Abbot, Charles Greeley, 1872–1973, American astrophysicist, b. Wilton, N.H. He was acting director in 1896 and director in 1907 of the astrophysical observatory of the Smithsonian Institution; he was secretary of the institution from 1928 to 1944, when he became a research associate. Many of his research studies were initiated by S. P. Langley, his predecessor. He completed the mapping of the infrared solar spectrum and carried out systematic studies of variation in solar radiation, its relation to the sunspot cycle, and its effect on weather variation. He also studied the nature of atmospheric transmission and absorption. Abbot perfected various standardized instruments now widely used for measuring the sun's heat, and he invented devices utilizing solar energy.