Robert McNeesAstronomer Williamina Fleming was born #OTD in 1857. She developed a system to classify stars according to their spectra; cataloged over 10k stars; and discovered numerous novae, nebulae, and variable stars.
Image: Harvard College Observatory
Kevin Russell"Identify them through their spectra" sounds so simple.
Light sources can be identified by, at its simplest, the colour of the light, which is determined by what is burning, energized.
This "classification" is still the single most powerful tool in astronomy. As a leap in science, it brought humanity past watch-the-specs-move up to -- "WHAT is out there" -- a leap.
Before this insight, was astrology.