1920-1930 correspondence, 1911-1940, bulk: 1921-1930

This subseries contains correspondence between Shapley and a variety of correspondents, including many notable astronomers from the United States and abroad, such as Walter Sydney Adams, John Duncan, Theodore Duncan, Edwin Frost, Paul Guthnick, Ejnar Hertzsprung, A.O. Leuschner, Willem Jacob Luyten, Adriaan van Maanen, S.A. Mitchell, William Henry Pickering, Harry Hemley Plaskett, Pieter Johannes van Rhijn, Henry Norris Russell, and Frank Schlesinger. Letters with these scientists share scientific data, such as information about the performance of various astronomical equipment and telescopes, advancements and discoveries within the field, as well as personal conversations, which give insight into the close-knit community that many of these astronomers shared. Letters with Harvard University professors, such as George R. Agassiz, Theodore Lyman, and Edwin Bidwell Wilson, also share scientific information and discuss budgetary issues and strategies for procuring funding from the school.

Shapley also corresponded regularly with many Harvard University departments, including the Maintenance Department, the Treasurer’s Office, the Board of Overseers, and president A. Lawrence Lowell, discussing the Observatory's finances, funding, and budgets, as well as equipment needs, staffing and salary discussions, and other administrative issues. Correspondence with Radcliffe College demonstrates Shapley's dedication to mentoring and employing female students, a theme that can be found throughout the series with various female students, employees, and astronomers. Shapley’s communications with organizations, such as the American Association for the Advancement of Science, the American Association of Variable Star Observers, and the National Research Council, highlight his involvement with professional institutions, and show his commitment to the advancement of the field of astronomy outside of Harvard University. Writing to scientific instrument-maker J.W. Fecker, Shapley discusses orders for 24-inch and 30-inch telescopes. Also contains various blueprints and sketches of a 1925 eclipse, as well as correspondence discussing the eclipses of 1806, 1925, 1927, and 1930.