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
Kos (unit) Kos (unit) The kos (Sanskrit: कोस), also spelled Kosh, Krosh, krosha and Koss, is an ancient Indian subcontinental "Arthashastra standard unit" of distance, since at least 4 BCE. A kos is about 3.00 km or 1.91 miles. The ""Arthashastra: Chapter XX. Measurement of space and time"", authored in 4th century BCE by Chanakya (Vishnugupta Kauṭilya), sets this standard breakup of Indian units of length: Kos may also refer to roughly 1.8 km (1 mile) or 3.2 km (2 miles). "Arthashastra Standard unit" of Kos or krosh is equal to 3075 metres in SI units and 1.91 miles in Imperial units.