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Light-year. It’s a measure of distance. And it’s pretty straightforward 

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– the distance light can travel in a year. But light travels ­fast. 

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One light-year is about 5.879 trillion miles 

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or 9.461 trillion kilometers. 

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So if we have kilometers and miles and inches to measure distance, why do we use light years? 

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Well, space is big. Like really big. 

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The nearest star to our solar system – Proxima Centauri – is about

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4.2465 light-years away, or 25 trillion miles. And that’s a close star. 

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So when we start talking about even longer distances, like to other galaxies, 

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we need bigger units of distance. Cue light-years.

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And by the way, it’s not just light-­years. There are also light-seconds, 

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the distance light can travel in a second, and light-minutes, how far 

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light travels in a minute. In fact, our Sun is about 8 light-minutes away from Earth, 

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which means the sunlight you can see right now left the Sun about 8 minutes ago. 

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Seriously – space is big.