Stephen van fielder, age 10, of Dorval, Quebec, Canada, for his question:     

How does a prism make colors?     

You may find this hard to believe, but all those rainbow colors are there in every sunbeam    also in every ray of light from a lamp or a bulb, a candle or a campfire. Most of the time we do not see them because they blend together to make themselves invisible. But a little glass prism, shaped like a stretched pyramid, can separate a blended sunbeam and make it show its separate colors.

One reason why light is so hard to understand is because we cannot see it. Even if we could, it moves too fast for our eyes. Besides, it carries little bundles of energy too small to imagine and it pulses along in tiny waves that make a miniature molehill look like a mountain. But we can try to imagine its antics    and then strain our brains to figure out what happens when a beam of light strikes a glass prism.     

Imagine a zillion straight lines running this way and that way across every corner of a roam. They zoom back and forth fast enough to circle the equator seven times in a single second. They bounce back from this and that solid surface and fan out in all sorts of different directions. These frantic antics are invisible to our eyes, but they go on wherever there is light.     

It also is hard to imagine the pulsing little wavelengths of light. That is, unless you can picture one inch sliced into 250 million equal pieces. Each one of these tiny lengths is called an "angstrom"  and the wavelengths of light are measured in angstroms. Those that we can see in rainbow colors range from 4,000 to 7,000 angstrom units. The shortest ones are the violet blues in the 4,000 range. Greens have longer wavelengths, the yellow and orange are still longer. The red rays have the longest wavelengths in the 7,000 angstrom range.     

A glass prism creates a rainbow by bending the blended wavelengths of a sunbeam at different angles. Its sloping side bends the shorter wavelengths the most and the longest ones the least. This separates them and fans them out in different directions., When they are separated from their invisible blend, they have to show their true colors. And they must arrange themselves in a special order to match the different wavelengths.

The shortest blue rays are sorted into their colored bands, then the greens, the yellow and orange tints. The reds appear at the opposite end from the blues, because their longest wavelengths are bent the least.

This pattern is called the visible spectrum. Its colored bands match those in the rainbow because all light is a blend of the same wavelengths. Sometimes an oily puddle also separates the colors hidden in invisible light. This pattern may be a bit blurry, but its spectrum colors copy the orderly bands created by a prism.