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Speaking of Nature

Nature’s fireworks

24 point deck head

Today is the Fourth of July and many of us are gathering together for cookouts, fun and fireworks. I don’t know about you, but I love fireworks and I can remember many wonderful evenings with my family at the Amherst fireworks displays that were held at UMass-Amherst. As far as I’m concerned, the fireworks are best when they are big and colorful.

Before fireworks were invented, the only way that we humans could look up and see colors in the sky was if we were lucky enough to see a rainbow. And, as luck would have it, we have had some very stormy days this week and those storms came at just the right time of day to create rainbows. Still, rainbows are rare, wonderful and shot-lived.

The secret behind rainbows lies in a phenomenon called refraction. Ever since humans have been playing around with eye glasses, magnifying glasses, telescopes, and anything else that has a lens in it, we have be aware of the idea of refraction. Basically, refraction is the bending of light by materials that are transparent to light. Glass does this, as does plastic. But, before humans had invented either of these things there was another common substance that is good at refracting light — water.

Now light is a peculiar thing. Sometimes it acts like a wave and other times it acts like a particle. When people think of the particle idea, they often talk about little packets of light energy called “photons.” All photons are the same when it comes to the speed at which they travel, but it turns out that not all photons are the same when it comes to the frequency at which they vibrate and this is where the magic of rainbows comes from.

The light from the sun contains all sorts of different photons and when they are all blended together our eyes see the color we call “white.” However, if you were to look at one particular photon you would see a very specific color. So, photons are all just as fast as one another, but they are all different colors.

So imagine a tour bus filled with photons all on a trip to planet Earth. This particular tour bus comes in on a day when it happens to be raining, but it is able to zoom in under some clouds because of the angle it approached the planet. But even though it was able to avoid the clouds, it was unable to avoid a raindrop falling underneath it. And so, the bus driver only just realizing that his bus has no brakes, the bus plows into the raindrop.

The bus dissolves instantly and all of the photons inside it start ricocheting around. They are still traveling at the same speed, but because they vibrate slightly differently they ricochet at slightly different angles. When they finally leave the raindrop, they go their separate ways and, if lots of them do this, they can create beams of colored light.

So when it rains late in the afternoon, at a time when the sun is low on the horizon, the sun can get under the clouds and hit the raindrops. When millions of different drops send out millions of different beams of light, we see the effect as a rainbow.

If you don’t want to have to wait for a rainy day, you can make your own rainbow anytime you want. All you need is a hose with a “mister” setting. Go out into the lawn on a very bright, sunny day and turn until you can see your own shadow. Then, while looking at your shadow, spray the hose at the ground and you should see your very own rainbow.

So here’s what I want you to do. Get some paper and crayons, or colored pencils, and draw me a picture of a bus filled with photons on vacation. I imagine that breaking into a rainbow is actually quite a lot of fun, so don’t be afraid to show the photons smiling with excitement. Then send me a copy of the picture and I’ll post it on my website.

Bill Danielson has worked as a naturalist for 16 years. In that time, he has been a national park ranger, a wildlife biologist and a field researcher. He currently works as a high school chemistry and biology teacher. His Speaking of Nature column runs weekly in The Recorder, except for the first Thursday of each month, which is when his Kids and Critters column for young readers appears. To contact Bill, or to learn more about his writing, visit
www.speakingofnature.com

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