British born Cecilia Payne is the reason we know basically anything about variable stars (stars whose brightness as seen from earth fluctuates) as literally every other study on variable stars is based on her work.
Cecilia won a scholarship to Cambridge in 1919. When she completed her studies, Cambridge wouldn’t give her a degree because she was a woman (Cambridge did not grant degrees to women until 1948), so she moved to the US to work at Harvard.
Cecilia Payne was the first person ever to earn a PhD in astronomy from Radcliffe College (now part of Harvard), with what the eminent astronomer Otto Strauve called “the most brilliant PhD thesis ever written in astronomy.”
Her PhD thesis is considered by many astronomers as one of the best and most influential in the field of astronomy. Cecilia managed to explain what stars are made of, including the Sun. However, she was never given proper credit for the discovery, as astronomer Henry Norris Russell persuaded her not to present her conclusion. He later published the discovery on his own behalf. He did mention Cecilia in her paper, but it was Russell who got all the credit for the discovery.
Cecilia was the first woman to be promoted to full professor from within Harvard, and is often credited with breaking the glass ceiling for women in the Harvard science department and in astronomy, as well as inspiring entire generations of women to take up science.