The sources of visual material are as follows (numerals refer to figures).
By permission of AT&T Archives (27); by permission of Brown University (36); courtesy of European Space Agency (46); courtesy of Joan Gallup Grier (1); by permission of Harvard University Libraries (14); by permission of Iowa State University Library/Special Collections Department (26, 34); courtesy of Library of Congress (2, 3a, 3b, 5, 7–10, 12, 13, 15–19, 23, 25, 29, 33, 35, 37, 41); courtesy of Library of Congress, Manuscript Division (4a, 4b, 20); by permission of the MIT Museum (42); courtesy of National Archives and Records Administration (24, 32, 38, 40, 45); by permission of Paris Observatory (3c); by permission of Schlesinger Library, Harvard University (21, 22, 28); by permission of the Science Museum, London (6); courtesy of Smithsonian Institution (11); courtesy of Stern Family (31, 44); courtesy of John Todd (39, 43); by permission of Yeshiva University (30).