<P> 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 . </P>
<P> 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 . </P>
what is the length of one light year
what is the length of one light year
9.5 trillion kilometres or 5.9 trillion miles
9.5 trillion kilometres or 5.9 trillion miles