Baade, Walter

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Baade, Walter (1893–1960) US astronomer, b. Germany. From Mount Wilson Observatory, in the 1943 wartime blackout, he observed individual stars in the Andromeda Galaxy and distinguished the younger, bluer Population I stars from the older, redder Population II stars. He went on to improve the use of Cepheid variable stars as distance indicators, and showed that the universe was older and larger than had been thought.