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
light-years,
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.
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
First recorded in 1885–90
How does light-year compare to similar and commonly confused words? Explore the most common comparisons:
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
To visualize this density, imagine placing the solar system inside a cube one light-year on each side.
From Science Daily ● Nov. 29, 2025
The entire image is about half a light-year across, or 4.7tn km.
From BBC ● Jul. 12, 2023
Goldfish by the ton, aphids by the light-year.
From Slate ● Apr. 3, 2023
Though that is extremely close in astronomy terms, there are 5.88 trillion miles in one light-year.
From Salon ● Feb. 16, 2023
That unit of length, the distance light goes in a year, is called a light-year.
From "Cosmos" by Carl Sagan
One light year is 5.88 trillion miles, so “there’s quite a difference between the two. Yet, there’s the planet, superimposed over the star cluster.”
From Seattle Times ● Dec. 21, 2022
It shined with the light of 2 trillion stars, yet it was only about the size of our solar system, less than a light year, while the Milky Way is 100,000 light years in diameter.
From Los Angeles Times ● Sep. 23, 2022
Southern Ring Nebula Another spellbinding nebula, the Southern Ring Nebula looks like a giant turquoise ring in the night sky, one that actually spans half a light year wide.
From The Verge ● Jul. 12, 2022
Maybe a light year will have been a good thing and all will be well?
From Washington Post ● Jun. 29, 2021
Light year after light year they raced toward the distant base.
From Invaders from the Infinite by Campbell, John Wood
Although that distance is enormous by human standards, it is a remarkably fine level of detail inside a galaxy that spans hundreds of thousands of light-years.
From Science Daily ● Jul. 18, 2026
The disk stretches nearly 800 light-years across, and some of the material inside it is moving at speeds of up to 600 kilometers per second.
From Science Daily ● Jul. 18, 2026
The planet, called LHS 1140 b, is 48 light-years from Earth orbiting a red star much smaller and cooler than our Sun.
From BBC ● Jul. 17, 2026
In 2022, Swift captured this image of a gamma-ray burst from a massive star dying two billion light-years from Earth.
From BBC ● Jul. 3, 2026
About ten million years ago, the Sun emerged from the Gould Belt complex of the Orion Spiral Arm, which is now a little less than a thousand light-years away.
From "Cosmos" by Carl Sagan
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
