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light-year (ly)

A light-year (ly) is the distance traveled by light, moving at 300,000 km per sec (186,282 miles per sec), in one year – about 9.406 trillion km (5.88 trillion miles or 63,240 AU). The nearest star, Proxima Centauri, lies at a distance of 4.28 light-years or just over 40 trillion km (25 trillion miles). A unit generally preferred by professional astronomers is the parsec.

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