A post by Sabine Winters

Somnium, seu Opus posthumum de astronomia lunari – ‘The Dream, or Posthumous Work on Lunar Astronomy’ by Johannes Kepler (1571–1630) tells the (story of a dream about the) adventures of Duracotus who, after much wandering and lengthy training in astronomy, is transported to the Moon by occult forces and the services of a demon. It was written over a period of more than 21 years (1609–1630) and published posthumously in 1634 by Kepler’s son Ludwig. Somnium discusses a wide range of topics but most extensively the movement of the Earth around its own axis, as Kepler writes:

The object of my Somnium, was to work out, through the example of the Moon, an argument for the motion of the Earth; or rather, to overcome objections taken from the general opposition of mankind. (Kepler, Somnium, ed. Lear (1965), Note 3,89.)

Somnium is not simply an exercise of idle imagination, full of metaphors and allegories for their own sake. Rather, Somnium aims to foster a better understanding of the structures of the universe by actively prompting the audience to imagine what (the motions of) the Earth would look like from the Moon. In this perspective, Somnium should be understood a thought experiment in which imagination is a guide to epistemic possibilities.