The light - year is a unit of length used to express astronomical distances and measures about 9.5 trillion kilometres or 5.9 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, as a year is a unit of time equivalent to approximately 365 days.
what is the length of one light year
9.5 trillion kilometres or 5.9 trillion miles