Have you ever seen a rainbow? Have you walked into a room that has a chandelier hanging from the ceiling and seen tiny patches of colored light shining on the walls? Have you noticed colors swirling on a soap bubble or on the surface of an oily puddle on the street? When you've seen these colorful sights, you've been watching the behavior of light.
The "white" light that illuminates our world is made up of seven different colors. Certain things, such as a droplet of water, can break white light up into its parts. When that happens, you see a rainbow effect.
The spectrum -- the range of different colors mixed up in white light -- becomes visible. British scientist Sir Isaac Newton, who lived from 1642 until 1727, made up the word "spectrum." It comes from the word "specter," which means ghost. Newton must have thought that the colored bits of light that fan out of a ray of white light looked like little ghosts.
Here's a funny name that will help you remember the colors in the spectrum: ROYGBIV. It's made up of the first letter of each of the colors: red, orange, yellow, green, blue, indigo and violet. Indigo is a color somewhere between blue and purple. These colors always appear in the same order.
Light moves through the air in rays that travel in a straight line. But when light meets objects, it acts in several ways. It might be soaked up or absorbed. It might be reflected or bounced back. Or it might bend or refract.
Two things are necessary to produce a rainbow in the sky: sunlight and water in the atmosphere. If rain showers fall on a sunny day, the conditions are right for rainbows, and you should keep your eye out for them. A rainbow is the result of both refraction -- the bending of light -- and reflection.
When light passes through a water droplet in the air, each color in the light bends a little differently. Violet bends more than blue; blue bends more than green, and so on. Red bends least of all. If sunlight enters a raindrop at just the right angle, its colors fan out and spread. But that's not the end of it. The fanned-out colors reach the back of the raindrop. They reflect, or bounce off, the back of the drop. Then the reflected light gets refracted again. Sounds complicated, doesn't it? By producing this effect, each raindrop sends a fan of color out into the air.
The colored light projecting from millions of raindrops in the sky combines to form the shining arch of color we call a rainbow. Crystals on chandeliers, the surfaces of a diamond and the filmy layers of a soap bubble or a slick of oil on a puddle cause rainbow effects the same way. They bend, or refract, light so that it breaks up into the spectrum.
Depending on the conditions in the atmosphere and on where you're standing when you see it, a rainbow can look different. Sometimes, you can only see part of an arch; sometimes, you see a complete one. Sometimes, you might get really lucky and see a double rainbow!
You can make your own rainbow by spraying a fine mist from a hose on a bright day. It will be easier to see your creation if you look through the mist against a background of dark trees. This trick works best if you do it early in the morning or late in the afternoon, keeping your back to the sun.
Often, only a few of the colors of the spectrum seem visible in a rainbow. Actually, all the colors are there, but they blend into each other. It can be especially hard to tell the difference between blue, indigo and violet. But whether you're lucky enough to see a complete arch, or just part of one, a rainbow is one of nature's most beautiful sights.
On a sunny day, you can make a rainbow inside. You'll need a shallow baking dish, some water, a small mirror and a sheet of white paper. Put the pan on the floor directly in the sunlight coming in from a window. Fill the pan almost to the top with water. Put the mirror in the water with its reflecting part facing up. Hold the mirror at an angle. Have a friend sit opposite you and hold the piece of paper up to catch the light reflected from the mirror. You may have to fiddle around a bit to get the angles of the mirror and the paper right, but eventually you'll "catch" a rainbow right on the white paper. Look carefully to see all seven colors in the spectrum. You can read about this experiment and many others in "Science Sensations" by Diane Willow and Emily Curran (Addison-Wesley; $8.95), a book of activities from the Children's Museum in Boston.
Catherine O'Neill is a freelance children's writer.