American astronomer who pioneered in the classification of stellar spectra.

Mina Stevens was educated in public schools and from age 14 was a teacher as well as student. In May 1877 she married James O. Fleming, with whom she immigrated to the United States and settled in Boston the next year. The failure of her marriage in 1879 forced her to seek employment, and she soon became housekeeper for Edward C. Pickering (Pickering, Edward Charles), professor of astronomy and director of the Harvard College Observatory. Before the year was out Pickering had asked her to work at the observatory as a temporary employee, and in 1881 she became a permanent member of the research staff. For the next 30 years she collaborated on the analysis of stellar spectrum photography, and in 1898 she was appointed curator of astronomical photographs at Harvard.

Fleming is best known for her work on the classification of stellar spectra—the pattern of lines caused by the dispersion of a star's (star) light through a prism placed before a telescope lens. Using a technique that came to be known as the Pickering-Fleming system, she studied the tens of thousands of celestial photographs taken for the Draper Memorial—a project dedicated to the amateur astronomer Henry Draper (Draper, Henry) of New York. In the course of her work she discovered 10 novae, 52 nebulae, and hundreds of variable stars. She also established the first photographic standards of magnitude used to measure the variable brightness of stars.

Fleming's most important works include the Draper Catalogue of Stellar Spectra (1890), “A Photographic Study of Variable Stars” (1907), and “Stars Having Peculiar Spectra” (1912). In 1906 she became the first American woman elected to the Royal Astronomical Society. Her work provided the foundation for the future contributions of Annie Jump Cannon (Cannon, Annie Jump).