At day camp yesterday, the sprogs (and their fellow campers) had a visitor:
Elder Free-Ride offspring; She was an astrophysicist. You know what that is, right?
She talked to us about studying light that comes from space, and all the different kinds of light there are traveling across space. There’s infrared, and ultraviolet, and even X-rays. And, of course, there’s white light that we can see with our eyes.
While there are many different kinds of lights, there are only some colors of light that our eyes can detect. A bunch of those are actually mixed together in white light. You can separate them with a prism.
The astrophysicists was telling us about separating the light coming from space. Because you wouldn’t want to put a big prism into orbit, they made thin sheets with many, many, many little prisms in them.
Dr. Free-Ride: A diffraction grating?
Elder Free-Ride offspring: I think so.
Younger Free-Ride offspring: Then we did an activity. We each got a cardboard tube and a piece of the degrading thing.
Dr. Free-Ride: The diffraction grating?
Younger Free-Ride offspring: Yeah, thin sheet with lots of little prisms. We got a silver sticker with a hole in it. We put the diffraction grating under the hole in the sticker, then covered one end of the tube with it.
When I looked through, it looked like a prism with lots of light all over. When I held up my finger at the end, it looked like a flower with reflections all around it.
Then we covered the open end up the tube with a sticker. I looked through and saw nothing.
Dr. Free-Ride: Because no light was getting into the tube?
Younger Free-Ride offspring: Yeah. And then we poked a hole in the middle and looked through. We could see a little rainbow on the side of the tube. Then we poked one more hole and looked through. Then three more and looked through. She said the smaller the holes, the better the rainbows.
We went outside and looked at the blacktop and didn’t see many rainbows. But then we pointed it at other objects that were red or green or blue and saw really good rainbows.
Elder Free-Ride offspring; The prism splits the white light into all the different colors that make up white light. Colored light is the opposite of colored pigments. If you mix lots of different colors of pigment, what you get is darker and darker. But if you mix red, orange, yellow, green, blue, and purple light, you get white light.
This site describing how to make a simple spectroscope seems pretty similar to the activity the sprogs describe.