Hi Stanley,

My friend's children once asked me this same question!

Part of the reason why the sky in between the Moon, stars, and planets looks black at night is that outer space is very empty. There isn't much out there to reflect the light from the Sun or the stars. People often refer to space as a vacuum. This doesn't mean that it is like your vacuum cleaner at home, though! What this means is that the density of particles (atoms, ions, electrons, microscopic dust, etc.) is generally extremely low. For example, in the solar wind, the density of particles (mostly electrons and hydrogen ions) is about 3-20 particles per cubic centimeter. A cubic centimeter is about the size of a sugar cube, which has millions of molecules in it. If you could take away all of those molecules except for 3, the space formerly occupied by the sugar cube would be pretty empty!

The other part of the reason why the sky is black at night is that the stars are very far apart. Many of the stars we see in the sky at night are as large as our Sun, and some of them are even bigger. However, they are so very far away that they just look like tiny pinpricks of light in the sky. The intensity of sunlight falls off as the square of the distance away from the Sun, so the further you are away from the Sun, the smaller and dimmer it appears. This works the same way for the stars too. Imagine you have a single, dim lightbulb (our pretend star), such as a Christmas tree bulb, at one end of a very large, dark room, like your school gymnasium with all of the lights turned off (our stunt double for "outer space"). An observer at the opposite side of the room might be able to see the tiny pinprick of light made by the lightbulb, but it is so far away that the rest of the room remains dark.

Kris