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Sunset Colors

Sunset Colors

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Thanks for the great Q&A website!

Here's my question. Why is there no green in the sunset. Going from the horizon upwards, the colors follow the rainbow, but there isn't much green. Lots of red, orange, yellow near the horizon and blue and violet higher in the sky, but between yellow and blue there's no green. I hope this makes sense. Thanks!

Greg in Logan


When we watch a sunset, often it looks fantastic but sometimes it's just blah with not much color. The colors of the sunset factor in a couple of things. What's in the sky whether it's ice crystals, rain drops or water vapor. And other things like dust or air pollution. Also light is bent as the sun goes down, this also helps to create the colors we see.

You might remember from back in Physics class that light comes in different wave lengths. The shorter wavelengths are violets and blues and longer wavelenghts are reds and oranges.

The shorter wavelengths are scattered more efficiently, thus we see a blue sky each day. Our eyes are more sensitive to blue light so we see blue instead of violet. At the sunset time, the light has to take a longer path to reach our eyes, it has to travel a longer distance and the blue and violets are scattered out and we are left looking at the reds. A good example of this is given by a diagram in a Corfidi paper, the link is on the right. While in the late afternoon here in the west we may see a bright blue sky but that light is being bent to our east, and our eastern neighbors in the Appalachians are seeing a reddish sunset.

Sunsets can appear very vivid with the presence of some clouds like cirrus clouds which are high up in the sky and made up of ice. The cloud is intercepting the light and there is less color loss because the beam hasn't hit the ground or moved through that haze and dust layer.

But where's the green you ask. Here's the deal. During the day we see those shorter wavelengths of blue and violet. In the evening, that is scattered out so we end up with the longwave colors of visible light, the reds, oranges and yellows. Poor green is stuck in the middle. We sometimes do see pale greens and yellows but no vivid greens usually.

However, when the sun does go down you can sometimes see the green flash, but that's doesn't happen all the time. This is a tricky question but it just has to do with the wavelength of light and long vs. short. Green is a middle length.

Answered by KSL Meteorologist Dina Freedman.

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