Drawing by Kepler: Lunar Days and Nights
History of Astronomy

“Somnium”: Kepler’s Dream of Alien Worlds

Johannes Kepler’s complete works comprise more than 20 volumes—a veritable repository for historians of science. Among them there is the probably first novel incorporating elements of “hard sci-fi”: Somnium (The Dream), posthumously published by Kepler’s son in 1634. Kepler’s text, rather a short story than a fully elaborated novel, describes a flight to the moon and an encounter with its inhabitants. Among them, earth is known as “Volva” (the phonetic resemblance to “vulva” is hardly a coincidence) while their lunar home is called “Levania” (apparently Kepler, who had taken Hebrew classes at the University of Tübingen, is alluding to the poetic name for the moon in Hebrew, “לְבָנָה”).

The story includes many autobiographical details, e.g. the storyteller’s father dies prematurely, and his mother possesses all attributes of a witch (Kepler’s mother was accused of witchcraft and he wrote an extensive—and eventually successful—objection in her defense). Like Kepler, the central character becomes an assistant for Tycho Brahe.

Overall, the narration is an amalgam of supernatural (e.g. friendly demons are helping with the launch) and science-based elements. Kepler places a high value on scientific accuracy when it comes to the view from the moon’s surface: How large, exactly, would earth appear on the lunar horizon? What would a terrestrial eclipse look like? How about the intensity of the sunlight? etc.

Almost four centuries before the “Earthrise”-picture, Kepler describes the vista of earth from its satellite: The inhabitants of the near side of the moon, writes Kepler, enjoy in this way the most delightful spectacle: Earth rising above the horizon (“Omnium verò jucundissima est in Levania, speculatio Volvae suae [..].”, Kepler 1993, p. 326). From an epistemological point of view, this is indeed a remarkable change of perspective: our planet observed from another celestial body.

In Kepler’s opinion, the existence of extraterrestrial life is not only a science fiction theme but a fact, or, at least, a most likely phenomenon. In his „Dissertatio cum Nuncio Sidereo“ (1610) he speculates that some odd circular objects on the moon, as discovered by Galilei, could be in fact artificial structures built by the “Selenites”, the inhabitants of the moon, to protect themselves against extreme variations in temperature. Furthermore, he supposes that even Jupiter’s moons are inhabited, and turns out to be quite optimistic about the possibility of human spaceflight to Jupiter. 

Visiting and even colonizing other planets, is just a matter of time from Kepler’s point of view: “Having once ships or sails for the skies, there will be men who will not be in fear of the vastness.” The task of his and Galilei’s work, he continues, is to prepare the ground for future space travel (“Da naves, aut vela caelesti aurae accommoda, erunt qui ne ab illa quidem vastitate sibi metuant. Adeoque quasi propediem affuturis, qui hoc iter tentent, Ego Lunarem, tu Galilaee Iovialem condamus Astronomiam.”; Kepler 1941, p. 305).

In lines like these, Kepler displays true modern thinking. The celestial spheres do not consist of a mysterious fifth element as asserted by Greek cosmology, but of the same elements as earth does; the fundamental ontological difference between terrestrial and cosmic matter has disappeared for good. From now on, space is ready to be explored, intellectually as well as physically. In Kepler’s mind, mankind is not earthbound anymore

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