The star Spica, which is quite close to the Moon tonight, is quite different from the Sun. It consists of two stars, not one. Both stars are many times bigger and heavier than the Sun. And their surfaces are tens of thousands of degrees hotter, so the stars shine blue-white.

On the other hand, the Sun and Spica are made of almost exactly the same ingredients: mainly hydrogen and helium, with only a smattering of heavier elements. That composition was figured out by an astronomer who was born 125 years ago tomorrow, in England.

Cecilia Payne caught the astronomy bug when she saw a lecture by Arthur Eddington, one of the world’s leading astronomers. She started her education in England, then finished in the United States. She earned a Ph.D. in 1925. And her doctoral thesis shook up the field. Decades later, in fact, Otto Struve, the first director of McDonald Observatory, called it the most brilliant thesis ever written in the field.

Astronomers already had the techniques for measuring what stars are made of. Their work led them to believe that stars contain the same mixture of elements as Earth. But Payne used a new way to analyze the readings, taking into account the charge of atoms. She concluded that stars were made mainly of hydrogen and helium – elements formed in the Big Bang.

By a few years later, just about everyone accepted her analysis – completely changing our concept of the stars.

Script by Damond Benningfield