- 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
- a very great distance, especially in development or progress: The new computer is light-years ahead of the old one.
- 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
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
Examples from the Web for light-year
One magnetar is only about a light-year from the black hole at the center of the Milky Way.The Weirdest Object in the Universe
Matthew R. Francis
May 18, 2014
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
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
- 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 © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.