light-year
Say it: LIGHT-yeer /ˈlaɪtjɪə/ · noun
What “light-year” means
The distance light travels in one year.
More precisely: The distance light travels in a year, about 9.5 trillion kilometres; a measure of distance, not time.
Example: “Proxima Centauri, the nearest star after the Sun, is about 4.2 light-years away.”
When to use it
In astronomy, when describing enormous distances between stars; use it for distance rather than elapsed time.
Memory trick
The year tells you how long light travels; the word measures how far.
Similar words
interstellar distance, astronomical distance
Quick check
Light from a distant star takes one year to reach a telescope. Which unit describes the distance it travelled?
a solar year or a light-year?
Show the answer
a light-year
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