Scottish astronomer Williamina Paton Stevens Fleming was born #OTD in 1857.
Fleming's most significant contributions came in the field of stellar classification. She developed a system for classifying stars based on their spectra, which became known as the Harvard Classification Scheme. In 1890, she published the first catalog of stellar spectra, which contained over 10,000 stars classified according to her system.
https://en.wikipedia.org/wiki/Stellar_classification#Harvard_spectral_classification