Williamina Fleming, Scottish-American astronomer and academic (born 1857)

Williamina Paton Stevens Fleming was a pioneering Scottish astronomer, who made significant contributions to the field despite facing gender biases. She was a single mother hired by the director of the Harvard College Observatory to help in the photographic classification of stellar spectra. She helped develop a common designation system for stars and cataloged more than ten thousand stars, 59 gaseous nebulae, over 310 variable stars, and 10 novae and other astronomical phenomena. Among several career achievements that advanced astronomy, Fleming is noted for her discovery of the Horsehead Nebula in 1888. Fleming's work has had a lasting impact on our understanding of the universe.

May 21 is the 141st day of the year in the Gregorian calendar; 224 days remain until the end of the year.