Light-year Light-year The light-year is a unit of length used to express astronomical distances and measures about 9.46 trillion kilometres or 5.88 trillion miles. As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in vacuum in one Julian year (365.25 days). Because it includes the word "year", the term light-year is sometimes misinterpreted as a unit of time. The light-year is most often used when expressing distances to stars and other distances on a galactic scale, especially in nonspecialist and popular science publications. The unit most commonly used in professional astrometry is the parsec
Rocheworld focusing light onto the smaller sail, slowing the craft. Using the light sail system, the spaceship "Prometheus" continued to accelerate for 20 years, traveling 2 light years' distance toward Barnard's Star before going into coast mode and traveling an additional 20 years' time at a constant speed of 0.2 "c", covering the remaining 4 light years (ca. 23 trillion miles; 38 trillion km). Flouwen (the Middle English word for 'flow') are the alien creatures in the book. They are the sole intelligent inhabitants of the planet Eau, which makes up the watery half of Rocheworld. Flouwen are blob-like, happy-go-lucky aliens