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

To visualize this density, imagine placing the solar system inside a cube one light-year on each side.

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The dying star was relatively close in astronomical terms: about 22 million light-years away, making it shine very bright.

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"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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