A light-year is a unit of length defined by the distance that light travels through the vacuum in an entire Julian year (365.25 days of 86,400 seconds each; or 31,557,600 seconds), being exactly equivalent to 9,460,730,472,580,800 meters or about 9.5 trillion kilometers. The abbreviation of a light-year is ly.
- ↑ Measuring the Universe. The IAU and astronomical units. International Astronomic Union. Retrieved 24 July 2016.