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The light-year is a unit of length used to express astronomical distances. It is about 9.5 quadrillion metres or 5.9 trillion miles. As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in vacuum in one Julian year (365.25 days). Because it includes the word "year", the term light-year is sometimes misinterpreted as a unit of time.
Gigameter or gigametre is equal to 1,000,000,000 meters or 106 meters (unit of length), comes from a combination of the metric prefix giga (G) and the SI unit of length meter (m). Plural name is gigameters.