A light year is a unit of length that is used to espress distances that are astronomical. It is equivalent to 5.9 trillion miles or 9.5 quadrillion meters. Light year is defined by the distance a beam of light would travel in one year. One light year is equivalent to the distance that light would travel in vacuum on one Julian year or 365 days as defined by the IAU or the International Astronomical Union. So, one light year is traveled for 1 year here on Earth. So, in order to drive to the alpha centauri, you would take about 4.4 years to do so.
