Light year (ly)
Definition: A light year (symbol: ly) is the distance light travels in a vacuum in one Julian year, equal to about 9.4607 trillion kilometers or 9.4607 × 10^15 meters.
History/origin: The light year was adopted by astronomers as a practical way to express vast interstellar distances that would otherwise require extremely large numbers in kilometers or miles.
Current use: Light years are used mainly in astronomy and science communication to describe distances between stars, nebulae, and other objects beyond our solar system.


