The distance traveled by a beam of light in a vacuum in one year, approximately 9.46 trillion (million million) kilometers or 5.99 trillion miles: A light-year has an average speed of 186,291 miles or 299,792 kilometers, per second; which equals approximately 5.88 trillion miles or 9.4607 trillion kilometers, or 63,246 astronomical units.

The light-year is also divided into light-minutes and light-seconds; for example, the Moon is 1.3 light-seconds from the Earth and the Sun is 8.3 light-minutes away from the Earth.

Although a light-year is a measurement of distance and not time, it does imply time, such as the light from a star that is ten light-years from the Earth takes ten years to reach the Earth. So, an observer on Earth is seeing the star as it appeared ten years ago.