1. See Michael Hoskin, “The Great Debate: What Really Happened,” Journal for the History of Astronomy 7 (1976), 169–82.
2. Owen Gingerich, “The Mysterious Nebulae, 1610–1924,” Journal of the Royal Astronomical Society of Canada 81, no. 4 (1987), 113–27, on 123.
3. Peter van de Kamp, “The Galactocentric Revolution: a Reminiscent Narrative,” Publications of the Astronomical Society of the Pacific 77, no. 458 (1965), 325–35, on 325.
4. Harlow Shapley and Heber Curtis, “The Scale of the Universe,” Bulletin of the National Research Council 2, no. 11 (1921), 171–217. Available at https://apod.nasa.gov/debate/1920/cs_nrc.html.
5. According to Michael Hoskin, the argument and counterargument, that characterizes a debate, belong to the published papers and correspondence, not to the NAS session. Hoskin, “The Great Debate” (ref. 1), 169–74.