time - How long did it take for the universe to become 1 one light year? - Physics Stack Exchange
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What is a light-year and how is it used??
Light-year Definition (Illustrated Mathematics Dictionary)
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What is a light-year? – Exoplanet Exploration: Planets Beyond our Solar System
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What is a light-year? 1 light-year = 9.4605284 × 1015 meters | kiranvoid
Light-year - Wikipedia
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Light Year | National Schools' Observatory
