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[lahyt-yeer, -yeer] /ˈlaɪtˌyɪər, -ˈyɪər/
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.
Abbreviation: lt-yr.
  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.
Origin of light-year
First recorded in 1885-90 Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for light-year
Contemporary Examples
Historical Examples
  • The figures of the light-year dials were meaningless to his comprehension.

    The World Beyond Raymond King Cummings
  • By your figuring, we shouldn't be yet one light-year on the way.

    Out Around Rigel Robert H. Wilson
  • Our task was easy, because we were about half a light-year from the sun.

    Accidental Death Peter Baily
  • You were about right for distance, and within a few tenths of a light-year laterally.

    Skylark Three Edward Elmer Smith
  • The light-year is the distance that light travels in one year.

    Astronomy for Young Folks Isabel Martin Lewis
  • Bearings agree, and distances check to within a light-year, which is as close as we can hope to check on as small a mass as a man.

    Skylark Three Edward Elmer Smith
  • We are still one light-year distant from Alpha Centauri, the nearest of the bright stars.

    Astronomy for Young Folks Isabel Martin Lewis
  • One could imagine falling forty-two thousand miles, where one couldn't imagine falling a light-year.

    Pariah Planet Murray Leinster
  • "The distance is half a light-year now, sir," reported the navigation officer.

    The Ultimate Weapon John Wood Campbell
light-year in Science
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. Compare astronomical unit, parsec.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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