Why Is the Night Sky Dark?
Looking at the stars takes you back through time. All the way to the beginning.
By Charlie Wood
You might have wondered why the sky is blue. Or what gives sunsets their brilliant red. These bright colors stick out in the natural world and beg for an explanation. But have you ever wondered why the night sky is black?
The question barely makes sense the first time you hear it. “It’s like asking why is water wet,” says Will Kinney, a cosmologist at the University at Buffalo, currently on sabbatical at Stockholm University in Sweden. But for centuries the darkness of the night sky had astronomers stumped. They called the puzzle Olber’s Paradox.
Distant stars look weak, and very distant stars shine too dimly for you to see with your eyes. But when space telescopes like Hubble peer deep into the darkest spots of sky, they uncover bunches of incredibly faint galaxies. And the deeper they look, the more they find. If the universe went on forever with stars sprinkled evenly throughout — as many early stargazers assumed — the night sky would be full of so many points of light that it would never look dark.
“The fact that the stars are everywhere makes up for the fact that some of the stars are far away,” says Katie Mack, an astrophysicist at North…
