My increasing curiosity about Henrietta Swan Leavitt could hardly have been sated without the help of Louisa Gilder, who searched the archives at Harvard and Radcliffe with a thoroughness and a connoisseur’s eye for detail that went far beyond mere research.
I would also like to thank Kathleen Rawlins and Susan E. Maycock of the Cambridge Historical Commission; Jolene Passey, Faye Leavitt, and Joseph Leavitt of the Western Association of Leavitt Families, and Winston Leavitt of the National Association of Leavitt Families. I greatly benefited from the excellent work of several historians of early-twentieth-century astronomy, including Gale Christianson, J. D. Fernie, Owen Gingerich, Dorrit Hoffleit, Michael Hoskin, Peggy Aldrich Kid-well, Pamela Mack, Robert W. Smith, and Virginia Trimble (their books and papers are cited in my notes). At Harvard College Observatory, Alison Doane guided me through the stacks of photographic plates and old notebooks and helped me find the office where Henrietta Leavitt and the other computers probably worked.
Several people generously read the manuscript, helping me strike a balance between clarity and precision. First I thank the experts: Owen Gingerich, Research Professor of Astronomy and of the History of Science at Harvard University; Alison Doane, Curator of Astronomical Photographs at Harvard College Observatory; her predecessor, Martha Hazen; Stephen Maran of the American Astronomical Society; and Virginia Trimble, Professor of Astronomy and the History of Science at the University of California in Irvine. Just as valuable were the comments of smart, general readers, the kind of people this book is written for: Louisa Gilder, Julie Kinyoun, Douglas Maret, Nancy Maret, and Olga Matlin.
At James Atlas Books and Norton, I would like to thank Mr. Atlas himself, Jesse Cohen, Ed Barber, and Angela Von der Lippe, for their support and enthusiasm. Thanks also go to Trent Duffy, the excellent copy editor, and Esther Newberg and Christine Bauch at International Creative Management.