There’s no doubt, to anyone who’s ever experienced it, that the night sky is in fact dark. But explaining this simple fact, if you think about it deeply, raises a lot of questions that need to be addressed. (WIKIMEDIA COMMONS USER FORESTWANDER)

Why Is The Sky Dark At Night?

The darkness of the night sky was a mystery for generations of humans. Here’s the reason why.

From our perspective here in the Solar System, it makes absolute intuitive sense why we see what we do at day versus night. During the day, sunlight floods our atmosphere in all directions, with both direct and reflected sunlight coming to us from everywhere we can see. At night, the sunlight doesn’t flood the atmosphere, and so it’s dark everywhere in the sky that there isn’t a point of light at, like a star, planet, or the Moon.

But you might start to wonder a little more deeply than that. If the Universe is infinite, shouldn’t our line-of-sight eventually run into a star no matter what direction we look in? Given that there are trillions of galaxies out there, and that telescopes that are capable of seeing the faint ones that our eyes cannot, why doesn’t the light from all of them combined illuminate every point on the sky? It’s not an easy question to answer, but science is up to the challenge.

The Milky Way near the Grand Canyon, coincidentally the first place I myself ever saw the Milky Way, which didn’t happen until my 20s, as I grew up in urban areas. The plane of the Milky Way appears dark, silhouetted against the background stars located in the plane of our galaxy. (BUREAU OF LAND MANAGEMENT, UNDER A CC-BY-2.0 LICENSE)

This is a puzzle that’s troubled scientists for centuries. If you think about it deeply, it might not even make sense to you…