A light-year is the total distance that light can travel in 1 year. Since, We know the speed of light (c) in vacuum= 299792458 metres per second And, there are 365.25 days in an year, or t= (365.25*24*60*60) seconds Hence a light-year (d)=c*t =299792458Ă—365.25Ă—24Ă—60Ă—60 metres =9,460,730,472,580,800 metres â‰9.46073Ă—10^15 metres