Question: why is space dark

Dave Constable answered on 13 Mar 2020:

A really good question!

Space is dark because it mostly doesn’t have anything in it. The space between planets and solar systems is mostly really empty of particles. The reason the sky on Earth is blue during the day (if it’s not cloudy!) is because light from the sun is scattered by particles in the atmosphere. At night, the sun isn’t shining on that part of Earth, and so there isn’t a lot of light to scatter. In space, there’s not a lot of particles to scatter the light from the stars.

Also, most of the electromagnetic radiation (which visible light is part of) that we can detect here on Earth has been redshifted beyond the part of the electromagnetic spectrum we can see. This happens because the universe is expanding, and so the stars we can see are moving away from us. The radiation is shifted toward the microwave region, and so, we can see something called cosmic microwave background radiation, which is really bright in every direction.