- Astron. a unit of distance equal to the distance that light travels in a vacuum in one year, c. 9,460,000,000,000 km (5,880,000,000,000 mi): abbrev. lt-yr or ly
- a very great distance, amount of time, etc.: usually used in pl.: light-years ahead in basic research
- An example of a light-year is over five trillion miles.
- An example of a light-year is how far ahead one child may be in class when compared to another child; light-years ahead.
- The distance that light travels in a vacuum in one year, approximately 9.46 trillion kilometers (5.88 trillion miles).
- often light years Informal A long way: a small town light years away from the action of the capital.
Compare astronomical unit
- Alternative spelling of light year.
light year - Computer Definition
The distance light travels in one year, which is approximately 5.9 quadrillion miles. Abbreviated "ly," light years are used to measure distances in the universe. For example, the galaxy is presumed to be about 100 ly across. Proxima Centauri, at about 4.22 ly from the sun, is the closest star to the sun. It's About Distance, Not Time Because the word "year" is used, light years are often erroneously used to measure time. The phrase "I spent light years doing that" might sound triumphant, but it is like saying "I spent a million miles doing that."