Meaning & use
light-year
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Meanings
nouncountabletechnicalphysics
A unit of distance used for outer space, equal to how far light travels in a year, about nine and a half trillion kilometers.
Grammar: Measures distance, not time: the star is four light-years away.
Patterns
- something light-years away
- two light-years from something
The nearest star beyond our sun is just over four light-years away.
The galaxy lies millions of light-years from Earth.
Astronomers measure the distance to stars in light-years.
nounusually pluralinformalfigurative
A very long way or a huge difference, used in an exaggerated way, usually in the plural.
Grammar: Often found in the phrase light-years ahead of someone or something.
Patterns
- light-years ahead of something
- light-years away from something
This new phone is light-years ahead of my old one.
Their ideas were light-years away from what voters wanted.
The two teams are light-years apart in skill.
Word forms
| plural | light-years |
|---|
Common combinations
- light-years away
- The nearest galaxy is thousands of light-years away.
- light-years ahead
- Her design is light-years ahead of the competition.
- light-years apart
- Their opinions were light-years apart.
- light-years from here
- The planet is light-years from here.
- billions of light-years
- The telescope can see objects billions of light-years away.
Synonyms and how they differ
- parsec
- A parsec is another astronomical unit of distance, equal to about 3.26 light-years, and professionals use it more than the public does.
- astronomical unit
- Astronomical unit is the average distance from Earth to the sun, so it is used for distances inside the solar system, much smaller than a light-year.
- miles
- Miles is the everyday unit, but it is far too small to measure the distances between stars.
Word family
- light-second noun
- the distance light travels in one second
- light-minute noun
- the distance light travels in one minute
- lightspeed noun
- the speed at which light travels
Commonly confused: light-year or year?
light-year vs year
A light-year is a distance, not a length of time, even though year appears in the name.
Practice
The star is eight light-years from Earth. This statement describes ____.
Choose one answer.
A light-year measures distance, the length light travels in a year. It is not a time, speed or brightness, though year appears in the name.
Make it your own
Write a sentence using “light-year”, then check it and compare it with the examples above.