* Astronomy

Wilhelm Heinrich Walter Baade (March 24, 1893 - June 25, 1960) was a German astronomer who worked in the USA from 1931 to 1959.
He took advantage of wartime blackout conditions during World War II, which reduced light pollution at Mount Wilson Observatory, to resolve stars in the center of the Andromeda galaxy for the first time, which led him to define distinct "populations" for stars (Population I and Population II). The same observations led him to discover that there are two types of Cepheid variable stars. This discovery led him to recalculate the size of the known universe, doubling the previous calculation made by Hubble in 1929.
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