From August Derleth's foreword to the excerpt published in Beyond Time & Space: "Kepler's Somnium was originally written circa 1610, but the notes for it were set down considerably later, some time after 1622 and after the manuscript had been privately circulated. Its first printing came in 1634, four years after Kepler's death. From the perspective of science-fiction, Somnium is important because it is one of the earliest expositions of the physical sciences, whereas other interplanetary ventures were largely social science. Everett Bleiler, who made this first published English translation, is co-editor of The Best Science-Fiction Stories ...."
