When you look at the night sky, in the mountains, away from any light pollution, the stars are super vibrant. Yet, astronauts say that when you orbit the night side of Earth that you experience a profound darkness. Why wouldn’t the stars pop out to you even more when in outer space?

The stars DO pop. Way more than anywhere on the ground. But even removing all light pollution, starlight is still ridiculously less strong then even a night-light so the astronauts aren’t going to be working by star-light. No, it’s not the sort of total darkness you’d find in a cave, there’s still stars and the astronauts can still see them. The thing they’re commenting on is that there’s zero background glow from some fraction of sunlight reflecting off the atmosphere.

The stars in space are even more brilliant than on the ground. The blackness between them is also blacker, completely devoid of light.

You have to be in a really dark setting to see the stars. You can’t have a giant glowing sunlit earth beneath you, and you can’t have sunlight shining on the space station lighting it up. You can’t even have the cabin lights illuminating the inside of the space station while you look out the window. You’ve gotta be in the dark. Which is actually relatively uncommon in space.

If it’s not dark, the light of the stars is washed out by the light of everything else you see. That’s really what causes the difference, not the atmosphere.

I mean, they don’t turn all the lights on the ISS off everytime it goes around the earth.

So while they might be on the dark side of the earth, their eyes are still adjusted to the lights that they’re using to work, and therefore cannot see the stars very well.

Two reasons:

• The ISS is lit, and if the astronaut is spacewalking they’ve got the area they’re in spotlighted so everyone can see them in case of emergency
• The ISS moves in and out of the night side too quickly for the eyes to adjust.