Kelly McSweeney

Jun 29th 2020

Cecilia Payne-Gaposchkin Discovered What Stars Are Made Of


Today, we know that the universe is mostly made of hydrogen and helium. However, the person who discovered what stars are made of, Cecilia Payne-Gaposchkin, never got the accolades she deserved.

So, who was this unsung hero of astronomy?

Who Was Cecilia Payne-Gaposchkin?

Cecilia Helena Payne was born in Wendover, England, on May 10, 1900. She was always interested in science from a young age, but she grew up in a time and place that didn’t allow women to become scientists. According to ScienceNews, when she was a teenager, school administrators told her to leave because they couldn’t meet her math and science needs.

Next, she attended the University of Cambridge, where she attempted to study physics and astronomy, but the university didn’t encourage her talents, nor did it award her a degree for completing her studies.

Cecilia went to the United States to round out her academic career, and in 1925 she became the first person to earn a Ph.D. in astronomy from Radcliffe College, a women’s college that is now part of Harvard University. According to her obituary in Harvard’s archives, the prominent astronomer Otto Struve called her research “the most brilliant Ph.D. thesis ever written in astronomy.” Her doctoral thesis was a turning point in her career and in astronomy, although her claims were so shocking that colleagues dismissed them at first. At the time, the common belief was that the stars were made of the same elements as Earth. Through meticulous observation, Payne demonstrated that the sun is actually mostly made of hydrogen and helium.

The key to Payne’s research was spectroscopy, which NASA explains involves breaking the light from a single material into its component colors the way a prism splits white light into a rainbow. First, Payne developed a way to quantify the intensity of absorption lines, the lines that astronomers use to identify elements based on their unique signature. Then, she spent her days and nights going through Harvard’s extensive library of spectra to analyze hundreds of stars, according to Famous Scientists. She used ionization theory to build a temperature scale for stars based on their intensities, which allowed her to calculate the chemical composition of the stars.

A Shocking Discovery About the Universe

She was surprised to discover that all stars had similar compositions. Contrary to popular belief, Cecilia Payne-Gaposchkin found out what stars are made of: hydrogen and helium. These elements were so abundant in stars that there was more hydrogen and helium than all the other elements combined. This was such an outlandish conclusion that her thesis supervisor Harold Shapley and the highly influential astronomer Henry Norris Russell both said that she must have made a mistake. As a result, Payne-Gaposchkin downplayed her conclusion.

In 1925, she printed her thesis as a book called Stellar Atmospheres. Four years later, Russell published a paper (now archived by Harvard) in which he detailed the abundance of hydrogen and helium in the sun. Astronomers continued to build on her work, eventually agreeing that stars are mostly made of hydrogen.

Today, we understand that the sun is made of 91% hydrogen and 8.87% helium. Everything else — all the other elements combined — makes up only 0.13% of the composition of the sun.

By analyzing the composition of stars, Cecilia Payne-Gaposchkin changed the way we understand the universe. And she accomplished this during a time when women were overtly excluded from science. According to ScienceNews, she taught at Harvard for nearly 20 years before being listed in the course catalog. Eventually, she became the first woman to be full professor at Harvard, and the first woman to chair a department at the prestigious university.

Ironically, in 1977, she received the highest honor of the American Astronomical Society, the Henry Norris Russell Lectureship, which celebrates lifetime achievement in astronomy. According to her obituary, near the end of her life, Cecilia Payne-Gaposchkin wrote:

“Young people, especially young women, often ask me for advice. Here it is, valeat quantum.

Do not undertake a scientific career in quest of fame or money. There are easier and better ways to reach them. Undertake it only if nothing else will satisfy you; for nothing else is probably what you will receive. Your reward will be the widening of the horizon as you climb. And if you achieve that reward you will ask no other.”