Kepler's Somnium: a dream of lunar astronomy
Johannes Kepler's Somnium, published posthumously in 1634: Duracotus, the daemon of Levania, the Earth seen from the Moon and his mother's witchcraft trial.
Among the tales of lunar journeys, one bears the signature of a great astronomer. Johannes Kepler, discoverer of the laws governing the motion of the planets, wrote the Somnium, or Dream, to explain how the sky would look to someone living on the Moon. The core of the work dates back to his university years in Tübingen and a first draft to 1609, but the book was published only in 1634, four years after the author's death, by his son Ludwig.
Duracotus and the daemon of Levania
The frame is deliberately fairy-tale-like. The narrator falls asleep and dreams of reading a book in which a young Icelander, Duracotus, tells his own story. Son of Fiolxhilde, a woman who gathers herbs and knows the spirits, the boy is handed over to a ship's captain and ends up in Denmark, where he studies astronomy for five years with Tycho Brahe on the island of Hven.
Back in Iceland, he discovers that his mother is in contact with a daemon from Levania, the name Kepler gives the Moon, derived from a Hebrew word. The daemon explains that the journey is possible only during an eclipse, along the cone of shadow joining the Earth to the Moon, and is so violent that few people can endure it. The magical tone serves to introduce what follows: a rigorously astronomical description.
The Earth seen from the Moon
The heart of the Somnium is an exercise in scientific imagination. Kepler describes Levania as divided into two hemispheres: Subvolva, which always sees Volva, that is the Earth, hanging in the sky, and Privolva, which never sees it. Day and night each last about fifteen Earth days, heat and cold are extreme, and the Earth appears motionless in the lunar sky while it turns on itself, showing its continents.
It was an ingenious way of defending Copernican theory. If from the Moon the Earth seems still and the stars move, then from the Earth too the apparent motion of the heavens may depend on the motion of the observer. Kepler enriched the text with a body of notes far longer than the story itself, in which he explained the allusions and the scientific basis of every detail.
A book and a trial
The notes also contain a painful reference. In 1615 Kepler's mother, Katharina, was accused of witchcraft in her town in Württemberg; the trial dragged on for years, and only in 1621, thanks to a defence conducted by her son himself, was she released. Kepler suspected that the manuscript of the Somnium, which had circulated among the curious, with its herbalist mother summoning daemons, had fuelled the rumours.
The Somnium was published together with Kepler's own Latin translation of Plutarch's dialogue On the Face Which Appears in the Orb of the Moon, an ancient text that had already imagined a Moon similar to the Earth. The meeting between that tradition and the new astronomy has made the Dream one of the founding books of scientific fiction, written by someone who truly knew the laws of the sky.