For those of you who wonder why I answer some questions, but pass yours by, I offer this list of possible solutions:
-Your question was so intriguing and complicated that it is taking me some time to compose a reply worthy of your obvious percipience.
-Your question was so stupid that I actually lost IQ points just by reading it.
-You didn’t promise (and then deliver) cookies.
-You didn’t suck up enough.

Dear Mad-Dog:
Love the column and love to make cookies. Sense the connection??? Anyway, my question is: Why is the sky blue? My three year old niece won’t leave me alone until I give a good enough answer. If you can get her off my back there are lots and lots of cookies for you.

Oh boy, niece removal is my specialty. No nuts in those cookies, right sweetie?

It is questions like this which make me weep for the younger generation. I feel that if all the three-year-olds in the world spent less time watching Barney spread his diseased form of mirth and more time reading my column, they, as a species, would fare much better in the future. Think of all the fun things they could discuss with their chums in pre-school...

This is probably going to mess with your poor niece’s head (but, hey, what are nieces for?) and perhaps it will mess with your head too (just so you retain enough mental functioning to enable you to bake cookies for your favorite canine columnist). I regret to inform you and your charming charge that the sky is not, nor has it ever been, blue. Neither is the ocean, in case she should hit you with that query in the future.

The blue we perceive when we look at the sky is caused by a phenomenon known as scattering of light. In order to explain how this principle works so that a three year old can understand, I offer you this description from, Light and Color, by Clarence Rainwater: “Scattering partly polarizes light from the sky. Light rays from the sun excite transverse electric vibrations in air molecules, which then scatter polarized light in directions perpendicular to the vibrations.”

Yeah, well, it’s still better than that friggin’ “I love you” song that Barney sings...

Okay, let’s try it again, only in English this time. I guess I was just giddy with the thought of cookies...

Light from the sun is, for our purposes, pure white light, which is composed of all the colors in the visible spectrum. The three primary colors of light (additive color mixing) are blue, green, and red, which, I imagine, will cause your niece some trouble as the three primary colors that she is probably familiar with are those used in painting (subtractive color mixing): blue, yellow, and red. She’s just gonna have to cope.

So, all the colors combined form pure white light, okay? When this pure white light passes through the earth’s atmosphere, it is passing through molecules of gas (oxygen, hydrogen, carbon dioxide and a few other gasses, mostly formed from the ingestion and processing of bean burritos). If there were no atmosphere, the sky would appear black, but we’d be dead anyway, so who cares? When the white light passes gas (hyuck, hyuck) or, more precisely, passes through gas, the shorter wavelengths (the blue ones) of light are scattered uniformly, pulling the blue out of the white light and making the sky appear blue.

Let’s summarize where we are at this point, okay? The air is not blue; the light passing through it is broken up so the sky appears blue. So far, so good.

When the sun is directly overhead (at noon), the light has to pass through less atmosphere before it reaches us, so less blue light is scattered and the sun appears bright yellow. As night falls, the sunlight has to pass through more and more gas molecules before it reaches us, so more blue light is scattered and lost (leaving only the longer, red wavelengths), making the sun and surrounding sky appear deep orange or red, giving us the pretty sunsets that Barry Manilow writes songs about.

The ocean (because kids will ask stuff like this) is not blue either. Shallow water will appear greenish due to the combination of the yellow reflected from the bottom and the blue reflected from the sky. As the water gets deeper, there is less light reflected from the bottom and the ocean appears deep blue.

By way of giving an example closer to home, people with blue eyes actually have no blue pigmentation in their eyes. The iris appears blue because the light which reflects off it is scattered. The presence of melanin (a brown pigment) in the eyes absorbs light and reflects back brown. All eye colors are the result of various concentrations of melanin in the iris.

Here is a nifty experiment that you can try with your niece. All you need is a freshly exhumed corpse, a can of Cheez-Whiz and 17,000 volts of electricity.... No, wait, wrong experiment. You’ll need a glass of water, a lightbulb, and a few drops of milk. Look at the lightbulb through the water, then add a few drops of milk to the water and look at the lightbulb again. See how it changes as light is scattered? I haven’t actually tried this experiment, but I hear that it’s more fun than an all night faith-healer marathon on one of those religious channels.

If your niece still isn’t getting this, you just have her write me a letter, I’ll straighten her out...

My milk is getting warm, where are those cookies?

I have a question. I read somewhere that when someone gives blood they, on an average, save the lives of two people. And you can give blood once a month, twelve times a year. So I can save an average of 24 lives. Does that mean I can kill 23 people and still come out ahead?


Mad-Dog: Master of the Universe
123 Ball Hill Rd.
Milford, NH 03055
Mad-Dog e-mail hotline:

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