Cecilia Payne-Gaposchkin was a pioneering astrophysicist born on May 10, 1900, in England. She is best known for her groundbreaking work in the field of stellar atmospheres and for proposing that stars are primarily composed of hydrogen and helium. Her 1925 doctoral thesis at Harvard University challenged existing theories about the composition of stars and laid the foundation for modern astrophysics. In addition to her research, Payne-Gaposchkin became the first woman to hold a full professorship at Harvard University. She also played a significant role in the development of the Harvard College Observatory and mentored many young scientists throughout her career, contributing to the advancement of women in science.