Stellar spectrum measurement. Historical artwork of a female assistant measuring the spectrum of a star during the 1880s. She is viewing a spectrogram, a photographic plate of the component wavelengths of light emitted from the star, through a moveable microscope. The width and position of the spectrogram's lines provide information about the chemical and physical characteristics of the star. This woman was one of the 'Harvard Women's Team' working at this American university under Edward Pickering (1846-1919) to produce a catalogue of stellar spectra.