900 in Wendover, England. Exceptionally bright, she won a scholarship to study at Cambridge University, where she focused on physics and chemistry. However, at that time, women were not awarded degrees, even if they completed all their studies — an early sign of the challenges she would face in her career.

After attending a lecture by the famous astronomer Arthur Eddington, who had confirmed Einstein’s theory of relativity through his observations of a solar eclipse, Payne became captivated by astrophysics. She realized that to pursue her passion, she would have to leave England, where opportunities for women in science were minimal.

So, in 1923, she sailed to the United States to join the Harvard College Observatory, under the direction of Harlow Shapley, who was building a program to attract talented young scientists. Harvard at the time didn’t grant PhDs in astronomy through Harvard University itself, but through Radcliffe College, the women’s college associated with it. Payne became one of its first doctoral students in astronomy.

The Discovery

At Harvard, Payne worked with a vast collection of stellar spectra — photographic plates capturing the light emitted by stars, broken down into distinct wavelengths. Each element leaves unique “fingerprints” in these spectra, so by analyzing the lines, one can determine which elements are present in a star.

Using new developments in quantum physics and atomic theory (particularly the work of Niels Bohr and Meghnad Saha’s ionization theory), Payne realized she could calculate the abundances of different elements in stars more accurately than anyone before her.

When she performed her analysis, the results were shocking:Stars appeared to be composed mostly of hydrogen and helium, with only tiny amounts of heavier elements like iron.

This finding went against everything scientists then believed. It suggested that the most common elements in the universe were not the metals and rocks of Earth, but the simplest atoms of all.

Payne knew her result was correct — the data was overwhelming. Yet she also knew it would be controversial. When she published her doctoral thesis in 1925, “Stellar Atmospheres, A Contribution to the Observational Study of High Temperature in the Reversing Layers of Stars,” she carefully noted that the hydrogen result was “almost certainly not real,” having been advised by senior astronomers to temper her claims.

One of those was Henry Norris Russell, a highly respected astronomer. He told her that such a conclusion was “impossible” because it contradicted accepted wisdom. But just a few years later, Russell himself, after conducting his own study, reached the same conclusion — and published it. For decades, many credited him with discovering that the stars are made mostly of hydrogen and helium, though it had been Cecilia Payne who found it first.

A Career of Perseverance

Despite the discouragement, Payne continued her research. She married Russian astronomer Sergei Gaposchkin and continued publishing influential work on stellar composition, variable stars, and stellar evolution. She eventually became a leading expert in astrophysics, authoring several major books and cataloging hundreds of thousands of variable stars.

For many years, she held academic positions without proper recognition or pay equal to her male colleagues. But in 1956, after decades of dedication, Cecilia Payne-Gaposchkin finally became the first woman to be promoted to full professor at Harvard University — and later, the first woman to chair a department there.

Her Legacy

Cecilia Payne-Gaposchkin’s story is not just one of scientific brilliance, but of perseverance in the face of institutional bias. Her 1925 PhD thesis has since been called “the most brilliant PhD thesis ever written in astronomy.” Her discovery that hydrogen is the dominant element in the universe reshaped physics, astronomy, and cosmology, forming the basis for our modern understanding of stars and galaxies.

Today, she is finally recognized as the scientist who discovered the composition of the stars — a fundamental truth about the cosmos that changed science forever.