Outdoor Observations-example of Rayleigh Scattering

Rayleigh (RAY-lee) Scattering is probably something you have never heard of. I bet, you have seen examples of it many times

Named after the British scientist that studied it, Rayleigh Scattering creates our blue sky and objects in the distance to appear pale/blue.

Years ago I learned about this from my art professor. I’m not sure he knew the name of this atmospheric effect. I don’t remember him calling it that, but he certainly understood how it works. Years later, when I was teaching art, I explained it the same way.

I’ll do my best to illustrate this without getting too scientific.

Mountains/Hills

The scattering of light particles causes distant mountains to appear blue. The more atmosphere between you and the distant mountain, the more light blue it will appear. Shorter wavelength of light blue are scattered more effectively in the atmosphere than longer wavelengths like red.

Mountains with pine trees or cedars gives the illusion of blue purple. Then in the evening when the sun starts to set, those same mountains will turn from a blue purple to a red purple. These are based on my personal observations.

Flat ground

Earlier, I stated that Rayleigh scattering causes our sky to be blue. If you are in an area with no mountains or hills, this optical effect can still be seen on a cloudless day.

Wait until you have a bright blue bird sky with low humidity. Sometime in the early afternoon, look straight up in the sky (without looking at the sun). Then lower your gaze to the horizon. You’ll see the sky above you is a darker blue than it is towards the horizon. When you look toward the horizon, The sky will almost be white.

Sunrise/Sunset

When the sun is low in the sky, sunlight has to pass through more atmosphere. Blue light is scattered away before it reaches our eyes. This causes the longer wavelengths like red and orange to be more visible. It tends to be a little more pinkish in the winter months, especially on those cold frosty mornings.

Clouds

Based on what I have observed, dark cloudy days are contrary to everything I have stated above. When the atmosphere is unsettled and you have a storm rolling in or a major cold front. Things tend to be right the opposite or they appear opposite to what we see. For example, on a partly cloudy day, if the land in front of you is lit up. Notice the distance areas that are under clouds, they will appear much darker.

People tend to not notice these things when they see them in real life. However, in a painting, most are like “Oh yeah, I have seen this before on our hike last fall”.

Get outside and look around to see it for yourself. It’s good for the body and soul. Not only that, it’s a pretty cool thing.

Until next time

Thanks for reading

Bryan bramblett