U.S. physicist and astronomer who introduced the use of the meridian photometer to measure the magnitude of stars and established the Harvard Photometry (1884), the first great photometric catalog.

In 1867 Pickering became professor of physics at the Massachusetts Institute of Technology, Cambridge, where he established the first U.S. laboratory in which students were required to use laboratory instruments to make measurements. In 1876 he was appointed professor of astronomy and director of the Harvard College Observatory.

He invented the meridian photometer, which utilized a calcite prism to juxtapose the image of a star with one of a designated group of north polar stars to compare their brightnesses, and used it to compile his catalog. After the Arequipa Observatory was established in Peru in 1891, it became possible to include measurements of the southern stars within the scope of the work of the Harvard College Observatory. Under Pickering this work included photometry, a scale of photographic magnitudes, a system of classification of variable stars, and a system of stellar spectroscopy that was for many years universally adopted.