Why is the sky blue?

JohnSnownw · Sep 13, 2007, 10:41 AM

Light refracting off of nitrogen particles. That's why. Sort of.

The blue color of the sky is due to Rayleigh scattering. As light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of the red, orange and yellow light is affected by the air.

However, much of the shorter wavelength light is absorbed by the gas molecules. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky. Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue.

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Blue Sky - Why is the Sky Blue?

NeedKarma · Sep 13, 2007, 10:41 AM

Blue Sky - Why is the Sky Blue?

Howstuffworks "Why is the sky blue?"

J_9 · Sep 13, 2007, 10:42 AM

A clear cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light. When we look towards the sun at sunset, we see red and orange colours because the blue light has been scattered out and away from the line of sight.

You can read all about it here.

Why is the sky Blue?

JohnSnownw · Sep 13, 2007, 10:45 AM

Also:

When we look up at the sky, the red cones respond to the small amount of scattered red light, but also less strongly to orange and yellow wavelengths. The green cones respond to yellow and the more strongly-scattered green and green-blue wavelengths. The blue cones are stimulated by colours near blue wavelengths which are very strongly scattered. If there were no indigo and violet in the spectrum, the sky would appear blue with a slight green tinge. However, the most strongly scattered indigo and violet wavelengths stimulate the red cones slightly as well as the blue, which is why these colours appear blue with an added red tinge. The net effect is that the red and green cones are stimulated about equally by the light from the sky, while the blue is stimulated more strongly. This combination accounts for the pale sky blue colour. It may not be a coincidence that our vision is adjusted to see the sky as a pure hue. We have evolved to fit in with our environment; and the ability to separate natural colours most clearly is probably a survival advantage.

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Why is the sky Blue?

geographymatt · Sep 13, 2007, 11:09 AM

Wow that's really interesting takes a bit to get your head round, and its much more physics than I expected. And you've also explained why the sky turns different colours at sunset and sunrise which is a bonus. Also very interesting what was mentioned on how our eyesight has adapted to see these colours, and how this might appear different according to adaptation and survival, for example what a bird of prey migh see!

gallivant_fellow · Sep 19, 2007, 08:20 PM

Me to my step dad when I was little.

"Why is the water blue?"
-"Cuz it reflects off the sky."
"Then, why is the sky blue?"
-".......because it reflects off the water."

The sad part is he was probably serious. But yeah, J9 and Johnsnow are right.

br_hjs · Sep 19, 2007, 10:14 PM

My dad told me that even in the day its actually black but the sun or something makes it look blue... I don't know if its true because a lot of times my dad doesn't know what he's talking about but that's what he told me

Clough · Sep 19, 2007, 10:23 PM

Quote:

Originally Posted by gallivant_fellow

Me to my step dad when I was little.

"Why is the water blue?"
-"Cuz it reflects off the sky."
"Then, why is the sky blue?"
-".......because it reflects off the water."

The sad part is he was probably serious. But yeah, J9 and Johnsnow are right.

I like this "reflective" answer!

Why is the sky blue?

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