Camille Flammarion (Figure 5.1) is an important if enigmatic figure in the history of modern astronomy. He was undoubtedly one of the most influential popularizers of astronomy of the nineteenth and early twentieth centuries, and a key voice in the plurality-of-worlds debates of that period (Crowe, 1999; Dick, 1996). His example paved the way for the scientist popularizers who followed, such as Carl Sagan. However, his philosophical approach and involvement in the spiritist movement make him appear to be a figure from an earlier century. Indeed, Flammarion’s populist and philosophical approach to astronomy ultimately fell outside of the boundaries of the new astronomy constructed in the late nineteenth century as its centers of authority moved to mountain tops, its methods became increasingly instrumental, and its ethos became defined by “professionalism, expertise, and scientific method” (Nall, 2019, p. 75).