A unit of distance used in astronomy; the distance travelled by light in a vacuum during one year. It is equal to 9.4650×1015 metres or 5.8785×1012 miles.
Mathematics
The distance travelled by light in 1 year. A light year is approximately 9.46×1012 km. Because of the vast distances in space, the light year is the basic unit of distance in astronomy.
Astronomy
The distance travelled by light, or other electromagnetic radiation, in one tropical year through space. One light year equals 9 460 730 472 580.8 km, or 63 241 astronomical units, or 0.3066 parsecs.
Space Exploration
The distance travelled by a beam of light in a vacuum in one year. It is equal to approximately 9.4605 × 1012 km.