Somnium — full title: Somnium, seu opus posthumum De astronomia lunari — is a novel written in Latin in 1608 by Johannes Kepler. It was first published in 1634 by Kepler's son, Ludwig Kepler, several years after the death of his father. In the narrative, an Icelandic boy and his witch mother learn of an island named Levania from a daemon. Somnium presents a detailed imaginative description of how the Earth might look when viewed from the Moon, and is considered the first serious scientific treatise on lunar astronomy. Carl Sagan and Isaac Asimov have referred to it as one of the earliest works of science fiction.

Johannes Kepler was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws of planetary motion, and his books Astronomia nova, Harmonice Mundi, and Epitome Astronomiae Copernicanae, influencing among others Isaac Newton, providing one of the foundations for his theory of universal gravitation. The variety and impact of his work made Kepler one of the founders and fathers of modern astronomy, the scientific method, natural and modern science. He has been described as the "father of science fiction" for his novel Somnium.