# Astronomical unit

An astronomical unit (abbreviated as AU) is a unit of length now defined as about $$1.5 \times 10^8$$ km(about $$93$$ million miles), or roughly the mean Earth–Sun distance. A light-year (symbol: LY), is a unit of length (not time), too. As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in vacuum in one Julian year. If the speed of light in vacuum is $$3 \times 10^8$$ m/s, then how many AU's are there in a LY?

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