Cecilia Payne-Gaposchkin, who revolutionized our understanding of what stars & the Universe are made of, was born #OTD in 1900.
In 1926, she wrote what is considered the "undoubtedly most brilliant PhD thesis ever written in astronomy".
She continued in the same spirit - only to be denied a professorship (or even the a proper astronomer position). She finally became a professor at Harvard at 1956(!) & first woman to chair a department.