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Why Is The Sky Blue?
Stumped? Here's how to answer those Frequently Asked Questions (and sound like you know what you're talking about).

By Jonn Salovaara
Date 08/15/01

My seven-year -old son still occasionally asks the sort of question that younger kids are famous for, the kind where you probably ought to know the answer but don't exactly. You start to explain why leaves turn colors in the autumn and then realize you're not so clear about it. "Well it all has something to do with chlorophyll," you mumble.
Even if you manage to give a fairly clear answer to such a question, you frequently get follow-ups that test your knowledge of fine points. For instance, you think you know the whole Groundhog Day routine. The rodent sees its shadow if it's sunny and goes back in its hole: this means six more weeks of winter. The rodent doesn't see its shadow because it's overcast on that particular February 2, he stays out, and this means an early spring.

Your child asks, "How early a spring?" or "Why does the weather on one particular day make any difference?" or "Who decided on the groundhog in Punxatawny, Pennsylvania? There are groundhogs in other places. Do they predict for those places?"

At a certain point, I find myself using this expression, borrowed from Tevye: "It's a tradition." Or this, from Chicago's Mayor Daley: "It's a convention." Or, the ever-popular, "I don't know."

But you're the dad, right? You're supposed to know everything.

So to help you prolong your child's comforting illusion about your expertise in science, moral philosophy, religion, and beyond, we offer the following selection of kids' questions (with some answers!).

What is thunder?
When your kids are ready for something besides angels-on-the-conga-drums, you explain that a flash of lightning heats the air around it. The hot air crashes into the cold air and the soul-stirring bang-rumble of thunder is born.

You see the lightning before you hear the thunder because the speed of light is way faster than the speed of sound. (If you can remember the exact speed of either of these, your brain cells are holding up a lot better than mine.)

In case you've forgotten since your own childhood: the rule of thumb is five seconds per mile when you start counting after you see the flash. That is, if you count five seconds between the lightning and the thunder, the storm is a mile away. Most kids would like to keep it there.

Why is the sky blue?
So what color would you make it? The sky is blue because if it was green it would be harder to distinguish from the grass in landscape paintings. Besides that, it's only blue about one out of every three days this time of year where I live. Why is the sky gray? Because humans were meant to suffer from seasonal affective disorder?

It seems the real answer has to do with which part of the sun's light gets scattered by dust particles or gas molecules in the atmosphere. When the sky appears blue, it's because the light rays with shorter wavelengths (the blues) are being scattered. If there is a lot of dust in the air, especially big particles, then a wider variety of wavelengths, both long and short, are scattered, and the sky appears faded, white, or hazy, as a result of mixing those various colors of light.

Where does the goldfish go when it dies?
Well, anywhere you put it, actually. At our house this was down the toilet which might have made it a perfect occasion to remember some details of the sewer system gleaned from a Magic School-bus episode.

Since those are the kind of details that tend to slip from memory, you may prefer a discussion of decomposition and the value of fish as fertilizer, explaining that this is something purportedly taught to Europeans by Native Americans. You can go just about anywhere from here: the problem of corn mono-culture in the world today, the varieties of civilizations and their interactions....

On the other hand, this question may signal an interest in the possibility of an afterlife. Your kid may want to know more than the details of waste disposal.

A more psychologically correct response might be to emphasize the sadness we're all feeling at the loss of this loyal, entertaining pet, and to suggest some kind of ceremony to mark his or her passing.

You might also mention the concept of the soul and its possible migration, whether to heaven or into some other mortal form. Who knows? The goldfish may come back as a tilapia.

Why is his skin a different color than mine?
As we adults say, echoing Professor Bindon at the University of Alabama, "The primary determinant of skin color is the amount, density, and distribution of the pigment melanin in the skin." Thanks, Doc: that's saying your skin is dark because you've got more dark stuff in your skin. Why do some people have more? It might be best to stay at the level of "Some of his ancestors came from a place where most people have that color of skin."

If you want to get into the more contentious part of the why, there are a couple possible hypotheses. More melanin may help prevent skin cancer from exposure to ultraviolet light: this could mean natural selection for darker skin in areas of the world where people are exposed to high levels of UV.

But what selects for lighter skin in other areas of the world? It may be that lighter skin was selected by nature because light skin does a better job making Vitamin D from sunlight. In some places (like parts of Europe), high latitude and low altitude combine to limit the amount of sunlight getting to people. They need that Vitamin D-producing boost. (Clothing and some tricky things about Vitamin D have to be factored into all this.)

