Why isn't the sky ever green? It can be, sort of

Why isn't the sky ever green? It can be, sort of

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by Jeff Renner / KING 5 Meteorologist

Bio | Email | Follow: @Jeffrennerwx

KING5.com

Posted on August 19, 2011 at 6:12 PM

Updated Friday, Aug 19 at 6:43 PM

WEATHER MINDS QUESTION: Why isn't the sky ever green?

It is occasionally green, though not often. Let's begin...at the beginning.

Color in the sky comes from particles; what meteorologists call aerosols that scatter the light. These can come from many sources-pollen, dust, smoke particles, pollutants. All of those particles scatter sunlight. Keep in mind that in space, without any atmosphere, the sun is white, and that white light is made up of many different colors at what we call different wavelengths. We see those different colors when light passes through a prism, or ice crystals or water droplets.

Different particles scatter different colors more efficiently; because they're of different sizes, shapes, etc. Because colors in the blue end of the spectrum, or range of colors, are more energetic, they get scattered first. That's why when we look away from the sun (and of course it's never a good idea to look directly at the sun), we see blue -- it's bouncing off all the particles in the atmosphere.

As the sun sets lower in the sky, the sun's rays are passing through the atmosphere at an angle. The light encounters more particles, and more rays are scattered -- sometimes we can briefly see green, but that's a very brief period, before the sunlight encounters the thickest path through the atmosphere, scattered orange and red.

During the setting sun, if the visibility is good and the density of the atmosphere is just right, we may see a green "flash." I've seen it in Hawaii...you have to watch carefully.

There's another instance that produces a green sky: during a severe thunderstorm. Meteorologists aren't certain what causes this, it may be the size and density of raindrops. They now know it is not because of hail, which has frequently been given as an explanation.

It doesn't happen often, proving, as Kermit the Frog often says, "it's not easy being green!"

To ask Jeff a Weather Minds question, email him at jrenner@king5.com

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