Scottish-born US astronomer, assistant to Edward Pickering, with whom she compiled the first general catalogue classifying stellar spectra.

Fleming was born in Dundee and emigrated to the USA 1878. From 1879 she was employed by Pickering, director of the Harvard College Observatory, initially as a 'computer' and copy editor. In 1898 she was appointed curator of astronomical photographs.
Photographs were taken of the spectra obtained using prisms placed in front of the objectives of telescopes. In the course of her analysis of these spectra, Fleming discovered 59 nebulae, more than 300 variable stars, and 10 novae.
The spectra of the stars observed in this manner could be classified into categories. Fleming designed the system adopted in the 1890 Draper Catalogues, in which 10,351 stellar spectra were listed in 17 categories ('A' to 'Q'). This system was to be superseded by the work of Annie Jump Cannon at the same observatory.