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

Example Sentences

"What makes this especially valuable is that its host star is close by, at just about 18 light-years away. Cosmically speaking, it's practically next door."

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The supernova is located in the galaxy NGC 3621, in the direction of the constellation Hydra, approximately 22 million light-years away.

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Joe and his colleagues detected this brief, intense radio signal and traced it to a star located around 130 light-years away.

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A possible "super-Earth" located less than 20 light-years from Earth is giving researchers renewed optimism in the search for planets that might host life.

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The Large Magellanic Cloud, located about 160,000 light-years from Earth, is an ideal environment for studying how stars form in conditions resembling those of the early universe.

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