Bad Astronomy: Misconceptions and Misuses Revealed, from ...

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Blue Skies Smiling at Me:
Why the Sky Is Blue
I n
the course of every parent’s life there comes the inevitable
question from their child: “Why is the sky blue?” As we grow
to adulthood we sometimes learn not to ask such questions, or we
just forget how. The vast majority of adults in the world have seen
a clear-blue sky tens of thousands of times, yet only a few know
just why it’s blue. If you don’t know, don’t fret: the question baffled
scientists for hundreds of years. Nowadays we are pretty confident
that we know the real reasons, but I’ve never heard of them
being taught in schools. Even worse, a lot of web sites I’ve seen
give an incorrect answer to the question. College textbooks on
optics and atmospheric physics cover the topic correctly, but who
wants those lying around the house?
Well, I do, but then I’m a huge geek. I’m operating on the principle
that you are a normal human. And, lucky for you, the reason
behind the blue sky isn’t all that complicated, and it can be easily
explained, even to a five-year-old. Let’s start with some of the
incorrect reasons given for the sky’s cerulean hue.
Probably the most common idea is that the sky is blue because
it reflects the blue color of the ocean. However, a moment’s reflection
(ha-ha) reveals that this can’t be right: if it were true, the sky
would look bluer when you are sailing on the ocean than when you
are on land. But that’s not the way it happens. It still looks just as
blue from say, Kansas—a healthy hike from the nearest significant
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