When my own kids asked, I said, "That's the way some people are," and this really seemed to be enough.

What causes earthquakes?
People on the West Coast already know this one. For the rest of us, I have a story.

Once I was at this costume party. A guy was arriving in drag, wearing a hoop skirt, and the skirt got caught in the doorway. He was stuck for a minute until he pushed hard enough, overcame the resistance of the hoops and shot into the room. That's what causes earthquakes.

Remember plate tectonics? This is the idea that the outer surface of the earth is divided into plates that sort of float independently on the earth's mantle. Sometimes the plates bump into each other, sometimes they dip beneath one another, and sometimes they slide against each other along a fault-line. This sliding can happen at a very slow rate, a couple centimeters a year, without a problem.

Remember plate tectonics? This is the idea that the outer surface of the earth is divided into plates that sort of float independently on the earth's mantle. Sometimes the plates bump into each other, sometimes they dip beneath one another, and sometimes they slide against each other along a fault-line. This sliding can happen at a very slow rate, a couple centimeters a year, without a problem.

Sometimes though, a part of one plate (the hoop skirt) will sort of get caught on a part of the other plate (the doorway) while the rest of the plate (the guy inside the costume) continues to move. Eventually the force builds up enough that the friction is overcome and there is a sudden movement of one plate past the other (the guy shooting into the room).

The force of that sudden movement sends waves though the rock of the earth's crust. Those are the waves that can knock over buildings, break apart gas-lines, and do all sorts of things better left undone.

If you don't have a hoopskirt handy, you can demonstrate this so-called elastic rebound principle to your kids using blocks, sandpaper, and a rubber band. See the Web site ( of the Exploratorium in San Francisco (where else?) for details.

Why is there war?
If your kids come anywhere near a radio or television news program, this question is going to arise, along with a fear that bombs may soon start dropping in their own neighborhood. I start my response by assuring the child that the United States is so powerful, no country will dare to attack it.

Having thus allayed some fears (while inadvertently supporting continued astronomical "defense" spending), I feel better about a combination of guilt-tripping and buck-passing in the rest of my response.

I mention my kids' inability, nearly incessant, to get along with each other. "If two people sharing a common ancestry, language, economic status, and even parents can't get along, why would you be surprised that there is war in parts of the world where striking differences and divisions exist?" I ask rhetorically.

"The reason there is war is because people think they can't settle their differences any way other than fighting. You fight with your brother and you've got to learn to talk to him instead. Use your words. Once you learn to talk to your brother instead of fighting, you'll be ready to help find talking solutions for problems in these other parts of the world. We're counting on people like you to help prevent war in the future."

The downside to this response is that a sensitive kid will begin to feel vaguely responsible for most of the world's trouble spots. The upside: your kid considers a diplomatic career. Is that an upside?

What is tofu?
I tell my vegetarian ten-year-old daughter that tofu is a rectangular albino sea creature slaughtered in great numbers for the sake of oriental cuisine. There's nothing more inspiring, I say, than the sight of a school of free-range tofu swimming, or at least squirming, in the wild.

She knows better. She knows it's got something to do with beans. If your child is willing to eat tofu, you might want to leave it at that. If you give greater detail, you run the risk of turning off the kid's appetite.

Tofu-grade soybeans are soaked and then mashed, the resulting mash is boiled in water and then filtered, and the liquid filtered off is called soymilk. The soymilk is then separated into curds and whey, solid and liquid, by the introduction of a "coagulating agent," for instance, sea salt. The solid part, the curds, are pressed and shaped into those cute little blocks we can find floating in water in their store packages. Hence a common menu alias for tofu: bean curd.

How come you can use bad words and I can't?
It is going to happen. It probably already has. They catch you violating your own principles, especially your hard and fast rule against cursing and swearing. There are ways to wiggle around in these "Do as I say, not as I do" situations.

You can try: "Well I'm a grownup and you're not," which should immediately bring up the question, "Well why do grownups get to do it then?" You fire back: "Grownups know when it's appropriate to say bad words and when it isn't. We normally wait until we do something like drop a bowling ball on our big toe. Children who are allowed to use such words tend to do so indiscriminately, for the sheer joy of hearing them come out of their mouths, at the drop of a hat."

Pluckier youngsters will quibble with this response, promising to be discreet, so I recommend adding the "I said so" codicil to this debate. "I don't want to hear you saying this, ever; got it?" "Yes, Dad." Then they run off, thinking, "Well, as long as he doesn't hear me...."

Jonn Salovaara, a writer who lives in Chicago, has two children ages 7 and 11. He reviews books for

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