what is a light year distance
A light-year (abbreviation: ly), sometimes written light year, is a unit of length used informally to express astronomical distances. It is approximately 9 trillion kilometres (or about 6 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. Because it includes the word year, the term light-year is sometimes misinterpreted as a unit of time.