Why the Sky is Blue.

For an abbreviated version of this entry that more quickly gets to “the science involved” go ahead and skip right on down to paragraph 4.

From a young age I was taught that having a healthy curiosity was a good thing, a skill to be honed and perfected. Curiosity helps drive intellect, leads to experimentation, and thus new discoveries. This being said, I have, as I’m sure you have at some point, wondered why the sky is blue. The old [and easy] explanation people have always given is one of a perpetual paradox: The sky is blue because it reflects the ocean; the ocean is blue because it reflects the sky. When I was younger, it seemed a good enough excuse; when you observe the ocean at sunset, do you not see the sun setting below the horizon as well as above. When you look at a puddle, can’t you sometimes distinguish clouds reflected in it? But if this is the answer, as I doubted also from a young age, where does this eternal reflection begin and where does it end?

(some right reserved, site of original picture: http://www.flickr.com/photos/jamtea/1304114060/)

Dr. Steven Loiselle was the first, other than Bill Nye the science guy, to attempt the rough explanation as to the color of the water and sky. I’m happy to say he succeeded where none before him have… Let’s consider a white piece of paper. Why is it white? Almost every person I ask would stare at me as if I am an oaf, squint their eyes, wrinkle their nose while they examine me from head to toe, consider the fact that maybe I am simply slow for asking such an undemanding question, and then proceed to explain to me the concept of how white paper lacks color because it reflects all the light that is incident upon it, whereas black things are black because they absorb all the light incident upon it. They might even go on to explain how things of color retain that specific color because its specific chemical make up allows it to selectively absorb and reflect only certain colors. See where I’m going with this?

Though I am sure by now you must have figured out exactly what I am going to say, I will proceed for my own benefit. To keep your interest, though, I will take you on a journey through space and time. Still want to read? ’ Thought so. You’re Neil Armstrong stepping onto the moon. What do you see when you look up at the small little ball we call earth; think big picture, not just the earth, but everything. In front of you lies the vast open, black, empty vacuum we call space, and billions of tiny little balls of burning gas. Beautiful, isn’t it? But wait. The sky is black. Oh, it’s the moon, never mind… it must always be night on the moon, right? Now it’s my turn to scrutinize you, wrinkle my nose and look you up and down if you are actually really accepting this explanation. NO. Walk on a little further and you may see a huge, bright, ball of flaming white light we call the sun, peaking out just to the other side. SO. Not only is the sky black, but the sun is white. I must just be pulling your leg. Ah, sadly, no. I am not it a joking mood today. What do we know is different on the moon? Why can’t we just simply pack up our things, mozy on over there in our little spaceship, and colonize the moon? Oh, there’s no oxygen. Oh that makes sense. The earth has an atmosphere that allows us to breathe… thankfully.

So this is what we know: The sky is blue, the ocean is blue, colors are created by emission and reflection of light at certain wavelengths (fancy restatement), on the moon the sky is black and the sun is white, on the earth the sun is yellow-ish, the moon lacks an atmosphere, and the earth has an atmosphere! It’s a lot to handle, I’m sure, but nothing you couldn’t deduce on your own. So how does this all fit together? As Dr. Loiselle explained so indulgingly to me, clouds and other molecules in the air [up high] change the optical properties of the atmosphere, and thus the color of the sky. The sky is blue because of the photons that arrive at these molecules in the atmosphere, which then spectrally scatter the photons that arrive. Certain wavelengths of light are scattered more than others, like lower wavelengths, such as blue. This is the fancy way of saying that light enters the atmosphere and that blue light is bounced off the molecules in the atmosphere and that is why the sky is blue.

Water is blue because of much the same reason, which makes sense when you consider the fact that clouds are made up, mostly, of water, the same molecules that make up WATER! The view from the moon is black because of the lack of an atmosphere to scatter light. If I’ve managed to steal your attention and you would like to learn more… stay tuned…. Next time I’ll address the even more trippy idea of why sunsets are such beautiful colors, why the sun is white on the moon and yellow on earth, and also why water in a glass is clear, while in the ocean it is blue, or in other areas appear yet other colors!!!!