In simple terms, a nebula is a large incomprehensibly massive cloud of dust and gas floating in the depths of outer space. In even simpler terms, nebulae (the correct plural of nebula) are the beautifully colored, abstract-expressionist-looking forms in some of the most popular deep space photographs ever taken. (See below.)
Far more than simple floating blobs of space dust, nebulae come in three varieties: emission nebulae, which emit their own light and seemingly glow; reflection nebulae that reflect light from other sources like nearby stars; and absorption nebulae, which block light, sometimes called “dark nebulae”. This last type is perhaps the hardest to imagine, as they are reverse-invisible. This handy dandy Demo Science science demo will help students get a better idea of what an absorption nebula looks like (or doesn’t).
Better Nebulae Than Never
For this experiment, you’ll need just a handful of supplies. First, a lamp, flashlight, or other fairly powerful portable light source. Second, a sheet of white paper, the bigger the better—maybe see if you can get some truly huge sheets from your school’s art teacher. (It has to be paper paper, though—a sheet of tag board won’t work). Third, a bunch of powdered…anything. Could be sugar, could be chalk dust, pretty much whatever you can find that’s in fine particulate form. You need, specifically, a lot of the stuff, whatever it is(for simplicity, we’ll just call it “powder” from here on out). Fourth, a few volunteers to assist you (don’t pick Kevin). And, fifth—not 100 percent necessary but you’ll probably want it on hand—a vacuum to clean up the mess you’ll inevitably make.
Because absorption nebulae are clouds of dust that block light, you need to recreate that very thing in the classroom. Have your student helpers hold up your big ol’ sheet of paper (maybe rotate through your volunteers so all the kids can properly see the experiment performed) and turn the lamp on behind it—that is, with the paper between the light source and your observers. Station the lamp about a yard behind the paper.
Then, turn out the rest of the lights in the room. Give everyone enough time for their eyes to adjust, then start tossing handfuls of your powder into the space between the light and the paper. It will undoubtedly take a few tries to get it right, but when you do, you’ll have created a floating cloud that will block the light from reaching the paper. The resulting shadow the students see from the opposite side will more or less mimic what absorption nebulae look like in deep-space photography.
Important Safety Note
Be careful not to toss any powder onto the lamp itself. Many finely-powdered substances are highly flammable/combustible in high enough concentrations, even if the source of said powder is generally not on its own. (Regular granulated sugar, for example, won’t burst into flame if touched with a match, but grind it down fine enough for it to float in the air, and it will fire up right quick.) Unlikely though it may seem, just the heat of your lightbulb may be enough to touch off a blast. When dealing with combustible dust, ignition can come from improbable sources.
The more powder you toss into the air, the more the potential for disaster grows. If a little bit of your fine powder flares up, NBD; if half the classroom is hazy with the stuff, a fire could be catastrophic. Combustible dust mitigation is important for safety in many industrial settings, so your classroom should be held to an even higher standard, what with all the smelly little kids running around and all. Keep a fan on hand to clear the air when you’re done.