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What Are Stars Made Of?

In 1925, trailblazing scientist Cecilia Payne figured it out—and changed astronomy forever.

By Mackenzie Carro

From the March 2026 Issue

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Smithsonian Institution/Science Service

Cecilia Payne

Have you ever looked up at a starry night sky and wondered what exactly those twinkly lights are?

In ancient times, many believed they were gods. Other theories included that stars were holes in the sky made by giants, the souls of warriors, or golden nailheads holding up the universe.

From the mid-1800s through the early 1920s, astronomers believed stars were made of the same materials that planet Earth is—mostly metals like iron and metalloids like silicon.

But in 1925, a bright young scientist from Wendover, England, named Cecilia Payne boldly challenged this belief. She hypothesized that stars are made mostly of gases. And she was right.

The problem?

Few believed her.

Not Where But What

COURTESY OF THE HARVARD LIBRARY ARCHIVES

At Harvard in the 1920s, women were generally only hired as lab assistants, or “computers.” These women did the important but often overlooked job of calculating mathematical equations for astronomers.

Payne began her scientific studies at Cambridge University in 1919. While there, she became dazzled by the field of astrophysics—the branch of astronomy that uses physics to study the stars, planets, and other celestial objects.

But at the time, women couldn’t obtain degrees from Cambridge. They could only attend classes. So Payne set her sights on the Harvard College Observatory in Massachusetts. Back then, Harvard was one of the few places where women could work in astronomy—though their roles were limited. When Payne was offered a chance to earn her graduate degree there, she gladly accepted.

In the early 20th century, many astronomers were focused on charting where stars were. Payne was interested in learning about what stars were. She spent hours studying data and running complex equations, drawing on her background in physics to try to figure out a star’s makeup. Ultimately, she discovered that stars were made mostly of two gases: hydrogen and helium. She published her findings in May 1925, knowing they would be controversial.

And they were. One of the leading astronomers at the time, Henry Norris Russell, said that Payne’s results were “impossible.” However, four years later, he proved Payne right in his own study. After that, her theory became widely accepted—though she did not get credit for it for some years.

Forging a Path

Payne is considered one of history’s most influential astronomers. And yet, her title at Harvard remained technical assistant for years. She was not recognized as a full professor until 1956. But in that same year, she was named chair of the astronomy department—the first woman to hold such a position at the prestigious school.

In 1976, while accepting an award for her achievements, she said, “The reward of the young scientist is the emotional thrill of being the first person in the history of the world to see something or to understand something.”

So next time you have a question about the world around you, follow Payne’s lead and look for the answer. You could be the one who finds it!

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