This page provides all possible meanings and translations of the word light-year
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An alternative spelling of light year.
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A light-year, also light year or lightyear, is an astronomical unit of length equal to just under 10 trillion kilometres. As defined by the International Astronomical Union, a light-year is the distance that light travels in a vacuum in one Julian year.
The light-year is mostly used to express distances to stars and other distances on a galactic scale, especially in non-specialist and popular science publications. The preferred unit in astrometry is the parsec, because it can be more easily derived from, and compared with, observational data.
Note that the light-year is a measure of distance. It is not a measure of time, for which it is sometimes mistaken.
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