light year


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light year

a unit of distance used in astronomy, equal to the distance travelled by light in one year, i.e. 9.4607 × 1012 kilometres or 0.3066 parsecs
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

light year

The distance light travels in one year, which is roughly 6 trillion miles or 9.5 trillion kilometers. Abbreviated "ly," light years are used to measure distances in the universe. For example, our 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 trillions of miles doing that."
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References in periodicals archive ?
We've reduced our galaxy, 100,000 light years in diameter, first to 170 miles, and now to the size of a plate you could hold in your hand.
A Chandra X-ray image (1) of Eta Carinae, our galaxy's most luminous star (7,500 light years from Earth), as compared to an optical image by the Hubble Space Telescope (2).
Thank your lucky stars that a magnetar--a new type of star astronomers discovered earlier this year--lies 20,000 light years from Earth.