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The color of night

Really. That would be the general color of the night sky if the universe wasn’t expanding. You’ve probably never wondered why the night sky is black. “No sun,” you point out. “Duh.” But it’s not that simple. Every single bit of sky is full of stars, all blazing away. The light may take a long time to get here, but it does get here. So, on that basis, the night sky ought to be a carpet of light from all those uncountable stars. But since the universe is expanding, they’re all moving away from us. Since they’re moving, there’s a Doppler effect and the light is shifted to other wavelengths. The further away they are, the more it’s shifted, until all their light shifts right out of the visible range. And that’s why the night sky is dark except for the few stars whose light is still visible.

So the next time you’re admiring the night, look at the dark, too, and remember that you’re watching the universe grow.

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