One light year is the distance that light travels in a vacuum in one Julian year (365.25 days). It equals approximately 9.46 trillion kilometers (about 9,460,730,472,580.8 kilometers) or about 5.88 trillion miles. This measurement is used primarily in astronomy to describe vast distances between stars and galaxies. Light travels at about 299,792 kilometers per second (186,282 miles per second), so over the span of an entire year, this distance adds up to around 9.46 trillion kilometers. Despite its name, a light year is a unit of distance, not time.