light-year

[lahyt-yeer, -yeer]

noun

1. Astronomy.,  the distance traversed by light in one mean solar year, about 5.88 trillion mi. (9.46 trillion km): used as a unit in measuring stellar distances. lt-yr

2. light-years,

   1. a very great distance, especially in development or progress.

      The new computer is light-years ahead of the old one.

   2. a very long time.

      It's been light-years since I've seen my childhood friends.

light year

noun

1. a unit of distance used in astronomy, equal to the distance travelled by light in one year, i.e. 9.4607 × 10 ¹² kilometres or 0.3066 parsecs

light-year

1. The distance that light travels in a vacuum in one year, equal to about 9.46 trillion km (5.88 trillion mi). Light-years are used in measuring interstellar and intergalactic distances.

2. Compare astronomical unit parsec

light year

1. The distance traveled by light in a year (over five trillion miles); a unit for measuring distances outside the solar system. The star nearest to our sun, Alpha Centauri, is more than four light years away.

Word History and Origins

Origin of light-year¹

First recorded in 1885–90