Across the Divide: From the One Galaxy Universe to the Expanding Universe

Between the end of the nineteenth century and the early 1930s, astronomical thinking on the large-scale nature of the universe was transformed. At the end of the nineteenth century, astronomers were little concerned with the large-scale properties of the universe, its history and what was beyond our Galaxy. In this talk I will discuss these attitudes as well as what happened to change them during the first few decades of the twentieth century. I will conclude by examining the establishment of the expanding universe in the late 1920s and early 1930s.