Edward Charles Pickering (1846-1919), US astronomer. In 1889, Pickering discovered the first spectroscopic binary star system by noting that the spectrum of light observed was changed due to Doppler shifting. Around 1890 Pickering introduced the colour index which measured the difference between a star's photographic (blue light) and visual (yellow light) brightness; this index indicates a star's temperature. Pickering also discovered the first variable star in a globular cluster. With his large team of female assistants, Pickering made Harvard Observatory, USA, the main centre for stellar photometry and spectroscopy, producing several star catalogues.