If you’ve ever seen a photo from the Hubble or another stargazing telescope, you probably noticed that outer space is, like, super dark. Sure, there are tons of stars and galaxies that give off light—a.k.a., the interesting part of any space pic you’ve ever seen—but the surrounding area, space itself, is as dark as it gets. But with all those stars, etc., out there, doesn’t it seem like it should be a lot brighter? This simple experiment will help you explain to your students why and how outer space is darker than the Milky Way.
Space Is Dark & Full of Terrors
For this Demo Science science demo, all you’ll need is a flashlight and something to set it on, like a desk or table. The more powerful the flashlight the better, but don’t go too crazy with it.
Turn the flashlight on, set in on the edge of the table, then darken the room. You want it as dark as possible, so draw the shades over the windows and stuff your coat under the door to keep light from the hallway from seeping in. If any of your students turns on a screen (lookin’ at you, Kevin!), take it away immediately and smash it with a hammer.
With the room all darked up, you should be able to see a big, bright circle of light on the wall where the flashlight is shining, and that’s about it. Have your students attempt to (visually) follow the flashlight beam across the room. Then, stick your hand into the flashlight beam, about a foot from the source. What do they see now?
With your light in the beam, all they’ll see is the circle of light on your hand, with little to no light visible betwixt the flashlight and your hand. Why is the light visible on the wall and your hand, but not in the space between? It’s undoubtedly there, but why can’t it be seen?
That’s What I Call “A Bright Idea”
The light is visible on the wall and your hand because it is reflected by both of them. There’s nothing in the air between the flashlight and its targets to reflect the light, so it’s essentially invisible. This is the same reason space is dark. The sun, stars, etc. continuously shine, but their light is only visible when it’s reflected off an object like a planet or moon.