nothing but blue skies

We woke up to snow this morning - not much, maybe 0.5" at the most. In true NM fashion, it was almost completely melted by the time we went to Mass, and was totally gone by the time Mass was over, about noon. It was a gorgeous day - dusting of snow still on the Sandias, warm enough that even I didn't need a jacket outside, and a few clouds in bright, bright, blue skies.

I was out for a run this afternoon - couldn't pass up the amazing weather - looking at those blue skies, and the obvious geek girl blog post crossed my mind.

What makes the sky blue?

So, I'm going to geek out on you tonight, and explain this. Hopefully you weren't looking for me to offer any deep non-scientific thoughts this evening. ;-)

What makes the sky blue... is a phenomenon known as Rayleigh scattering. Basically, light from the sun enters the atmosphere and is scattered by molecules in the atmosphere. To get technical, this scattering is inversely proportional to the light's wavelength raised to the fourth power. That pretty much means that, the shorter the wavelength, the greater the scattering effect.

Blue light is on the shorter end of wavelengths in the visible region of the spectrum, and so blue light scatters more when it enters the atmosphere - it scatters all over the sky, causing it to appear blue. The yellow/red wavelengths are not scattered as strongly, and so travel a straighter path to our eyes, and the sun itself appears yellowish red.

When the sun is low on the horizon, like at sunrise or sunset, its rays have to pass through a much greater mass of atmosphere to reach our eyes than at midday. Greater mass of atmosphere = more molecules = more scattering possibilities - the blue wavelengths are scattered so intensely, they largely scatter away from our field of view. We see the longer wavelengths left behind... and the sunset is red, or pink, or yellow, etc...

There ya go. Science lesson for the weekend. Peace, and all good for your Sunday evening! +